Macula Dense Question

[stuw]

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So Macula Densa is located in the DCT of the kidneys and they act as chemoreceptors that monitor the osmolarity of the filtrate. TPR says that when the macula densa senses a filtrate's low osmolarity, it's suggesting that the filtrate rate has been reduced, thus telling the JG cells to secrete renin to increase blood pressure/blood flow.

My question is: Why does filtrate's low osmolarity = low filtrate rate?

 

[LabratABQ]

So Macula Densa is located in the DCT of the kidneys and they act as chemoreceptors that monitor the osmolarity of the filtrate. TPR says that when the macula densa senses a filtrate's low osmolarity, it's suggesting that the filtrate rate has been reduced, thus telling the JG cells to secrete renin to increase blood pressure/blood flow.

My question is: Why does filtrate's low osmolarity = low filtrate rate?

I believe that osmolarity is the measurement of concentration of a solution, total number of solute particles per liter. Therefore, when the "filtrate's low osmolarity" that means less solute particles being filtered or the filtrate rate has been reduced/decreased, and it might be due to low blood pressure. Thus, in order to compensate the low blood flow/pressure, renin acts as enzyme to hydrolyze angiotensinogen into angiotensin I and sends that to the lungs to be cleaved into angiotensin II(by ACE), which then acts as a vasoconstriction agent to constrict and increase the blood pressure/flow through the kidney to compensate that low osmolarity.

I'm not sure if this answered your question...i could be wrong, but that is how i understand it.

 

[stuw]

I believe that osmolarity is the measurement of concentration of a solution, total number of solute particles per liter. Therefore, when the "filtrate's low osmolarity" that means less solute particles being filtered or the filtrate rate has been reduced/decreased, and it might be due to low blood pressure. Thus, in order to compensate the low blood flow/pressure, renin acts as enzyme to hydrolyze angiotensinogen into angiotensin I and sends that to the lungs to be cleaved into angiotensin II(by ACE), which then acts as a vasoconstriction agent to constrict and increase the blood pressure/flow through the kidney to compensate that low osmolarity.

I'm not sure if this answered your question...i could be wrong, but that is how i understand it.

Thanks for the answer! I don't know whether TPR meant it this way, but it just jumps out to me that having the macula densa sense low osmolarity and concluding that globular filtration rate is low just seems kind of strange and prone to error. What if by the time the filtrate reaches the macula densa, it actually is more dilute with high fluid volume and low filtrate osmolarity?

 

[LabratABQ]

Thanks for the answer! I don't know whether TPR meant it this way, but it just jumps out to me that having the macula densa sense low osmolarity and concluding that globular filtration rate is low just seems kind of strange and prone to error. What if by the time the filtrate reaches the macula densa, it actually is more dilute with high fluid volume and low filtrate osmolarity?

I think there are other chemoreceptors in your body besides that one in the kidneys alone...

 

[Chrisz]

So Macula Densa is located in the DCT of the kidneys and they act as chemoreceptors that monitor the osmolarity of the filtrate. TPR says that when the macula densa senses a filtrate's low osmolarity, it's suggesting that the filtrate rate has been reduced, thus telling the JG cells to secrete renin to increase blood pressure/blood flow.

My question is: Why does filtrate's low osmolarity = low filtrate rate?

Yes, this statement is correct. Think about what happens when you have a low filtration rate. When your filtration rate is low, your filtrate goes up the ascending tubule slowly. The slower the filtrate goes up the ascending tubule, the more dilute the filtrate becomes because more NaCl is ACTIVELY pumped out of the tubule. When it reaches the distal tubule, it tells Macula Densa, " hey bro, the filtrate flows too slow, you gotta do something." Then blood pressure goes up. Lol

 

[stuw]

You know, i completely forgot about the ascending tubule. That makes perfect sense haha thanks chris!

 

[Chrisz]

You know, i completely forgot about the ascending tubule. That makes perfect sense haha thanks chris!

np😉