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HOMEOSTASIS: the maintenance of a stable internal environment.
This is achieved by maintaining stable conditions within the blood which gives rise to the tissue fluid that bathes the body cells:
In the blood the concentration of glucose, ions and carbon dioxide must be kept within narrow limits.
The water potential (determined by the concentration of solutes in the blood), pH and temperature are tightly regulated.
THE ROLE OF NEGATIVE FEEDBACK
Each condition that is controlled has a set point that the homeostatic mechanisms are `trying' to maintain.
Receptors are used to detect deviations from the norm.
These receptors are connected to a control mechanism, which turns on or off effectors (muscles and glands) to bring the condition
back to the norm value.
Because a deviation from the norm results in a change in the opposite direction, back to the norm, the process is known as negative
Thermoregulation is the control of body temperature, which is very stable at 37.5 degrees. This temperature allows enzyme-controlled
reactions to occur at a reasonable rate.
Temperature is maintained by the negative feedback mechanism: the receptors that detect changes in blood temperature are located in a
structure in the brain called the hypothalamus: this is the control mechanism which acts as a thermostat, turning on the effectors necessary
to return the temperature to the norm.
There are also thermo-receptors in the skin, if the skin is warm, the impulses are sent to the hypothalamus initiating the heat-loss responses
and inhibiting heat-gain responses.
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SWEATING: sweat released on the skin via sweat ducts evaporate, taking heat energy from the skin. Sweat glands are stimulated by impulses
from the hypothalamus.
HAIRS: these are raised in cold weather by contractions of the erector muscles this is a reflex. The aim is to trap a layer of air that insulates
VASOCONSTRICTION: in colder conditions the muscles in the arteriole walls contract, causing the arterioles to constrict, reducing the blood
supply to the surface capillaries.…read more