HFST 4 Fysiologie - Bloedsomloop ^M hart.pptx

# General functions and composition of blood Blood is a vital bodily fluid that serves multiple critical functions, including transport, regulation, and protection, and its composition comprises both a liquid plasma and solid cellular components. ### 1.1 General functions of blood Blood plays a multifaceted role in maintaining homeostasis within the body, acting as a transport medium, a regulator of physiological conditions, and a key component of the immune system. #### 1.1.1 Transport Blood is responsible for the transportation of essential substances throughout the body: * **Gases:** It carries dissolved gases like oxygen ($\text{O}_2$) from the lungs to the tissues and carbon dioxide ($\text{CO}_2$) from the tissues back to the lungs for exhalation. * **Nutrients:** Blood transports absorbed nutrients from the digestive system to all cells in the body. * **Hormones:** It delivers hormones secreted by endocrine glands to their target cells, enabling communication and regulation of various bodily processes. * **Waste products:** Blood carries metabolic waste products from active cells to excretory organs, primarily the kidneys, for elimination. #### 1.1.2 Regulation Blood is crucial for maintaining stable internal conditions: * **Heat regulation:** It helps in the regulation of body temperature by distributing heat generated by active muscles to other tissues and by facilitating heat exchange with the environment through the skin. #### 1.1.3 Protection and defense Blood provides defense mechanisms against injury and infection: * **Blood clotting:** It initiates processes to limit fluid loss during injuries by forming clots. * **Immunity:** Blood contains components that defend the body against toxins and pathogens like bacteria and viruses. ### 1.2 Composition of blood Blood is composed of approximately 55% plasma and 45% solid components, collectively known as the "corpuscular fraction." The total blood volume is roughly 1 liter per 13 kilograms of body weight. #### 1.2.1 Plasma Plasma is the liquid component of blood, making up about 55% of its total volume. * **Water:** Constitutes approximately 90% of blood plasma. * **Dissolved proteins:** Plasma contains a significant amount of dissolved proteins, including: * **Albumin:** This is the most abundant protein (about 60%). Its large size prevents it from easily crossing blood vessel walls, helping to maintain osmotic pressure and draw water from the tissues into the vessels. * **Globulins:** These proteins (about 35%) include antibodies (immunoglobulins) involved in immunity and transport proteins that bind to small ions, hormones, and other poorly soluble compounds. * **Fibrinogen:** This protein is essential for blood clotting. * **Serum:** Plasma from which clotting proteins have been removed. * **Other dissolved substances:** Plasma also contains various other molecules: * **Organic nutrients:** Such as glucose, lipids, and amino acids. * **Electrolytes:** Including ions like sodium ($\text{Na}^+$), potassium ($\text{K}^+$), magnesium ($\text{Mg}^{2+}$), and calcium ($\text{Ca}^{2+}$). * **Organic waste products:** Such as urea, creatinine, and bilirubin. #### 1.2.2 Solid blood components (corpuscular fraction) The solid components of blood, which constitute about 45% of the total blood volume, are collectively called the "corpuscular fraction" or formed elements. The hematocrit is a measure of the volume of red blood cells relative to the total blood volume, typically around 45%. * **Red blood cells (erythrocytes):** Primarily responsible for oxygen ($\text{O}_2$) and carbon dioxide ($\text{CO}_2$) transport. * **White blood cells (leukocytes):** Key components of the immune system, involved in defense against pathogens and foreign substances. * **Platelets (thrombocytes):** Crucial for blood clotting and hemostasis. ### 1.3 Red blood cells (erythrocytes) Red blood cells are specialized cells designed for efficient gas transport. #### 1.3.1 Structure * **Biconcave disc shape:** This shape increases the surface area relative to the volume, facilitating efficient diffusion and exchange of gases. * **Flexibility:** They are flexible enough to squeeze through narrow capillaries. * **Anucleated:** Mature red blood cells lack a nucleus, which allows for more space to be filled with hemoglobin. This also means they cannot divide. * **Lack of mitochondria:** Red blood cells generate energy solely through anaerobic processes, preventing them from consuming the oxygen they transport. * **Lifespan:** Their lifespan is approximately 120 days. #### 1.3.2 Function The primary function of red blood cells is the transport of oxygen ($\text{O}_2$) and carbon dioxide ($\text{CO}_2$) via the protein hemoglobin. #### 1.3.3 Hemoglobin Hemoglobin is the molecule within red blood cells responsible for oxygen binding. * **Structure:** It consists of four subunits, each containing a protein chain (globin) and a heme group. * **Heme group:** This iron-containing part of hemoglobin is responsible for its red color and its ability to bind oxygen. Each heme group contains an iron ion ($\text{Fe}^{2+}$) that can bind to one molecule of oxygen. * The reversible reaction is represented as: $\text{Hb} + 4 \, \text{O}_2 \rightleftharpoons \text{Hb(O}_2\text{)}_4$ * $\text{Hb}$ represents deoxygenated hemoglobin (dark red). * $\text{Hb(O}_2\text{)}_4$ represents oxygenated hemoglobin or oxyhemoglobin (bright red). #### 1.3.4 Carbon monoxide (CO) intoxication Carbon monoxide is a colorless, odorless, and toxic gas that poses a significant health risk due to its interaction with hemoglobin. * **High binding affinity:** CO binds to hemoglobin approximately 150 times more strongly than oxygen. * **Formation of carboxyhemoglobin (COHb):** The reaction is: $\text{Hb} + \text{CO} \rightarrow \text{COHb}$. * **Consequences:** This binding effectively reduces the amount of hemoglobin available for oxygen transport, leading to oxygen deprivation (hypoxia). #### 1.3.5 Oxygen dissociation curve The oxygen dissociation curve (or $\text{O}_2$-binding curve) illustrates the relationship between the partial pressure of oxygen ($\text{pO}_2$) and the percentage of hemoglobin saturated with oxygen ($\text{sO}_2$). * **S-shaped curve:** The curve has an S-shape, indicating that the binding of the first oxygen molecule to hemoglobin is relatively difficult. However, this binding causes a conformational change in the hemoglobin molecule, making it easier for the subsequent three oxygen molecules to bind. * **In the lungs:** At a high partial pressure of oxygen (e.g., 102 mmHg), hemoglobin is nearly 100% saturated with oxygen ($\text{sO}_2 = 100\%$). The equilibrium shifts to the right, favoring oxygen binding. Even with small changes in $\text{pO}_2$ in the lungs, $\text{sO}_2$ remains close to maximum. * **In resting tissues:** At a $\text{pO}_2$ of approximately 40 mmHg, hemoglobin releases about 25% of its bound oxygen, with $\text{sO}_2$ remaining around 75%. * **In active tissues:** As tissues consume oxygen, the local $\text{pO}_2$ can drop to 15-20 mmHg. Under these conditions, hemoglobin readily releases oxygen, potentially releasing up to 80% of its stored oxygen ( $\text{sO}_2$ drops to 20%). Active tissues receive approximately