Blood & RBCs PDF

Dr. Zakaria Rajeh Composition of blood  Blood consists of cells suspended in a clear yellowish fluid called the plasma. A. The cellular elements are about 40- 45% of the total blood volume and are 3 types: 1- Red blood cells (R.B.C.s) or erythrocytes.  In R.B.C.s  anaemia.  In R.B.C.s  poly...

Dr. Zakaria Rajeh Composition of blood  Blood consists of cells suspended in a clear yellowish fluid called the plasma. A. The cellular elements are about 40- 45% of the total blood volume and are 3 types: 1- Red blood cells (R.B.C.s) or erythrocytes.  In R.B.C.s  anaemia.  In R.B.C.s  polycythaemia. 2- White blood cells (W.B.C.s) or leukocytes.  In W.B.C.s  leucopenia.  In W.B.C.s  leukocytosis. 3- Platelets or thrombocytes.  In Platelets  thrombocytopenia.  In Platelets  thrombocytosis. B. The plasma The plasma is about 55-60 % of total blood volume, and consists of water (90 %) and dissolved solutes (10 %), include: 1- Organic substances: plasma proteins (7.1 %), lipids, hormones, enzymes and waste products (2 %). 2- Inorganic substances (0.9 %), which include the different electrolytes e.g. Na⁺, K⁺⁺ , Clˉ, HCO3ˉ, Ca⁺² and PO4ˉ. Plasma proteins: The blood volume is normally about 8% of the body weight. Factors affecting blood volume: Physiological factors Age. Sex. Pregnancy ++. Muscular exercise++. Hot weather. High altitude++. 2. Pathological factors: A. Blood volume is increased in: Overhydration. Polycythaemia vera. Leukaemia. B. Blood volume is decreased in: Dehydration. Anaemia. Burns. Hemorrhage. General functions of the blood 1. It is the major transport medium in the body. This is essential for: Nutrition. Respiration. Excretion. Regulation of body temperature. Regulation of metabolism. 2. It is essential in maintaining the acid- base balance. 3. It is important in the regulation of water balance. 4. The blood viscosity shares in producing peripheral resistance to the blood flow. 5. The blood clotting is a major hemostatic mechanism for prevention of excessive blood loss. 6. The W. B. C. s provide the main defense mechanisms against different of microorganisms  are circular non-nucleated biconcave discs containing haemoglobin.  Count: the average R.B.Cs. count in adults is 5 million /mm3. In adult female: 4.5-5 million /mm3. In adult male: 5-5.5 million /mm3. In newly born infant: about 7 million /mm3. Physiological factors that affect red cell count  Age: high in newly born infants.  Sex: higher in males (erythropoiesis is stimulated by the male hormone)  Exercise, hot weather and emotions. increased due to spleen contraction  High altitudes. increase due to polycythemia  Diurnal variation 5% change: highest in the evening and lowest during sleep Function of R.B.Cs. 1. Major function of RBCs is to transport hemoglobin, HB content of RBCs is important for:  Transport of O2 from the lungs to tissues.  Transport of CO2 from the tissues to the lungs.  HB helps in the regulation of blood PH. 2. Carbonic anhydrase enzyme of RBCs is important for CO2 carriage. 3. Histaminase enzyme of the RBCs inactivates histamine. 4. RBCs cell membrane keeps the HB inside them and prevents its loss in urine.  Formation of R.B.Cs. (Erythropoiesis)  Site of formation of R.B.Cs. : 1. In the fetus, they are formed in the liver and spleen. 2. In the last three months of fetal life and after birth, they are formed in the bone marrow of all bone until adolescent. 3. By the age of 20, they are formed by the bone marrow of upper parts of humerus and femur and of membranous bones. 4. After the age of 20 years, they are formed in bone marrow of membranous bone as vertebrae, sternum and ribs. Relative rates of red blood cell production in the bone marrow Factors affecting erythropoiesis: 1. Blood O2 tension: Erythropoiesis is inhibited when the blood O2 tension increases and stimulated when it is decreased (e.g. in high altitudes, after haemorrhage and in chronic heart and lung diseases). 2. The kidneys: the kidneys secrete a hormone called erythropoietin which stimulates red cell formation in bone marrow.  The release of erythropoietin is stimulated by: Hypoxia. Male sex hormone. Cobalt salts. Factors affecting erythropoiesis: 3. Hormones:  Androgen and thyroxin. 4. The liver: a) Forms the globin part of Hb. b) Stores vitamin B12 and several minerals. c) Secrets some erythropoietin. 5. The bone marrow.  Factors affecting erythropoiesis: 6. Stomach: Gastric HCL is needed to convert ferric iron into ferrous. Intrinsic factor secreted by the gastric mucosa. 7. Small intestine. 8. Diet: Proteins of high biological value. Iron. Other minerals e.g. copper and cobalt. Vitamins e.g. vitamin B12 and folic acid. Life span of R.B.Cs.:  The R.B.Cs. life span in the body is about 120 days.  The rate of destruction equals that of regeneration. Fate of red blood cells:  Old R.B.Cs. are fragmented and engulfed by phagocytic cells of the reticuloendothelial system mainly in spleen.  The HB is hydrolyzed as follow:  HB  Haem + globin.  Globin  Amino acids.  Heam  Iron + biliverdin.  Biliverdin  Bilirubin. Haemoglobin (Hb)  is red, oxygen carrying pigment in the RBCs.  It is a protein with molecular weight 64450.  It is a globular in shape, made up of 4 subunits.  The haem is formed of protoporphyrin containing one ferrous atom.  It consists of 2 alpha polypeptide chains and 2 beta polypeptide chains. Types of Hb 1. Hb A (α2 β2). 2. Hb A2 (α2 δ2). 3. Hb F (α2 γ2). Abnormalities of Hb formation 1. Haemoglobinopathies: abnormal polypeptide chains are produced e.g. Hb S formation in sickle- cell anemia. 2. Thalassemia:  the polypeptide chains are normal in structure but they are produced in decreased amount or absent due to defect in the globin genes.  There are 2 types of this disorder: alpha and beta. THANK YOU…