Blood Physiology Chapter 3 PDF

# Blood Physiology Chapter (3) ## Red Blood Corpuscles (RBCs) Erythrocytes - **Image:** A biconcave disc with dimensions. - Side view: 7.5 µm - Top view: 2.0 µm ## Shape and Structure of RBCs - RBCs are non-nucleated biconcave discs. - Have no nuclei and are therefore called corpuscles...

# Blood Physiology Chapter (3) ## Red Blood Corpuscles (RBCs) Erythrocytes - **Image:** A biconcave disc with dimensions. - Side view: 7.5 µm - Top view: 2.0 µm ## Shape and Structure of RBCs - RBCs are non-nucleated biconcave discs. - Have no nuclei and are therefore called corpuscles. - There are no mitochondria in RBCs. - Derive their energy from anaerobic metabolism of glucose (glycolysis). ## Most important content of RBCs - Hemoglobin (Hb). ## Main intracellular cation - K+ ## Carbonic anhydrase (C.A.) - Is an enzyme present in RBCs, which is important for the transport of CO2. ## RBCs Count - **In adult male:** 5.4 million/mm³ - **In adult female:** 4.8 million/mm³ - It is higher in new born infants, athletes and at high altitudes - It is decreased in old age. ## Hemoglobin (Hb) - It is the red oxygen-carrying pigment of RBCs - Hb% is the amount of hemoglobin in 100 ml (dl) of blood. It is - **in adult male:** 15-16 g/dl - **in adult female:** 13-14 g/dl - **In newborns:** 19 g/dl. ## Functions of RBCs ### A. Functions of Hemoglobin: 1. Transport of oxygen from lungs to tissues and carbon dioxide from tissues to lungs. Most important function of RBCs. 2. Carbonic anhydrase in RBCs converts the carbon dioxide taken up by them: - $CO_2 + H_2O \xrightarrow[]{C.A} H_2CO_3 \xrightarrow[]{ } H + HCO^{-3}$ 3. Hemoglobin is an important buffer. - Has 6 times more buffering power than plasma proteins. - Can buffer H+ inside RBCs (they are formed during CO2 transport) and - Can carry CO2 with minimal change in pH. ### B. Functions of Membrane: 1. As the membrane of RBCs is plastic, - allows changes in volume of RBCs (increased volume in venous blood) with minimal change in tension on the membrane. - allows RBCs to squeeze through narrow capillaries. 2. The biconcave shape of RBCs is suitable for the diffusion of gases, as it gives a maximum surface area in relation to the size of RBCs. 3. The membrane of RBCs keeps hemoglobin inside. If hemoglobin becomes free, it passes to plasma and will: - pass to kidneys → block renal capillaries → renal failure - Increase blood viscosity → increase blood pressure and the work done by the heart. - Increase colloidal osmotic pressure of plasma proteins → prevent filtration of fluid across capillaries. The heart increases its work to be able to filter fluid to tissues. ## Life Span and Fate of RBCs - The life span of RBCs is 120 days. - **Fate:** - Old RBCs have fragile walls, which rupture easily when RBCs pass through very narrow blood vessels, especially in the spleen where it is broken. ## Erythropoiesis - **Definition:** - It is the process of formation of new RBCs. - **Sites of Erythropoiesis:** - **In the fetus:** RBCs are formed in the liver (mainly) and spleen. - **After birth:** RBCs are formed in red bone marrow of long bones. - **By the age of 20:** The red bone marrow in long bones becomes replaced by fatty tissue and cannot produce RBCs. - **After the age of 20:** The bone marrow of flat membranous bones, such as ribs, vertebrae, pelvis, sternum and skull produce RBCs. ## Factors Affecting Erythropoiesis: ### I. Oxygen Supply to the Tissues - Role of Erythropoietin: - There is an increased rate of production of RBCs in conditions associated with decreased oxygen supply to the tissues (hypoxia), such as in: - 1. Hemorrhage: due to loss of RBCs. - 2. High altitude: due to decreased O2 tension in atmospheric air. - 3. Athletes: athletes have a relative oxygen deficiency since they have higher oxygen requirements than normal. - 4. Heart failure: due to decreased blood flow in peripheral vessels. - 5. Lung diseases: due to decreased oxygen diffusion from lungs to blood. - Tissue hypoxia stimulates the release of a hormone called "erythropoietin". ## II. Diet: ### A. Proteins: - High biological value proteins (containing all essential amino acids) of animal origin are needed for the formation of the globin part of hemoglobin. ### B. Vitamins: - All vitamins are essential for erythropoiesis, especially vitamin C, B12 and folic acid. ### 1. Vitamin B12 (= Cyanocobalamin = Extrinsic Factor = Maturation Factor) - **Functions of vitamin B12:** - a. Vitamin B12 is essential for synthesis of DNA and nuclear maturation in RBCs and so is known as the maturation factor. - b. It is also essential for the metabolism of the myelin sheath of nerves. - **Effect of vitamin B12 deficiency:** - a. Failure of nuclear maturation and division of erythroblasts in bone marrow leading to "megaloblastic or Macrocytic anemia": Erythroblasts increase in size and develop into megaloblasts and megalocytes. They are larger in size, contain a larger amount of hemoglobin and have a shorter life span than erythrocytes. - b. Marked reduction in the number of RBCs in blood. - c. Neurological symptoms: Vitamin B12 is essential for the metabolism of the myelin sheath of nerves. ### 2. Folic Acid: - It is one of the B complex vitamins. - **Functions of folic acid:** - Folic acid is needed for DNA synthesis needed for RBCs division and maturation. - **Effect of folic acid deficiency:** - Failure of maturation of RBCs → development of macrocytes resulting "Macrocytic anemia". ### C. Iron: - **Functions of iron:** - 1. Iron is important for formation of hemoglobin RBCs and myoglobin in muscles. - 2. It is required as a co-factor by some oxidation enzymes, e.g., catalase, peroxidase and cytochrome oxidase. - **Total body iron:** 4g (70 % in hemoglobin, 3 % in myoglobin, 1% in oxidative enzymes and 26% stored in liver and spleen). - **Effect of iron deficiency:** - Iron deficiency causes microcytic hypochromic anemia. - **Causes of iron deficiency:** - 1. Decreased iron intake in diet, which may occur: - In infants fed milk only, as milk is poor in iron - In females during pregnancy and lactation. - 2. Failure of iron absorption, which may be due to: - Partial gastrectomy (insufficient HCl secretion) - Diseases of upper small intestine (where iron is absorbed) - Vitamin C deficiency - Too much phytic acid, oxalates and phosphates in diet - 3. Chronic blood loss: as in: - Excessive bleeding during menstruation in females - Bleeding peptic ulcer and piles. ### D. Trace Elements: Copper and Cobalt. ## III. Hormones: - Several hormones increase the rate of erythropoiesis, including: - 1. Thyroxin (released by thyroid gland - 2. Androgens. - 3. Glucocorticoids (secreted by suprarenal cortex) ## IV. Healthy Bone Marrow: - Bone marrow must be healthy for normal RBCs production. - Bone marrow destruction leads to a decrease in all types of blood cells, i.e., RBCs, WBCs and platelets. This condition is called aplastic anemia., ## V. Healthy Liver: - Liver diseases are associated with anemia as the liver: - Forms the globin part of hemoglobin - Stores vitamin B12 and iron. - Produces 15% of erythropoietin.