Summary
# Introduction to anatomy and physiology
This section provides a foundational understanding of anatomy and physiology, covering their definitions, historical context, terminology, and the fundamental organizational and chemical principles of the human body.
## 1\. Introduction to anatomy and physiology
Anatomy and physiology are intertwined disciplines that explore the structure and function of the human body. Anatomy focuses on the body's structure, while physiology examines how that structure functions.
### 1.1 The concepts of 'anatomy' and 'physiology'
* **Anatomy**
* Derived from Greek words meaning "to cut up," essentially meaning dissection.
* Studies the structure of organisms.
* Has its own specialized language, \_Terminologia Anatomica, often originating from Greek or Latin.
* **Levels of anatomical study:**
* **Macroscopic anatomy:** Deals with structures visible to the naked eye.
* **Microscopic anatomy:** Examines structures requiring magnification, such as cells and tissues.
* **Systemic anatomy:** Studies the body by organ systems.
* **Regional anatomy:** Examines all structures within a specific body region.
* **Physiology**
* Studies the functions and processes of living organisms.
* Often investigates processes at an invisible level (molecular or cellular).
* **Homeostasis:** A key concept in physiology, referring to the maintenance of a stable internal environment despite external changes.
* **Historical Context:**
* Andreas Vesalius is considered a foundational figure in anatomy.
* Significant milestones in physiology include the discovery of blood groups (around 1900) and the Krebs cycle (1953).
### 1.2 Fundamental concepts of anatomy
#### 1.2.1 Anatomical terminology
The specialized language of anatomy (\_Terminologia Anatomica) is crucial for clear communication among healthcare professionals.
#### 1.2.2 Anatomical position
The **anatomical position** is the standardized reference position for describing body parts and movements. It is defined as:
* Body standing erect.
* Face and feet directed forward.
* Arms hanging loosely at the sides.
* Palms of the hands facing forward.
#### 1.2.3 Body regions
The human body can be divided into several major areas:
* **Cephalic region (head):** Includes the oral region (mouth area).
* **Cervical region (neck).**
* **Truncus (trunk):**
* **Thorax (chest):** Bounded by the ribs and diaphragm.
* **Abdomen (belly):** Between the diaphragm and pelvic girdle.
* **Pelvis (pelvic girdle).**
* **Upper limbs (arms).**
* **Lower limbs (legs).**
Specific areas have unique anatomical names:
* Oral region: around the mouth.
* Sternal region: around the breastbone.
* Axillary region: armpit.
* Mammary region: breast area.
* Brachial region: arm.
* Umbilical region: around the navel.
* Inguinal region: groin.
* Carpal region: wrist.
* Tarsal region: ankle.
* Pedal region: foot.
* Dorsal region: back.
* Vertebral region: around the spinal column.
* Lumbar region: lower back.
* Gluteal region: buttocks.
#### 1.2.4 Pluralization of anatomical terms
Latin nouns in anatomical terminology often change their endings when pluralized. Common patterns include:
* '-a' becomes '-ae' (e.g., \_maxilla to \_maxillae).
* '-us' becomes '-i' (e.g., \_musculus to \_musculi).
* '-is' becomes '-es' (e.g., \_pulmonalis to \_pulmonales).
#### 1.2.5 Body planes and directional terms
To describe locations and relationships within the body, specific planes and directional terms are used.
* **Views (Aanzichten):**
* Anterior/Ventral view: Front.
* Posterior/Dorsal view: Back.
* Inferior/Caudal view: Below.
* Superior/Cranial view: Above.
* Lateral view: Side (left or right).
* **Planes of section:**
* **Frontal plane (Coronal plane):** Parallel to the forehead, dividing the body into anterior and posterior parts.
* **Sagittal plane:** Parallel to the plane passing between the eyes, dividing the body into left and right parts. A \_midsagittal plane divides the body exactly in half.
* **Transverse plane (Horizontal plane):** Parallel to the ground, dividing the body into superior and inferior parts.
### 1.3 Levels of organization of the body
The human body is organized into several hierarchical levels:
1. **Atomic level:** The smallest units of matter.
2. **Molecular level:** Atoms combine to form molecules.
3. **Cell level:** The basic structural and functional unit of life.
4. **Tissue level:** Groups of similar cells working together.
5. **Organ level:** Structures composed of different types of tissues working together for a specific function.
* **Orgaanstelselniveau (Organ system level):** Groups of organs working together to perform major functions.
* **Organismeniveau (Organism level):** The complete living being.
### 1.4 Chemical basis of life
Chemistry is fundamental to understanding life processes. Many physiological events occur at the molecular level.
#### 1.4.1 Atoms and elements
* An **atom** is the smallest particle of matter that retains the properties of an element. The term "atomos" means indivisible in Greek.
* Atoms combine to form **molecules**.
* There are 118 known elements, with 92 found in nature. Our bodies contain 26 different elements.
* The four most abundant elements in the human body are Oxygen (O), Carbon (C), Hydrogen (H), and Nitrogen (N).
* Other important elements include macrominerals (e.g., calcium, phosphorus, potassium) and trace elements (e.g., iron, iodine).
#### 1.4.2 Chemical bonding
Atoms form chemical bonds to achieve stability. The main types of bonds are:
* **Ionic bonds:**
* Formed when an atom loses or gains electrons, becoming an ion (charged atom).
* Atoms that lose electrons become positively charged **cations**.
* Atoms that gain electrons become negatively charged **anions**.
* The attraction between oppositely charged ions forms an ionic bond.
* These bonds are relatively weak and can break apart in water.
* **Covalent bonds:**
* Formed when atoms share electrons.
* **Single covalent bond:** One shared pair of electrons.
* **Double covalent bond:** Two shared pairs of electrons.
* **Triple covalent bond:** Three shared pairs of electrons.
* Covalent bonds are strong and are the most common type of bond in the body, forming stable molecules like DNA.
* **Polar covalent bonds:**
* Occur when electrons are shared unequally between atoms due to differences in electronegativity.
* The atom that attracts electrons more strongly develops a partial negative charge ($\\delta^-$), while the atom that attracts electrons less strongly develops a partial positive charge ($\\delta^+$).
* **Nonpolar covalent bonds:**
* Occur when electrons are shared equally between atoms.
#### 1.4.3 ATP as an energy-carrying molecule
* **Adenosine triphosphate (ATP)** is the primary molecule for short-term energy storage and transport within cells.
* It consists of an adenosine molecule and three phosphate groups.
* The energy is stored in the chemical bond between the second and third phosphate groups.
* When the terminal phosphate bond is broken, energy is released, forming adenosine diphosphate (ADP) and an inorganic phosphate.
* The body stores large amounts of energy long-term in fats and carbohydrates, which are then converted to ATP for immediate use.
#### 1.4.4 Inorganic chemistry
* Molecules are broadly classified into organic and inorganic compounds.
* **Water (H₂O)** is the most important inorganic molecule in the body, making up 55-65% of body weight.
* It acts as a universal solvent for polar molecules and ions.
* It is essential for most chemical reactions.
* **pH and Acidity:**
* Water can dissociate into hydrogen ions ($H^+$) and hydroxide ions ($OH^-$).
* The concentration of $H^+$ ions determines the **pH** of a solution.
* **pH = $-\\log\_{10}\[H^+\]$**
* A low pH (< 7) indicates an acidic solution (high $H^+$ concentration).
* A neutral pH (7) indicates an equal concentration of $H^+$ and $OH^-$.
* A high pH (> 7) indicates a basic (alkaline) solution (low $H^+$ concentration).
* **Acids** donate $H^+$ ions, lowering pH.
* **Bases** accept $H^+$ ions, raising pH.
* **Alkalosis:** Blood pH > 7.45.
* **Acidosis:** Blood pH < 7.35.
* **Buffer systems:**
* These systems resist drastic changes in pH.
* The bicarbonate-carbonic acid system ($HCO\_3^- / H\_2CO\_3$) is a crucial buffer in the blood.
* Buffers can act as acids in alkaline conditions and as bases in acidic conditions.
#### 1.4.5 Organic chemistry
Organic molecules are primarily carbon-based and form about 35% of the body's mass. They are classified into four main groups:
* **Carbohydrates:**
* Composed of carbon, hydrogen, and oxygen.
* Primary energy sources.
* **Monosaccharides (monomers):** Single sugar units (e.g., glucose, fructose, galactose).
* **Disaccharides (dimers):** Two monosaccharides linked together (e.g., lactose, sucrose).
* **Polysaccharides (polymers):** Many monosaccharides linked together (e.g., starch, glycogen, cellulose).
* **Lipids (Fats):**
* A diverse group of nonpolar molecules poorly soluble in water.
* **Triglycerides:** The most common type of fat, comprising about 95% of body fat.
* **Steroids:** Include cholesterol, important for cell membranes and hormone synthesis.
* **Phospholipids:** Key components of cell membranes.
* **Proteins:**
* Composed of amino acids linked by peptide bonds.
* Polypeptides fold into complex three-dimensional structures, forming functional proteins.
* Proteins are vital for tissue structure, enzymes, hormones, and more.
* **Enzymes:** Proteins that catalyze biochemical reactions, with a specific active site for substrate binding.
* **Nucleic acids:**
* Long chains of nucleotides.
* **Deoxyribonucleic acid (DNA)** carries genetic information.
* **Ribonucleic acid (RNA)** is involved in protein synthesis.
* **Adenosine triphosphate (ATP)** is a nucleotide important for energy currency.
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# The chemical basis of life and cellular organization
This topic delves into the fundamental chemical principles that underpin all biological processes and outlines the hierarchical structure of living organisms.
### 2.1 Levels of biological organization
Life is organized into distinct hierarchical levels, each building upon the one below:
* **Atomic level:** The simplest level, consisting of individual atoms, which are the smallest units of matter that retain the properties of an element.
* **Molecular level:** Atoms combine to form molecules, which are chemical structures composed of two or more atoms held together by chemical bonds.
* **Cellular level:** Molecules interact and assemble to form cells, the basic structural and functional units of all living organisms.
* **Tissue level:** Groups of similar cells and their extracellular matrix work together to perform a specific function.
* **Organ level:** Different tissues are organized into organs, which are structures composed of at least two different types of tissues that perform specific functions.
* **Organ system level:** A group of organs that work together to perform a major life function.
* **Organism level:** All organ systems work together to form a complete living organism.
### 2.2 The chemical basis of life
Life is fundamentally a chemical process, with most physiological functions occurring at the molecular level.
#### 2.2.1 Atoms and elements
* **Atoms:** The smallest indivisible particles of matter.
* The average size of an atom is approximately $0.3 \\text{ nm}$.
* The human body contains approximately 26 different elements.
* **Elements:** Different types of atoms. The periodic table lists all known elements.
* **Most abundant elements in the human body:** Oxygen (O), Carbon (C), Hydrogen (H), and Nitrogen (N).
* **Macrominerals:** Calcium (Ca), Phosphorus (P), Potassium (K), Sulfur (S), Sodium (Na), Chlorine (Cl), and Magnesium (Mg).
* **Trace elements:** Present in smaller amounts, such as Fluorine (F), Chromium (Cr), and Iron (Fe).