three times more oxygen compared to resting tissues due to this efficient release mechanism. #### 1.3.6 Transport of carbon dioxide ($\text{CO}_2$) Carbon dioxide is produced in the tissues and transported to the lungs for elimination through three main mechanisms: * **Dissolved in plasma:** Approximately 7% of $\text{CO}_2$ is transported dissolved directly in the blood plasma. * **Bound to hemoglobin:** About 23% of $\text{CO}_2$ binds to hemoglobin, forming carbaminohemoglobin. * **As bicarbonate ions:** The majority (70%) of $\text{CO}_2$ is converted into carbonic acid ($\text{H}_2\text{CO}_3$) within red blood cells. Carbonic acid then dissociates into hydrogen ions ($\text{H}^+$) and bicarbonate ions ($\text{HCO}_3^-$). The bicarbonate ions are then transported in the plasma. This reaction occurs primarily within red blood cells due to the presence of the enzyme carbonic anhydrase. #### 1.3.7 Erythropoiesis (red blood cell production) Erythropoiesis is the process of producing new red blood cells, which is essential given their limited lifespan. * **Production site:** Occurs in the bone marrow. * **Process:** Hematopoietic stem cells in the bone marrow differentiate through various intermediate stages to become mature red blood cells that enter the bloodstream. * **Influencing factors:** The maturation of red blood cells is influenced by several factors: * **Iron:** Essential for hemoglobin synthesis. * **Vitamins:** Specifically Vitamin B12 is crucial. * **Erythropoietin (EPO):** A hormone produced by the kidneys in response to low oxygen concentrations. EPO stimulates the division of stem cells and the maturation of red blood cells. * **High altitude adaptation:** At high altitudes, the lower oxygen concentration stimulates increased EPO production by the kidneys, leading to enhanced red blood cell production. This increases the total number of red blood cells and hemoglobin, thereby improving the body's capacity for oxygen transport and uptake. #### 1.3.8 Blood groups Blood groups, such as A, B, AB, and O, are determined by specific membrane antigens on the surface of red blood cells. These also influence the presence of antibodies in the blood plasma, which is critical for blood transfusions. ### 1.4 White blood cells (leukocytes) White blood cells are the primary components of the body's immune system. They are broadly classified into three main groups: #### 1.4.1 Granulocytes These cells contain granules in their cytoplasm and represent the first line of defense. * **Neutrophils:** They are the first responders to injury and infection, characterized by their difficulty in staining. * **Eosinophils:** Stain red with eosin dye and are involved in allergic reactions. * **Basophils:** Stain blue/purple with basic dyes and are involved in inflammatory responses and in wound healing. #### 1.4.2 Monocytes These are larger than red blood cells and lack granules in their cytoplasm. * **Macrophages:** In tissues, monocytes differentiate into macrophages, which are phagocytic cells responsible for clearing cellular debris from dead cells, pathogens, and foreign substances. #### 1.4.3 Lymphocytes Lymphocytes are central to specific immunity. * **B-lymphocytes:** Mature in the bone marrow and are involved in humoral immunity. * **T-lymphocytes:** Mature in the thymus and are involved in cellular immunity. #### 1.4.4 Function: Defense and immunity White blood cells form the immune system, which protects the body from foreign invaders. * **Antigen (Ag):** A structure that can trigger an immune response. Antigens are typically found on the membranes of cells. If an antigen is not recognized as "self" by the immune system, an immune response is initiated. * **Types of immune responses:** * **Non-specific (innate) immunity:** Mediated by granulocytes and monocytes (macrophages). This is a rapid, general defense mechanism involving phagocytosis. * **Specific (adaptive) immunity:** Directed against a particular type of pathogen or antigen. This includes: * **Cellular immunity:** Primarily mediated by T-lymphocytes. * **Humoral immunity:** Primarily mediated by B-lymphocytes, which produce antibodies. #### 1.4.5 Cellular immunity This type of specific defense involves T-lymphocytes, which act like soldiers attacking foreign organisms. * **Process:** A T-lymphocyte recognizes an antigen on an invader or target cell. The T-lymphocyte then releases cytotoxins at the contact zone, damaging the cell membrane of the target cell and leading to its elimination. #### 1.4.6 Humoral immunity This type of specific defense involves B-lymphocytes, which produce antibodies. * **Process:** A B-lymphocyte recognizes an antigen on an invader or target cell. The B-lymphocyte then releases antibodies that are specific to that antigen, marking the target for destruction or neutralizing it. This is often likened to firing weapons from a distance. #### 1.4.7 Example: Non-specific immunity When pathogens like bacteria breach the skin's defenses, granulocytes and/or monocytes and macrophages are rapidly mobilized. They engage in phagocytosis, engulfing and destroying the invaders. For instance, a puncture wound can introduce bacteria, attracting phagocytes from the bloodstream. These phagocytes then surround and digest the bacteria. #### 1.4.8 Application: ABO blood groups The ABO blood group system involves different antigens on the surface of red blood cells and corresponding antibodies in the plasma. This is crucial for blood transfusions: * **Universal donor:** Blood group O is considered the universal donor because it lacks A and B antigens, minimizing the risk of an immune reaction in recipients with different blood types. * **Universal acceptor:** Blood group AB is considered the universal acceptor because it has both A and B antigens and lacks anti-A and anti-B antibodies, allowing it to receive blood from donors of other ABO groups without immediate agglutination. ### 1.5 Platelets (thrombocytes) Platelets are not true cells but rather cell fragments derived from large cells called megakaryocytes in the bone marrow. #### 1.5.1 Structure and Origin * **Origin:** Megakaryocytes shed small packets of cytoplasm, surrounded by a membrane, into the bloodstream. These are platelets. * **Characteristics:** Platelets lack a nucleus but contain mitochondria. * **Lifespan:** Their lifespan is approximately 10 days. #### 1.5.2 Function The primary function of platelets is blood clotting (hemostasis), which prevents excessive blood loss from injured blood vessels. ### 1.6 The circulatory system (bloedsomloop) The circulatory system comprises the heart and blood vessels, facilitating the continuous movement of blood throughout the body. #### 1.6.1 The heart The heart is a muscular organ that pumps blood. * **Pulmonary circulation (small circulation):** Blood is pumped to and from the lungs. * **Systemic circulation (large circulation):** Blood is pumped to and from the rest of the body. #### 1.6.2 Blood vessels Blood vessels form a network through which blood flows. * **Arterial system:** Carries blood away from the heart. This includes the aorta (the main artery), arteries, and arterioles. * **Capillaries:** A vast network of tiny vessels within tissues where the exchange of gases and substances between blood and tissue