Homeostasis

Last Updated on Tuesday, 26 October 2010 08:29 Written by Sandesh Wednesday, 7 April 2010 10:00

HOMEOSTASIS:

Homeostasis is the maintainance of the internal environment of the body at a constant state i.e. maintaining a constant pH, temperature, OP and solute-solvent concentration.

the important organs involved are kidney, liver and skin.

i.Regulation of NA+ and K+ ions in the body:

* Achieved by the steroid hormone aldesterone from adrenal gland.

* Aldosterone causes:

i. Increased uptake of Na+ ions from the gut

ii.Increased uptake of Na+ ions and water from the kidney, with the elimination of K+ ions

* So the Na+ ion in blood increases and K+ ion falls.

ii. Regulation of Ca+2 and Phosphorous:

* It is also under hormonal control.

* Parathormone secreted by parathyroid glands causes increased uptake (absorption) of Ca+2 ions     from the gut and kidney.

* It also increases release of Ca+2 and PO4-3 ions into the blood from bones.

* It also increases elimination of phosphate ions from kidney.

* So, it causes to raise the concentration of Ca+2 ions than phosphate ions.

* When Ca+2 ions in the blood is increased, release of parathormone is inhibited.

* The effect of parathormone is opposed by another hormone called calcitonin from (thyroid    gland).

iii. Temperature regulation:

* Body temperature is maintained at constant level (36.7 c).

* It depends on the balance of heat production and heat loss.

* Heat is prodeced by metabolic activities inside the body.

* Liver has high metabolic processes and high blood supply.

* Heat is lost through skin and directing more blood flow to skin.

* Sweat production and its evaporation from the skin cause heat loss of the blood flowing to the    skin.

* Heat is also lost from nostrils, lungs, urine and faeces.

* Subcutaneous fat and rising of hair reduce heat loss.

* Body temperature is controlled by thermoregulatory centre in hypothalamus.

Maintainance of pH:

* Normal pH is about 7.35 to 7.45.

* Depends in concentration of acid and base.

* This is acquired by buffering mechannism in the blood removing excess H+ ions.

* Lungs expel CO2, which otherwise can accumulate and combine with water to form carbonic acid.

* The kidneys get rid of H+ ions and retain bicarbonates.

* The proximal tubular cells pump H+ ions into the lumen.

* If the H+ ion is excess in tubular lumens, it combines with NH3 to form ammonium ions (NH4+) which are then excreted.

Other functions of Kidney:

* Production of erythropoietin: It influences the production of Red Blood Cells in bone marrow.When the kidney detects that the number of red blood cells in the body is declining,  it secretes erythropoietin. This hormone travels in the bloodstream to the bone marrow, stimulating the production and release of more red cells.

* Production of renin (regulation of blood pressure): When blood pressure starts to fall, the kidney releases an enzyme (a specialized protein) called renin, which converts a blood protein    into the hormone angiotensin. This hormone causes blood vessels to constrict, resulting in        a rise in blood pressure. Angiotensin then induces the adrenal glands to release aldosterone, which promotes sodium and water to be reabsorbed, further increasing blood volume and blood       pressure.

* Activation of VitaminD: Function of the kidney is the processing of vitamin D; the kidney converts this vitamin to an active form that stimulates bone development.