#### 2.2.2 Chemical bonding
Atoms form chemical bonds to achieve stability, primarily through interactions involving their outermost electrons.
* **Ionic bonding:**
* Occurs when atoms gain or lose electrons to become ions (charged particles).
* An atom that loses an electron becomes a positively charged ion (cation).
* An atom that gains an electron becomes a negatively charged ion (anion).
* The electrostatic attraction between oppositely charged ions forms an ionic bond.
* Ionic bonds are relatively weak and tend to break apart in water.
* **Covalent bonding:**
* Occurs when atoms share electrons to form stable molecules.
* Atoms come very close, and their outermost electron shells overlap.
* **Single covalent bond:** One shared pair of electrons.
* **Double covalent bond:** Two shared pairs of electrons.
* **Triple covalent bond:** Three shared pairs of electrons.
* Covalent bonds are strong and form the basis of stable molecules like DNA.
* **Polar covalent bonds:** Electrons are shared unequally, creating partial positive ($\\delta+$) and partial negative ($\\delta-$) charges on the atoms due to differences in electronegativity.
* **Nonpolar covalent bonds:** Electrons are shared equally between atoms.
#### 2.2.3 Adenosine triphosphate (ATP)
ATP is the primary energy currency of the cell, crucial for powering numerous biological processes.
* **Structure:** Composed of one adenosine molecule and three phosphate groups linked by covalent bonds.
* **Function:** Stores and transports energy.
* ATP is often referred to as a "charged battery."
* Adenosine diphosphate (ADP) is a "discharged battery."
* **Energy Storage:** The energy is primarily stored in the bond between the second and third phosphate groups.
* **Energy Needs:** While ATP is vital for direct energy transfer, the body cannot store all its energy as ATP, as this would be prohibitively heavy. Instead, energy is stored long-term in fats and carbohydrates and converted to ATP as needed.
#### 2.2.4 Inorganic chemistry
Inorganic molecules generally lack carbon-hydrogen bonds.
* **Water ($H\_2O$):**
* The most abundant inorganic molecule in the human body, making up $55%–65%$ of body weight.
* **Solvent:** Water's polar nature allows it to dissolve polar molecules and ions, facilitating countless chemical reactions. Nonpolar molecules (like fats) dissolve poorly.
* **pH:** Water can dissociate into hydrogen ions ($H^+$) and hydroxide ions ($OH^-$). The concentration of $H^+$ determines the pH of a solution.
* $pH = -\\log\_{10}\[H^+\]$
* **Acidic:** $pH < 7$ (high $H^+$ concentration)
* **Neutral:** $pH = 7$
* **Basic (alkaline):** $pH > 7$ (low $H^+$ concentration)
* **Acids:** Substances that release $H^+$ ions into a solution, lowering pH.
* **Bases:** Substances that accept $H^+$ ions from a solution, raising pH.
* **Acidosis:** Blood pH below $7.35$.
* **Alkalosis:** Blood pH above $7.45$.
* **Buffers:** Systems that resist drastic changes in pH. The bicarbonate-carbonic acid system ($HCO\_3^- / H\_2CO\_3$) is crucial for buffering blood pH.
#### 2.2.5 Organic chemistry
Organic molecules are carbon-based compounds, often containing hydrogen and other elements. They are the building blocks of life.
* **Four major classes of organic molecules (biomolecules):**
* **Carbohydrates:** Primarily composed of carbon, hydrogen, and oxygen. They are the main energy sources.
* **Monosaccharides:** Simple sugars (e.g., glucose, fructose, galactose).
* **Disaccharides:** Two monosaccharides linked together (e.g., lactose, sucrose).
* **Polysaccharides:** Long chains of monosaccharides (e.g., starch, glycogen, cellulose).
* **Lipids (Fats):** A diverse group of nonpolar molecules, poorly soluble in water.
* **Fats (triglycerides):** The most common type, used for energy storage.
* **Steroids:** Include cholesterol and hormones like testosterone.
* **Phospholipids:** Essential components of cell membranes.
* **Proteins:** Polymers of amino acids linked by covalent peptide bonds. They are crucial for structure, function, and regulation of the body's tissues and organs.
* **Enzymes:** Proteins that catalyze (speed up) biochemical reactions by binding to specific substrates.
* **Nucleic acids:** Long chains of nucleotides.
* **DNA (Deoxyribonucleic acid):** Carries genetic information.
* **RNA (Ribonucleic acid):** Involved in protein synthesis.
* **ATP:** While an energy molecule, it is also a nucleotide.
### 2.3 Cellular organization
Cells are the fundamental units of life, each performing essential functions to maintain life and contribute to the organism's overall well-being.
#### 2.3.1 The cell
* **Cell theory:** All living things are composed of cells, cells are the basic units of life, and all cells come from pre-existing cells.
* **Human body:** Composed of trillions of cells.
* **Cell formation:** Occurs through cell division (mitosis or meiosis).
* **Cellular processes:** Involve metabolism (the sum of all chemical reactions within a cell), constant breakdown and synthesis of molecules, and maintaining homeostasis.
#### 2.3.2 Basic cell structure
Every human cell has three main components:
* **Plasma membrane (cell membrane):** The outer boundary of the cell.
* **Phospholipid bilayer:** Forms the basic structure, with hydrophilic heads facing outward and inward, and hydrophobic tails facing each other.
* **Semi-permeable:** Controls the passage of substances into and out of the cell.
* **Transport proteins:** Embedded in the membrane to facilitate the movement of specific molecules across it, some requiring ATP (active transport, e.g., sodium-potassium pump), others not (facilitated diffusion).
* **Receptors:** Proteins that bind to specific signaling molecules (ligands), initiating cellular responses.
* **Cytoplasm:** The material or protoplasm within a living cell, excluding the nucleus.
* **Cytosol:** The gel-like fluid portion of the cytoplasm.
* **Organelles:** Specialized structures within the cytoplasm that perform specific functions.
* **Nucleus (cell core):** Contains the cell's genetic material (DNA).
* **Chromosomes:** Structures made of DNA and proteins that carry genetic information.
* **DNA:** Encodes the instructions for protein synthesis.
#### 2.3.3 Key organelles
* **Endoplasmic Reticulum (ER):** A network of membranes involved in protein and lipid synthesis.
* **Rough ER:** Studded with ribosomes; involved in protein synthesis and modification.
* **Smooth ER:** Lacks ribosomes; involved in lipid synthesis and detoxification.
* **Ribosomes:** Responsible for protein synthesis (translation of mRNA into polypeptide chains). Can be free in the cytoplasm or attached to the rough ER.
* **Golgi apparatus:** Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.
* **Lysosomes:** Contain digestive enzymes to break down waste materials and cellular debris (autophagy).
* **Mitochondria:** The "powerhouses" of the cell; generate ATP through cellular respiration.
#### 2.3.4 Transport across the cell membrane
Substances move across the cell membrane via several mechanisms:
* **Passive transport:** Does not require cellular energy.
* **Diffusion:** Movement of a substance from an area of high concentration to low concentration.
* **Osmosis:** The diffusion of water across a selectively permeable membrane from an area of lower solute concentration to higher solute concentration.
* **Hypertonic solution:** Higher solute concentration outside the cell; water moves out.
* **Hypotonic solution:** Lower solute concentration outside the cell; water moves in.
* **Isotonic solution:** Equal solute concentration inside and outside the cell.
* **Active transport:** Requires cellular energy (ATP) to move substances against their concentration gradient.
* **Vesicular transport:** Movement of substances enclosed in membrane-bound sacs (vesicles).
* **Endocytosis:** Movement of substances into the cell.
* **Exocytosis:** Movement of substances out of the cell.
#### 2.3.5 Metabolism
Metabolism encompasses all chemical processes that occur within a cell or organism.
* **Anabolic reactions:** Build larger molecules from smaller ones, requiring energy (ATP). Essential for growth, repair, and maintenance.
* **Catabolic reactions:** Break down larger molecules into smaller ones, releasing energy (often as ATP or heat). Examples include glycogenolysis, glycolysis, lipolysis, and beta-oxidation.
#### 2.3.6 Cell division
* **Mitosis:** Produces two identical diploid daughter cells from one diploid parent cell. Essential for growth, repair, and asexual reproduction.
* **Meiosis:** Produces four haploid gametes (sex cells) from one diploid parent cell. Essential for sexual reproduction.
### 2.4 Tissues
Tissues are groups of similar cells and their extracellular matrix that perform a specific function. Histology is the study of tissues.
#### 2.4.1 Epithelial tissue (covering tissue)
* Covers body surfaces and lines cavities.
* Composed of tightly packed cells with little to no extracellular matrix.
* **Key characteristics:** Densely packed cells, basal membrane attachment, avascularity (no blood vessels), and high regenerative capacity.
* **Classified by:**
* **Number of layers:** Simple (one layer) or stratified (multiple layers).
* **Cell shape:** Squamous (flat), cuboidal (cube-shaped), or columnar (tall).
* **Glands:** Epithelial cells specialized for secretion, divided into exocrine (ducts to surface) and endocrine (hormones into bloodstream).
#### 2.4.2 Connective tissue
* Supports, protects, and binds other tissues.
* Characterized by an extracellular matrix containing fibers (collagen, elastic, reticular) and a ground substance.
* **Types:**
* **Blood:** Matrix is plasma; functions in transport.
* **Cartilage:** Firm, flexible, and elastic; found in joints, nose, and ears. Types include hyaline, fibrous, and elastic cartilage.
* **Bone tissue:** Provides structural support and protection; includes compact and spongy bone.
* **Dense connective tissue:** Rich in collagen fibers; found in tendons, ligaments, and the dermis.
* **Loose connective tissue:** Abundant matrix and cells; acts as packing material.
* **Adipose tissue (fat):** Specialized for energy storage and insulation.
#### 2.4.3 Muscle tissue
* Specialized for contraction, producing movement.
* Composed of cells containing actin and myosin filaments.
* **Types:**
* **Skeletal muscle:** Voluntary, striated muscle attached to bones; responsible for body movement.
* **Smooth muscle:** Involuntary muscle found in the walls of internal organs and blood vessels.
* **Cardiac muscle:** Involuntary, striated muscle found only in the heart.
#### 2.4.4 Nervous tissue
* Found in the brain, spinal cord, and nerves.
* Composed of neurons (nerve cells) that transmit electrical signals and glial cells (support cells).
* **Neurons:** Specialized for transmitting nerve impulses at high speeds.
### 2.5 The role of chemistry in cellular organization
The chemical basis of life is directly intertwined with cellular organization. The specific arrangement of atoms and molecules dictates the structure and function of organelles, cells, and ultimately, the entire organism. For instance, the polarity of water molecules is essential for dissolving ions needed for nerve impulses, while the precise sequence of nucleotides in DNA dictates the proteins that determine cell structure and function. ATP's chemical structure facilitates the release and capture of energy, powering cellular activities. The formation and properties of molecules like phospholipids are fundamental to the structure of the cell membrane, controlling the internal cellular environment. Ultimately, understanding the chemical interactions and structures at the atomic and molecular level is crucial for comprehending how cells are organized and function as the building blocks of life.