fluid occurs. * **Venous system:** Carries blood back to the heart. This includes venules, veins, and the vena cava (the main vein). #### 1.6.3 Hemodynamic properties of blood vessels Blood vessels are designed to maintain continuous blood flow. * **Blood pressure:** The heart generates sufficient pressure to propel blood through the circulatory system. * **Vascular smooth muscle:** The walls of blood vessels contain smooth muscle that can contract (vasoconstriction) or relax (vasodilation) under the control of the autonomic nervous system, regulating blood flow and pressure. #### 1.6.4 Structure of the heart The heart is divided into four chambers: * **Right atrium:** Receives deoxygenated blood from the body via the vena cava. * **Right ventricle:** Pumps deoxygenated blood to the lungs via the pulmonary artery. * **Left atrium:** Receives oxygenated blood from the lungs via the pulmonary vein. * **Left ventricle:** Pumps oxygenated blood to the rest of the body via the aorta. The left ventricle has a thicker muscular wall due to the higher pressure required for systemic circulation. #### 1.6.5 Heart wall The heart wall consists of three layers: * **Endocardium:** Lines the inner surface of the heart chambers and valves. * **Myocardium:** The muscular layer of the heart, composed of cardiac muscle tissue. * **Epicardium:** Covers the outer surface of the heart and is part of the pericardium (the sac surrounding the heart). #### 1.6.6 Heart valves Heart valves ensure unidirectional blood flow and prevent backflow. * **Atrioventricular (AV) valves:** Located between the atria and ventricles (e.g., mitral valve and tricuspid valve). * **Semilunar valves:** Located between the ventricles and the major arteries (e.g., aortic valve and pulmonary valve). * **Valves at venous ostia:** At the openings where the vena cava and pulmonary veins enter the atria, there are no true valves, but a sickle-shaped rim of muscle fibers helps prevent backflow. #### 1.6.7 Cardiac conduction system The heart muscle contracts autonomously (without direct nervous system stimulation). This coordinated contraction is managed by a specialized conduction system: * **Sinoatrial (SA) node:** The natural pacemaker of the heart, initiating electrical impulses spontaneously (70-80 action potentials per minute). * **Atrioventricular (AV) node:** Receives the impulse from the SA node and delays it slightly before transmitting it to the rest of the heart. * **Conduction pathways:** From the AV node, specialized cells conduct the electrical impulse throughout the ventricles, triggering their contraction. #### 1.6.8 Path of blood flow Blood circulates through the body in two main loops: 1. **Pulmonary circulation:** Vena cava $\rightarrow$ Right atrium $\rightarrow$ Right ventricle $\rightarrow$ Pulmonary artery $\rightarrow$ Lungs (gas exchange: $\text{CO}_2$ release, $\text{O}_2$ uptake) $\rightarrow$ Pulmonary vein $\rightarrow$ Left atrium. 2. **Systemic circulation:** Left atrium $\rightarrow$ Left ventricle $\rightarrow$ Aorta $\rightarrow$ Systemic capillaries (gas exchange: $\text{O}_2$ release, $\text{CO}_2$ uptake) $\rightarrow$ Veins $\rightarrow$ Vena cava $\rightarrow$ Right atrium. #### 1.6.9 Heart contraction (cardiac cycle) The cardiac cycle refers to the sequence of events from the beginning of one heartbeat to the beginning of the next, involving periods of contraction (systole) and relaxation (diastole) of the heart chambers. * **Atrial systole:** Atria contract, pushing blood into the ventricles, which are relaxed (diastole). This occurs under the influence of the SA node. Blood flows passively through the open AV valves. * **Ventricular systole:** Ventricles contract under the influence of the AV node. As pressure within the ventricles rises, the AV valves close. When ventricular pressure exceeds that in the arteries, the semilunar valves open, and blood is ejected into the aorta and pulmonary artery. * **Ventricular diastole:** Ventricles relax. As ventricular pressure falls, the semilunar valves close. When ventricular pressure drops below atrial pressure, the AV valves open, and blood passively flows from the atria into the ventricles. Both atria and ventricles are in diastole towards the end of this phase. #### 1.6.10 Heart sounds Heart sounds, audible with a stethoscope, are produced by the closing of heart valves: * **First heart sound ("lub"):** Caused by the closing of the AV valves (mitral and tricuspid), marking the beginning of ventricular systole. It is a relatively soft sound. * **Second heart sound ("dub"):** Caused by the closing of the semilunar valves (aortic and pulmonary), marking the beginning of ventricular diastole. It is a louder, shorter sound. #### 1.6.11 Electrocardiogram (ECG) An electrocardiogram (ECG) is a recording of the electrical activity of the heart. It is used to detect abnormalities in heart rhythm and function. Key components of an ECG represent the depolarization and repolarization of the atria and ventricles. ### 1.7 Blood pressure Blood pressure is the force exerted by blood on the walls of the blood vessels. * **Pressure gradient:** Blood pressure is highest in the arteries close to the heart and decreases as the distance from the heart increases. * **Systolic and diastolic pressure:** Blood pressure fluctuates between two extreme values: * **Systolic pressure:** The peak pressure during ventricular contraction when blood is pumped into the arteries. * **Diastolic pressure:** The lowest pressure when the heart is relaxed and not actively pumping blood into the arteries. #### 1.7.1 Factors influencing blood pressure Several factors can affect blood pressure: * **Age:** Blood pressure tends to increase with age as blood vessels become less elastic. * **Circadian rhythm:** Blood pressure typically decreases during sleep. * **Diet:** High salt intake can lead to increased blood volume and consequently higher blood pressure. * **Physical activity:** While moderate exercise generally benefits cardiovascular health, strenuous activity can have transient effects on blood pressure. --- # Red blood cells and gas transport This section delves into the structure and function of red blood cells (erythrocytes), their crucial role in oxygen and carbon dioxide transport mediated by hemoglobin, the mechanics of the oxygen dissociation curve, and the process of erythropoiesis. ### 2.1 Red blood cells (erythrocytes) #### 2.1.1 Structure of red blood cells Red blood cells, also known as erythrocytes, are characterized by their biconcave disc shape. This morphology significantly increases their surface area to volume ratio, which is advantageous for efficient diffusion and gas exchange. Their flexibility allows them to navigate through narrow capillaries. Mature red blood cells lack a nucleus and mitochondria. The absence of a nucleus means they cannot divide, and their lifespan is approximately 120 days. The lack of mitochondria dictates that they generate energy solely through anaerobic processes. #### 2.1.2 Function of red blood cells The primary function of red blood cells is the transport of oxygen ($O_2$) and carbon dioxide ($CO_2$) throughout the body, primarily facilitated by hemoglobin. #### 2.1.3 Hemoglobin Hemoglobin is the key protein responsible for gas transport within red