Renin angiotensin system I don't understand?

sameeralord

Hello everyone,

So in renin angiotensin system, the NaCl concentration reaching the macula densa is monitored. Now my question if if there is loss of fluid from the body and both NaCl and water is lost from the body,plasma NaCl would be normal, now how would this affect macula densa. Okay so GFR decreases, but both NaCl and water filtration is decreased, so nacl reaching macula densa would be normal. I know I have really confused myself and I nedd some help. Thanks

EDIT: Ok now I understand it is to do with glomerulotubular balance. But now I don't undertand that. Ok if there is high GFR, there is lots of proteins in peritubular capillary fluid and they can increase reabsorption of sodium. But sodium moves out tubular cells via active transport so how can this work? If there is decreased GFR how does glomerulotubular balance decrease sodium reabsorption?

bobze

Look into flow rates and how that might affect what the macula densa "sees".

sameeralord

Hello Bobze. Ok if there is high GFR, flow rate would be high and there would be less absorption and vise versa. But what I'm saying is sodium moves into tubular cell passvely, then moves out of the cell actively and requires ATP. So how can these things have any effect, if sodium is reabsorbed actively. Also if there is high GFR and there is less absorption, then tubuloglomerulr balance would not be maintained.

bobze

From your original question;

So if you have an isoosmotic volume loss, what happens to the amount of fluid entering the tubule? Does it increase or decrease?

If it decreases, then what does (regarding electrolytes, particularly that all important one Na+) macula densa "see" per unit time? Does it "see" more sodium? Less? The same amount?

What is the MD's response to more sodium? What is the response to less?

Then apply what you know of the RAA (renin-angiotensin-aldosterone) system and how that affects the; afferent and/or efferent vessels, the BP, the blood volume etc.




When you solve clinical problems or think about clinical problems Sameer, use a system to get you to the answer.

Remember that our bodies are millions of years in the making and are very good problem solvers. Not much, isn't there for a reason or doesn't help to maintain a "normal" state for us.

So when you look at a problem like "isoosmotic loss of fluid" ask yourself "what does the body want to do", "how will it correct this problem". Answer that, then "reverse-engineer" yourself to through the problem.

Spoiler (try and solve it yourself, you'll learn it better that way, but if you get stuck look at the spoiler below)