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# Cell structure and function
This section provides a comprehensive overview of the cell, the fundamental unit of life, detailing its structural components, their functions, and essential life processes.
### 3.1 The cell as the basic unit of life
The cell is recognized as the smallest independently functioning unit of life and a primary building block of all living organisms. The cell theory posits that all living things are composed of one or more cells, and that cells arise from pre-existing cells through division. The human body comprises an immense number of cells, estimated in the trillions. Cellular formation occurs via mitosis or meiosis, and cells operate as self-sustaining units requiring nutrients to maintain their structure and function, thereby preserving homeostasis.
### 3.2 Structure of a cell
Every human cell is fundamentally composed of three main components:
* **Cell membrane (plasma membrane):** The outer boundary of the cell.
* **Cytoplasm:** The internal environment of the cell, which includes cytosol and organelles.
* **Cell nucleus:** The control center of the cell.
#### 3.2.1 The plasma membrane
The plasma membrane, often referred to as the cell membrane, acts as the cell's outer covering, separating the intracellular environment from the extracellular environment. It is primarily constructed from a phospholipid bilayer, characterized by a polar head and a nonpolar tail. This structure makes the membrane semi-permeable, restricting the passage of large polar molecules and ions. Embedded within this lipid bilayer are transport proteins that facilitate the movement of specific molecules across the membrane.
* **Transport proteins:** These proteins, embedded within the plasma membrane, are responsible for transporting specific molecules. Some transport processes require energy in the form of ATP, while others do not. A notable example is the sodium-potassium pump, which actively moves potassium ions into the cell and sodium ions out, maintaining an electrochemical gradient across the membrane.
* **Ion channels:** These are specialized transport proteins that are selectively permeable to specific ions.
* **Receptors:** Protein receptors embedded in the plasma membrane bind to specific molecules called ligands, such as hormones. This binding initiates a cascade of reactions within the cell.
#### 3.2.2 The cell nucleus
With the exception of red blood cells, most cells possess a nucleus. The nucleus contains the cell's genetic material, organized into 46 chromosomes, each composed of DNA tightly wound around histone proteins. Before cell division, these chromatin threads condense to form visible chromosomes. The DNA within the nucleus encodes the instructions for protein synthesis, which is crucial for cellular function. The nucleus is enclosed by a nuclear membrane that contains nuclear pores, regulating the passage of molecules between the nucleus and the cytoplasm.
#### 3.2.3 The cytoplasm
The cytoplasm is the gel-like substance filling the cell, enclosing the organelles. It comprises:
* **Cytosol:** The fluid portion of the cytoplasm, where organelles are suspended. It is also known as intracellular fluid.
* **Organelles:** These are specialized structures within the cell, each performing a specific function.
##### 3.2.3.1 Endoplasmic reticulum (ER)
The endoplasmic reticulum is a network of interconnected membranes surrounding the nucleus. It exists in two forms:
* **Rough ER:** Characterized by the presence of ribosomes, the rough ER is involved in protein synthesis and modification.
* **Smooth ER:** Lacking ribosomes, the smooth ER is primarily involved in lipid and carbohydrate synthesis.
##### 3.2.3.2 Ribosomes
Ribosomes are small organelles responsible for protein synthesis. They play a critical role in translation, the process by which messenger RNA (mRNA) is converted into polypeptide chains. Ribosomes can be found freely floating in the cytoplasm or attached to the rough ER.
##### 3.2.3.3 Golgi apparatus
The Golgi apparatus is a stack of membrane-bound sacs that functions in modifying, sorting, and packaging proteins and lipids synthesized in the ER. These molecules are then packaged into vesicles for transport within or outside the cell.
##### 3.2.3.4 Lysosomes
Lysosomes are small vesicles containing powerful digestive enzymes. They act as the cell's recycling center, breaking down waste materials, cellular debris, and foreign invaders. They are also involved in autophagy, the process of degrading old or damaged cell components.
##### 3.2.3.5 Mitochondria
Mitochondria are often referred to as the "powerhouses" of the cell. They are responsible for generating most of the cell's supply of adenosine triphosphate (ATP), used as a source of chemical energy. This process, known as cellular respiration, involves the breakdown of nutrients like proteins, carbohydrates, and fats.
### 3.3 Transport within and outside the cell
Substances can move across the cell membrane through various mechanisms:
* **Passive transport:** This includes diffusion and osmosis, which do not require cellular energy.
* **Diffusion:** The movement of molecules from an area of high concentration to an area of low concentration until equilibrium is reached.
* **Osmosis:** The movement of water across a semi-permeable membrane from an area of lower solute concentration to an area of higher solute concentration.
* **Hypertonic solution:** A solution with a higher solute concentration than the cell.
* **Hypotonic solution:** A solution with a lower solute concentration than the cell.
* **Isotonic solution:** A solution with an equal solute concentration to the cell.
* **Active transport:** This process requires cellular energy (ATP) to move molecules against their concentration gradient, often facilitated by specific membrane proteins.
* **Vesicular transport:** This involves the formation of membrane-bound sacs (vesicles) to move substances across the membrane.
* **Endocytosis:** The process by which the cell takes in substances from the outside by engulfing them in a vesicle.
* **Exocytosis:** The process by which the cell releases substances to the outside by fusing vesicles with the plasma membrane.
### 3.4 Metabolism
Metabolism encompasses all the biochemical processes occurring within an organism. It is broadly divided into two categories:
* **Anabolic reactions:** These reactions build larger molecules from smaller ones, requiring energy (ATP). They are essential for growth, repair, and maintenance of cellular components.
* **Catabolic reactions:** These reactions break down larger molecules into smaller ones, releasing energy, often in the form of ATP or heat. Examples include glycogenolysis (breakdown of glycogen to glucose), glycolysis (breakdown of glucose to pyruvate), and lipolysis (breakdown of triglycerides).
Cellular respiration is a key catabolic process occurring in the mitochondria, where oxygen is used to produce ATP.
### 3.5 Cell division: Mitosis and meiosis
Cell division is essential for growth, repair, and reproduction.
* **Mitosis:** This process results in two identical diploid daughter cells from a single diploid parent cell. It is responsible for growth and tissue repair.
* **Meiosis:** This process occurs in the precursor cells of gametes (sex cells) and results in four genetically distinct haploid daughter cells. It is crucial for sexual reproduction.
### 3.6 Histology: The study of tissues
Histology is the study of tissues, which are groups of similar cells and their extracellular matrix that perform a specific function. The four primary tissue types in the human body are:
#### 3.6.1 Epithelial tissue (covering tissue)
Epithelial tissue covers body surfaces, lines body cavities, and forms glands. Key characteristics include:
* Closely packed cells with little extracellular matrix.
* Attachment to an underlying basement membrane.
* Avascularity (lack of blood vessels), with nutrients supplied by diffusion from underlying tissues.
* High regenerative capacity through mitosis.
Epithelial tissues are classified based on cell shape (squamous, cuboidal, columnar) and the number of cell layers (simple or stratified).
* **Glands:** Epithelial cells can form glands, which are classified as exocrine (secreting onto a surface) or endocrine (secreting hormones into the bloodstream).
#### 3.6.2 Connective tissue
Connective tissue supports, connects, or separates different types of tissues and organs. It is characterized by a rich extracellular matrix containing fibers (collagen, elastic, reticular) and a ground substance. Types include blood, lymph, cartilage, bone, dense connective tissue, loose connective tissue, and adipose tissue.
* **Bone tissue:** Composed of osteocytes embedded in a mineralized matrix, it provides structural support, protection, and serves as a reservoir for calcium and phosphate. Bone is a dynamic tissue that undergoes continuous remodeling by osteoblasts (bone formation) and osteoclasts (bone resorption).
* **Cartilage tissue:** Firm, flexible, and elastic, cartilage is avascular and found in joints, the nose, and ears. Types include hyaline, fibrocartilage, and elastic cartilage.
* **Blood:** Considered a connective tissue, blood consists of plasma (the liquid matrix) and various blood cells (red blood cells, white blood cells, and platelets).
#### 3.6.3 Muscle tissue
Muscle tissue is specialized for contraction, enabling movement. There are three types:
* **Skeletal muscle tissue:** Striated and under voluntary control, responsible for movement of the skeleton.
* **Smooth muscle tissue:** Non-striated and involuntary, found in the walls of internal organs and blood vessels.
* **Cardiac muscle tissue:** Striated, involuntary muscle found exclusively in the heart.
#### 3.6.4 Nervous tissue
Nervous tissue is composed of neurons (nerve cells) and glial cells. Neurons are responsible for transmitting electrical signals, facilitating rapid communication throughout the body. Glial cells provide support and protection to neurons.
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# The skeletal system
Here is a comprehensive study guide section on the skeletal system:
## 4 The skeletal system
The skeletal system provides structural support, protects vital organs, facilitates movement, stores minerals, and produces blood cells.
### 4.1 Functions of the skeletal system
The skeletal system, comprising approximately 206 bones (excluding sesamoid bones), works in conjunction with muscles as the musculoskeletal system. Tendons connect muscle to bone, while ligaments connect bone to bone. Articulations or joints are the points where bones meet. The skeletal system serves five primary functions:
1. **Support and posture:** It bears the body's weight and maintains upright posture, with a delicate balance between bone formation and resorption; imbalances can lead to conditions like osteoporosis, particularly in older individuals or post-menopause.
2. **Anchorage for muscles:** Bones act as levers, providing attachment sites for muscles to facilitate movement.
3. **Protection of vital organs:** Structures like the skull protect the brain, the sternum guards the heart, and the vertebral column shields the spinal cord.
4. **Mineral storage:** The bone matrix serves as a reservoir for crucial minerals like calcium and phosphate ions, as well as collagen fibers.
5. **Hematopoiesis:** Red bone marrow within bones is the site for the production of red blood cells, white blood cells, and platelets from hematopoietic stem cells.
The skeleton is divided into two main groups:
* **Axial skeleton:** Consists of 80 bones located in the midsagittal plane, forming the central axis of the body, including the skull, vertebral column, ribs, and sternum.
* **Appendicular skeleton:** Includes the clavicle, scapula, bones of the arms and legs, and the os coxae (hip bones), connecting the limbs to the axial skeleton.
### 4.2 Macroscopic structure of a bone
Bones are classified into four main categories based on their shape:
* **Long bones (or pipe bones):** Characterized by a shaft (diaphysis) and expanded ends (epiphyses), e.g., humerus, femur.
* **Short bones:** Roughly cube-shaped, e.g., carpal bones (ossa carpi).
* **Flat bones:** Thin, flattened, and often curved, providing protection or large surface areas for muscle attachment, e.g., skull bones, scapula.
* **Irregular bones:** Bones with complex shapes that do not fit into the other categories, e.g., vertebrae, mandible.
* **Sesamoid bones:** Small, rounded bones embedded within tendons or ligaments, often providing leverage or protection, e.g., patella.
#### 4.2.1 Structure of long bones
Long bones are composed of two types of bone tissue:
* **Compact bone:** Dense, solid, and strong, forming the outer layer.
* **Spongy bone (or cancellous bone):** Honeycomb-like structure with trabeculae, found internally, especially in the epiphyses.
