The following points highlight the four main factors affecting homeostasis. The factors are: 1. Sugar level 2. Osmotic pressure 3. Respiratory gases 4. Temperature.
Maintenance of a constant internal environment is known as homeostasis. For normal functioning cells need a surrounding which does not change much. The cells are bathed in the interstitial or tissue fluid, consists of plasma fluid, glucose, salts, respiratory gases, etc. To maintain a constant state of the fluid, the amount and ratio of all the constituents have to be ensured.
The factors effecting these are:
1. Sugar Level:
The human blood normally contains 90 mg/100 ml glucose. The excess glucose, if any, is transported to the muscles and liver, converted into glycogen and stored there. In case the glucose level in blood falls, the glycogen is converted into glucose and the level is maintained. Both the processes are controlled by insulin, secreted by the pancreas.
2. Osmotic Pressure:
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The osmotic pressure of the tissue fluid is maintained by kidney (osmoregulation). Antidiuretic hormone (ADH) secreted by the posterior lobe of the pituitary regulates reabsorption of water in the kidney tubules.
3. Respiratory Gases:
In the event of oxygen depletion and carbon dioxide increase in the interstitial fluid, increased heart rate helps in greater absorption of oxygen by the respiratory membrane and the respiration rate also increases. Further, with more carbon dioxide entering into it, the blood becomes more acid and extra oxygen is given up by the haemoglobin than that in the normal state.
4. Temperature:
In animals, the normal metabolism is carried only within a range of temperature, which varies in different groups. The homeotherms maintain a near constant body temperature by their efficient metabolic activities and insulation against heat loss by the deposition of a layer of fat beneath the skin and feathers or furs covering the body.
The poikilotherms are unable to maintain the optimal range of temperature by metabolism. Some of them collect heat from sun rays, while the majority shelter them in burrows or under some covers or even hibernate to bring down metabolism to a minimum.