Functions of Blood

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Blood is a bodily fluid that delivers substances such as oxygen and nutrients to the cells and removes waste products from them. All vertebrates have blood and in humans, blood travels in a double circulated system in which oxygenated blood and deoxygenated blood work separatly. Some vertebrates, such as the counter-current mechanism in fish, have single circulatory system. There are four constituent parts in blood which are the blood plasma, red blood cell, platelets and white blood cells. Plasma and red blood cells transport substances to or away from cell. White blood cells and platelets are parts of the immune system. Blood plasma is mostly made up of water which is from respiration and is absorbed from the large intestine. Water can also be reabsorbed from the kidney. This is very important as this allows osmosis occurs in our bodies. Plasma is forced out of the capillaries under high hydrostatic pressure to form tissue fluid. Some of the tissue fluid is return in capillary ends and some is returned to the blood by the lymphatic system. Plasma carries glucose, ions, waste product, respiratory gases and hormones around the body. Small molecules such as oxygen and carbon dioxide can diffuse in and out of the cells through the phospholipid bilayer; ions and glucose molecules enter and leave the cell via the channel proteins. Waste products such as nitrogenous compounds are carried to the kidneys and are excreted in the form of urine. Antidiuretic hormone, (ADH), is a hormone secreted by the pituitary gland. It is carried by the plasma to the kidney and stimulate the occurrence of water reabsorption. When the body is dehydrated, ADH is released, causing the collecting ducts to become more permeable. Therefore more water is reabsorbed and more concentrated urine is excreted. Red blood cells contain haemoglobin. Haemoglobin is a globular protein, in which
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