Key features of a long bone include:
* **Shaft (diaphysis):** Composed of compact bone, enclosing the central medullary cavity. This cavity contains yellow bone marrow in adults, which is rich in fat tissue and serves as an energy reserve.
* **Epiphyses:** The expanded ends of the long bone, covered with hyaline cartilage at the articular surfaces. They contain red bone marrow, the site of hematopoiesis.
* **Metaphysis:** The region between the epiphysis and diaphysis. In children, this area contains the epiphyseal plate (growth plate), responsible for longitudinal bone growth. Upon cessation of growth, this plate ossifies, forming the epiphyseal line.
* **Periosteum:** A tough, fibrous membrane that covers the outer surface of the bone, except at articular surfaces. It contains blood vessels, lymph vessels, and nerves and is strongly fused with tendons and ligaments, ensuring strong attachment points.
Bone markings are surface features like projections, depressions, and openings that serve specific functions. Bones have a remarkable capacity for self-repair, with fractures typically healing within about six weeks.
### 4.3 The skull
The skull is divided into two main parts: the cranium (braincase) and the facial skeleton.
#### 4.3.1 Cranial bones (cranium cerebrale)
The cranium, composed of eight bones, protects the brain and provides attachment sites for muscles of the tongue, throat, neck, and facial muscles. It also houses sensory organs like the eyes, nose, and ears. The cranial bones are named after the underlying lobes of the brain:
* Frontal bone
* Parietal bones (paired)
* Temporal bones (paired)
* Occipital bone
* Sphenoid bone
* Ethmoid bone
These bones are joined by immovable joints called sutures, which allow for skull growth and passage through the birth canal. Fontanelles are temporary, unossified connective tissue membranes in infants that allow for skull flexibility.
#### 4.3.2 Facial bones (cranium viscerale)
The facial skeleton consists of 14 bones that form the structure of the face. Some cranial bones also contain air-filled cavities called sinuses, which lighten the skull and contribute to voice resonance. These include the frontal, sphenoid, ethmoid, and maxillary sinuses. Inflammation of these sinuses is known as sinusitis.
### 4.4 The vertebral column and thorax
The vertebral column, or spine, is a flexible column of approximately 33 vertebrae, though typically only 26 are distinct in adults due to fusion.
#### 4.4.1 Vertebral column
The vertebral column comprises five regions:
* **Cervical vertebrae (7):** Located in the neck (C1-C7). C1 is the atlas, supporting the skull, and C2 is the axis, with the dens (odontoid process) allowing rotation of the head. C7 is the vertebra prominens.
* **Thoracic vertebrae (12):** Located in the chest region (T1-T12), articulating with the ribs.
* **Lumbar vertebrae (5):** Located in the lower back (L1-L5).
* **Sacrum:** Formed by the fusion of 5 sacral vertebrae, typically fused by age 25.
* **Coccyx (tailbone):** Formed by 3-5 fused coccygeal vertebrae.
The vertebral column exhibits four natural curves when viewed laterally:
* **Cervical lordosis:** An anterior curve in the cervical region.
* **Thoracic kyphosis:** A posterior curve in the thoracic region.
* **Lumbar lordosis:** An anterior curve in the lumbar region.
* **Sacral kyphosis:** A posterior curve in the sacral region.
Typical vertebrae share common features:
* **Vertebral body (corpus vertebrae):** The weight-bearing anterior part.
* **Vertebral foramen (foramen vertebrale):** The opening through which the spinal cord passes. Below T12/L1, this forms the cauda equina.
* **Vertebral arch (arcus vertebrae):** Forms the posterior and lateral aspects of the vertebral foramen.
* **Transverse processes (processus transversi):** Lateral projections serving as muscle attachment sites.
* **Spinous process (processus spinosus):** Posterior projection for muscle attachment.
* **Articular processes (processus articulares):** Four projections (two superior, two inferior) that articulate with adjacent vertebrae.
Differences exist between vertebral regions: cervical vertebrae have foramina transversaria for the vertebral artery, thoracic vertebrae have facets for rib articulation, and lumbar vertebrae have large vertebral bodies to support more weight.
**Intervertebral discs:** Fibrocartilaginous discs located between vertebral bodies (except between C1 and C2), acting as shock absorbers. Each disc consists of an outer fibrous ring (anulus fibrosus) and a gel-like inner core (nucleus pulposus). Degeneration or rupture of these discs can lead to a herniated disc, compressing nerves. The nucleus pulposus loses water with age, contributing to height reduction in older adults.
#### 4.4.2 Thorax
The thoracic cage, or rib cage, consists of:
* **12 Thoracic vertebrae:** Form the posterior attachment of the ribs.
* **12 Pairs of ribs:** Articulate posteriorly with the thoracic vertebrae.
* **True ribs (1-7):** Attach directly to the sternum via costal cartilage.
* **False ribs (8-10):** Attach indirectly to the sternum via the costal cartilage of the rib above.
* **Floating ribs (11-12):** Do not attach to the sternum.
* **Sternum (breastbone):** A flat bone in the anterior midline, composed of the manubrium, body, and xiphoid process.
### 4.5 Shoulder girdle and upper limb
The shoulder girdle connects the upper limb to the axial skeleton and consists of the scapula and clavicle.
#### 4.5.1 Shoulder girdle
* **Scapula (shoulder blade):** A triangular bone on the posterior thorax. Key features include the acromion (forming the "shoulder roof" and articulating with the clavicle at the AC joint), the glenoid cavity (articulates with the humerus), and the coracoid process.
* **Clavicle (collarbone):** An S-shaped bone palpable along its length. It is frequently fractured due to its role in absorbing impact from falls.
#### 4.5.2 Upper limb
The upper limb consists of the humerus, radius, ulna, and the bones of the hand.
* **Humerus (upper arm bone):** The longest bone of the upper limb.
* **Proximal epiphysis:** Features the head (caput humeri) that articulates with the glenoid cavity of the scapula, and the greater and lesser tubercles for shoulder muscle attachment. The anatomical neck is superior to the tubercles, while the surgical neck is the common site of fractures.
* **Distal epiphysis:** Includes the medial and lateral epicondyles, the capitulum (articulates with the radius), and the trochlea (articulates with the ulna). The olecranon fossa receives the olecranon of the ulna when the elbow is extended.
* **Forearm:** Composed of the radius and ulna.
* **Radius (radial bone):** Located laterally (on the thumb side). The proximal end has a disc-shaped head and a tuberosity for biceps brachii attachment. Distal fractures of the radius are common, especially in older adults with osteoporosis.
* **Ulna (ulnar bone):** Located medially (on the pinky finger side). The proximal end features the trochlear notch (articulates with the humerus) and the olecranon (the "point" of the elbow).
* **Hand (manus):** Consists of 27 bones:
* **Carpals (hand bones):** 8 small bones arranged in two rows (scaphoid, lunate, triquetrum, pisiform in the proximal row; trapezium, trapezoid, capitate, hamate in the distal row).
* **Metacarpals (5):** Form the palm of the hand.
* **Phalanges (finger bones):** 14 bones, with 3 in each finger (proximal, middle, distal) and 2 in the thumb (proximal, distal).
### 4.6 Pelvic girdle and lower limb
The pelvic girdle, or pelvis, connects the lower limbs to the axial skeleton and supports the body's weight.
#### 4.6.1 Pelvic girdle
The pelvis is formed by the two hip bones (ossa coxae), the sacrum, and the coccyx. Each hip bone is composed of three fused bones:
* **Ilium (darmbeen):** The largest and uppermost part, forming the iliac crest.
* **Ischium (zitbeen):** The lower posterior part, forming the ischial tuberosity (what we sit on).
* **Pubis (schaambeen):** The anterior and inferior part, meeting its contralateral counterpart at the pubic symphysis.
The hip bones articulate with the sacrum posteriorly at the auricular surfaces. The acetabulum is a deep socket formed by all three hip bones, receiving the head of the femur. The pelvis differs between males and females; the female pelvis is wider and shallower to accommodate childbirth.
#### 4.6.2 Lower limb
The lower limb consists of the femur, patella, tibia, fibula, and the bones of the foot.
* **Femur (thigh bone):** The longest, strongest, and heaviest bone in the body, approximately one-quarter of total body height.
* **Proximal epiphysis:** Features the head (caput femoris) that articulates with the acetabulum, and the greater and lesser trochanters for muscle attachment.
* **Shaft (diaphysis):** Has the linea aspera on its posterior surface, a roughened ridge for muscle attachment.
* **Distal epiphysis:** Includes the medial and lateral condyles and epicondyles, which articulate with the tibia. The patellar surface articulates with the patella.
* **Patella (kneecap):** A large sesamoid bone embedded in the patellar tendon, protecting the knee joint and improving leverage for the quadriceps muscle.
* **Lower leg:** Composed of the tibia and fibula, connected by the interosseous membrane.
* **Tibia (shin bone):** The larger, medial bone that bears the majority of the body's weight. Its proximal end forms the tibial plateau, articulating with the femur. The tibial tuberosity serves as the attachment point for the patellar tendon. The medial malleolus forms the inner bump of the ankle.
* **Fibula:** The smaller, lateral bone that does not bear significant weight but provides stability to the ankle. The lateral malleolus forms the outer bump of the ankle.
* **Foot (pes):** Consists of 26 bones, divided into three regions:
* **Tarsals (7):** Form the ankle and upper part of the foot. The talus articulates with the tibia and fibula to form the ankle joint. The calcaneus (heel bone) is the largest tarsal and bears much of the body's weight. Other tarsals include the navicular, cuboid, and three cuneiform bones.
* **Metatarsals (5):** Form the sole of the foot.
* **Phalanges (toe bones):** 14 bones, with 3 in each toe (proximal, middle, distal) and 2 in the great toe (hallux).
### 4.7 Bone connections
Bone connections, or articulations, are points where two or more bones meet. There are approximately 360 articulations in the body, connecting the 206 bones. These are classified based on their structure and degree of movement.
#### 4.7.1 Structural classification of joints
* **Fibrous joints:** Bones are connected by dense collagenous fibers. These are typically immovable (synarthroses) or slightly movable (amphiarthroses). Examples include sutures of the skull and syndesmoses (e.g., between tibia and fibula).
* **Cartilaginous joints:** Bones are connected by cartilage. These can be immovable (synarthroses) or slightly movable (amphiarthroses). Examples include symphyses (e.g., pubic symphysis) and synchondroses (e.g., epiphyseal plates in growing bones).
* **Synovial joints:** These are freely movable joints (diarthroses), characterized by a joint cavity filled with synovial fluid. They are the most common type of joint in the body.
#### 4.7.2 Synovial joint structure
Synovial joints have a specific structure that allows for a wide range of motion:
* **Articular cartilage:** Hyaline cartilage covering the surfaces of articulating bones, reducing friction and absorbing shock.
* **Joint capsule:** A fibrous outer layer enclosing the joint, continuous with the periosteum of the articulating bones.
* **Synovial membrane:** The inner lining of the joint capsule, producing synovial fluid.
* **Synovial fluid:** A viscous, lubricating fluid that reduces friction, nourishes the articular cartilage, and acts as a shock absorber.
* **Joint cavity:** The space within the joint capsule, filled with synovial fluid.
