Types of Blood Cells

Blood comprises of around 9% of body mass in adult human. In an average man, blood is 90 milliliter per kg of body weight and in an average woman blood is 65 milliliter per kg of body weight. Its specific gravity {specific gravity means Relative density) is 1.060 {this means slightly more than water} and average pH is 7.4 {means blood is little alkaline). Its osmotic pressure at room temperature is 7.6 atmospheres. Hemoglobin in normal healthy adult is 14-16 gm per 100 milliliter.

Blood is a connective tissue and means of substance transportation in body. It distributes nutrients, oxygen, hormones, antibodies and cells specialized in defense to tissues and collects waste such as nitrogenous wastes and carbon dioxide from them. It is made of two portions viz. fluid part (plasma) and cellular part (blood cells or corpuscles).

Plasma

Plasma is 55% of the blood by volume and constitutes 5% of the body weight. Plasma is a pale yellow transparent clear fluid which consists of 90-92% water and 8-10% organic and inorganic substances. Organic substances are mainly plasma proteins viz. albumin, globulin, prothrombin and fibrinogen. Albumins are responsible for maintenance of osmotic pressure of Blood. Globulins are chief sites for formation of antibodies; while prothrombin and fibrinogen are essential for clotting of blood. Inorganic substances in plasma include Glucose, Fructose, cholesterol, nucleosides, Vitamins, hormones, uric acid etc. and gases such as oxygen and carbon dioxide in dissolved phase.

Red Blood Corpuscles

RBCs or Erythrocytes are biconcave cells which don’t have a nucleus. They are responsible for transporting oxygen from the lungs to tissues with the help of respiratory pigment hemoglobin, which is main constituent of RBCs.

In the embryonic stage RBC are produced in Liver, spleen and Lymph nodes (all the three). Up to 20 years of age, they are produced in bone marrow of long bones such as femur. After 20 years they are produced in the bone marrows of membranous bones. RBCs complete a circulation in the body in 20 seconds. Their life span is 100-120 days. Their main constituent Hemoglobin is made of four polypeptide chains and four heme (iron) groups. The spleen is the main organ where old red blood cells are destroyed. During the destruction of red blood cells, the heme groups turns into bilirubin and this substance is then captured by the liver and later excreted to the bowels as a part of bile.

White Blood Corpuscles

White Blood Cells leukocytes are specialized in the defense of the body against foreign agents and are part of our immune system. There are several types of WBCs such as lymphocytes, monocytes, neutrophils, eosinophils and basophils. Out of them, the neutrophils, eosinophils and basophils are called granulocytes because their cytoplasm looks containing granules when viewed under microscope. Lymphocytes and monocytes are called agranulocytes.

Monocytes

Monocytes are largest WBCs and have a horse shoe shape. They are most powerful phagocytes {cells which eat other cells} which work as scavengers. Monocytes make around 5% of the total WBC count.

Lymphocytes

Lymphocytes make around 25% of the WBC count and they are made in lymph nodes and lymphatic tissues in spleen, liver etc. They are able to show some amoeboid movement. Their function is to make antibodies.

Neutrophils

Neutrophils are WBCs with multi-lobbed nucleus. They ingest and destroy the bacteria or other foreign bodies. Wherever there is some infection, neutrophils pass out from the blood streams and accumulate creating puss by eating debris and bacteria.

Eosinophils

The main function of histamine rich eosinophils is to combat the multicellular parasites and certain infections. Along with the mast cells, they also control mechanisms associated with allergy and asthma.  Thus, their number increases during chronic bronchitis, asthma or allergic conditions.

Basophils

Basophils appear during inflammatory reactions which cause allergy. They contain anticoagulant heparin, which prevents blood from clotting too quickly.

White blood cells perform several functions in the body as:

Leucocytosis

Leucocytosis and leukopenia are clinical conditions in which a blood sample contains an abnormal count of leukocytes. When the leukocyte count in a blood sample is above the normal level for the individual, it is called leukocytosis. When the leukocyte count is lower than the expected normal level, it is called leukopenia. Leukocytosis generally happens when body is suffering from infections or in cancer of these cells. Leukopenia, occurs when some diseases, such as AIDS, attack the cells or when immunosuppressive drugs are used.

Platelets and Hemostasis

Platelets or thrombocytes are fragments of large bone marrow cells called megakaryocytes. Through their properties of aggregation and adhesiveness, they are directly involved in blood clotting as well as release substances that activate other hemostatic processes. When tissue wound contains injury to a blood vessel, the platelets and endothelial cells of the wall of the damaged vessel release substances (platelet factors and tissue factors, respectively) that trigger the clotting process.

Blood Clotting

Blood clotting is basically a sequence of chemical reactions whose products are enzymes that catalyze the subsequent reactions. This is the reason that clotting reactions are called cascade reactions. In plasma, thromboplastinogen transforms into thromboplastin, a reaction triggered by tissue and platelet factors released after injury to a blood vessel. Along with calcium ions, thromboplastin then catalyzes the transformation of prothrombin into thrombin. Thrombin then catalyzes a reaction that produces fibrin from fibrinogen. Fibrin, as an insoluble substance, forms a network that traps red blood cells and platelets, thus forming the blood clot and containing the hemorrhage.

Clotting factors

Clotting factors are substances (enzymes, coenzymes, reagents) necessary for the clotting process to happen. In addition to the triggering factors and reagents already described (tissue and platelet factors, thromplastinogen, prothrombin, fibrinogen, calcium ions), other substances participate in the blood clotting process as clotting factors. One of these is factor VIII, the deficiency of which causes hemophilia A, and another is factor IX, the deficiency of which causes hemophilia B. Most clotting factors are produced in the liver. Vitamin K participates in the activation of several clotting factors and is essential for the proper functioning of blood coagulation.

Lymphatic System

The lymphatic system is a network of specialized vessels with valves, which drains interstitial fluid called lymph. The lymphatic system is also responsible for the transport of chylomicrons (vesicles that contain lipids) produced after the absorption of fats by the intestinal epithelium.

Along lymphatic vessels are ganglial-like structures called lymph nodes, which contain many immune system cells. These cells filter impurities and destroy microorganisms and cellular waste. The lymphatic vessels drain to two major lymphatic vessels, the thoracic duct and the right lymphatic duct, which in turn drain into tributary veins of the superior vena cava.

The lymph nodes, or lymph glands, have lymphoid tissue that produces lymphocytes (a type of leukocyte). In inflammatory and infectious conditions, it is common to see the enlargement of lymph nodes in the lymphatic circuits that drain the affected region due to the reactive proliferation of leukocytes.