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Whats involved in Homeostasis.

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Introduction

Homeostasis Homeostasis is involved in keeping the body's internal environment constant (like the thermostat of a central heating system). Homeostasis keeps the body's temperature at a certain level (36.5oC) and it keeps the pH of the body at a certain level so that enzymes don't denature. Blood glucose is kept constant, CO2 levels and O2 levels are monitored to ensure that enough oxygen and not too much carbon dioxide are in the blood. The overall concentration and volume of blood is also monitored homeostatically. Cannon first used the term Homeostasis in the late 1920s. Homeostasis is very important to animals because it allows them to rely on the external environment. A constant internal environment allows a considerable degree of independence and allows animals to live in areas from the arctic to the tropics. Many of the mechanisms involved rely on negative feedback. A movement from the set level (e.g. a rise or fall in body temperature) is detected by receptors. These receptors then send information to the control centre in the brain which reacts by returning to the original value. For example, the temperature control mechanism. Humans maintain body temperature within 1oC of 36.5. ...read more.

Middle

The ventromedial hypothalamus has been found to function as an 'off' switch to tell us when to stop eating. Animals with damage to this area have been found to overeat and become obese, sometimes tripling their body weight (Hetherington and Ranson, 1940). Olds (1958) stimulated the ventromedial hypothalamus with electrodes and found that this decreased eating. When the animal is full then the VMH sends impulses to say that it is time to stop eating, if the VMH is destroyed then the signal is not sent and the animal does not stop eating therefore becoming obese. The lateral hypothalamus is seen as the opposite, an 'on' switch. Animals who have damage to that area do not receive the signal to start eating and so they don't and consequently starve to death (Anand and Brobeck, 1951). Hess 91954) found that stimulating this area caused the animal to eat compulsively. The Glucostatic hypothesis says that the levels of glucose in the bloodstream determine how hungry we are. Neurons detect the level of glucose in the body, they are situated in the hypothalamus, the blood vessels and other organs. If the glucose level in the body drops and no more food is available then the liver releases more (this is stored in the liver in the form of glycogen). ...read more.

Conclusion

put two groups in two rooms, an obese group and a control group. They both had equal numbers of shelled and unshelled nuts. The control group ate equal amounts of shelled and unshelled nuts, the obese group ignored the unshelled and ate only the shelled nuts. Rats with LH damage have been able to be coaxed into eating and although they do not show any interest in food, they do not show interest in anything (Teitelbaum and Epstein, 1962). Therefore the idea of the LH being the 'on' switch is a little too simple and is a much more complex interaction of several systems together. The nervous system's involvement in the regulation of hunger is a little doubtful. The theories above have supporting and contradictory evidence. The 'on/off' model of the control of the hypothalamus is said to be too simple to control such a complicated and important mechanism in the body. There is evidently more to hunger than Canon and Washburn's empty and full stomach hypothesis. The glucostatic theory leaves some questions unanswered and there are definite problems. The theories alone don't seem to explain the complex mechanism of hunger control and regulation but an interaction of all of the theories may be a little closer to what really happens. ...read more.

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