Which of the following statements are correct?
A. An excessive loss of body fluid from the body swit

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Question

Which of the following statements are correct?
A. An excessive loss of body fluid from the body switches off osmoreceptors.
B. ADH facilitates water reabsorption to prevent diuresis.
C. ANF causes vasodilation.
D. ADH causes increase in blood pressure.
E. ADH is responsible for decrease in GFR.
Choose the correct answer from the options given below:
(1) B, C and D only
(2) A, B and E only
(3) C, D and E only
(4) A and B only

Accepted Answer

Correct Answer: A — B, C and D onlyStep-by-step Solution:Statement A (False): Excessive loss of body fluids (from dehydration, haemorrhage, sweating) increases plasma osmolality (the concentration of solutes in blood rises). This ACTIVATES (turns ON) the hypothalamic osmoreceptors (neurons sensitive to plasma osmolality). The activated osmoreceptors stimulate thirst and trigger ADH release from the posterior pituitary. The statement incorrectly says they are 'switched off' — the opposite is true.Statement B (True): ADH (antidiuretic hormone, vasopressin) is secreted by the posterior pituitary in response to high plasma osmolality, low blood volume, or low blood pressure. ADH acts on the principal cells of the collecting duct and late distal convoluted tubule of the nephron, stimulating the insertion of aquaporin-2 (AQP2) water channels into the apical membrane. This dramatically increases water permeability, allowing passive reabsorption of water down the osmotic gradient into the hypertonic medullary interstitium. The result is production of concentrated (hypertonic) urine, prevention of diuresis, and restoration of blood volume/osmolality.Statement C (True): ANF (Atrial Natriuretic Factor / ANP — Atrial Natriuretic Peptide) is released from the cardiac atria in response to stretching of the atrial walls (caused by increased blood volume or blood pressure). One of its key effects is vasodilation — it relaxes vascular smooth muscle by activating particulate guanylyl cyclase → increased cGMP → smooth muscle relaxation → decreased peripheral resistance → decreased blood pressure. ANF also promotes natriuresis (Na⁺ excretion) and diuresis.Statement D (True): ADH (vasopressin) causes an increase in blood pressure through two mechanisms: (1) At high concentrations, ADH directly causes vasoconstriction of blood vessels (acting on V1 receptors on vascular smooth muscle) → increased total peripheral resistance → increased blood pressure. (2) By increasing water reabsorption → increased blood volume → increased cardiac output → increased blood pressure. The vasoconstrictive/blood pressure-raising effect gives ADH its alternative name 'vasopressin.'Statement E (False): ADH does not significantly decrease GFR (glomerular filtration rate). GFR is primarily regulated by autoregulation (myogenic mechanism) and the renin-angiotensin-aldosterone system (RAAS). If anything, ADH's vasoconstrictive effects at high doses can mildly reduce GFR by constricting afferent arterioles, but this is not its primary or well-recognised action. The statement as given is not a standard, correct description of ADH's physiology.Key Concepts:ADH (Vasopressin): Synthesised in hypothalamus, stored in posterior pituitary; promotes water reabsorption (aquaporin-2); causes vasoconstriction at high concentrations; increases blood pressure and blood volume; reduces urine volume.ANF (ANP): From cardiac atria; decreases blood pressure; causes vasodilation; promotes Na⁺ and water excretion; counteracts RAAS.Osmoreceptors detect plasma osmolality changes; activated by dehydration or hyperosmolality to trigger ADH release and thirst.

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