Blood Physiology PDF

Blood components Blood is the only fluid tissue. It is composed of liquid plasma and formed elements. Formed elements include: 1- Erythrocytes, or red blood cells (RBC). 2- Leukocytes, or white blood cells (WBC). 3- Platelets. Average blood volume is 5--6 L for male and 4--5 L for female. The...

Blood components Blood is the only fluid tissue. It is composed of liquid plasma and formed elements. Formed elements include: 1- Erythrocytes, or red blood cells (RBC). 2- Leukocytes, or white blood cells (WBC). 3- Platelets. Average blood volume is 5--6 L for male and 4--5 L for female. The cells constitute about 45% of blood volume (packed cell volume or hematocrit=0.45). Blood temperature is 38C. Blood pH is 7.35--7.45. Formed Elements Erythrocytes, leukocytes, and platelets make up the formed elements. Only WBCs are complete cells. WBC count may increase to 11,000/mm3 as normal response to bacterial or viral invasion, leave capillaries via diapedesis and move through tissue spaces. RBCs have no nuclei or organelles, and platelets are just cell fragments. Most blood cells do not divide but are renewed in bone marrow. The RBC is a biconcave disc. It is an-ucleated (has no nucleus) and no organelles. The RBC is filled with hemoglobin (Hb). The plasma membrane protein gives the RBC its flexibility. The biconcave shape provides a huge surface area with minimum volume. The Hb constitutes bout 97% of solid cell contents. ATP is generated anaerobically, so the RBCs do not consume the O2 they transport. RBC function is transport of respiratory gas. Most O2 in the blood is bound to Hb. (oxyhemoglobin). Reduced Hb (Deoxyhemoglobin) is Hb without O2. Carbaminohemoglobin is Hb bound to CO2. Functions of Blood 1- Distribution (O2, CO2, nutrients, wastes, hormones \...) 2- Regulation (temperature, pH, fluid volume \...) 3- Protection (clotting, prevention of infection: WBC, antibodies, complement) Composition of blood plasma Blood plasma contains over 100 solutes, including proteins, nonprotein nitrogenous substances, organic nutrients, electrolytes and respiratory gases.  Production of Blood Cells The process of blood cell formation is referred to as hematopoiesis (or hemopoiesis). It occurs in the red bone marrow of the axial skeleton and girdles, epiphyses of the humerus and femur **Formation of WBC is called leucopoiesis**. Myeloid stem cell becomes myeloblast or monoblast. Lymphoid stem cell becomes lymphoblast. Myeloblast develops into eosinophil, neutrophil, or basophil. Monoblast develops into monocyte. Lymphoblast develops into lymphocytes (B or T). Formation of RBC (erythropoiesis) is triggered by hypoxia (less PO2) which leads to release of erythropoietin (EPO) from the kidneys. It depends on adequate supplies of iron, amino acids, and B vitamins, lipids, carbohydrates, iron and folic acid. The life span of an erythrocyte is 100--120 days. Human blood groups External surfaces of RBC membranes have 30 varieties of naturally occurring glycoprotein antigens. They promote agglutination and, so, called agglutinogens. Presence (or absence) of these antigens is used to classify blood groups. The ABO blood groups refer to the presence (or absence) of antigens A and/or B. Specific antibodies for theses antigens are present in (or absent from) the blood plasma. They are anti-A and anti-B antibodies. A subject with blood group A has antigen A on RBC membrane and antibody B in his plasma. Conversely, a subject with blood group B has antigen B on RBC membrane and antibody A in his plasma. The subject who donates his blood is called the donor while that who receives blood is called the recipient. When a subject with blood group B donates his blood to a subject with blood group A, the antibodies B in the recipient\'s plasma attack the antigens B on the received blood RBCs resulting in serious hemolytic reactions. Other probabilities are shown in the table below. Accordingly, the blood group O is the universal donor (the generous blood which gives all because it has no antigens to be attacked by the recipient\'s antibodies) while the blood group AB is the universal recipient (it receives from all because it has no antibodies to attack any antigen on the donated blood RBCs).  Presence of the Rh antigens on RBCs is indicated as Rh+. Subject with Rh+ blood has antigen Rh on RBC membrane (so, he has no Rh antibodies in his plasma). However, even the subject with Rh\_ blood has no Rh antibodies in his plasma (the Rh antibodies are not spontaneously formed in the plasma of Rh-- individuals), but if it happens that an Rh-- individual receives Rh+ blood (accidently or during operation), Rh antibodies will then be formed in his plasma and, hence, when that \"sensitized\" subject receives an Rh+ blood at a second occasion, a typical transfusion reaction will occur. Clinical considerations: Hemolytic disease of newborn Rh-- mother becomes sensitized when Rh+ blood (from her first Rh+ baby or an Rh+ transfusion) causes her body to synthesize Rh+ antibodies. Rh+ antibodies of mother cross the placenta and attack and destroy the RBCs of the second Rh+ baby. Pharmaceutical considerations: Hemolytic disease of newborn Drugs like RhoGAM can prevent the Rh-- mother from becoming sensitized by the first Rh+ baby\'s antigens and, hence, prevents the formation of Rh+ antibodies in the mother\'s plasma. Treatment of hemolytic disease of the newborn involves prebirth transfusions and exchange transfusions after birth. Transfusion Reactions Transfusion reactions occur when mismatched blood is infused. Donor's cells are attacked by the recipient's plasma agglutinins causing diminished oxygen carrying capacity, clumped cells that impede blood flow, ruptured RBCs that release free hemoglobin into the bloodstream, circulating hemoglobin precipitates in the kidneys and causes renal failure