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Where exactly is macula densa and what does it do?
macula densa- it is the name given to cells in the initial portion of the distal tubule of the nephron(these cells form a plaque on the wall of the nephron at the junction of the thick ascending limb of loop of henle and the distal tubule)
these cells form a functional complex with the juxtaglomerular cells in the afferent arteriole coming to the nephron and this complex is called the'juxtaglomerular complex'.
function of this complex-
autoregulation of the renal blood flow to maintain normal GFR despite changes in the arterial blood pressure( anywhere between 75 to 160 mm hg)
mech. of action of macula densa- these cells sense the nacl concentrations in the filtrate reaching the distal tubule. if the nacl content is less(which reflects decrease in GFR. As the gfr decreases, the nephric filterate flows more slowly in the nephron and hence more of nacl gets reabsorbed in the pct and thick ascending limb....causing less nacl to reach the macula densa cells)...as soon as the macula cells sense this decrease in nacl,they send signal to the afferent arteriole juxtaglomerular cells to secrete renin and also cause dilatation of afferent arteriole.
renin then stimulates secretion of angiotensin1 from liver...which gets converted into angiotensin2 and causes constriction of the efferent arteriole,thereby increasing the hydrostatic pressure in the glomerulus and increasing the GFR!
hope this helps
I had the same question and this was truly helpful.
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