Biology [[Control, Coordination and Homeostasis]] Homeostasis

[[Homeostasis]]

Maintaining a stable, internal environment. Internal environment is the conditions inside the body in which cells function. E.g. Tissue Fluid

The fuctioning of a cell can be determined by many things, including:

Temperature
* Low temps slow metaolic reactions, while high temps cause the denaturing of protiens and enzymes

Amount of Water
* lack of water in the tissues causes water to be drawn out of the cell by osmosis causing metabolic reactions to slow and/or stop.
* Too much water entering the cell can ccause it to swell and burst

Amount of Glucose
* lack of glucose causes respiration to slow and/or stop
* too much glucose may draw water in by osmosis

Homeostatic mechanisms wirk by controlling the composition of blood, which controls the composition of tissue fluid.
Most control mechanisms use a negative feedback control loop.

[[Negative Feedback Loops]]

The receptor picks up information about the parameter being regulated. This is known as the input. The input sets of a series of events culminating in some action by the effector. This is called the output. Continuous monitoring of the parameter by the receptor produces continuos adjustments of the output. This keeps the parameter oscilliating around an ideal level.

In negative feedback loops, a rise in parameter result in something happening which makes the parameter fall.

[[Positive Feedback Loops]]

There are a few instances of the opposite thing occuring in living organisms. If a person breathes air with a high percentage of CO2, there is a high percentage of CO2 in the blood. This is sensed by the carbon dioxide receptors, which causes breathing rate to increase. The person breaths faster, taking in even more CO2, which stimulates the receptors even more and makes the person breath faster. This is an example of positive feedback.

Positive feedback plays no role in keeoping things constant.