Blood Physiology Notes PDF

**Physiology of Blood** Blood is a vital fluid that performs multiple functions necessary for sustaining life. It transports essential nutrients and gases, regulates physiological processes, and provides protection against disease and injury. This unit explores the composition, functions, and key p...

**Physiology of Blood** Blood is a vital fluid that performs multiple functions necessary for sustaining life. It transports essential nutrients and gases, regulates physiological processes, and provides protection against disease and injury. This unit explores the composition, functions, and key physiological processes associated with blood. **1. Functions of Blood** **Transport:** - **Nutrient and Gas Transport:** Blood is responsible for transporting oxygen from the lungs to the tissues and carbon dioxide from the tissues back to the lungs for exhalation. It also delivers nutrients such as glucose, amino acids, and fatty acids to cells and carries away waste products to be excreted. - **Hormone Transport:** Blood acts as a conduit for hormones, which are produced by endocrine glands and transported to target organs or cells where they exert their effects. **Regulation:** - **Temperature Regulation:** Blood helps maintain body temperature by absorbing and distributing heat throughout the body. During increased physical activity or in warm environments, blood vessels in the skin dilate, allowing heat to escape and cool the body. - **pH Regulation:** Blood plays a crucial role in maintaining the body\'s pH within a narrow range (7.35-7.45), essential for proper cellular function. It achieves this through buffer systems that neutralise excess acids or bases. - **Ion Composition and Water Content:** Blood helps regulate the ion composition of interstitial fluid, ensuring that cells are surrounded by an optimal concentration of electrolytes. It also helps regulate water content by redistributing fluids across different compartments in the body. **Protection:** - **Immune Response:** Blood contains white blood cells (leukocytes) and antibodies that defend the body against infections and foreign invaders. It plays a central role in the immune response, including inflammation and the destruction of pathogens. - **Clotting Mechanism:** When a blood vessel is injured, blood initiates the clotting process to prevent excessive blood loss. Platelets and clotting factors work together to form a clot that seals the wound until it heals. **2. Components of Blood** Blood is a specialised connective tissue composed of several components: - **Plasma:** The liquid portion of blood, making up about 55% of its volume. Plasma is primarily water (about 90%) and contains dissolved proteins (such as albumin, globulins, and fibrinogen), electrolytes, nutrients, waste products, and hormones. - **Red Blood Cells (Erythrocytes):** These cells are responsible for carrying oxygen from the lungs to the tissues and returning carbon dioxide from the tissues to the lungs. Erythrocytes contain haemoglobin, a protein that binds oxygen. - **White Blood Cells (Leukocytes):** These cells are involved in protecting the body against infection and foreign invaders. Leukocytes are divided into several types, including neutrophils, eosinophils, basophils, monocytes, and lymphocytes. - **Platelets (Thrombocytes):** Small cell fragments that play a key role in blood clotting. When a vessel is damaged, platelets adhere to the site of injury and aggregate to form a temporary plug. **pH and Temperature:** - **pH:** Blood has a pH range of 7.35 to 7.45, slightly alkaline and tightly regulated by buffer systems. - **Temperature:** The temperature of blood is slightly higher than the body's average temperature, at approximately 38°C, which helps to maintain homeostasis. **3. Haematopoiesis** Haematopoiesis is the process of blood cell production, which occurs primarily in the bone marrow. This process ensures a constant supply of red blood cells, white blood cells, and platelets to maintain the body\'s physiological functions. **Erythropoiesis:** - **Process:** Erythropoiesis is the production of red blood cells. It begins with haematopoietic stem cells in the bone marrow differentiating into erythroid progenitors. These progenitors mature into reticulocytes, which are released into the bloodstream and develop into erythrocytes. - **Regulation:** Erythropoietin (EPO), a hormone produced mainly by the kidneys, regulates erythropoiesis. EPO stimulates the bone marrow to increase red blood cell production, particularly in response to hypoxia (low oxygen levels). **Leukopoiesis:** - **Process:** Leukopoiesis is the production of white blood cells. It involves the differentiation of haematopoietic stem cells into various types of leukocytes, each with specialised functions in the immune system. - **Regulation:** Cytokines, such as interleukins and colony-stimulating factors, regulate leukopoiesis by promoting the differentiation and proliferation of specific leukocyte lineages. **Thrombopoiesis:** - **Process:** Thrombopoiesis is the production of platelets. It involves the differentiation of haematopoietic stem cells into megakaryocytes in the bone marrow. Megakaryocytes produce platelets by releasing cytoplasmic fragments into the bloodstream. - **Regulation:** Thrombopoietin, a hormone produced by the liver and kidneys, regulates thrombopoiesis by stimulating the production and maturation of megakaryocytes. **Cytokines:** - **Function:** Cytokines are signalling molecules that mediate and regulate immunity, inflammation, and haematopoiesis. They act as messengers between cells, coordinating the immune response and influencing the production of blood cells. **4. Red Blood Cells (Erythrocytes)** **Structure and Function:** - **Haemoglobin:** Each red blood cell contains approximately 270 million molecules of haemoglobin, the protein responsible for oxygen transport. Haemoglobin consists of four polypeptide chains (two alpha and two beta in adult HbA), each with an iron-containing heme group that binds oxygen. - **Normal Ranges:** In males, the normal red blood cell count ranges from 4.7 to 6.1 million cells per microlitre of blood. **Types of Haemoglobin:** - **HbA (Adult Haemoglobin):** Comprises about 97% of the haemoglobin in adults and consists of two alpha and two beta chains. - **HbA2:** Constitutes about 2.5% of adult haemoglobin and consists of two alpha and two delta chains. - **HbF (Fetal Haemoglobin):** The primary haemoglobin during fetal development, consisting of two alpha and two gamma chains. HbF has a higher affinity for oxygen than HbA, facilitating oxygen transfer from the mother to the fetus. **5. White Blood Cells (Leukocytes)** Leukocytes are crucial for the body's defence mechanisms, each type playing a unique role in the immune response. **Neutrophils:** - **Function:** Neutrophils are the most abundant leukocytes, accounting for 50-70% of white blood cells. They are the first responders to infection, performing phagocytosis to engulf and destroy pathogens. - **Granules:** Neutrophils contain granules filled with enzymes like hydrolytic enzymes and hydrogen peroxide, which help in breaking down ingested pathogens. **Eosinophils:** - **Function:** Eosinophils account for 2-4% of white blood cells and are involved in combating parasitic infections and allergic reactions. They can phagocytise antigen-antibody complexes and release enzymes like histaminase to modulate inflammatory responses. - **Granules:** Eosinophil granules contain enzymes that counteract histamine, reducing inflammation. **Basophils:** - **Function:** Basophils are the least common leukocytes, involved in allergic reactions and inflammation. They release histamine, heparin, and serotonin from their granules to enhance the inflammatory response. - **Granules:** These granules contain chemicals that promote vasodilation and increase vascular permeability, aiding in the immune response. **6. Blood Types** Blood types are determined by the presence or absence of specific antigens on the surface of red blood cells. The two most important blood group systems are ABO and Rh. **ABO Blood Group System:** - **Group A:** Has A antigens on red blood cells and anti-B antibodies in the plasma. - **Group B:** Has B antigens on red blood cells and anti-A antibodies in the plasma. - **Group AB:** Has both A and B antigens on red blood cells and no antibodies in the plasma. It is known as the universal recipient in the ABO system. - **Group O:** Has no antigens on red blood cells but both anti-A and anti-B antibodies in the plasma. It is the universal donor in the ABO system. **Rh Blood Group System:** - **RhD Positive:** Red blood cells have the RhD antigen. - **RhD Negative:** Red blood cells lack the RhD