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The different chemical activities in the body produce many by-products several of which are wastes. These waste products if allowed to accumulate will turn out to be toxic and affect the physiological activities of the body. These wastes have to be expelled out or it may eventually result in the death of the organism.
The removal of harmful and unwanted toxic waste products of metabolism is known as excretion.
The process by which the water content and the ion concentration is regulated and kept constant in the cells is known as osmoregulation. This process results in maintaining the osmotic pressure in the blood and tissue fluids.
The two physiological processes, excretion and osmoregulation are interconnected as they both are responsible for bringing about homeostasis in the body. The physiological mechanisms involved are intimately bound with each other, so much so, in higher vertebrates like mammals, kidneys perform both functions, excretion and osmoregulation.
The terms secretion and egestion are often confused with excretion. Hence it is important to understand clearly what they mean.
Secretion is the production of useful chemical substances like hormones, enzymes or other molecules by the cells of glands like the bile, endocrine glands like the islets of Langerhans or unicellular glands like the epithelial mucosal lining of the large intestine.
Egestion is expelling the undigested wastes from the body. Food which is not digested and thus is not assimilated by the body is passed to the last part of the alimentary canal called the rectum and egested out in the form of faeces or excreta.
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