blood cells. Its structure consists of four subunits, each comprising a protein chain (globine) and a heme group. The heme group contains iron ($Fe^{2+}$) which is the site of oxygen binding. This iron-containing group is also responsible for the characteristic red color of blood. The binding of oxygen to hemoglobin is termed "oxygenation," represented by the equation: $$Hb + 4 O_2 \rightleftharpoons Hb(O_2)_4$$ where $Hb$ represents hemoglobin and $Hb(O_2)_4$ represents oxyhemoglobin. Oxygenated hemoglobin appears bright red, while deoxygenated hemoglobin is dark red. Carbon monoxide ($CO$) poses a significant danger due to its ability to bind to hemoglobin. $CO$ binds approximately 150 times more strongly to hemoglobin than oxygen does, forming carboxyhemoglobin ($COHb$): $$Hb + CO \rightarrow COHb$$ This greatly reduces the blood's capacity to transport oxygen, leading to oxygen deprivation. #### 2.1.4 Oxygen dissociation curve The oxygen dissociation curve, also known as the $O_2$-binding curve, illustrates the relationship between the partial pressure of oxygen ($pO_2$) and the percentage of hemoglobin saturated with oxygen ($sO_2$). The curve has an S-shaped (sigmoidal) form. * **Binding of the first oxygen molecule:** The binding of the first oxygen molecule to hemoglobin is relatively difficult. * **Conformational change:** Once the first oxygen molecule binds, hemoglobin undergoes a conformational change that increases its affinity for subsequent oxygen molecules. This facilitates the binding of the second, third, and fourth oxygen molecules more easily. * **Effect of $pO_2$:** An increase in $pO_2$ shifts the equilibrium to the right, leading to an increased $sO_2$. Conversely, a decrease in $pO_2$ shifts the equilibrium to the left, decreasing $sO_2$. **Situations affecting the oxygen dissociation curve:** * **Lungs:** In the lungs, the $pO_2$ is high (approximately 102 mmHg), resulting in nearly 100% $sO_2$. Even with small variations in $pO_2$, the $sO_2$ remains close to its maximum. * **Tissues:** * **Inactive tissues:** In tissues with low oxygen demand, the local $pO_2$ is around 40 mmHg. Under these conditions, hemoglobin releases approximately 25% of its bound oxygen, leaving the $sO_2$ at about 75%. * **Active tissues:** In metabolically active tissues, oxygen consumption causes the local $pO_2$ to drop significantly, to around 15-20 mmHg. Hemoglobin readily releases oxygen, potentially up to 80% of its stored oxygen, resulting in an $sO_2$ of about 20%. This means active tissues receive approximately three times more oxygen than inactive tissues. > **Tip:** Understanding the oxygen dissociation curve is crucial for comprehending how oxygen is loaded in the lungs and unloaded in the tissues based on local oxygen partial pressures. ### 2.2 Transport of carbon dioxide Carbon dioxide ($CO_2$), a metabolic waste product formed in the tissues, is transported to the lungs for elimination. It is transported in the blood via three main mechanisms: 1. **Dissolved in blood plasma:** Approximately 7% of $CO_2$ is transported dissolved directly in the plasma. 2. **Binding to hemoglobin:** About 23% of $CO_2$ binds to hemoglobin, forming carbaminohemoglobin. 3. **As bicarbonate ions:** The majority (70%) of $CO_2$ is converted into carbonic acid ($H_2CO_3$) within red blood cells. Carbonic acid then dissociates into hydrogen ions ($H^+$) and bicarbonate ions ($HCO_3^-$). These bicarbonate ions are then transported in the plasma. ### 2.3 Erythropoiesis (production of red blood cells) Given the 120-day lifespan of red blood cells, approximately 200 billion new RBCs are produced daily. Erythropoiesis, the production of red blood cells, occurs in the bone marrow. #### 2.3.1 Process of erythropoiesis A stem cell in the bone marrow undergoes several intermediate stages before maturing into a red blood cell that enters the bloodstream. #### 2.3.2 Factors influencing erythropoiesis Several factors are essential for the maturation of red blood cells: * **Iron:** Crucial for hemoglobin synthesis. * **Vitamins:** Specifically Vitamin $B_{12}$ plays a vital role. * **Erythropoietin (EPO):** This hormone is produced by the kidneys in response to low oxygen concentrations in the blood. EPO stimulates the division of stem cells and the maturation of red blood cells. > **Example:** High-altitude training involves exposure to lower oxygen concentrations. This stimulates the kidneys to produce more EPO, which in turn increases red blood cell production. The resulting higher number of red blood cells and hemoglobin allows the body to transport and utilize oxygen more efficiently. #### 2.3.3 Blood groups Blood groups, such as A, B, AB, and O, are determined by specific membrane antigens on the surface of red blood cells. These antigens are important in blood transfusions. ### 2.4 Other blood components While red blood cells are central to gas transport, other components are also vital: #### 2.4.1 White blood cells (leukocytes) White blood cells are the body's primary defense system, playing a crucial role in immunity. They are broadly classified into three groups: * **Granulocytes:** These contain granules in their cytoplasm and form the first line of defense. They include: * **Neutrophils:** Respond rapidly to injury. * **Eosinophils:** Involved in allergic reactions. * **Basophils:** Participate in inflammatory and allergic responses. * **Monocytes:** These are larger than red blood cells and, in tissues, differentiate into macrophages. Macrophages are responsible for engulfing and removing cellular debris, pathogens, and foreign substances. * **Lymphocytes:** These cells are critical for specific immunity. * **B-lymphocytes:** Mature in the bone marrow and produce antibodies. * **T-lymphocytes:** Mature in the thymus and are involved in cellular immunity. #### 2.4.2 Platelets (thrombocytes) Platelets are not true cells but rather cell fragments derived from large megakaryocytes in the bone marrow. They are small, lack a nucleus but possess mitochondria, and have a lifespan of about 10 days. Their primary function is to initiate blood clotting. ### 2.5 Gas exchange in tissues The exchange of gases between blood and tissues occurs primarily in the capillaries. This process is driven by diffusion gradients: oxygen moves from the capillaries into the tissue fluid and then into the cells, while carbon dioxide moves from the tissue fluid into the capillaries. --- # White blood cells and the immune system White blood cells, also known as leukocytes, are essential components of the blood responsible for defending the body against pathogens and foreign substances. ### 3.1 Composition and classification of white blood cells White blood cells constitute approximately 45% of the total blood volume, with the remaining 55% being plasma. They are a crucial part of the body's defense and immune system, categorized into three main groups based on the presence of granules in their cytoplasm and their staining characteristics: #### 3.1.1 Granulocytes These leukocytes contain granules in their cytoplasm and form the first line of defense. They are further subdivided into: * **Neutrophils:** These cells stain poorly and are the first responders to injuries, initiating the inflammatory process. * **Eosinophils:** These