Plasma and blood the fluid of lifeOur blood consists of a liquid portion called plasma and 3 types of cells. If we mix blood with an anti-coagulant (a chemical which prevents blood from clotting) and keep it in a tube cells settle down at the bottom leaving a liquid in the upper portion. If we allow blood to clot in a tube the liquid which separates is called serum. The three types of blood cells are red blood cells (RBCs) also called erythrocytes, white blood cells (WBCs) also called leucocytes and platelets also called as thrombocytes. The Red Blood Cells The RBCs are responsible for carrying oxygen to all the tissues. They contain a substance called hemoglobin which takes up oxygen when the blood goes through the lungs (respiratory system) and releases it when blood flows through the tissues (heart and circulation). The normal hemoglobin consists of two components-a protein component called globin which is made of four chains and a non protein component called heme containing iron. The RBCs contain two types of hemoglobin-fetal hemoglobin and adult hemoglobin. Adult hemoglobin is made up of two alpha chains and two beta chains. Fetal hemoglobin is made up of two alpha and two gamma chains. Most of the hemoglobin in the intrauterine life is fetal hemoglobin. The level gradually comes down after birth and is present in very small quantity after the newborn period. The type of hemoglobin present in blood can be ascertained using a test known as hemoglobin electrophoresis. The RBCs are produced inside the cavity of bones (bone marrow). They have a life span of 120 days, after which they are destroyed. Breakdown of RBSc releases hemoglobin into blood. Hemoglobin is split into heme and globin. Heme is converted in the liver to a yellow pigment called bilirubin. Accumulation of bilirubin either due to increased production or impaired elimination results in the clinical condition called jaundice. Bilirubin is normally excreted in bile (the greenish juice secretes by liver which aids absorption of fat) which reaches the small intestine through a tube called bile duct. Unlike other cells is the body the RBSc do not have nucleus. As they have to deliver oxygen to all cells they do not use oxygen themselves and derive energy through a different mechanism. They have a central depression and resemble a disc with concavity on both sides.
The diameter of an RBS is 7 to 8 micrometers. The total number of RBSc in one microliter (one millionth of a liter) of blood is a staggering 4.5 to 5.5 millions (four and half to five and a half millions). An adult has about 5-6 liters of blood in the body. Have some fun calculating the total number of RBSc in the blood. Fetal hemoglobin is different from adult hemoglobin in that it has greater affinity for oxygen. This is necessary as the fetal blood does not absorb oxygen directly from the atmospheric air but from the maternal blood-to be more specific from the hemoglobin in the maternal blood (it has to snatch oxygen from adult hemoglobin). In a disease known as thalassemia the synthesis of adult hemoglobin is impaired due to genetic defect. This causes abnormal destruction of RBCs leading to anemia and the affected child has to be given repeated blood transfusions. White blood cells (leukocytes) Normal blood contains five different types of leukocytes. They are neutrophils, eosinophils, basophils, lymphocytes and monocytes. They play a vital role in protecting the body against infections. Neutrophils are larger than RBSc and have a segmented nucleus. They swallow micro-organisms and kill them-a process called phogocytosis
Phagocytosis Basophils are responsible for mediating allergic reactions. They contain a substance called histamine which causes dilatation of blood vessels and increases the permeability of their walls. Theses changes lead to swelling and itching associated with allergic reactions. Eosinophils help the body to fight against parasites. Lymphocytes are of the same size as RBSc. They are of 2 types T lymphocytes and B lymphocytes. They protect the body in two ways-antibody mediated immunity and cell medicated immunity. Monocytes: They are the largest of the leukocytes in the blood.They are called macrophages when they migrate into the tissue. Both monocytes and macrophages are phagocytic like neutrophils. Monocyte numbers increase whenever there is increased cell damage. Platelets: What happens when you cut your finger? Blood flows out for some time and then a clot forms preventing continuous bleeding. Imagine what happens it blood starts clotting inside the blood vessels. Life will soon come to an end. . Blood has to in fluid form inside the blood vessels so that it keeps flowing, but should clot when there in an injury. Sounds simple but the clotting of blood is anything but simple. Platelets play an important role in the clotting of blood. Platelets are quite small in size and their number varies from 150,000 to 400,000 per microliter. They usually appear in clumps when a smear of blood is examined under a microscope.
When there is some injury to tissues the damaged tissues release certain chemicals which lead to a cascade of reactions which culminate in the formation of blood clot. There is a protein in the blood called fibrinogen. This gets converted into fibrin which forms a mesh. The platelets form clumps and get entangled in the mesh to form a clot. There are several proteins necessary for clotting. They are called clotting factors. Deficiency of many of these factors can occur resulting in abnormal bleeding. Hemophilia is one of these conditions which results from deficiency of factor VIII. Common disorders of blood Return from plasma and blood to human body
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