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Control of homeostasis.

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HOMEOSTASIS According to totora .......... Homeostasis can be defined as " the condition in which the body's internal environment remains constant, within physiological limits". Homeostasis is a dynamic condition as the body's equilibrium point can change over a narrow range that is compatible with maintaining life. E.g., the level of glucose in the blood does not normally fall below 70mg of glucose per 100ml of blood. Each body structure helps to contribute to keep the internal environment within its normal limits. For example, if the level of blood glucose within the drops then the body compensates it by using fats stores as a reserve supply of glucose Body fluids An important aspect of homeostasis is maintaining the volume and composition of body fluid. The fluid within cells is called intracellular fluid (ICF). The fluid outside the body cell is called extracelluar fluid (ECF). Dissolved in the ICF and ECF are substances needed to maintain life such as O2, nutrients, proteins and electrally charged ions. ...read more.


This is done to obtain homeostasis. Feed back systems The body can regulate its internal environment through feedback systems. A feedback system is a cycle of events in which the condition of the body is monitored, changed, re-monitored and re-evaluated. Each monitored variable such as temperature, blood glucose and blood pressure etc is termed controlled condition. Any disruption that changes a controlled condition is called a stimulus. Three basic components make up the feed back system - a receptor, a control center and an effector. Receptor - is a body structure that monitors changes in a controlled condition and sends input in the form of nerve impulses or chemical signals to the control center. E.g., nerve ending in the skin sense temperature. Flow of the message Control center - a control center in the body sets the range of values within which a controlled condition should be maintained, evaluated from its input received by the receptors and generate the output commands for when they are needed. ...read more.


A change in the homeostatic condition is detected by receptors and the information is transmitted to the control center. The control center activates effectors which generate a response which increases the stimulus further reinforcing the initial change. An example of positive feedback is the action of the hormone oxytoxin on the uterus during birth. During normal conditions the uterine muscle is passive and not contracting. Dilation of the cervix triggers stretch receptors which transmit nerve impulses to the Brain (hypothalamus). Stimulation of the hypothalamus results in oxytoxin (OT) being released from the posterior pituitary. Oxytocin is carried by the blood to the uterus where it causes uterine contractions. During the birth process dilation of the cervix initiates the release of OT which causes uterine muscle contractions. The uterine contractions begin to force the fetus through the cervix. As the fetus is pushed through the cervix this further stretches the cervix which results in more oxytocin being released. This positive feedback will continue until the baby has cleared the birth canal and the cervix is no longer stretched. ...read more.

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