Question

Question 4 Give a brief account of the counter current mechanism.

Class - XI - Biology Chapter Excretory Products and their Elimination Page No. 300

Answer 1

The counter current mechanism operating inside the kidney is the main adaptation for the conservation of water. The Henle’s loop and vasa rectaare two counter current mechanisms inside the kidneys. The flow of filtrate in the two limbs of Henle’s loop is in opposite directions and thus forms a counter current. As a result, blood entering the renal medulla in the descending limb comes in close contact with the outgoing blood in the ascending limb. The osmolarity increases from 300 mOsmolL-1 in the cortex to 1200 mOsmolL-1 in the inner medulla by counter current mechanism. It helps in maintaining the concentration gradient, which in turn helps in easy movement of water from collecting tubules. The gradient is a result of the movement of NaCl and urea.

Answer 2

Answer:

The juxtaglomerular apparatus contains specialised cells of the afferent arteriole known as juxtaglomerular cells. These cells contain the enzyme renin that can sense blood pressure. When glomerular blood flow (or glomerular blood pressure or glomerular filtration rate) decreases, it activates juxtaglomerular cells to release renin.

Renin converts the angiotensinogen in blood into angiotensin I and further into angiotensin II. Angiotensin II is a powerful vasoconstrictor that increases the glomerular blood pressure and filtration rate. Angiotensin II also stimulates the adrenal cortex of the adrenal gland to produce aldosterone. Aldosterone increases the rate of absorption of sodium ions and water from the distal convoluted tubule and the collecting duct. This also leads to an increase in blood pressure and glomerular filtration rate. This mechanism, known as renin-angiotensin mechanism, ultimately leads to an increased blood pressure.