cells stain red with eosin and are involved in allergic reactions. * **Basophils:** These cells stain purple/blue with basic dyes and are also involved in inflammatory responses, particularly at injury sites. #### 3.1.2 Monocytes Monocytes are agranular leukocytes, meaning they lack granules in their cytoplasm. In the blood, they mature into macrophages in the tissues. Macrophages are significantly larger than red blood cells and play a vital role in: * Phagocytosing and removing cellular debris from dead cells. * Engulfing pathogens and foreign substances. #### 3.1.3 Lymphocytes Lymphocytes are central to the specific immune response. They are produced in the bone marrow and mature in either the bone marrow (B-lymphocytes) or the thymus (T-lymphocytes). ### 3.2 Function: Defense and Immunity The primary function of white blood cells is to provide defense and immunity for the body. They act as the body's immune system, identifying and neutralizing foreign invaders. #### 3.2.1 Antigens An antigen (Ag) is a structure present on the surface of cells that can trigger an immune response. If an antigen is not recognized by the immune system as "normal," an immune reaction is initiated. #### 3.2.2 Types of Immune Responses The immune system employs two main types of defense mechanisms: * **Non-specific defense:** This is the first line of defense, mediated by granulocytes and monocytes (including macrophages). It is a rapid response that is not specific to any particular pathogen. A key mechanism of non-specific defense is phagocytosis, where immune cells engulf and destroy invaders. > **Example:** When bacteria penetrate the skin, neutrophils and macrophages are quickly mobilized. They surround and digest the bacteria, eliminating the threat. * **Specific defense:** This response is highly targeted against specific types of bacteria, viruses, or other pathogens. It is slower to develop but is more efficient and leads to immunological memory. Specific defense involves two main branches: * **Cellular defense:** Carried out by T-lymphocytes. T-cells can be likened to soldiers that directly attack foreign organisms or infected cells. > **Example:** A T-lymphocyte recognizes an antigen on an invading cell or a target cell. It then releases cytotoxins that damage the cell membrane of the target, leading to its destruction. * **Humoral defense:** Mediated by B-lymphocytes. B-cells act like an arsenal, producing antibodies (also called immunoglobulins). These antibodies are specific to the antigens of the foreign organism and help to neutralize or eliminate them. > **Example:** A B-lymphocyte recognizes an antigen. It then produces antibodies that bind to the antigen on the pathogen, marking it for destruction by other immune cells or directly neutralizing its function. ### 3.3 Application: ABO Blood Groups The ABO blood group system is a critical aspect of immunology related to red blood cell antigens. Red blood cells possess different antigens on their membranes, and antibodies can be formed against these in the blood plasma. This system is vital for blood transfusions: * **Blood group O:** Is considered the "universal donor" because individuals with blood group O generally lack A and B antigens on their red blood cells, making their blood compatible with most recipients. * **Blood group AB:** Is considered the "universal acceptor" because individuals with blood group AB have both A and B antigens and lack anti-A and anti-B antibodies in their plasma, allowing them to receive blood from all other ABO groups. ### 3.4 Blood Platelets Although not true cells, blood platelets (thrombocytes) are crucial components of blood. They are cell fragments derived from large cells called megakaryocytes in the bone marrow. Platelets lack a nucleus but contain mitochondria and have a lifespan of approximately 10 days. Their primary function is to initiate blood clotting. --- # Circulatory system components and function The circulatory system is a vital network responsible for transporting substances, regulating body temperature, and protecting against disease. ### 4.1 General functions of blood The circulatory system, primarily through blood, performs several crucial functions: * **Transport:** * **Gases:** Transports dissolved gases like oxygen ($O_2$) from the lungs to tissues and carbon dioxide ($CO_2$) from tissues back to the lungs. * **Nutrients:** Carries absorbed nutrients from the digestive tract to various body cells. * **Hormones:** Delivers hormones from endocrine glands to their target cells. * **Waste Products:** Moves waste products from active cells to excretory organs like the kidneys. * **Regulation of Heat:** * Stabilizes body temperature by distributing heat produced by active muscles to other tissues and by facilitating heat exchange with the environment through the skin. * **Protection and Defense:** * **Blood Clotting:** Prevents excessive fluid loss from injuries by initiating clot formation. * **Immunity/Defense:** Protects against toxins and pathogens. ### 4.2 Blood composition Blood is composed of a liquid plasma and solid blood components (corpuscular fraction). * **Volume:** Approximately 5 liters per 13 kilograms of body weight. * **Corpuscular Fraction (approximately 45% of total blood volume):** * **Hematocrit:** The volume of red blood cells (RBCs) relative to the total blood volume, typically around 45%. * **Red Blood Cells (Erythrocytes):** Primarily responsible for transporting oxygen ($O_2$) and carbon dioxide ($CO_2$). * **White Blood Cells (Leukocytes):** Essential for the immune defense system. * **Platelets (Thrombocytes):** Crucial for blood clotting. * **Plasma (approximately 55% of total blood volume):** The liquid component of blood. * **Water:** Constitutes 90% of blood plasma. * **Dissolved Proteins (Plasma Proteins):** * **Albumin (60%):** A large protein that helps maintain osmotic pressure within blood vessels and draws water from tissues, maintaining the osmotic balance. * **Globulins (35%):** Includes antibodies involved in immune defense and transport proteins that bind to ions, hormones, and poorly soluble compounds. * **Fibrinogen:** Essential for blood clotting. * **Serum:** Plasma without clotting proteins. * **Other Dissolved Substances:** * **Organic Nutrients:** Glucose, lipids, amino acids. * **Electrolytes:** Sodium ($Na^+$), potassium ($K^+$), magnesium ($Mg^{2+}$), calcium ($Ca^{2+}$). * **Organic Waste Products:** Urea, creatinine, bilirubin. ### 4.3 Red blood cells (Erythrocytes) * **Structure:** * Biconcave disc shape, providing a large surface area relative to volume for efficient gas diffusion. * Flexible, allowing passage through narrow capillaries. * Lack a nucleus, meaning they cannot divide. Their lifespan is approximately 120 days. * Lack mitochondria, relying solely on anaerobic processes for energy production. * **Function:** Transport of $O_2$ and $CO_2$ via hemoglobin. * **Hemoglobin:** * **Structure:** Composed of four subunits, each containing a protein chain (globin) and a heme group. The heme group contains iron ($Fe^{2+}$), which is responsible for binding oxygen. * **Oxygen Binding:** Hemoglobin binds oxygen to form oxyhemoglobin ($Hb(O_2)_4$). This process, known as oxygenation, turns blood a brighter red color. $$Hb + 4 O_2 \rightleftharpoons Hb(O_2)_4$$ (Hemoglobin) (Oxyhemoglobin) * **Carbon Monoxide (CO) Intoxication:** CO binds to hemoglobin about 150 times more effectively than $O_2$, forming carboxyhemoglobin (COHb). This significantly reduces the blood's oxygen-carrying capacity, leading to oxygen deprivation. $$Hb + CO \rightarrow COHb$$ * **Oxygen Dissociation Curve:** * Illustrates the percentage of hemoglobin bound to oxygen ($sO_2$) as a function of the partial pressure of oxygen ($pO_2$). * The curve has an S-shaped (sigmoidal) form. The initial binding of one oxygen molecule causes a conformational change in hemoglobin, making it easier for subsequent oxygen molecules to bind. * **At the Lungs:** High $pO_2$ (around 102 mmHg) leads to near 100% saturation ($sO_2 \approx 100\%$). A small change in $pO_2$ results in minimal change in $sO_2$ due to the high affinity. * **In Tissues:** * **Inactive Tissues:** Lower $pO_2$ (around 40 mmHg) results in approximately 75% saturation ($sO_2 = 75\%$), meaning hemoglobin releases about 25% of its stored $O_2$. * **Active Tissues:** Significantly lower $pO_2$ (15-20 mmHg) due to high $O_2$ consumption. Hemoglobin readily releases up to 80% of its stored $O_2$ ($sO_2 = 20\%$), allowing active tissues to receive about three times more oxygen than inactive tissues. * **Transport of Carbon Dioxide ($CO_2$):** $CO_2$, produced in tissues and released in lungs, is transported in three ways: * Dissolved in blood plasma (7%). * Bound to hemoglobin forming carbaminohemoglobin (23%). * As bicarbonate ions ($HCO_3^-$) within red blood cells (70%), formed through the conversion of $CO_2$ to carbonic acid ($H_2CO_3$) and its subsequent dissociation into $H^+$ and $HCO_3^-$. * **Erythropoiesis (RBC Production):** * Occurs in the bone marrow from stem cells. * Requires iron and vitamins (B12) for proper maturation. * **Erythropoietin (EPO):** A hormone produced by the kidneys in response to low oxygen concentrations ($pO_2$). EPO stimulates stem cell division and RBC maturation. * **Altitude Training:** At higher altitudes, lower $pO_2$ stimulates increased EPO production, leading to higher RBC production and thus increased oxygen-carrying capacity. * **Blood Groups:** Determined by specific membrane antigens on RBCs (e.g., A, B, AB, O). ### 4.4 White blood cells (Leukocytes) * **Function:** Serve as the body's immune system, defending against pathogens and foreign substances. * **Classification:** * **Granulocytes:** Contain granules in their cytoplasm and are part of the first line of defense. * **Neutrophils:** Involved in the initial inflammatory response to injury. * **Eosinophils:** Associated with allergic reactions. * **Basophils:** Play a role in inflammatory responses. * **Monocytes:** Found in the blood and differentiate into macrophages in tissues. They engulf cellular debris, pathogens, and foreign materials. * **Lymphocytes:** Crucial for specific immune responses. * **B-lymphocytes:** Mature in the bone marrow and produce antibodies. * **T-lymphocytes:** Mature in the thymus and are involved in cellular immunity. * **Immune Responses:** * **Non-specific Defense:** Rapid and general defense mediated by granulocytes and monocytes (macrophages) through phagocytosis. * **Specific Defense:** Targeted response against particular pathogens, involving lymphocytes. * **Cellular Immunity:** Mediated by T-lymphocytes, which directly attack infected or foreign cells. * **Humoral Immunity:** Mediated by B-lymphocytes, which produce antibodies that neutralize or tag pathogens for destruction. #### 4.4.1 Examples of Immune Responses * **Non-specific Defense:** When pathogens breach the skin barrier, granulocytes and macrophages rapidly engulf and destroy them via phagocytosis. * **Cellular Defense:** T-lymphocytes recognize antigens on foreign invaders or target cells. Upon recognition, they release cytotoxic substances that damage and destroy the target cell. * **Humoral Defense:** B-lymphocytes recognize antigens. They then produce and release antibodies that bind to the antigens, marking the pathogen for destruction by other immune cells or neutralizing its effects. ### 4.5 Platelets (Thrombocytes) * **Origin:** Are not true cells but are cytoplasmic fragments released from large bone marrow cells called megakaryocytes. * **Characteristics:** Lack a nucleus but contain mitochondria. * **Lifespan:** Approximately 10 days. * **Function:** Essential for blood clotting to prevent excessive blood loss. ### 4.6 The Heart The heart is a muscular organ that pumps blood throughout the body. It is divided into two circuits: the pulmonary circulation (to and from the lungs) and the systemic circulation (to and from the rest of the body). * **Heart Chambers:** * **Right Atrium (boezem/voorkamer):** Receives deoxygenated blood from the body via the vena cava. * **Right Ventricle (kamer):** Pumps deoxygenated blood to the lungs via the pulmonary artery. * **Left Atrium:** Receives oxygenated blood from the lungs via the pulmonary veins. * **Left Ventricle:** Pumps oxygenated blood to the rest of the body via the aorta. The left ventricle has a significantly thicker muscular wall due to the higher pressure required to pump blood systemically. * **Major Blood Vessels Connected to the Heart:** * **Vena Cava (holle ader):** Superior and inferior, carrying deoxygenated blood from the body to the right atrium. * **Pulmonary Artery (longslagader/arteria pulmonalis):** Carries deoxygenated blood from the right ventricle to the lungs. * **Pulmonary Vein (longader/vena pulmonalis):** Carries oxygenated blood from the lungs to the left atrium. * **Aorta (grote lichaamsslagader):** The largest artery, carrying oxygenated blood from the left ventricle to the rest of the body. * **Heart Wall:** Consists of three layers: * **Endocardium:** Lines the inner surface of the heart and heart valves. * **Myocardium:** The muscular wall of the heart, containing cardiac muscle tissue, blood vessels, and nerves. * **Epicardium:** Covers the outer surface of the heart and is part of the pericardium (the sac surrounding the heart). * **Heart Valves:** Ensure unidirectional blood flow and prevent backflow. * **Atrioventricular (AV) Valves:** Located between the atria and ventricles. * Tricuspid valve (right side). * Mitral (bicuspid) valve (left side). * **Semilunar Valves:** Located between the ventricles and the major arteries. * Pulmonary valve (between right ventricle and pulmonary artery). * Aortic valve (between left ventricle and aorta). * Note: There are no true valves where the vena cava and pulmonary veins enter the atria, but a sickle-shaped rim of muscle fibers helps prevent backflow. * **Electrical Conduction System:** The heart muscle contracts autonomously without direct neural stimulation, regulated by specialized cells that generate and conduct electrical impulses. * **Sinoatrial (SA) Node (Pacemaker):** Located in the right atrium, initiates electrical impulses at a rate of 70-80 action potentials per minute. * **Atrioventricular (AV) Node:** Receives impulses from the SA node and delays them slightly before transmitting them to the rest of the heart, allowing atria to complete contraction before ventricles begin. * The impulse then travels through the Bundle of His, bundle branches, and Purkinje