* **Ligaments:** Reinforce the joint capsule, providing stability and limiting excessive movement.
* **Bursae:** Small, fluid-filled sacs located around some synovial joints (e.g., near tendons) to reduce friction between moving parts.
* **Menisci (in some joints):** Fibrocartilaginous discs that improve the fit between articulating bones and absorb shock.
### 4.8 Skeletal muscle tissue
Skeletal muscles are responsible for voluntary movement, posture, joint stabilization, and heat generation.
#### 4.8.1 Functions of skeletal muscles
* **Movement and posture:** Muscles contract to move bones and maintain body position.
* **Joint stabilization:** Strong muscles surrounding joints help maintain stability.
* **Protection of soft tissues:** Muscles like the abdominal muscles shield internal organs.
* **Regulation of openings:** Sphincter muscles control the opening and closing of passages (e.g., mouth, anus).
* **Thermoregulation:** Muscle activity generates heat, contributing to body temperature maintenance.
#### 4.8.2 Structure and contraction of skeletal muscle
Skeletal muscle fibers are long, multinucleated cells containing myofibrils composed of actin and myosin filaments. Muscle cells do not typically divide; rather, they increase in size (hypertrophy) with training. Limited muscle repair is possible due to the presence of stem cells.
Muscle contraction occurs via the sliding filament mechanism. When a nerve impulse reaches the neuromuscular junction, acetylcholine (ACh) is released, triggering an action potential in the muscle fiber. This leads to the release of calcium ions ($Ca^{2+}$) from the sarcoplasmic reticulum (SR), which initiates the interaction between actin and myosin filaments, forming cross-bridges and causing muscle shortening. Relaxation occurs when ATP breaks these cross-bridges.
#### 4.8.3 Metabolic activities of skeletal muscles
Skeletal muscles are metabolically active, even at rest, and require a constant supply of ATP for contraction and relaxation. Energy sources vary depending on activity level:
* **Rest:** Muscles replenish energy stores, converting glucose to glycogen and fatty acids to ATP, which is then used to synthesize creatine phosphate.
* **Mild, aerobic activity:** Sufficient oxygen is available for cellular respiration, using fatty acids, triglycerides, and glucose from the blood.
* **Anaerobic activity:** During intense exercise with insufficient oxygen, muscles rely on rapid energy reserves like creatine phosphate and glycogen (producing lactate) in the cytosol.
#### 4.8.4 General structure and action of a muscle
* **Origin (origo):** The attachment point of a muscle to a stationary bone.
* **Insertion (insertie):** The attachment point of a muscle to a movable bone.
* **Muscle belly (spierbuik):** The fleshy, contractile portion of the muscle.
* **Head (caput):** A part of the muscle belly, often referring to muscles with multiple origins (e.g., biceps brachii has two heads).
Muscles are classified by the number of joints they cross:
* **Monoarticular muscles:** Cross one joint.
* **Biarticular muscles:** Cross two joints.
* **Polyarticular muscles:** Cross three or more joints.
#### 4.8.5 Movements
Muscles produce various movements:
* **General movements:**
* **Flexion:** Bending a joint.
* **Extension:** Straightening a joint.
* **Abduction:** Movement away from the midline.
* **Adduction:** Movement towards the midline.
* **Rotation:** Turning a bone around its axis (endorotation: towards the ventral side; exorotation: towards the dorsal side).
* **Specific movements:** Pronation/supination of the forearm, dorsiflexion/plantar flexion of the foot, inversion/eversion of the foot, elevation/depression, ulnar/radial abduction of the wrist, lateroflexion of the spine.
#### 4.8.6 Important muscles
Muscles are often named based on their shape, origin, insertion, or function. Key superficial muscles include:
* **Anterior:** Platysma, Rectus abdominis, Obliquus externus abdominis, Iliacus, Psoas major, Sartorius, Sternocleidomastoideus, Trapezius, Deltoideus, Pectoralis major, Biceps brachii, Brachioradialis, Obliquus internus abdominis, Transversus abdominis, Quadriceps femoris, Gastrocnemius, Soleus.
* **Posterior:** Sternocleidomastoideus, Latissimus dorsi, Gluteus medius, Gluteus maximus, Trapezius, Deltoideus, Triceps brachii, Brachioradialis, Gastrocnemius, Soleus.
Important muscle groups include the hamstrings (semimembranosus, biceps femoris, semitendinosus), muscles of the face (e.g., orbicularis oris, orbicularis oculi), deep back muscles, shoulder muscles (deltoid, trapezius, latissimus dorsi), chest and abdominal muscles (pectoralis major, rectus abdominis, obliques), arm muscles (triceps, biceps, brachioradialis), hip and thigh muscles (iliopsoas, quadriceps femoris, gluteals, hamstrings), and lower leg muscles (gastrocnemius, soleus). Intramuscular injections are commonly administered into the deltoid, vastus lateralis, or gluteus medius muscles due to their size and vascularization.
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# Muscular system
The muscular system is responsible for movement, stability, and thermoregulation, comprising specialized tissues that contract to produce force.
### 5.1 Functions of skeletal muscles
Skeletal muscles perform several crucial functions:
* **Movement and stabilization of bones:** They enable locomotion and maintain posture. For example, remaining upright requires continuous muscle engagement.
* **Stabilization of joints:** Strong muscles around joints provide stability, as seen with the calf muscles supporting the ankle.
* **Protection of soft tissues:** Muscles act as a protective layer for internal organs, such as the abdominal muscles safeguarding abdominal organs.
* **Opening and closing of entrances and exits:** Sphincter muscles, like those around the mouth, control the passage of substances.
* **Maintenance of body temperature:** Muscle contractions generate heat, contributing to thermoregulation.
### 5.2 Skeletal muscle tissue
Skeletal muscle cells, also known as muscle fibers, contain numerous myofibrils composed of actin and myosin filaments. The number of muscle cells remains constant throughout life, but they can increase in size through hypertrophy with training. Muscle fibers possess a limited number of stem cells, allowing for some degree of repair. Muscle contraction is initiated by a nerve signal reaching a synaptic knob, triggering the release of acetylcholine (ACh). ACh binds to receptors on the sarcolemma, opening ion channels and causing calcium ions ($Ca^{2+}$) to be released from the sarcoplasmic reticulum (SR). This calcium influx initiates muscle fiber contraction through the interaction of actin and myosin filaments via cross-bridges. Muscle relaxation occurs when ATP breaks these cross-bridges.
### 5.3 Metabolic activities of skeletal muscles
Skeletal muscles are metabolically active, consuming energy both during activity and at rest.
* **Rest:** Muscles replenish energy reserves by converting glucose to glycogen and fatty acids to ATP. Glycogen and creatine phosphate serve as rapid energy stores for muscle activity.
* **Mild, aerobic activity:** With sufficient oxygen, cells utilize aerobic respiration. Fuel sources include fatty acids from the blood, triglycerides within muscle cells, and glucose from the blood.
* **Anaerobic activity:** During oxygen-deficient conditions, aerobic respiration ceases. Muscles rely on rapid cytosolic reserves like creatine phosphate and glycogen, producing lactate as a byproduct.
### 5.4 General structure and action of a muscle
Muscles typically consist of a muscle belly and two tendons that attach to bones. When the muscle belly contracts, the bones move towards each other.
* **Origo:** The tendon attached to the stationary bone.
* **Insertie:** The tendon attached to the moving bone.
* **Caput:** The part of the muscle belly closest to the origo. Muscles can have multiple heads (e.g., biceps brachii, triceps brachii).
Muscles can be classified by the number of joints they cross:
* **Monoarticular muscles:** Cross and move one joint.
* **Biarticular muscles:** Cross two joints.
* **Polyarticular muscles:** Cross three or more joints.
### 5.5 Movements
Muscle actions produce various movements:
* **General movements:**
* **Sagittal plane:** Flexion (bending), Extension (straightening).
* **Frontal plane:** Abduction (movement away from the midline), Adduction (movement towards the midline).
* **Rotation:** Internal rotation (endorotation, rotating towards the ventral side), External rotation (exorotation, rotating towards the dorsal side).
* **Specific movements:**
* **Pronation and supination:** Rotation of the forearm (palm down vs. palm up).
* **Dorsiflexion and plantar flexion:** Bending of the foot at the ankle (towards the shin vs. towards the sole).
* **Palmar flexion:** Bending of the wrist towards the palm.
* **Inversion and eversion:** Turning the sole of the foot inwards or outwards.
* **Elevation and depression:** Lifting or lowering a body part.
* **Ulna and radial abduction:** Sideways movement of the wrist towards the ulna (pinky side) or radius (thumb side).
* **Lateral flexion:** Bending of the vertebral column to the side.
### 5.6 Key muscle groups
Muscle names often derive from their shape, origin, insertion, or function.
* **Head muscles:** Muscles like the platysma, sternocleidomastoid, and orbicularis oris (a sphincter for the mouth) are important for expression and function.
* **Back muscles:** Deep back muscles help maintain an upright posture.
* **Shoulder muscles:** The deltoid is the primary abductor of the shoulder. The trapezius covers the neck and upper torso, while the latissimus dorsi is the largest muscle in the body.
* **Chest and abdominal muscles:** Key muscles include the pectoralis major, external and internal obliques, transversus abdominis, and rectus abdominis. The linea alba is a midline connective tissue.
* **Arm muscles:**
* **Upper arm:** Triceps brachii (posterior) and biceps brachii (anterior) are primary movers. Brachioradialis also aids in forearm flexion.
* **Forearm:** Extensors and flexors of the forearm are important for hand and wrist movements. Overuse can lead to conditions like tennis elbow (lateral epicondylitis) or golfer's elbow (medial epicondylitis).
* **Hip and thigh muscles:**
* **Anterior hip:** Psoas major and iliacus combine to form the iliopsoas, a primary hip flexor. Sartorius is also a hip flexor.
* **Quadriceps femoris:** A four-headed muscle on the anterior thigh (rectus femoris, vastus medialis, vastus intermedius, vastus lateralis) responsible for knee extension.
* **Posterior hip/thigh:** Gluteus medius and maximus are posterior hip muscles. Hamstrings (semimembranosus, biceps femoris, semitendinosus) flex the knee and extend the hip.
* **Lower leg muscles:** Gastrocnemius and soleus are primary calf muscles responsible for plantarflexion.
* **Common injection sites:** Intramuscular injections are typically administered into the gluteus medius, vastus lateralis of the quadriceps femoris, or the deltoid muscle due to their size and vascularity.
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# The skin
The skin is a dynamic, protective organ that functions as the body's primary barrier against the external environment, playing crucial roles in thermoregulation, sensation, vitamin D production, and maintaining homeostasis.
### 6.1 Structure of the skin
The skin, also known as the integumentum, is the largest organ of the body, accounting for approximately 5.5% of total body weight. Its thickness varies, ranging from about 0.5 mm on the eyelids to 4 mm on the soles of the feet and palms. The skin is composed of three primary layers: the epidermis, dermis, and hypodermis.
