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Tuesday, 16 June 2020

The Biology

Blood Circulatory system is regarded as a kind of vascular system and therefore, it is called blood vascular system. A vascular system is that which has tubes full of fluids to be transported from one place to another. The blood vascular system comprises of Heart, the organ which pumps and receives the blood, and blood vessels, which are tubes through which the blood flows. Blood is mobile, reddish coloured fluid that circulates in blood vessels in the human body; supplies nutrients and oxygen to all the living cells and removes waste products and carbon It has two Components: Plasma and Blood Corpuscles. Blood corpuscles are of three types: red blood corpuscles, white blood corpuscles and blood platelets. Presence of oxygen carrying Haemoglobin pigment in red blood cells makes them looks red. Some of the important functions of the blood are as follows: 1. Circulation of blood is responsible for the transportation of soluble digested food from the small intestine to various parts of the body where they are stored or assimilated. Blood also carries glucose from Liver to the Muscles. 2. Blood carries soluble excretory materials, such as urea, to the organs of excretion. 3. Blood carries Hormones from the Endocrine glands to the target organs. 4. Circulation of blood helps to maintain a constant body temperature by distributing the excess heat from the deeply seated organs. 5. Blood transports oxygen from the Lungs to all parts of the body. In he blood, Oxygen combines with Haemoglobin to form oxyhaemoglobin. When the blood reaches the tissues, Oxygen from Haemoglobin diffuses into the tissue cells where it is utilised to release energy in the form of ATP. 6. Blood caries carbon dioxide produced by the tissues to the lungs for breathing out. 7. Blood has a property of clotting which prevents excessive blood loss. 8. The white blood cells acts as a soldiers of the body by killing the bacteria and other germs. Thus, the blood protects our body from the attack of foreign bodies and disease causing pathogens. 9. The blood acts as a buffer and maintains a constant soluble potential and pH. When a tissue is wounded or a blood vessel is ruptured due to some injury, the blood flows through it. If not checked, it may cause an excessive loss of blood. Sometimes, this immense loss of blood even leads to death. However, the body has its own natural device of preventing the loss of blood by forming a "blood clot" which plugs the injury and stops further loss of blood, and also checks the entry of pathogenic microorganisms. The process of blood clotting is a complex process which is initiated and maintained by the platelets which circulates around the body along with other blood components. In the region of Injury, the platelets rupture and release a substance called Thromboplastin. Vitamin K is essential for the formation of prothrombin in liver. Thrombin then changes soluble fibrinogen protein into fibrin. The latter undergoes rapid polymerization to form long fibres. The fibres form a network over the damaged region, entrap blood corpuscles and form a blood clot. We have just studied that the blood is an important medium which carries the required substances to carious organs of the body. The blood circulates round the body and reaches each and every organ throughout the blood circulatory system, which consists of the heart and the blood vessels. The blood vessels are elastic muscular tubes which carry blood. There are three kinds of blood vessels in the human body: Arteries are the thick walled blood vessels which carry blood away from the heart for distribution to the body. The walls of arteries, particularly those near the heart, are thick that enables them to dilate but not rupture when the heart contracts and forces blood into them. Thus, the blood passing through narrow lumen of arteries is aerated and has a considerable pressure. Veins are thin walled blood vessels which brings blood from the body back to the heart. They are larger and hold more blood than the arteries. The blood passing through wide lumen of veins is nonaerated and has low pressure. The veins have valves that allow the blood to flow only towards the heart and prevent the backflow. Capillaries are thin walled and extremely narrow which faciliates the exchange of food material, gases and waste products. The Heart is a hollow, muscular organ, roughly of the size of our 'clenched fist' that contacts regularly and continuously pumps blood to various parts of the body. Its average weight is about 300 grams in males-and about 250 grams in females. It is reddish brown in colour and somewhat conical in form. The heart is situated between the two lungs in the middle of the thoracic cavity. It is surrounded by a tough, two layered sac, the pericardium. The pericardial fluid is secreted in the pericardial cavity between the pericardium and heart which reduces the friction between the heart wall and surrounding tissues when the heart is beating. It is divided by septa into two halves: the right and the left. Each half consists of two communicating chambers: upper smaller auricle or atrium and lower larger ventricle. Thus, the heart has 4 chambers : The two upper chambers, called atria and two lower chambers called ventricles. There are valves between left atrium and left ventricle and between right atrium and right ventricle. These valves provides one-way passage and prevents the return of blood.

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