CBSE Class 10 Answered

The ability or tendency of an organism or cell to maintain internal equilibrium by adjusting its physiological processes is called homeostasis.

Example - Maintenance of temperature, blood volume, blood pressure, blood sugar, acid-base balance etc.

Following are some ways in which homeostasis is maintained in humans:

Body temperature in mammals is regulated by a sensor that consists of cells within the hypothalamus of the brain. Several effectors are involved, which vary among animals. These include increasing heat production through nonspecific muscle activity such as shivering; increasing heat loss through sweating, panting, and opening more blood vessels in the skin; and decreasing heat loss through thickening of fur (piloerection) and curling up.

Humans regulate their blood glucose with insulin and glucagon. These hormones are released by the pancreas. When blood sugar levels become too high, insulin is released from the pancreas, lowering the blood sugar levels. On the other hand, when blood sugar levels become too low, glucagon is released, increasing blood sugar levels.

Osmoregulation is the active regulation of the osmotic pressure of bodily fluids to maintain the homeostasis of the body's water content; that is it keeps the body's fluids from becoming too dilute or too concentrated.

When blood calcium becomes too low, calcium-sensing receptors in the parathyroid gland become activated. This results in the release of PTH, which acts to increase blood calcium, e.g. by release from bones. On the other hand, excessive blood calcium levels causes an activation of calcium-sensing receptors in the parathyroid gland, resulting in decreased PTH release and a decrease in blood calcium. Calcitonin works the opposite way, decreasing calcium levels in the blood.

The kidneys maintain acid-base homeostasis by regulating the pH of the blood plasma. Gains and losses of acid and base must be balanced.