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What is blood?
- Blood is a mobile connective tissue composed of a fluid, the plasma and the cells, the blood corpuscles.
- Blood is basis of life. Blood is the softest tissues in the body.
- Fluids outside the cells are generally called extracellular fluids (ECF).
- Blood forms about 30-35 percent of the ECF.
- The volume of blood in an adult person of 70 kg weight is about 5.5 litres.
- It is a slightly alkaline fluid having pH 7.4. pH of blood in arteries is more than in veins.
- Composition. As stated above blood is composed of a watery fluid called plasma and floating bodies termed formed elements (e.g. , blood corpuscles)
- It is slightly alkaline non - living intercellular substance which constitutes about 55 % part of the blood.
- It is a pale yellow but transparent and clear fluid.
- Water. Water alone forms about 90 % to 92 % of the plasma. Solids form about 8 % of the plasma.
- Minerals. These are Na+, Ca++, Mg++, HCO3- , Cl- , etc.
- Nutrients. These include glucose, aminoacids, lipids, etc. Minerals have been mentioned above.
- Proteins. They constitute about 6 to 8 % part of plasma. These mainly include albumin for osmotic balance, globulin for defence mechanism and fibrinogen for blood clotting
- Defence Compounds. Immunoglobulins which act as antibodies and some other substances, such as lysozyme (a polysaccharide) and properdin (a large protein ) are always found in the plasma. They destroy bacteria, viruses and toxic substances that may enter into the blood from outside.
- Excretory Substances. These include ammonia, urea, uric acid, creatine, creatinine, etc.
- Dissolved Gases. Water of blood plasma contains oxygen , carbon dioxide and nitrogen dissolved form
- Anticoagulant. Blood plasma contains a conjugated polysaccharide, the heparin which prevents coagulation of blood inside blood vessels.
- Hormones. These are secreted and released in blood by endocrine glands
- Vitamins and Enzymes. Different kinds of vitamins and enzymes are present in the blood plasma
- Factors for clotting of blood. These are also present in the plasma in an inactive form . Plasma without the clotting factors is called serum.
- Prevention of blood loss. Fibrinogen and prothrom bin play a role in blood clotting.
- Retention of fluid in the blood . Albumins and globulins retain water in blood plasma.
- Body immunity. Certain globulins called immunoglobulins (glycoproteins) act as antibodies in blood and tissue fluid, Thus all antibodies are immunoglobulins but all immunoglobins may not be antibodies.
- Maintenance of pH. Plasma proteins serve as acid - base buffers. It means they maintain pH of the blood by neutralizing acids and bases.
- Transport of certain materials. Thyroxine (hormone) is bound to albumin or specific globulin for transport in the plasma.
- Distribution of heat. Plasma proteins help in uniform distribution of heat all over the body.
- Enzymes. Some proteins acting as enzymes also occur in the plasma.
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