Renin release

[eur]

Im pretty much burned out right now, but i cant seem to understand why renin is released when there is too little nacl in the distal convoluted tubule detected by the macula densa. I would have thought it would have been the other way around because it wants to retain Na to increase the blood pressure correct? Can anyone explain?

thanks

---

Members don't see this ad.

 

[avishkar1984]

the answer is pretty simple
recall that renin angiotensin system acts on the zona glomerulosa in the adrenals to release aldosterone which controls the NaCl reabsorption

the release of aldosterone in turn forms a negative feedback loop with the renin release.

a decreased amt of NaCl reaching the kidney is detected by the kidney as a decrease in the amt of NaCl in the body
this in turn causes the release of renin to activate the release of aldosterone to reabsorb the NaCl

 

[LUBDUBB]

Im pretty much burned out right now, but i cant seem to understand why renin is released when there is too little nacl in the distal convoluted tubule detected by the macula densa. I would have thought it would have been the other way around because it wants to retain Na to increase the blood pressure correct? Can anyone explain?

thanks

Short answer:
Macula Densa senses low NaCl; Macula densa understands that low NaCl is a result of low perfusion - indicating a hypovolemic state; it stimulates renin release via local mechanisms.

Long answer:
There are several mechanisms that are in control of renin.

Pressure sensors in the afferent arteriole
Sympathetic b1 adrenergic receptor innervation of JG cells.
Macula Densa

hypovolemia is sensed by all three of these, and in response stimulates the release of renin.
1) low perfusion pressure sensed by afferent arteriole-->release renin by JG cells. This is a local mechanism.
2) Carotid Sinus senses hypovolemia--> CN IX perdominantley takes signal back to medulla to activate sympathetics -->renin release
3) Macula Densa senses low NaCl; Macula densa understands that low NaCl is a result of low perfusion - indicating a hypovolemic state; it stimulates renin release via local mechanisms.

Hope this helps.

You want to be a kidney beast, read
Renal physiology
by Bruce M Koeppen; Bruce A Stanton

 

[12beamup]

Im pretty much burned out right now, but i cant seem to understand why renin is released when there is too little nacl in the distal convoluted tubule detected by the macula densa. I would have thought it would have been the other way around because it wants to retain Na to increase the blood pressure correct? Can anyone explain?

thanks

Suppose that what you are thinking is true and a lot of NaCl detected by the macula densa would lead to more renin. Then this would be compounding the problem, right? Therefore, it shouldn't work like this. You don't want to accumulate more of something that you already have in excess! Right?

Think of the macula densa as sampling the fluid. If there is too much NaCLl, then you want to get rid of it. If there is too little, then you want to retain some. This is what the kidney does. In other words, too little NaCl --> macula densa sensing too little NaCl (NaCl DEFICIT)--> renin release --> cascade of reactions leading to production of Angiotensin II --> secretion of Aldosterone by Zona Glomerulosa of adrenals --> NaCl RETENTION.

Aside: Remember that angiotensin II does other things like functioning as a peripheral vasoconstrictor in volume depleted states (i.e. NaCl DEFICIT) which helps divert blood flow pressure to vital organs (i.e. brain and kidney) in such situations.

I hope this helps clarify things! Good luck with your studying!