Homeostasis is the control of the internal environment of an organism, allowing greater independence from external conditions. This control is usually achieved by a system of negative feedback.
Regulation of temperature and blood glucose levels in humans are two good examples of homeostasis. In the case of body temperature, any deviation from the optimum temperature of 37ú C is detected by the hypothalamic heat and cold receptors located in the hypothalamus and the peripheral cold receptors in the skin. In the case of a rise in temperature, the hypothalamic 'heat loss' centre stimulates corrective mechanisms of increased sweating and the relaxing of arterial muscles near the skin to cause vasodilation. In the case of a drop in temperature, the 'heat production and conservation' centre stimulates heat conservation in the form of inhibition of sweating, contraction of arterial muscles near the skin to cause vasoconstriction and contraction of pilli muscles to cause hair erection.
Hypothalamic nuclei
Reference ranges for blood tests, showing adult ma...
English: idealized curves of human blood glucose a...Heat can also be produced by shivering (rapid movement of muscle cells), which produces heat due to increased respiration to provide energy for movement and therefore increased production of heat from the electron carrier chain and increased metabolism.
Blood glucose level is monitored by the Islets of Langerhans in the pancreas. In these islets, the a-cells produce glucagon, while the b-cells produce insulin. In the event of a rise in blood glucose level, the b-cells secrete insulin into the blood, which then causes the conversion of glucose in glycogen in the liver and muscles. If blood glucose falls, a-cells secrete glucagon, which causes conversion of glycogen back into glucose in the liver and muscles. A constant supply of glucose is vital as the brain cannot store its own carbohydrate. The system works as insulin and glucagon are proteins with a specific tertiary structure, so they are recognised...