Define the term homeostasis PDF

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Summary

Homeostatsis described and examples of both positive and negative...

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1. Define the term homeostasis. Homeostasis is the ability or tendency for biological systems to maintain their parameters within optimum set-limits suitable for life. The number of homeostatic mechanisms or processes in the human body are many and varied but usually constant adjustment is required to maintain the internal environment in the face of constantly changing external pressures. 2. Describe the homeostatic control of blood calcium levels. In most people the optimum level of unbound calcium (Ca2+) in the blood is somewhere within the range of nine to eleven milligrams per one hundred millilitres of blood. When the levels fall below this optimum the parathyroid glands, which are embedded within the thyroid gland, start to release parathyroid hormone (PTH). PTH is released into the blood and when it’s circulating concentration increases osteoclasts respond by increasing the rate at which they degrade bone tissue. As a result, Ca2+ concentration in the blood increases. As circulating Ca2+ concentration returns to optimum levels of PTH production reduce until the next time circulating Ca2+ concentrations fall below critical levels. 3. Describe the homeostatic control of vasodilation and sweating in the skin that helps regulate body temperature. The homeostatic control of dermal vasodilation is based on a negative feedback loop. As free nerve endings in the dermis sense an increase in temperature they are activated and send electrical signals to the central nervous system. These signals are monitored by the hypothalamus, an area of the brain that is involved in many homeostatic mechanisms. In response the hypothalamus activates nerves that control dermal blood vessels and sweat glands. Blood vessels respond by vasodilating which allows deeper warm blood to flood into the dermis bringing excess heat energy to the surface. Thus, the blood and the deeper tissues are cooled. Eccrine sweat glands produce watery, salty sweat which is released on to the skin surface to cool it by evaporation. As the body cools the original stimulus is diminished so the response is reduced until the next time an increase in temperature is detected.

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Other homeostatically controlled mechanisms Blood glucose levels, blood oxygen levels, blood carbon dioxide levels, body water content, blood pressure, heart rate...