antigen. **Compatibility and Transfusion:** - **Importance of Matching:** Receiving blood from an incompatible ABO group can be life-threatening, as the recipient\'s antibodies can attack the donor\'s red blood cells. - **O RhD Negative:** Known as the universal donor type because it lacks A, B, and RhD antigens, making it safe for transfusions in emergencies when the recipient\'s blood type is unknown. **7. Blood Tests** Blood tests are essential diagnostic tools that provide valuable information about a person\'s health. **ESR (Erythrocyte Sedimentation Rate):** - **Purpose:** Measures the rate at which red blood cells settle at the bottom of a test tube. A faster rate may indicate inflammation or infection. **CRP (C-Reactive Protein):** - **Purpose:** CRP levels rise in response to inflammation. Measuring CRP can help diagnose conditions associated with acute or chronic inflammation. **Troponin:** - **Purpose:** Troponin is a protein released into the blood during a heart attack. Elevated troponin levels indicate myocardial damage and help in diagnosing acute coronary syndrome. **Lipid Profile:** - **Purpose:** This test measures levels of cholesterol and triglycerides in the blood, helping to assess the risk of cardiovascular disease. High levels of LDL cholesterol and triglycerides are risk factors for atherosclerosis. **Urea and Electrolytes:** - **Purpose:** These tests evaluate kidney function by measuring waste products (such as urea) and electrolyte levels (such as sodium, potassium, and chloride). Abnormal levels can indicate renal impairment or electrolyte imbalances. **Full Blood Count (FBC):** - **Purpose:** FBC provides information on the types and numbers of cells in the blood, including red blood cells, white blood cells, and platelets. It helps diagnose conditions like anaemia, infection, and leukaemia. **HbA1c:** - **Purpose:** This test measures the average blood glucose level over the past two to three months, providing an indication of long-term blood sugar control in people with diabetes. **Multiple Choice Questions (MCQs)** 1. **Which of the following is not a function of blood?** - a\) Transportation of nutrients - b\) Regulation of body temperature - c\) Production of hormones - d\) Protection against infection 2. **What is the main function of erythropoietin (EPO)?** - a\) Stimulate white blood cell production - b\) Regulate platelet production - c\) Protect red blood cells from destruction and stimulate their production - d\) Increase the production of plasma proteins 3. **Which blood group is considered the universal donor?** - a\) AB RhD positive - b\) O RhD positive - c\) O RhD negative - d\) A RhD negative 4. **Which white blood cell type is most involved in allergic reactions?** - a\) Neutrophils - b\) Eosinophils - c\) Basophils - d\) Monocytes 5. **Which of the following blood tests is used to assess kidney function?** - a\) Troponin - b\) ESR - c\) Urea and electrolytes - d\) HbA1c **Clinical Cases** **Case 1: Anaemia in a Young Adult** **Presentation:**\ A 25-year-old woman presents with fatigue, pallor, and shortness of breath on exertion. Blood tests reveal a low haemoglobin concentration and a reduced red blood cell count. **Discussion:** - **Question:** Explain the possible causes of anaemia and the role of erythropoiesis in managing this condition. What additional tests might be necessary to determine the cause? - **Answer:** Anaemia could be caused by iron deficiency, chronic disease, or a deficiency in erythropoiesis due to insufficient erythropoietin production. Additional tests, such as iron studies, vitamin B12, folate levels, and reticulocyte count, may be needed to identify the underlying cause. **Case 2: Diagnosing a Heart Attack** **Presentation:**\ A 58-year-old man arrives at the emergency department with chest pain radiating to his left arm. Blood tests reveal elevated troponin levels. **Discussion:** - **Question:** Describe the significance of elevated troponin levels in this patient. What other tests should be conducted to confirm the diagnosis and assess the extent of myocardial damage? - **Answer:** Elevated troponin levels indicate myocardial injury, consistent with a heart attack. Additional tests, such as an ECG, echocardiogram, and coronary angiography, should be performed to confirm the diagnosis, assess heart function, and determine the severity of the coronary artery blockage.