Homeostasis is the maintenance of a constant internal environment within narrow limits, despite changes in the external or internal environment.'Constant' does not mean fixed. Each variable fluctuates around a set point (norm), in a state of dynamic equilibrium. Variables controlled in mammals include:- core body temperature (about 37 °C in humans);
- blood glucose concentration;
- the water potential of the blood (osmoregulation);
- blood pH and carbon dioxide concentration.Why homeostasis mattersEnzymes work fastest at an optimum temperature and pH. If body temperature rises too high, enzymes denature; if it falls, reactions slow down. Changes in pH alter the charges on amino acids, changing the shape of enzyme active sites. If the water potential of the blood changes, water moves into or out of cells by osmosis, so cells may swell and burst or shrink. A steady supply of glucose is needed for respiration, but too much lowers the water potential of the blood.Keeping the internal environment constant lets cells work efficiently and gives mammals some independence from the external environment, so they can stay active across a wide range of external conditions.Homeostasis depends on receptors that detect changes, a control centre such as the hypothalamus that compares them with the set point, and effectors that bring about a corrective response, linked by nerves or hormones.
- blood glucose concentration;
- the water potential of the blood (osmoregulation);
- blood pH and carbon dioxide concentration.Why homeostasis mattersEnzymes work fastest at an optimum temperature and pH. If body temperature rises too high, enzymes denature; if it falls, reactions slow down. Changes in pH alter the charges on amino acids, changing the shape of enzyme active sites. If the water potential of the blood changes, water moves into or out of cells by osmosis, so cells may swell and burst or shrink. A steady supply of glucose is needed for respiration, but too much lowers the water potential of the blood.Keeping the internal environment constant lets cells work efficiently and gives mammals some independence from the external environment, so they can stay active across a wide range of external conditions.Homeostasis depends on receptors that detect changes, a control centre such as the hypothalamus that compares them with the set point, and effectors that bring about a corrective response, linked by nerves or hormones.