The phenomenon of homeostasis is understood as the ability the body has to stabilise its internal environment despite the ever changing external conditions (Waterhouse, 2007). This internal environment is an atmosphere which surrounds the cells and is therefore the medium in which the cells are in direct contact with in the body (Sherwood, 2001). The internal environment is essential for cell survival because cells require a constant supply of oxygen and food which is exchanged from the external to the internal environment and then to the cell. Cells also require the removal of toxic wastes like carbon dioxide which is released in the internal and then the external environment (Sherwood, 2001). In addition these enzyme-mediated processes work only within restricted temperature, pH and ion concentrations therefore internal environments should be preserved (Waterhouse, 2004). This preservation mechanism is controlled by a feedback loop system which is said to be the backbone of homeostasis (Waterhouse, 2004).
Feedback loop sequences occur when a change in the internal environment deviates. This deviation is sensed by a receptor which sends a signal to the control centre that contains the set value points required for normal function. Effectors then take effect to control the deviation (Waterhouse 2004). See illustration below: [pic]
The series of events occurring in a negative feedback loop system aim to return low or high set point deviations to normal perimeters through a series of events (Jones, 2001). In a few instances however the deviation is increased from the ideal value resulting in a positive feedback. This according to Jones (2001) does not play any part in keeping things constant, therefore positive feedback cannot be used as a homeostatic mechanism.
Homeostasis is used as a survival tool because it enables animals to adapt to the ever changing environment (Tortora 1999). Without this ability death may occur, unless medical treatment is executed to bring about the natural occurrence of a feedback system (Clancy 2002). Disease will also result when there is a failure in the homeostatic control system because according to Clancy (2002) homeostasis provides a basis for health.
A body system which plays an important role in the control of homeostasis is the endocrine system which has the primary role of producing hormones that regulate the function of other organs. This system is responsible for the control of blood glucose levels which heavily depend on the secretion of insulin and glucagon (see fig 2). These hormones are produced in the pancreas, within specialist cells called Islets of langerhans containing alpha cells for glucagon production and beta cells for insulin production. The pancreas also contains the receptors responsible for monitoring blood glucose levels. [pic]
Fig 2 www.science aid.co.uk
Glucose is essential in the production of ATP, which according to Clancy (2002) will fluctuate therefore glucose levels available should be regulated in order to maximise its energy making potential. The two hormones produced by the pancreas target the liver every time there is an increase or decrease of glucose production. In cases where glucose levels rise usually after a meal due to the carbohydrates being absorbed, the pancreas releases less glucagon and more insulin. A decrease in glucose levels will however initiate the production of more glucagon and less insulin by the pancreas. Glucose levels can reduce by undertaking vigorous exercise. Fig 3 gives an illustration of the negative feedback control in the control of glucose levels.
Because the liver is the main target organ for insulin it therefore acts as storage for glycogen. This is because the secretion of insulin promotes the conversion of glucose into glycogen, where the excess glucose can be stored for later date in the liver. The secretion of glucagon however encourages the conversion of glycogen into glucose therefore...
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