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A Handbook of Biology
1. RËGÜLÅTÏØÑ BÝ ÅDH (VÅSØPRËSSÏÑ)
When body fluid level decreases, the osmoreceptors stimulate hypothalamus to
release antidiuretic hormone from neurohypophysis (It stimulates water reabsorption
from DCT & collecting duct) . Thus, ADH prevents diuresis and increases body fluid
volume. Increase in fluid volume switches off the osmoreceptors and suppresses
ADH release to complete the feedback.
(AIPMT 2011)
ADH constricts blood vessels resulting in an increase in BP. This increases the
glomerular blood flow and GFR.
2. RËGÜLÅTÏØÑ BÝ JGÅ (RËÑÏÑ-ÅÑGÏØTËÑSÏÑ MËÇHÅÑÏSM)
JGA (Juxta glomerular apparatus) is a sensitive region formed by
cellular modification of DCT and the afferent arteriole at the location of
their contact.
JGA regulates the GFR.
A fall in glomerular blood flow/glomerular blood pressure/GFR activates
the JG cells to release renin.
(AIPMT 2012)
Renin converts angiotensinogen in blood to angiotensin-I and further to
angiotensin II (a vasoconstrictor). This mechanism is generally known as
the Renin-Angiotensin mechanism
Angiotensin II performs the following functions:
Increases glomerular blood pressure and thereby GFR.
Activates adrenal cortex to release Aldosterone.
Aldosterone causes reabsorption of Na+ and water from the distal parts
of the tubule. This also leads to an increase in blood pressure and GFR.
(NEET 2020)
3. RËGÜLÅTÏØÑ BÝ ÅÑF
ANF check on the renin angiotensin mechanism.
An increase in blood flow to the atria of the heart causes the release of Atrial
Natriuretic Factor (ANF).
(NEET 2017)
ANF causes vasodilation (dilation of blood vessels) and thereby decreases
the blood pressure.