#### 6.1.1 Epidermis
The epidermis is the outermost layer of the skin and serves as the primary protective barrier. It is composed of keratinized stratified squamous epithelium and lacks blood vessels. The epidermis is constantly renewed through cell division. Its main cell types are:
* **Keratinocytes (90%):** These cells produce keratin, a tough protein that makes the epidermis harder, stronger, and water-repellent. They originate in the stratum basale and migrate to the surface, undergoing programmed cell death.
* **Melanocytes (8%):** These cells produce melanin, a pigment that provides color to the skin (yellow-red to brown-black) and protects keratinocytes from damaging ultraviolet (UV) radiation from the sun.
The epidermis is further divided into four or five distinct layers, from deepest to most superficial:
* **Stratum basale:** Contains stem cells responsible for continuous keratinocyte division.
* **Stratum spinosum:** Cells begin to flatten and interlock.
* **Stratum granulosum:** Cells undergo programmed cell death.
* **Stratum lucidum:** A thin, clear layer found only in the palms of the hands and soles of the feet.
* **Stratum corneum:** Composed of 25-30 layers of dead, flattened keratinocytes that are eventually shed. The epidermis renews itself approximately once a month.
##### 6.1.1.1 Epidermal pathologies
* **Melanoma:** A dangerous form of skin cancer that arises from mutations in melanocytes due to excessive UV exposure.
* **Psoriasis:** A condition where keratinocyte maturation is disrupted, leading to a thickened stratum corneum, scaling, and itching.
#### 6.1.2 Dermis
The dermis, or corium, is the layer beneath the epidermis, primarily composed of dense connective tissue. It is thicker than the epidermis and provides strength and elasticity to the skin. The dermis contains:
* **Fibroblasts:** Produce collagen and elastin fibers.
* **Macrophages:** Involved in immune defense.
* **Adipocytes:** Present in smaller quantities.
* Numerous blood vessels and nerve cells, which are crucial for thermoregulation and sensation.
The dermis is divided into two sub-layers:
* **Stratum reticulare:** The thicker, deeper layer.
* **Stratum papillare:** The superficial, thinner layer, containing numerous blood vessels that play a role in regulating body temperature through vasodilation (widening of blood vessels to release heat) and vasoconstriction (narrowing of blood vessels to conserve heat).
##### 6.1.2.1 Dermal pathologies
* **Stretch marks (striae):** Occur due to the stretching of the dermis, causing damage to collagen fibers and small blood vessels. Initially red, they fade to silver or white scars.
The dermis is rich in nerve endings, making the skin sensitive to pressure, touch, temperature, and pain. It also houses hair follicles, sebaceous (oil) glands, and sweat glands.
#### 6.1.3 Hypodermis
The hypodermis, also known as the subcutaneous layer, lies beneath the dermis. It is not technically part of the skin but anchors the skin to underlying muscles and bones. It consists of loose connective tissue and adipose (fat) tissue.
* **Functions of adipose tissue in the hypodermis:**
* Thermal insulation.
* Energy storage.
* Mechanical protection (acting as a shock absorber).
##### 6.1.3.1 Hypodermal pathologies
* **Lanugo:** In cases of severe malnutrition (e.g., anorexia nervosa), a fine, downy hair may develop to compensate for the lack of insulating fat.
### 6.2 Functions of the skin
The skin performs several vital functions:
* **Homeostasis:** Maintaining a stable internal environment.
* **Thermoregulation:** Regulating body temperature through sweating and blood vessel diameter.
* **Protection:** Acting as a physical barrier against pathogens, UV radiation, and dehydration.
* **Vitamin D synthesis:** Producing vitamin D when exposed to UV radiation.
* **Sensation:** Detecting pain, pressure, temperature, and touch through nerve endings.
* **Excretion:** Eliminating small amounts of waste products through sweat.
### 6.3 Skin color determination
Skin color is determined by three pigments:
* **Melanin:** The primary pigment, produced by melanocytes, responsible for brown-black and yellow-red hues. Higher melanin content offers better UV protection.
* **Carotene:** A yellowish-orange pigment obtained from diet, which can be converted to vitamin A.
* **Hemoglobin:** The oxygen-carrying pigment in red blood cells, which can impart a pinkish hue to lighter skin.
#### 6.3.1 Skin color pathologies
* **Cyanosis:** A bluish discoloration of the skin indicating low oxygen levels in the blood.
* **Icterus (Jaundice):** A yellowish discoloration of the skin, often indicative of liver, gallbladder, or bile duct problems, or due to bilirubin buildup from the breakdown of red blood cells.
* **Albinism:** A genetic disorder characterized by a lack of melanin production, resulting in very pale skin, hair, and eyes, and increased risk of skin cancer.
### 6.4 Accessory structures of the skin
#### 6.4.1 Hair
Hair is found all over the body except for the palms, soles, and fingertips. Its growth is influenced by genetics and hormones. Hair provides protection from UV radiation and plays a role in thermoregulation (though less significant in humans). Arrector pili muscles attached to hair follicles contract in response to cold or stress, causing "goosebumps."
#### 6.4.2 Glands
The skin contains two main types of glands:
* **Sweat glands (sudoriferous glands):** Approximately 3-4 million sweat glands are present, connected to hair follicles or directly to the skin surface.
* **Eccrine glands:** Distributed widely, especially on the forehead, palms, and soles. They primarily regulate body temperature.
* **Apocrine glands:** Located in the axillae, groin, anus, areolae, and navel. They become active at puberty and are associated with pheromone production. Sweat itself is odorless; body odor results from bacterial decomposition.
* **Sebaceous glands (oil glands):** These glands are usually associated with hair follicles. They produce sebum, an oily substance that lubricates the hair and skin, prevents excessive water evaporation, and inhibits bacterial growth. Sebaceous glands are sensitive to hormones and can become overactive during puberty, leading to acne.
### 6.5 Wounds and healing
The skin has a remarkable capacity for repair. Minor cuts and abrasions heal relatively quickly. Deeper wounds can involve the dermis and may lead to scar formation. The epidermis regenerates from stem cells in the stratum basale, while the dermis, composed of connective tissue, has a more limited regenerative capacity.
### 6.6 Skin pathologies
Beyond those mentioned earlier, various conditions affect the skin, including infections (bacterial, fungal, viral), inflammatory conditions (eczema, dermatitis), and neoplastic growths. Understanding the skin's structure and function is crucial for diagnosing and managing these diverse pathologies.
* * *
## Common mistakes to avoid
* Review all topics thoroughly before exams
* Pay attention to formulas and key definitions
* Practice with examples provided in each section
* Don't memorize without understanding the underlying concepts
Glossary
| Term | Definition |
|------|------------|
| Anatomy | The study of the structure of an organism and the relationship of its parts. |
| Physiology | The study of the functions of the body and the sciences that underpin the functions of the human body. |
| Terminologia Anatomica | The specialized language used by medical and paramedical professionals, often derived from Greek or Latin, for anatomical descriptions. |
| Macroscopic Anatomy | The study of anatomical structures that can be observed with the naked eye. |
| Microscopic Anatomy | The study of anatomical structures that can only be observed with the aid of a microscope. |
| Systemic Anatomy | The study of the body by systems (e.g., the nervous system, skeletal system). |
| Topographical Anatomy | The study of the body by regions (e.g., the head, thorax, abdomen). |
| Homeostasis | The maintenance of a stable internal environment within the body, despite changes in external conditions. |
| Anatomical Position | A standardized reference position for the body, used to describe locations and movements, characterized by standing erect, face and feet forward, arms hanging at the sides with palms forward. |
| Cephalic Region | The head area of the body. |
| Cervical Region | The neck area of the body. |
| Truncus | The main part of the body, excluding the head and limbs, consisting of the thorax, abdomen, and pelvis. |
| Thorax | The chest cavity, bounded by the ribs and diaphragm. |
| Abdomen | The body area between the diaphragm and the pelvic girdle. |
| Pelvis | The lower part of the trunk, between the abdomen and the thighs. |
| Anterior View | A view from the front of the body. |
| Posterior View | A view from the back of the body. |
| Inferior View | A view from below. |
| Superior View | A view from above. |
| Lateral View | A view from the side. |
| Frontal Plane | A plane parallel to the forehead that divides the body into anterior and posterior portions. |
| Sagittal Plane | A plane parallel to the midsagittal plane that divides the body into left and right portions. |
| Transverse Plane | A plane parallel to the ground that divides the body into superior and inferior portions. |
| Atomic Level | The fundamental level of organization in the body, consisting of atoms. |
| Molecular Level | The level of organization where atoms combine to form molecules. |
| Cellular Level | The level of organization where molecules form cells, the basic units of life. |
| Tissue Level | The level of organization where similar cells group together to perform a specific function. |
| Organ Level | The level of organization where different tissues combine to form an organ with a specific function. |
| Organ System Level | The level of organization where multiple organs work together to perform a major life function. |
| Organism Level | The complete living being, composed of multiple organ systems. |
| Atom | The smallest particle of an element that retains the chemical properties of that element. |
| Ion | An atom or molecule that has gained or lost one or more electrons, resulting in a net electrical charge. |
| Cation | A positively charged ion, formed when an atom loses electrons. |
| Anion | A negatively charged ion, formed when an atom gains electrons. |
| Ionic Bond | A chemical bond formed by the electrostatic attraction between oppositely charged ions. |
| Covalent Bond | A chemical bond formed by the sharing of electrons between atoms. |
| Polar Covalent Bond | A covalent bond in which the electrons are shared unequally between atoms, creating partial positive and negative charges. |
| Nonpolar Covalent Bond | A covalent bond in which the electrons are shared equally between atoms, resulting in no net charge. |
| Molecule | A group of two or more atoms held together by chemical bonds. |
| ATP (Adenosine Triphosphate) | The primary energy currency of the cell, used to power cellular processes. |
| Inorganic Chemistry | The branch of chemistry that deals with compounds that do not primarily contain carbon, such as water and salts. |
| Organic Chemistry | The branch of chemistry that deals with compounds containing carbon, such as carbohydrates, lipids, proteins, and nucleic acids. |
| Water | An inorganic molecule essential for life, acting as a solvent and participating in many chemical reactions. |
| pH | A measure of the acidity or alkalinity of a solution, based on the concentration of hydrogen ions ($H^+$). |
| Acid | A substance that donates protons ($H^+$) to a solution, lowering its pH. |
| Base | A substance that accepts protons ($H^+$) from a solution, raising its pH. |
| Buffer | A substance that minimizes changes in pH when an acid or base is added to a solution. |
| Carbohydrates | Organic molecules composed of carbon, hydrogen, and oxygen, serving as primary energy sources for the body. |
| Lipids | A diverse group of hydrophobic organic molecules, including fats, oils, steroids, and phospholipids, important for energy storage and cell membrane structure. |
| Proteins | Complex organic molecules composed of amino acids, essential for numerous bodily functions, including structure, enzymes, and transport. |
