Blood Physiology PDF

# Blood Physiology ## Chapter (3) ## BLOOD - Blood is part of the extracellular fluid. It is continuously circulating in blood vessels throughout the cardiovascular system (CVS) by the pumping action of the heart. - It constitutes 8% of the body weight, i.e., 5.6 L in an average adult male. ## C...

# Blood Physiology ## Chapter (3) ## BLOOD - Blood is part of the extracellular fluid. It is continuously circulating in blood vessels throughout the cardiovascular system (CVS) by the pumping action of the heart. - It constitutes 8% of the body weight, i.e., 5.6 L in an average adult male. ## Composition of Blood Blood is composed of two parts: 1. **Plasma**: This is the fluid part of blood. It constitutes 55% of blood. 2. **Cellular part**: This part includes red blood corpuscles, white blood cells and platelets. It constitutes 45% of blood. - A diagram showing the composition of blood ## PLASMA - It is a yellow clear fluid of the blood. - Its volume is about 3.5 L (5% of body weight). - It clots on standing. The remnant is called serum. ## Composition of Plasma 1. **Water**: 90% 2. **Organic substances**: 9.1% - Plasma proteins (7.2-7.4 g/dl) - Lipids - Others: glucose, amino acids, vitamins, enzymes and waste products. 3. **Inorganic constituents**: 0.9% - Na+: It is the chief inorganic cation. - Cl: It is the chief inorganic anion. - HCO3: phosphates and sulfates. 4. **Blood gases**: O2, CO2 and N2. ## Plasma Proteins - **Types of Plasma Proteins**: There are many types of plasma proteins in blood. The most important types include: | Type | Concentration (g/dl) | Molecular weight | |--------------|-----------------------|--------------------| | Albumin | 3.5-5 | 69,000 | | Globulin | 2.5 | 90,000-156,000 | | Fibrinogen | 0.4 | 340,000 | | Prothrombin | 0.01 | 68,700 | - **Sites of Formation of Plasma Proteins**: 1. Albumin, fibrinogen and prothrombin: synthesized in the liver. 2. Globulins: - 50% are synthesized in the liver. - 50% are synthesized in the plasma cells of the reticuloendothelial system (RES), which is a diffuse system of cells present in the liver, spleen, lymph nodes and bone marrow. ## Functions of Plasma Proteins 1. **Osmotic Function**: - The total osmotic pressure of plasma is about 5000 mmHg. - 25 mmHg pressure are caused by plasma proteins. It is known as the colloidal osmotic pressure or oncotic pressure. - The remaining pressure is caused by crystalloids, e.g. Na+, Cl, HCO3, and is called the crystalloid osmotic pressure. - The colloidal osmotic pressure regulates the exchange of fluid between interstitial fluid and blood across the capillary membrane and regulates the blood volume. 2. **Transport function**: - Albumin and globulin (α and β) act as carriers for some substances such as hormones, vitamins, lipids and minerals to prevent their loss in urine. 3. **Defensive function**: - γ-globulins are also called immunoglobulins (= antibodies). - They defend the body against microorganisms and their toxins. 4. **Blood clotting function**: - Prothrombin and fibrinogen are essential for blood clotting. 5. **Viscosity**: - Whole blood is 3-5 times as viscous as water, while plasma is 1.5 times as viscous as water. 6. **Capillary function**: - Plasma proteins are required for normal capillary permeability. They partially block the pores of the capillary membrane, and therefore limit its permeability. 7. **Buffer function**: - Plasma proteins have free acidic and basic groups which are easily dissociated and act as weak acids or bases maintaining the pH of blood constant at 7.4 in spite of the addition of acids or alkalis. They constitute 15% of the buffering power of blood. 8. **Function as a source of tissue proteins**: - Plasma proteins act as a source of rapid protein replacement of tissue proteins in case of tissue protein depletion. They can split into amino acids in liver and macrophages and transported back in the blood to be used by the tissues to build new proteins.