fibers to stimulate ventricular contraction. ### 4.7 Blood vessels Blood vessels form a closed network through which blood circulates. * **Arterial System:** Carries blood away from the heart. * Aorta $\rightarrow$ Arteries $\rightarrow$ Arterioles. * **Capillaries (Haarvaten):** A vast network of microscopic vessels where the exchange of gases, nutrients, and waste products occurs between blood and tissue fluid. * **Venous System:** Carries blood towards the heart. * Venules $\rightarrow$ Veins $\rightarrow$ Vena Cava (or pulmonary veins). * **Hemodynamic Function:** The circulatory system requires continuous blood flow, maintained by pressure generated by the heart. * **Vascular Wall Properties:** The smooth muscle in the walls of blood vessels allows for vasoconstriction (narrowing) and vasodilation (widening) under the control of the autonomic nervous system, regulating blood flow and pressure. ### 4.8 Pathway of blood flow The circulatory system comprises two main loops: 1. **Pulmonary Circulation (Small Circulation):** * Deoxygenated blood flows from the **right ventricle** to the **pulmonary artery**, then to the **lungs**. * In the **lung capillaries**, $CO_2$ is released, and $O_2$ is picked up. * Oxygenated blood returns via the **pulmonary veins** to the **left atrium**. 2. **Systemic Circulation (Large Circulation):** * Oxygenated blood flows from the **left ventricle** to the **aorta**, then to **arteries** and **arterioles** throughout the body. * In the **systemic capillaries**, $O_2$ is delivered to tissues, and $CO_2$ is picked up. * Deoxygenated blood returns via **veins** and the **vena cava** to the **right atrium**. > **Tip:** Trace the path of a red blood cell starting from the right atrium, through both circulations, and back to the right atrium. This exercise helps solidify understanding of the entire blood flow pathway. ### 4.9 Heart contraction and cardiac cycle * **Cardiac Muscle Structure:** Cardiac muscle is striated and interconnected by intercalated discs with gap junctions, allowing for rapid electrical communication and synchronized contraction. * **Contraction:** A single stimulus elicits a single contraction in cardiac muscle fibers. The long refractory period prevents tetanic contractions, ensuring each heartbeat is a discrete event. * **Cardiac Cycle:** The period from the beginning of one heartbeat to the beginning of the next, consisting of phases of contraction (systole) and relaxation (diastole) for each heart chamber. Blood flows from areas of high pressure to low pressure, with valves preventing backflow. #### 4.9.1 Stages of the Cardiac Cycle 1. **Atrial Systole:** * Atria contract, stimulated by the SA node. * Ventricles are relaxed (diastole). * Blood is pushed from the atria into the ventricles through the open AV valves. * Lasts approximately 100 milliseconds. 2. **Ventricular Systole:** * Ventricles contract, stimulated by the AV node. * The AV valves close, preventing backflow into the atria. * As pressure in the ventricles exceeds that in the major arteries, the semilunar valves (aortic and pulmonary) open. * Blood is ejected into the aorta and pulmonary artery. 3. **Ventricular Diastole:** * Ventricles relax. * Pressure in the ventricles drops below that in the arteries, causing the semilunar valves to close. This marks the beginning of the second heart sound. * As ventricular pressure falls below atrial pressure, the AV valves open. * Blood passively flows from the atria into the ventricles. * Both atria and ventricles are in diastole at this point. > **Tip:** The closure of the AV valves ("lub") marks the start of ventricular systole, and the closure of the semilunar valves ("dub") marks the start of ventricular diastole. These are the two primary heart sounds. * **Electrocardiogram (ECG/EKG):** Records the electrical activity of the heart, used to detect abnormalities in heart rhythm. Key components include the P wave (atrial depolarization), QRS complex (ventricular depolarization), and T wave (ventricular repolarization). ### 4.10 Blood Pressure Blood pressure is the force exerted by blood on the walls of blood vessels. * **Measurement:** Blood pressure fluctuates between two extreme values: * **Systolic Pressure (Bovendruk):** The peak pressure in the arteries during ventricular contraction (systole). * **Diastolic Pressure (Onderdruk):** The minimum pressure in the arteries during ventricular relaxation (diastole). * **Factors Affecting Blood Pressure:** * **Age:** Blood pressure generally increases with age as blood vessels become less elastic. * **Circadian Rhythm:** Blood pressure typically decreases during sleep. * **Diet:** High salt intake can increase blood pressure by causing the body to retain more water, increasing blood volume. * **Muscle Activity:** Has relatively little influence on blood pressure. #### 4.10.1 Blood Group Compatibility for Transfusion * **Universal Donor:** Blood group O individuals can donate to all other blood groups because their RBCs lack A and B antigens. * **Universal Recipient:** Blood group AB individuals can receive blood from all other blood groups because their plasma lacks antibodies against A or B antigens. * **For a patient with blood group B:** They can receive blood from blood groups B and O. (Plasma antibodies: Anti-A). ### 4.11 Blood Flow Return to the Heart * Blood from the systemic circulation returns to the **right atrium** via the **vena cava**. * Blood from the pulmonary circulation returns to the **left atrium** via the **pulmonary veins**. --- ## 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

| Term | Definition | |------|------------| | Red blood cells (RBC) | Also known as erythrocytes, these cells are responsible for the transport of oxygen ($O_2$) and carbon dioxide ($CO_2$) throughout the body via hemoglobin. They are biconcave discs with no nucleus, allowing for flexibility and efficient gas exchange. | | White blood cells (WBC) | Also known as leukocytes, these cells are a key component of the body's immune system, providing defense against pathogens, toxins, and disease. They are classified into granulocytes, monocytes, and lymphocytes. | | Blood platelets | Also known as thrombocytes, these are small, irregular cell fragments derived from megakaryocytes in the bone marrow. They play a crucial role in blood clotting to prevent excessive fluid loss during injury. | | Plasma | The liquid component of blood, making up about 55% of its total volume. It consists of about 90% water and contains dissolved proteins, nutrients, electrolytes, waste products, hormones, and other substances. | | Albumin | The most abundant protein in blood plasma (about 60%). It is a large protein that helps maintain osmotic pressure in blood vessels by attracting water from tissues and contributes to the transport of various substances. | | Globulins | A diverse group of proteins found in blood plasma (about 35%), including antibodies (immunoglobulins) involved in immunity and transport proteins that bind to small ions, hormones, and poorly soluble compounds. | | Fibrinogen | A soluble protein in blood plasma that is essential for blood clotting. When activated, it is converted into fibrin, which forms a meshwork to trap blood cells and form a clot. | | Hemoglobin | A protein found within