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Excretory Products and Their Elimination - Regulation of kidney function (RAAS, ADH and ANF)

Grade 11CBSEBiology

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Regulation by ADH (Antidiuretic Hormone): Osmoreceptors in the body are activated by changes in blood volume, body fluid volume, and ionic concentration. An excessive loss of fluid stimulates the hypothalamus to release ADH or Vasopressin from the neurohypophysis.

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ADH Function: ADH facilitates water reabsorption from the distal parts of the tubule (DCT and Collecting Duct), thereby preventing diuresis. It can also affect kidney function by its constrictory effects on blood vessels, increasing blood pressure and thereby GFRGFR.

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RAAS (Renin-Angiotensin-Aldosterone System): A fall in glomerular blood flow/glomerular blood pressure/GFRGFR can activate the Juxtaglomerular (JG) cells to release Renin.

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Angiotensin Cascade: Renin converts Angiotensinogen in the blood to Angiotensin I and subsequently to Angiotensin II (by ACE). Angiotensin II is a powerful vasoconstrictor that increases glomerular blood pressure and GFRGFR.

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Aldosterone Action: Angiotensin II also stimulates the adrenal cortex to release Aldosterone. Aldosterone causes reabsorption of Na+Na^{+} and H2OH_{2}O from the distal parts of the tubule, leading to an increase in blood pressure and GFRGFR.

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ANF (Atrial Natriuretic Factor): An increase in blood flow to the atria of the heart causes the release of ANF. ANF causes vasodilation (dilation of blood vessels) and thereby decreases the blood pressure. It acts as a check on the RAAS mechanism.

📐Formulae

Angiotensinogen→ReninAngiotensin I→ACEAngiotensin II\text{Angiotensinogen} \xrightarrow{\text{Renin}} \text{Angiotensin I} \xrightarrow{\text{ACE}} \text{Angiotensin II}

Angiotensin II→Adrenal Cortex→Aldosterone\text{Angiotensin II} \rightarrow \text{Adrenal Cortex} \rightarrow \text{Aldosterone}

GFR=125 ml/min (approximate normal regulation target)\text{GFR} = \text{125 ml/min (approximate normal regulation target)}

💡Examples

Problem 1:

During a hot summer day, a student experiences excessive sweating and does not drink enough water. Explain the hormonal response of the kidneys to maintain homeostasis.

Solution:

The loss of H2OH_{2}O leads to an increase in blood osmolarity, stimulating osmoreceptors. This triggers the release of ADHADH (Vasopressin) from the posterior pituitary. ADHADH increases the permeability of the DCT and Collecting Duct to water, allowing more H2OH_{2}O reabsorption into the blood, resulting in concentrated urine.

Explanation:

This is a compensatory mechanism to prevent dehydration by minimizing water loss through urine (anti-diuresis).

Problem 2:

In a clinical scenario, a patient has a sudden drop in blood pressure. How does the Juxtaglomerular Apparatus (JGA) respond?

Solution:

The JGA detects the fall in GFRGFR and blood pressure. JG cells release the enzyme Renin, which initiates the RAASRAAS pathway: Angiotensinogen→Angiotensin I→Angiotensin II\text{Angiotensinogen} \rightarrow \text{Angiotensin I} \rightarrow \text{Angiotensin II}. Angiotensin II increases blood pressure via vasoconstriction and stimulates Aldosterone for Na+Na^{+} and H2OH_{2}O retention.

Explanation:

The RAAS mechanism ensures that the glomerular filtration rate is restored to its normal range through both structural (vasoconstriction) and chemical (ionic reabsorption) changes.

Regulation of kidney function (RAAS, ADH and ANF) Revision - Class 11 Biology CBSE