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Homeostatic Mechanisms

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Homeostatic Mechanisms Homeostasis, from the Greek words for "same" and "steady," refers to any process that living things use to actively maintain fairly stable conditions necessary for survival. It is the maintenance of a constant internal environment (the immediate surroundings of cells) in response to changes in the conditions of the external and/or internal environment. The skin of an adult person has a surface area of about 2m squared and varies in thickness from 0.5mm in most body regions to 3mm on the soles of the feet. It is tough and flexible and provides mechanical protection for the underlying tissue. In addition, it is a major sensory surface, manufactures vitamin D, screens the body from harmful ultraviolet radiation, and prevents the entry of bacteria and other micro-organisms. It also plays an essential role in temperature regulation. Two distinct regions, the epidermis, and the dermis, are easily recognised in a vertical section of human skin. The epidermis, or outer layer of skin, is a specialized epithelial tissue. It is covered by a protective layer of dead cells produced by underlying living epidermal cells. These dead cells are packed with the protein - keratin, which helps keep the skin both airtight and relatively waterproof. ...read more.


When water needs to be conserved, the posterior pituitary gland secretes more ADH, and this hormone increases the number of water channels in the plasma membranes of the collecting ducts to water so that more water is reabsorbed and less is excreted in the urine. As well as regulating water balance, the kidneys also regulate the balance of electrolytes in the blood, also through reabsorption and secretion. This regulation is called homeostasis. Homeostasis provides cells within the body with a relatively constant environment, and this helps them to work efficiently, no matter what is going on outside the body. Whatever the air temperature around you, the temperature around a cell in your liver is always just below 38oC. However much or little carbohydrate you have eaten, the concentration of glucose in your body fluids does not normally fluctuate very far from 800mg per dm3. Processes which aim to keep a potentially fluctuating feature within narrow limits, use negative feedback mechanisms. These maintain the organism's internal environment within tolerance limits - the narrow range of conditions where cellular processes are able to function at a level consistent with the continuation of life. ...read more.


Endocrine glands lack ducts and thus must secrete into surrounding blood capillaries. Hormones secreted by endocrine glands belong to four different chemical categories; Polypeptides (ADH), Glycoproteins (FSH), Amines, derived from amino acids tyrosine and tryptophan, and steroids such as testosterone and progesterone. The endocrine system is an extremely important regulatory system in it's own right, but it also interacts and co-operates with the nervous system to regulate the activities of other organ systems in the body. The secretory activity of many endocrine glands is controlled by the nervous system. Among such glands are the adrenal medulla, posterior pituitary, and pineal gland. These three glands are derived from the neural ectoderm, the same embryonic tissue layer that forms the nervous system. The major site for neural regulation of the endocrine system, however, is the brain's regulation of the anterior pituitary gland. The hypothalamus controls the hormonal secretions of the anterior pituitary, which in turn regulates other endocrine glands. On the other hand, the secretion of a number of hormones is largely independent of neural control. The release of insulin by the pancreas and aldosterone by the adrenal cortex, for example, are stimulated primarily by increases in the blood concentration of glucose and potassium respectively. ...read more.

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