red blood cells that binds to oxygen ($O_2$) and carbon dioxide ($CO_2$). It consists of four subunits, each containing a heme group with an iron atom, which is responsible for the red color of blood and oxygen binding. | | Oxygen dissociation curve | A graphical representation showing the relationship between the partial pressure of oxygen ($pO_2$) and the percentage of hemoglobin saturation with oxygen ($sO_2$). It illustrates how readily hemoglobin picks up or releases oxygen under different conditions. | | Erythropoiesis | The process of the production of red blood cells, which occurs in the bone marrow. It is stimulated by erythropoietin (EPO), a hormone produced by the kidneys in response to low oxygen levels. | | Granulocytes | A type of white blood cell characterized by the presence of granules in their cytoplasm. They are part of the innate immune system and include neutrophils, eosinophils, and basophils, involved in the initial response to injury and infection. | | Monocytes | A type of white blood cell that circulates in the blood and differentiates into macrophages in tissues. Macrophages are phagocytic cells that engulf and digest cellular debris, pathogens, and foreign substances. | | Lymphocytes | A type of white blood cell that plays a central role in specific immunity. They include B-lymphocytes, which produce antibodies, and T-lymphocytes, which are involved in cell-mediated immunity. | | Antigen (Ag) | A molecule, typically found on the surface of cells or pathogens, that can trigger an immune response. The immune system recognizes antigens as "non-self" and initiates defense mechanisms. | | Non-specific immunity | An innate defense mechanism of the immune system that provides a rapid, generalized response to foreign invaders. It is carried out by granulocytes and monocytes/macrophages through processes like phagocytosis. | | Specific immunity | An adaptive immune response that is targeted to a specific antigen. It is mediated by lymphocytes (B-cells and T-cells) and involves the development of immunological memory. | | Cellular immunity | A component of specific immunity mediated by T-lymphocytes. Cytotoxic T-lymphocytes directly attack and destroy infected cells or foreign organisms. | | Humoral immunity | A component of specific immunity mediated by B-lymphocytes. B-cells produce and secrete antibodies (immunoglobulins) that neutralize pathogens or mark them for destruction by other immune cells. | | Antibodies (Antilichamen) | Proteins produced by B-lymphocytes that specifically bind to antigens on foreign invaders. They play a crucial role in humoral immunity by neutralizing toxins, preventing pathogens from infecting cells, and marking pathogens for elimination. | | Megakaryocytes | Large cells found in the bone marrow that are responsible for producing blood platelets. They fragment their cytoplasm into small, membrane-bound packets called platelets. | | Heart | A muscular organ that pumps blood throughout the body. It consists of four chambers: two atria (receiving chambers) and two ventricles (pumping chambers), responsible for circulating blood through the pulmonary and systemic circuits. | | Arterial system | The network of blood vessels that carries blood away from the heart. This includes the aorta, arteries, and arterioles, which branch into smaller vessels. | | Venous system | The network of blood vessels that carries blood towards the heart. This includes venules, veins, and the vena cava, which collect blood from the capillaries. | | Capillaries | The smallest blood vessels, forming an extensive network throughout the tissues. They are the primary site for the exchange of gases, nutrients, and waste products between the blood and the surrounding tissues. | | Vasoconstriction | The narrowing of blood vessels, typically caused by the contraction of smooth muscle in the vessel walls. This increases resistance to blood flow and can raise blood pressure. | | Vasodilation | The widening of blood vessels, typically caused by the relaxation of smooth muscle in the vessel walls. This decreases resistance to blood flow and can lower blood pressure. | | Atrium | An upper chamber of the heart that receives blood returning to the heart. The right atrium receives deoxygenated blood from the body, and the left atrium receives oxygenated blood from the lungs. | | Ventricle | A lower chamber of the heart that pumps blood away from the heart. The right ventricle pumps deoxygenated blood to the lungs, and the left ventricle pumps oxygenated blood to the rest of the body. | | Aorta | The largest artery in the body, originating from the left ventricle of the heart. It distributes oxygenated blood to all parts of the body through the systemic circulation. | | Vena cava | The largest vein in the body, returning deoxygenated blood from the body to the right atrium of the heart. There are two vena cavae: the superior vena cava (from the upper body) and the inferior vena cava (from the lower body). | | Pulmonary artery | An artery that carries deoxygenated blood from the right ventricle of the heart to the lungs for oxygenation. | | Pulmonary vein | A vein that carries oxygenated blood from the lungs to the left atrium of the heart. | | Heart valves | Structures within the heart that ensure unidirectional blood flow. They open to allow blood to pass through and close to prevent backflow. This includes atrioventricular valves and semilunar valves. | | Sinoatrial (SA) node | The natural pacemaker of the heart, located in the right atrium. It initiates electrical impulses that cause the atria to contract, setting the heart rate. | | Atrioventricular (AV) node | A node located between the atria and ventricles that receives electrical impulses from the SA node. It delays the impulse slightly before transmitting it to the ventricles, allowing the atria to fully contract. | | Heart cycle | The complete sequence of events in the heart from the beginning of one heartbeat to the beginning of the next. It includes periods of contraction (systole) and relaxation (diastole) of the atria and ventricles. | | Systole | The phase of the heart cycle during which the heart muscle contracts and pumps blood. Atrial systole involves contraction of the atria, and ventricular systole involves contraction of the ventricles. | | Diastole | The phase of the heart cycle during which the heart muscle relaxes and fills with blood. Atrial diastole involves relaxation of the atria, and ventricular diastole involves relaxation of the ventricles. | | Electrocardiogram (ECG) | A non-invasive test that records the electrical activity of the heart. It is used to diagnose heart rhythm abnormalities and other cardiac conditions. | | Blood pressure | The force exerted by circulating blood on the walls of blood vessels. It is typically measured in the arteries and expressed as systolic pressure (during ventricular contraction) over diastolic pressure (during ventricular relaxation). | | Systolic pressure | The higher number in a blood pressure reading, representing the maximum pressure in the arteries during ventricular contraction (systole). | | Diastolic pressure | The lower number in a blood pressure reading, representing the minimum pressure in the arteries when the heart is at rest between beats (diastole). |