Blood Physiology PDF

Blood Physiology Review about blood production HemoPoiesis Subjectives:- 1. orgin of blood elements 2. factors regulating hemopoiesis 3. Functions of blood. 4. Functions of Plasma Proteins. Blood is a viscous fluid that is pumped by the heart through a closed system of blood vessels. I...

Blood Physiology Review about blood production HemoPoiesis Subjectives:- 1. orgin of blood elements 2. factors regulating hemopoiesis 3. Functions of blood. 4. Functions of Plasma Proteins. Blood is a viscous fluid that is pumped by the heart through a closed system of blood vessels. It is composed of cells (red blood cells, white blood cells, and platelets) which are suspended in a fluid portion, the plasma. Functions of the blood include: 1. Transport of O2, nutrients and hormones to the tissues and carries CO2 to the lungs and other products of metabolism to the kidneys to be excreted. 2. It participates in the regulation of body temperature, the pH and electrolyte concentrations of interstitial fluid within the normal ranges through a constant exchange of molecules with the interstitial fluid. 3. Blood also serves essential body protective functions, such as combating invading microorganisms, mediating inflammation, initiating immune responses to foreign materials, and maintaining hemostasis. The normal total circulating blood volume is about 8% of the body weight (5600 ml in a 70 kg man). About 55% of this volume is plasma. 4. Plasma: Plasma is a part of the extracellular fluid of the body. The normal plasma volume is about 5% of the body weight (3500 ml in a 70-kg man). Plasma consists of an aqueous solution of proteins, electrolytes, and small organic molecules. Plasma Proteins: Its concentration is about 7 gm/dl. The major types of protein and their average normal concentrations present in the plasma are: Albumin, 4.5 g/dl. Globulins (a1, a2, B1, B2, and y), 2.5 g/dl. Fibrinogen, 0.3 g/dl. Functions of plasma proteins, in general, include: 1. Plasma proteins, mainly albumin, exert an osmotic pressure of about 25 mm Hg across the capillary wall. It is called the "colloid osmotic pressure" or "oncotic pressure". It tends to pull water into the blood. 2. Plasma proteins are responsible for 15% of the buffering capacity of blood by helping to keep the blood PH constant. 3. Some of the plasma proteins function in the transport of hormones and different substances in blood. 4. Circulating antibodies in the δ globulin fraction of the plasma proteins play a special role in providing the body with immunity. 5. Fibrinogen and other plasma proteins are concerned with blood clotting. 6. When the tissues become depleted of proteins, the plasma proteins can act as a source for rapid replacement of the tissue proteins. Liver forms all the albumin and fibrinogen of the plasma proteins, as well as, 50-80% of the globulins. The lymphoid tissues form the remainders of the globulins. They are mainly the y globulins that constitute the antibodies. The normal A/G ratio of about 1.8:1. The A/G ratio is reduced in liver disease due to decreased synthesis of albumin. Hemopoiesis: Formation of blood cells (hemopoiesis) occurs at different anatomical sites during the course of development from embryonic to adult life. →In the early few weeks of embryonic life, blood cells are produced in the yolk sac. →After the third month of pregnancy, they are formed mainly in the liver and in the lymph nodes and (1) the spleen. → During the latter part of fetal life and after birth, blood cells are produced by the bone marrow of all bones. → By the age of 20 and beyond, blood cells formation is restricted normally in the red marrow of flat or membranous bones (such as the vertebrae, sternum, ribs and pelvis) and the proximal ends of humerus and femur. This is because the active red marrow of long bones (except for the upper humerus and femur) has become inactive (yellow and fatty). Inactive yellow marrow produces no more blood cells. Even in these bones, the marrow becomes less productive as age increases. However, maturation, activation, and some proliferation of lymphoid cells occur in secondary lymphoid organs (spleen, thymus, and lymph nodes). In certain pathological states, when there is increased demand for blood cell production, red marrow reappears in the shafts of the long bones, replacing the fat. Diseases in which the bone marrow becomes destroyed, a significant hemopoietic activity occur in the liver, spleen and other sites, when it is referred to as extramedullary hemopoiesis. The bone marrow is one of the largest organs in the body and it is one of the most active. In the bone marrow, there are multipotent uncommitted stem cells (figure 1) from which all the cells in the circulating blood are derived. The uncommitted stem cells have two properties: 1. Ability of cell division to give rise to new stem cells (self-renewal). 2. Ability to differentiate into committed myloid stem cells and committed lymphoid stem cells. The committed myloid stem cells differentiated still further into: Committed stem cell that produces erythrocytes, the colony-forming unit-erythrocyte (CFU-E).. Committed stem cell that produces granulocytes and monocytes, the colony-forming units- granulocytes, monocytes (CFU-GM) Committed stem cell that produces megakaryocytes, the colony-forming units-megakaryocytes (CFU-Meg) (figure 3.1). Factors regulating hemopoiesis (hemopoietic growth factors): Production of blood cells is regulated by growth factors, which are multiple proteins that control growth, differentiation, and function of cells in one or more of the lines of blood cell production. These factors include: 1. Erythropoietin, 2. Thrombopoietin 3. Colony-stimulating factors (CSFS) & stem cell factor (SCF) 4. Interleukins (IL-1, IL-3, and IL-6). These growth factors affect their target cells through binding to specific receptors. Kidney cells produce erythropoietin, which is a circulating hormone. It is produced by interstitial fibroblasts in the kidney in close association with peritubular capillary and tubular epithelial cells. Macrophages, activated T- lymphocytes, fibroblasts, and endothelial cells produce the other factors. (3) (4) (5)