| Nucleic Acids | Macromolecules, such as DNA and RNA, that carry genetic information and are involved in protein synthesis. |
| Monosaccharide | A simple sugar, the basic unit of carbohydrates (e.g., glucose, fructose). |
| Disaccharide | A carbohydrate composed of two monosaccharide units linked together (e.g., sucrose, lactose). |
| Polysaccharide | A complex carbohydrate composed of many monosaccharide units linked together (e.g., starch, glycogen, cellulose). |
| Enzyme | A protein that acts as a biological catalyst, speeding up specific chemical reactions without being consumed in the process. |
| DNA (Deoxyribonucleic Acid) | The molecule that carries genetic instructions for the development, functioning, growth, and reproduction of all known organisms. |
| RNA (Ribonucleic Acid) | A molecule similar to DNA, involved in protein synthesis and gene regulation. |
| Cell | The basic structural, functional, and biological unit of all known organisms. |
| Plasma Membrane | The selectively permeable outer boundary of a cell, regulating the passage of substances into and out of the cell. |
| Cytoplasm | The jelly-like substance filling a cell, enclosing the organelles. |
| Nucleus | The central organelle of a eukaryotic cell, containing the cell's genetic material (DNA). |
| Organelle | A specialized subunit within a cell that has a specific function. |
| Cytosol | The aqueous component of the cytoplasm. |
| Endoplasmic Reticulum (ER) | A network of membranes within eukaryotic cells involved in protein and lipid synthesis. |
| Ribosomes | Cellular particles responsible for protein synthesis. |
| Golgi Apparatus | An organelle that modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles. |
| Lysosome | An organelle containing digestive enzymes that break down waste materials and cellular debris. |
| Mitochondrion | The powerhouse of the cell, responsible for cellular respiration and ATP production. |
| Cell Respiration | The metabolic process by which cells convert glucose and oxygen into ATP, carbon dioxide, and water. |
| Diffusion | The passive movement of molecules from an area of high concentration to an area of low concentration. |
| Osmosis | The passive movement of water across a selectively permeable membrane from an area of low solute concentration to an area of high solute concentration. |
| Active Transport | The movement of molecules across a cell membrane against their concentration gradient, requiring energy (ATP). |
| Vesicular Transport | A mechanism for moving large molecules or particles across the cell membrane using vesicles (e.g., endocytosis, exocytosis). |
| Metabolism | The sum of all chemical processes that occur within a living organism to maintain life. |
| Anabolism | Metabolic pathways that build complex molecules from simpler ones, requiring energy. |
| Catabolism | Metabolic pathways that break down complex molecules into simpler ones, releasing energy. |
| Mitosis | Cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent nucleus. |
| Meiosis | Cell division that reduces the chromosome number by half, producing gametes (sperm and egg cells). |
| Histology | The study of tissues, their structure, and their function. |
| Tissue | A group of similar cells and their extracellular matrix that perform a specific function. |
| Epithelial Tissue | Tissue that covers body surfaces, lines body cavities, and forms glands. |
| Connective Tissue | Tissue that supports, connects, or separates different types of tissues and organs in the body. |
| Muscle Tissue | Tissue composed of cells that have the special ability to shorten or contract in order to produce movement. |
| Nervous Tissue | Tissue that forms the nervous system, responsible for transmitting nerve impulses. |
| Skeletal System | The framework of bones that supports the body, protects organs, and allows for movement. |
| Musculoskeletal System | The integrated system of muscles, bones, and joints that produces movement. |
| Tendon | A fibrous connective tissue that attaches muscle to bone. |
| Ligament | A fibrous connective tissue that attaches bone to bone. |
| Articulation (Joint) | The connection between two or more bones. |
| Axial Skeleton | The part of the skeleton that lies along the central axis of the body, including the skull, vertebral column, and rib cage. |
| Appendicular Skeleton | The part of the skeleton that includes the limbs and girdles that attach them to the axial skeleton. |
| Long Bone | A bone that is longer than it is wide, such as the femur or humerus. |
| Short Bone | Bones that are roughly cuboidal in shape, such as the carpal and tarsal bones. |
| Flat Bone | Bones that are thin, flattened, and often curved, such as the sternum or scapula. |
| Irregular Bone | Bones that have complex shapes and do not fit into the other categories, such as vertebrae. |
| Sesamoid Bone | Bones that are embedded within a tendon or a muscle, such as the patella. |
| Compact Bone | Dense, hard bone tissue that forms the outer layer of most bones. |
| Spongy Bone | Porous, lattice-like bone tissue found within the inner part of bones. |
| Diaphysis | The shaft of a long bone. |
| Epiphysis | The expanded ends of a long bone. |
| Periosteum | A tough, fibrous membrane that covers the outer surface of bones. |
| Skull | The bony framework of the head. |
| Vertebral Column | The series of bones forming the spine, protecting the spinal cord. |
| Thorax (Rib Cage) | The bony structure of the chest, protecting the heart and lungs. |
| Shoulder Girdle | The set of bones that connect the upper limbs to the axial skeleton, consisting of the scapula and clavicle. |
| Upper Limb | The arm, forearm, and hand. |
| Pelvic Girdle | The set of bones that connect the lower limbs to the axial skeleton, consisting of the hip bones. |
| Lower Limb | The thigh, leg, and foot. |
| Joint | The articulation or connection between two or more bones. |
| Synovial Joint | A freely movable joint characterized by a joint capsule, synovial membrane, and synovial fluid. |
| Skeletal Muscle | A type of muscle tissue that is attached to bones and is responsible for voluntary movement. |
| Muscle Contraction | The process by which a muscle shortens and generates force. |
| Origin | The point of attachment of a muscle that is relatively fixed. |
| Insertion | The point of attachment of a muscle that is relatively movable. |
| Agonist | A muscle that is the primary mover of a movement. |
| Antagonist | A muscle that opposes the action of an agonist. |
| Pronation | A rotation of the forearm that turns the palm downward. |
| Supination | A rotation of the forearm that turns the palm upward. |
| Flexion | A movement that decreases the angle between two bones. |
| Extension | A movement that increases the angle between two bones. |
| Abduction | A movement away from the midline of the body. |
| Adduction | A movement toward the midline of the body. |
| Rotation | A movement around an axis. |
| Skin | The outer covering of the body, serving as a protective barrier and involved in sensation, temperature regulation, and vitamin D production. |
| Epidermis | The outermost layer of the skin, composed of stratified squamous epithelium. |
| Dermis | The layer of skin beneath the epidermis, composed of connective tissue. |
| Hypodermis | The layer of tissue beneath the dermis, composed primarily of adipose tissue. |
| Keratinocyte | A cell type in the epidermis that produces keratin, providing strength and waterproofing to the skin. |
| Melanocyte | A cell type in the epidermis that produces melanin, the pigment responsible for skin color and UV protection. |
| Melanin | A pigment that gives skin, hair, and eyes their color and protects against UV radiation. |
| Stratum Corneum | The outermost layer of the epidermis, composed of dead, keratinized cells. |
| Stratum Basale | The deepest layer of the epidermis, containing stem cells that divide to produce new keratinocytes. |
| Hair Follicle | A structure in the dermis from which a hair grows. |
| Sweat Gland | Glands in the skin that produce sweat for thermoregulation and excretion. |
| Sebaceous Gland | Glands in the skin that produce sebum, an oily substance that lubricates the skin and hair. |
| Sebum | The oily secretion of sebaceous glands. |
| Integumentary System | The skin and its accessory structures, including hair, nails, and glands. |
| Psoriasis | A chronic skin condition characterized by red, itchy, scaly patches. |
| Melanooma | A serious form of skin cancer that develops from melanocytes. |
| Cyanosis | A bluish discoloration of the skin resulting from poor oxygenation of the blood. |
| Icterus (Jaundice) | Yellowing of the skin and whites of the eyes caused by excess bilirubin in the blood. |
| Albinism | A genetic disorder characterized by a lack of melanin production, resulting in pale skin, hair, and eyes. |
| Homeostasis (Cellular Context) | The maintenance of a stable internal environment within a cell. |
| Plasmalemma (Cell Membrane) | Another term for the plasma membrane. |
| Endoplasmic Reticulum (ER) | A network of membranes within eukaryotic cells involved in protein and lipid synthesis. |
| Rough ER | Endoplasmic reticulum with ribosomes attached, involved in protein synthesis. |
| Smooth ER | Endoplasmic Reticulum without ribosomes, involved in lipid synthesis and detoxification. |
| Golgi Apparatus | An organelle that modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles. |
| Lysosome | An organelle containing digestive enzymes that break down waste materials and cellular debris. |
| Mitochondrion | The powerhouse of the cell, responsible for cellular respiration and ATP production. |
| Cell Respiration | The metabolic process by which cells convert glucose and oxygen into ATP, carbon dioxide, and water. |
| Endocytosis | The process by which cells absorb molecules from outside the cell by engulfing them with their cell membrane. |
| Exocytosis | The process by which cells move molecules from within the cell to the outside of the cell. |
| Metabolic Pathway | A series of chemical reactions that occur in a cell, catalyzed by enzymes. |
| Anabolic Reactions | Metabolic pathways that build complex molecules from simpler ones, requiring energy. |
| Catabolic Reactions | Metabolic pathways that break down complex molecules into simpler ones, releasing energy. |
| Glycogenolysis | The breakdown of glycogen to glucose. |
| Glycolysis | The breakdown of glucose into pyruvate. |
| Lipolysis | The breakdown of triglycerides into glycerol and free fatty acids. |
| Beta-oxidation | The breakdown of fatty acids into acetyl-CoA. |
| Glycogenesis | The synthesis of glycogen from glucose. |
| Gluconeogenesis | The synthesis of glucose from non-carbohydrate sources. |
| Lipogenesis | The synthesis of triglycerides from glycerol and free fatty acids. |
| Mitosis | Cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent nucleus. |
| Meiosis | Cell division that reduces the chromosome number by half, producing gametes (sperm and egg cells). |
| Diploid | Having two complete sets of chromosomes, one from each parent. |
| Haploid | Having a single set of unpaired chromosomes. |
| Gametes | Reproductive cells (sperm and egg) that are haploid. |
| Tissue | A group of similar cells and their extracellular matrix that perform a specific function. |
| Histology | The study of tissues, their structure, and their function. |
| Epithelial Tissue | Tissue that covers body surfaces, lines body cavities, and forms glands. |
| Connective Tissue | Tissue that supports, connects, or separates different types of tissues and organs in the body. |
| Muscle Tissue | Tissue composed of cells that have theSPECIAL ABILITY to shorten or contract in order to produce movement. |
| Nervous Tissue | Tissue that forms the nervous system, responsible for transmitting nerve impulses. |
| Bone Tissue | A specialized type of connective tissue that forms the bones of the skeleton. |
| Cartilage Tissue | A flexible connective tissue found in joints, the ear, nose, and other parts of the body. |
| Blood | A fluid connective tissue that circulates throughout the body, transporting oxygen, nutrients, and waste products. |
| Lymph | A fluid that circulates through the lymphatic system, helping to remove waste products and fight infection. |
