Monday, April 11, 2011

Blood and its components

Blood (about 8% of total body weight) is a specialized type of connective tissue which has the liquid portion called the plasma (roughly about 55% of the whole blood) and the solid portion (about 45%) known as formed elements.

The formed elements are mainly the Erythrocytes (Red blood corpuscles or cells or RBCs), Leucocytes or Leukocytes (White blood corpuscles or cells or WBCs) and the Thrombocytes (Platelets). The formed elements of the blood are formed in the red bone marrow in adults mainly found in the ends of long bones like the femur, humerus, and flat bones like the skull bones, sternum, ribs, hip bone etc. In fetus and neonate the blood formation (hemopoiesis) also goes on in the liver and spleen.

The bone marrow which constitutes about 4% of the total body weight in adults is mainly of two types: Red bone marrow (hematopoietic) and the Yellow bone marrow (fat cells and stem cells).

The Plasma, by itself, is straw-yellow in color is aqueous (watery) solution of water (92% of plasma is water) and proteins (roughly close to the rest of the 8% of plasma) and traces of other materials. Plasma contains proteins (Albumin - mainly a carrier protein; Globulins alpha, beta and gamma types- gamma globulins  are Immunoglobulins which are antibodies,  20 types of complement proteins also used for defense), electrolytes (Na+, K+, Cl-, HCO3-  etc), glucose and traces of other sugars, amino acids, other organic acids, cholesterol, and other lipids, hormones, clotting factors, fibrinogen, urea and other wastes.

The Erythrocytes or the RBCs are mainly involved in the transport and exchange of O2 (Oxygen) and CO2 (Carbon dioxide) in the lungs and in the tissues. RBCs appear red and give the human blood its red color due to the presence of a red pigment carrier protein called Hemoglobin. Each hemoglobin molecule can bind to 4 molecules of oxygen. After binding with oxygen it’s called oxyhemoglobin which gives the oxygenated blood its bright red color.

The Leukocytes are divided into two categories bases on the presence of granules (Granulocytes) or the absence of granules (Agranulocytes). The Granulocytes are further divided into three types based on the dye that they pick up on being stained using the Hematoxylin and Eosin stain (H&E). The cells that appear blue after picking up the Hematoxylin stain (blue in color) are called Basophils. The ones that stain Lilac, red or pink shades are called Eosinophils. The ones that stay neutral to the dye and stay clear are called Neutrophils. The Agranulocytes are of two types Lymphocytes and Monocytes.

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