Physiology

• Blood is the red fluid found in the blood vessels, pumped around the body by the heart, and it delivers necessary substances to the body cells, such as nutrients and oxygen, and transports waste products away from those cells.
• Blood represents about 8% of total body weight and has an average volume of 5 liters in woman and 5.5 liters in men.
• Blood consists of fluid part "plasma" which makes up 55% of blood volume, and cellular elements which make up 45% of blood volume.
• Types of cellular elements in blood are red blood cells "Erythrocytes" (RBC), white blood cells "Leukocytes" (WBC), and platelets "Thrombocytes".
• Blood components after centrifugation are cellular components under a microscope.
• Plasma is the fluid portion of blood, with a volume of 3.5 L in a 70 Kg man, and its composition includes water, plasma proteins, inorganic constituents, and others such as glucose, amino acids, lipids, vitamins, dissolved gases (O2 and CO2), and waste products.
• Types of plasma proteins include albumin, globulin, fibrinogen, prothrombin.
• Albumin, Fibrinogen, and Prothrombin are synthesized by the liver, while Globulins are synthesized by the liver and lymphocytes.
• Plasma proteins provide about 15% of the buffering capacity of the blood.
• Fibrinogen, prothrombin are clotting factors.
• Globulins are immunoglobulins (antibodies).
• Plasma proteins close the pores of capillaries.
• Plasma proteins transport a number of substances in the plasma, preventing their rapid loss in urine.
• Red blood cells are non-nucleated, flat, biconcave discs, with an average count of 5 million/mm3 (μL), higher in newly born infants, and their life span is 120 days.
• Red blood cells are the most abundant cells in the blood.
• The most important constituent of RBCs is hemoglobin (34%), followed by water (60%) and 6% inorganic and organic substances.
• Hemoglobin is a red oxygen-carrying pigment with an average concentration of 15 g/dl.
• In adult males, the average hemoglobin concentration is 15-16 g/dl, while in adult females it is 13-14 g/dl.
• In newborns, the average hemoglobin concentration is 19 g/dl.
• The functions of the RBC membrane include being plastic, keeping hemoglobin inside and preventing its loss in urine, and determining the blood grouping.
• Hemoglobin functions include carrying oxygen from the lungs to the tissues, helping in the carriage of carbon dioxide from the tissue to the lungs, and acting as an important buffer in blood.
• Erythropoiesis is the formation of new RBCs.
• During intrauterine development, erythrocytes are produced by the developing liver and spleen.
• In children, blood cells are formed in the marrow of most bones.
• In adults, RBCs are formed in the red bone marrow, which remains only in the sternum (breast bone), vertebrae (back bone), ribs, base of the skull and upper ends of long limb bones.
• The principle stimulus for RBCs production in low oxygen states is a hormone called erythropoietin hormone, which is produced from the kidney and the liver when there is hypoxia.
• Proteins of high biological value (animal proteins), iron, vitamin B 12 and Folic acid are essential for normal formation of DNA during red blood cell maturation.
• Copper and cobalt are other trace elements essential to erythropoiesis.
• Androgens, thyroxine and glucocorticoids stimulate erythropoiesis, while estrogen inhibits it.
• Healthy bone marrow, normal functioning liver, and normal hemoglobin levels are essential for erythropoiesis.
• Anemia is a decrease in RBCs number or decrease in Hb concentration or both.
• Normocytic normochromic anemia is a condition where RBCs are normal in size and Hb content per cell is normal, with causes including destruction of bone marrow and acute blood loss.
• Microcytic hypochromic anemia is a condition where RBCs are smaller in size and Hb is decreased in each cell, with the causes being iron deficiency anemia.
• Macrocytic hyperchromic anemia: RBCs are larger in size and Hb content is increased per cell.
• Causes of macrocytic hyperchromic anemia include Vitamin B12 deficiency anemia (megaloblastic anemia).
• Blood of different individuals has been classified according to its antigenic activity according to ABO system and Rhesus (Rh) antigen.
• The membranes of human RBCs contain the A- and/or B-agglutinogens.
• Types A individuals have the A-antigen, Type B have the B-antigen, Type AB have both antigens, Type O have neither antigens.
• Agglutinins (antibodies) against A (anti-A) (α) and B-agglutinogens (anti-B)(β) occur naturally in plasma.
• Types A individuals have anti-B antibodies, Type B individuals have anti-A antibodies, Type O individuals have both antibodies, Type AB individuals have neither antibodies.