| Compact Bone Tissue | Dense, hard bone tissue that forms the outer layer of most bones. |
| Spongy Bone Tissue | Porous, lattice-like bone tissue found within the inner part of bones. |
| Skeletal Muscle Tissue | A type of muscle tissue that is attached to bones and is responsible for voluntary movement. |
| Smooth Muscle Tissue | A type of muscle tissue found in the walls of internal organs and blood vessels, responsible for involuntary movements. |
| Cardiac Muscle Tissue | A type of muscle tissue found only in the heart, responsible for pumping blood. |
| Neuron | A nerve cell that transmits electrical and chemical signals. |
| Glial Cell | Supporting cells that surround and protect neurons. |
| Skelet | The bones of the body, forming a framework that supports and protects. |
| Musculoskeletal System | The integrated system of muscles, bones, and joints that produces movement. |
| Tendon | A fibrous connective tissue that attaches muscle to bone. |
| Ligament | A fibrous connective tissue that attaches bone to bone. |
| Articulation (Joint) | The connection between two or more bones. |
| Axial Skeleton | The part of the skeleton that lies along the central axis of the body, including the skull, vertebral column, and rib cage. |
| Appendicular Skeleton | The part of the skeleton that includes the limbs and girdles that attach them to the axial skeleton. |
| Long Bone | A bone that is longer than it is wide, such as the femur or humerus. |
| Short Bone | Bones that are roughly cuboidal in shape, such as the carpal and tarsal bones. |
| Flat Bone | Bones that are thin, flattened, and often curved, such as the sternum or scapula. |
| Irregular Bone | Bones that have complex shapes and do not fit into the other categories, such as vertebrae. |
| Sesamoid Bone | Bones that are embedded within a tendon or a muscle, such as the patella. |
| Compact Bone Tissue | Dense, hard bone tissue that forms the outer layer of most bones. |
| Spongy Bone Tissue | Porous, lattice-like bone tissue found within the inner part of bones. |
| Diaphysis | The shaft of a long bone. |
| Epiphysis | The expanded ends of a long bone. |
| Periosteum | A tough, fibrous membrane that covers the outer surface of bones. |
| Red Bone Marrow | Bone marrow that produces red blood cells, white blood cells, and platelets. |
| Yellow Bone Marrow | Bone marrow that consists primarily of fat and is found in the medullary cavity of long bones. |
| Skull | The bony framework of the head. |
| Cranium | The part of the skull that encloses the brain. |
| Facial Skeleton | The bones of the face. |
| Sinus | Air-filled cavities in the bones of the skull. |
| Fontanelle | Soft spots on the skull of a newborn that allow for brain growth and passage through the birth canal. |
| Vertebral Column | The series of bones forming the spine, protecting the spinal cord. |
| Vertebra | A single bone of the vertebral column. |
| Thoracic Cage | The bony structure of the chest, protecting the heart and lungs. |
| Sternum | The breastbone, located in the center of the chest. |
| Ribs | The curved bones that form the rib cage, protecting the chest organs. |
| True Ribs | The first seven pairs of ribs that attach directly to the sternum. |
| False Ribs | The remaining five pairs of ribs that do not attach directly to the sternum. |
| Floating Ribs | The last two pairs of false ribs that do not attach to the sternum at all. |
| Shoulder Girdle | The set of bones that connect the upper limbs to the axial skeleton, consisting of the scapula and clavicle. |
| Scapula | The shoulder blade. |
| Clavicle | The collarbone. |
| Humerus | The bone of the upper arm. |
| Radius | The bone of the forearm on the thumb side. |
| Ulna | The bone of the forearm on the pinky finger side. |
| Hand | The part of the upper limb from the wrist to the fingertips, including the carpal bones, metacarpal bones, and phalanges. |
| Carpals | The eight small bones of the wrist. |
| Metacarpals | The five bones of the palm. |
| Phalanges | The bones of the fingers and toes. |
| Pelvic Girdle | The set of bones that connect the lower limbs to the axial skeleton, consisting of the hip bones. |
| Pelvis | The bony structure of the lower torso, supporting the spine and protecting the pelvic organs. |
| Hip Bone (Os Coxae) | Each of the two bones that make up the pelvis. |
| Femur | The thigh bone, the longest and strongest bone in the body. |
| Patella | The kneecap, a sesamoid bone located in front of the knee joint. |
| Tibia | The shin bone, the larger of the two bones in the lower leg. |
| Fibula | The smaller of the two bones in the lower leg, located lateral to the tibia. |
| Ankle | The joint between the tibia, fibula, and talus. |
| Foot | The part of the lower limb from the ankle to the toes, including the tarsal bones, metatarsal bones, and phalanges. |
| Tarsals | The seven bones of the ankle and hindfoot. |
| Calcaneus | The heel bone. |
| Metatarsals | The five bones of the midfoot. |
| Phalanges | The bones of the fingers and toes. |
| Joint | The articulation or connection between two or more bones. |
| Fibrous Joint | A joint in which bones are connected by dense fibrous connective tissue. |
| Cartilaginous Joint | A joint in which bones are connected by cartilage. |
| Synovial Joint | A freely movable joint characterized by a joint capsule, synovial membrane, and synovial fluid. |
| Synovial Fluid | A lubricating fluid found in synovial joints. |
| Bursae | Small fluid-filled sacs that reduce friction between tendons and bones. |
| Skeletal Muscle | A type of muscle tissue that is attached to bones and is responsible for voluntary movement. |
| Muscle Fiber | A single muscle cell. |
| Myofibril | A contractile filament within muscle cells. |
| Actin | A protein filament that plays a role in muscle contraction. |
| Myosin | A protein filament that interacts with actin to produce muscle contraction. |
| ATP (Adenosine Triphosphate) | The primary energy currency of the cell, used to power cellular processes. |
| Creatine Phosphate | A high-energy molecule that can rapidly replenish ATP stores in muscles. |
| Aerobic Respiration | The process by which cells produce ATP in the presence of oxygen. |
| Anaerobic Respiration | The process by which cells produce ATP in the absence of oxygen, resulting in the production of lactic acid. |
| Lactic Acid | A byproduct of anaerobic respiration that can build up in muscles and cause fatigue. |
| Origo | The origin or fixed attachment point of a muscle. |
| Insertie | The insertion or movable attachment point of a muscle. |
| Muscle Belly | The main body of a muscle. |
| Agonist | A muscle that is the primary mover of a movement. |
| Antagonist | A muscle that opposes the action of an agonist. |
| Monoarticular Muscle | A muscle that crosses only one joint. |
| Biarticular Muscle | A muscle that crosses two joints. |
| Polyarticular Muscle | A muscle that crosses three or more joints. |
| Pronation | A rotation of the forearm that turns the palm downward. |
| Supination | A rotation of the forearm that turns the palm upward. |
| Dorsiflexion | Bending the foot upward toward the shin. |
| Plantar Flexion | Bending the foot downward away from the shin. |
| Inversion | Turning the sole of the foot inward. |
| Eversion | Turning the sole of the foot outward. |
| Elevation | Raising a body part. |
| Depression | Lowering a body part. |
| Radial Abduction | Movement of the wrist away from the midline of the body toward the thumb. |
| Ulnar Abduction | Movement of the wrist away from the midline of the body toward the pinky finger. |
| Lateral Flexion | Bending the vertebral column to the side. |
| Gluteus Maximus | The large muscle of the buttocks, responsible for hip extension. |
| Quadriceps Femoris | A group of four muscles on the front of the thigh, responsible for knee extension. |
| Hamstrings | A group of three muscles on the back of the thigh, responsible for knee flexion and hip extension. |
| Gastrocnemius | The calf muscle, responsible for plantar flexion of the foot. |
| Soleus | A muscle in the calf that lies beneath the gastrocnemius, also involved in plantar flexion. |
| Deltoid | The shoulder muscle, responsible for arm abduction. |
| Pectoralis Major | The large chest muscle. |
| Biceps Brachii | The muscle on the front of the upper arm, responsible for elbow flexion. |
| Triceps Brachii | The muscle on the back of the upper arm, responsible for elbow extension. |
| Sternocleidomastoid | A muscle in the neck that helps to move the head. |
| Trapezius | A large muscle that covers the upper back and neck, involved in shoulder and neck movements. |
| Latissimus Dorsi | The largest muscle of the back, involved in arm extension and adduction. |
| Rectus Abdominis | The abdominal muscle that runs vertically along the front of the abdomen. |
| Obliquus Externus Abdominis | The outermost of the three flat muscles of the side of the abdomen. |
| Obliquus Internus Abdominis | The middle of the three flat muscles of the side of the abdomen. |
| Transversus Abdominis | The innermost of the three flat muscles of the side of the abdomen. |
| Psoas Major | A deep muscle of the abdomen that connects the lumbar spine to the femur, involved in hip flexion. |
| Iliacus | A muscle of the hip that joins with the psoas major to form the iliopsoas muscle. |
| Sartorius | The longest muscle in the body, running diagonally across the thigh. |
| Brachioradialis | A muscle in the forearm that flexes the elbow. |
| Hand Muscles | Small muscles in the hand that control finger movements. |
| Carpal Tunnel | A narrow passageway in the wrist through which the median nerve and tendons pass. |
| Carpal Tunnel Syndrome | A condition caused by compression of the median nerve in the carpal tunnel. |
| Hip Muscles | Muscles of the hip joint, including the gluteal muscles and hip flexors. |
| Quadriceps Femoris | A group of four muscles on the front of the thigh, responsible for knee extension. |
| Hamstrings | A group of three muscles on the back of the thigh, responsible for knee flexion and hip extension. |
| Gastrocnemius | The calf muscle, responsible for plantar flexion of the foot. |
| Soleus | A muscle in the calf that lies beneath the gastrocnemius, also involved in plantar flexion. |
| Foot Muscles | Intrinsic muscles within the foot that control toe movements. |
| Intramuscular Injection | An injection of medication directly into a muscle. |
| Skin | The outer covering of the body, serving as a protective barrier and involved in sensation, temperature regulation, and vitamin D production. |
| Epidermis | The outermost layer of the skin, composed of stratified squamous epithelium. |
| Dermis | The layer of skin beneath the epidermis, composed of connective tissue. |
| Hypodermis | The layer of tissue beneath the dermis, composed primarily of adipose tissue. |
| Keratinocyte | A cell type in the epidermis that produces keratin, providing strength and waterproofing to the skin. |
| Melanocyte | A cell type in the epidermis that produces melanin, the pigment responsible for skin color and UV protection. |
| Melanin | A pigment that gives skin, hair, and eyes their color and protects against UV radiation. |
| Stratum Corneum | The outermost layer of the epidermis, composed of dead, keratinized cells. |
| Stratum Basale | The deepest layer of the epidermis, containing stem cells that divide to produce new keratinocytes. |
| Hair Follicle | A structure in the dermis from which a hair grows. |
| Sweat Gland | Glands in the skin that produce sweat for thermoregulation and excretion. |
| Sebaceous Gland | Glands in the skin that produce sebum, an oily substance that lubricates the skin and hair. |
| Sebum | The oily secretion of sebaceous glands. |
| Integumentary System | The skin and its accessory structures, including hair, nails, and glands. |
| Psoriasis | A chronic skin condition characterized by red, itchy, scaly patches. |
| Melanooma | A serious form of skin cancer that develops from melanocytes. |
| Cyanosis | A bluish discoloration of the skin resulting from poor oxygenation of the blood. |
| Icterus (Jaundice) | Yellowing of the skin and whites of the eyes caused by excess bilirubin in the blood. |
| Albinism | A genetic disorder characterized by a lack of melanin production, resulting in pale skin, hair, and eyes. |