The Homeostasis Concept What Is Meant By This Term, Examples Of How Mechanisms Achieve Homeostasis, Negative And Positive Feedback.

945 words - 4 pages

Improvement suggestions: history of homeostasis? Further consideration of positive feedback, e.g. in pathological conditions.The Homeostasis ConceptHomeostasis is a system of automatic control mechanisms which maintain the internal environment of an organism despite changes in the external environment (Campbell & Reece, 2005). The internal environment consists of extracellular fluids that bathe every cell of the body, supplying nutrients and receiving wastes (Purves et al., 2001). Regulators (animals which use homeostasis), maintain suitable physical conditions such as body temperature and water potential of cells, and the supply of nutrients e.g. O" and glucose, and removal of wastes e.g. CO" and urea, by the interaction of a number of body systems including the respiratory, digestive, circulatory, excretory and immune systems, controlled by the brain via the endocrine and nervous systems (Campbell & Reece, 2005; www.emc.maricopa.edu; www.gonzaga.k12.nf.ca/academics). Homeostasis is based on feedback mechanisms whereby sensory nerves or receptors receive a stimulus, for example a change in temperature, and inform the control centre in the brain. This sensory input is processed and a signal is sent to an effector system, e.g. muscles or glands that cause the response to the stimulus (Purves et al., 2001). Most examples are of negative feedback loops in which any deviation from the set point is made smaller or resisted. Positive feedback is occasionally used e.g. release of oxytocin during childbirth - nerve stimulation caused by the baby's head pushing the cervix, stimulates uterine contractions, causing further nerve stimulation and therefore more oxytocin is released until the cut-off point of birth (Seeley, Stevens & Tate, 2006).Thermoregulation, controlled by the autonomic nervous system, maintains body temperature within an optimal range, enabling cells to function most effectively even as external temperatures fluctuate (Campbell & Reece, 2005). This is important as many enzymes in the body work within specific temperature ranges (Seeley, Stevens & Tate, 2006). Thermoreceptors of sensory nerves in the skin, body core and hypothalamus detect a change in temperature and send impulses to the control centre in the hypothalamus. When body temperature is lower than the set point, the heat gain centre is stimulated causing; vasoconstriction (blood flow to the skin is restricted to retain heat), erector-pili muscle contraction - erecting hairs, skeletal muscle contraction -shivering, and reduced sweating, thus generating and conserving heat (www.revision-notes.co.uk/revision/858.html). The hypothalamus also produces a release factor substance which stimulates its target organ the anterior pituitary gland to secrete thyroid stimulating hormone (TSH). This reaches the thyroid gland via the blood and stimulates the release of thyroxine, generating heat by increasing cellular metabolism. Once a higher level of TSH is detected in the...

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