Blood - The Fluid of Life
The human body is organized into different systems. However, these systems need a mode of receiving the substrates to function while eliminating the waste products formed. This function of transportation is provided by the blood. Hence, blood has a main role of transportation; though this is not the only function the blood is providing the human body.
Functions of Blood
1. Transporting oxygen from the lungs to the tissues and transporting carbon dioxide from the tissues to the lungs
2. Transporting the nutrients absorbed from the gastro-intestinal tract to be utilized and stored by the tissues
3. Transporting the waste products produced by the tissues t be eliminated by the liver and the kidney
4. Acting as a medium of buffer, maintaining the pH and the osmolality within the normal limit
5. Conducting the endocrine signals (transporting the hormones produced by the endocrine glands to the target tissues)
6. Acting as a reservoir of certain elements (e.g. – iron)
7. Functioning as an important component of the immune system – transporting the cells and the chemical compounds to the infected foci in order to eliminate infections
8. Protecting the body from external injuries as a second line of defense (forming a clot of blood at a site of injury to prevent further bleeding and promoting the process of repair)
The Plasma and Its Role
The blood is composed of plasma and the cells. The plasma is the medium in which the cells are embedded and is predominantly formed of water. In addition it contains a variety of proteins, sodium, chloride, bicarbonate and other minerals in lesser quantities. The plasma proteins can be categorized mainly into albumins and globulins. Albumins provide the blood with a high osmolality and help to transport different hormones and chemicals bound to them. One type of the globulins, known as the gamma globulins, is an important component in the immune system. Other globulins function as clotting factors helping the blood to clot if a blood vessel sustains damage. Lack of certain types of these factors gives rise to diseases of coagulation (e.g. – haemophilias). Certain globulins, known as the acute phase reactants, tend to increase at times when the body faces acute threats. These act as important diagnostic markers of infections (e.g. – C-reactive protein – CRP).
The Blood Cells........
The cells forming the blood can again be divided into three types, all being produced in the bone marrow by the multiplication of precursor cells.
1. The red blood cells or erythrocytes – contain an important protein known as haemoglobin which gives the characteristic colour to the blood. This is responsible for binging and transporting oxygen from the lungs to the peripheries. In addition, the red cells also transport carbon dioxide to a lesser extent. Iron, folic acid, vitamin B12 and proteins are vital for the production of red cells and in their deficiency; the body becomes deficient of haemoglobin and red cells. This condition is known as anaemia.
2. The white blood cells or leukocytes – mainly have an immune function. The white cells can be further classified into neutrophils, eosinophils , basophils, lymphocytes and monocytes based on their staining characteristics and the functions. The proportions of these cells tend to vary in different kinds of illnesses and are therefore used to diagnose certain diseases. Lack of white cells gives rise to immune deficiency states while the over production of white cells is seen in many forms of leukaemias.
3. The platelets – play a major role in preventing bleeding from a site of injury. When the body sustains an injury, the damaged vessel wall secretes certain chemicals that attract the platelets. These tend to aggregate at the site of injury, helping the clotting factors in the blood to form a blood clot. Platelets tend to decrease in many diseases including certain tropical viral infections such as Dengue fever, causing the patient to bleed.
Thus, for the proper function of the human body, the blood has to be present in an adequate amount and the constituents of the blood should also be present in the correct proportions.
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