Macula Densa: Osmolarity Sensing

[justadream]

I forgot the exact place I found this quote but it's either from TBR or a physio textbook (silverthorn or saladin).


“Macula densa are chemoreceptors and monitor filtrate osmolarity in distal tubule. If it decreases (indicating a reduced filtration rate), macula densa stimulates JG cells to release renin.”



Why is renin released when filtrate osmolarity is low? I thought renin would be released if the osmolarity were high.

---

Members don't see this ad.

 

[t5Nitro]

I forgot the exact place I found this quote but it's either from TBR or a physio textbook (silverthorn or saladin).


“Macula densa are chemoreceptors and monitor filtrate osmolarity in distal tubule. If it decreases (indicating a reduced filtration rate), macula densa stimulates JG cells to release renin.”



Why is renin released when filtrate osmolarity is low? I thought renin would be released if the osmolarity were high.

In order to increase osmolarity, renin would be released to activate the renin-angiotensin-aldosterone system. Aldosterone release would then help bring the osmolarity back up to normal with Na reabsorption. The corresponding water retention also brings back the normal filtration rate (by increasing arterial pressure) that you listed was reduced.

Hope this helps.