Osmo-regulatory role of kidney:

1. Water: Excess of water in blood increases the volume of blood which increases the blood pressure and affect the cardiovascular functions. So, its level must be regulated in body.

 

• Excess of water: If volume of water increases in blood, it increases the blood pressure in glomerulus : also stops the release of ADH. Due to which water re-absorption decreases and more filtration occurs. Product urine formed is more dilute so water level is maintained.
• Shortage of water: Shortage of water decreases the blood pressure and stimulate the release of Anti-diuretic hormone. So, it leads to low BP, which causes less filtration in glomerulus and more re-absorption of water. It conserves water by making hypertonic (concentrated) urine.    

2.  Na⁺ Level: When Na⁺ level reduces in blood then special cells at Juxta glomerular apparatus releases a protein called renin. This renin converts the angiotensinogen into angiotensin I and angiotensin II.

• Angiotensin I is a powerful vasoconstrictor (the process of contraction of blood vessels due to which blood pressure in them increases is called vasoconstriction).
• Angitensin II releases aldosterome, that increases the rate of re-absorption of Na⁺.

Re-absorption of water and Na⁺ increases blood volume and blood pressure which further increases the rate of glomerular filtration. This RAAS (Renin – angiotensin – Aldosterone – system) maintains Homeostasis (water and ionic level of blood).

 

Atrial natriuretic factor:

Now blood pressure is increased. Increase in blood pressure of atria of heart releases the (ANF) Atrial Natriuratic factor. This factor is a powerful vasodilator (that expands the blood vessels to decrease blood pressure). So, it stops the RAAS.

• RAAS increases the blood pressure.
• ANF (stops the RAAS) means decrease the blood pressure).