Increased Kidney Water = Higher BP

[Avicenna]

I know that ADH, angiotensin II, and aldosterone in response to low bp increase the water in the kidney by some way or other. How does the higher kidney water volume cause a higher blood pressure?

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[DownUnderBlunder]

In short, the kidney puts stuff originally destined into urine back into your blood, thereby increasing the volume of blood. Since there's more volume of blood/plasma in the same volume of space (i.e., your CVS), the pressure goes up. It's not unlike taking a filled tube and squeezing in just a bit more water, causing it to bulge (aka increase blood pressure).

The mechanism by which ADH, aldosterone, and angiotensin II achieve this are different, but I don't know if the MCAT cares if you know it.

 

[El-Rami]

I think it matters more that you just know that ADH causes resorption of water at the DCT and collecting ducts via aquaporin channels whereas aldosterone causes resorption of sodium (and water follows due to osmotic pressure) at the DCT.

 

[ChrisMack390]

I think it matters more that you just know that ADH causes resorption of water at the DCT and collecting ducts via aquaporin channels whereas aldosterone causes resorption of sodium (and water follows due to osmotic pressure) at the DCT.

This. Therefore, ADH dilutes blood (lowers osmolarity) and aldosterone does not. Both increase volume and pressure.

 

[jlp032892]

Receptors on afferent arteriole(Barroreceptors) detect low blood pressure -> Renin is released from specialized cells of the kidney -> Renin makes its way to the liver where it converts Angiotensinogen to angiotensin I (AI) -> AI makes its way to the lungs where it is converted to AII by the ENZ ACE -> AII has three main functions 1) Vasoconstricts Blood vessles in the periphery (Higher resistance= Higher TPR= Higher BP) Remember the equation Pressure= Flow Rate (Q) x Total Peripheral Resistance (TPR) 2) AII acts on the posterior pituitary and aids in the release of ADH-> ADH takes on its role and acts on the collecting duct/DCT and allows for greater reabsorption of water (Higher blood volume= Higher BP) 3) AII acts on the adrenal cortex (Glomerulosa) and aids in the release of aldosterone ( Aldosterone acts on DCT and causes greater reabsorption of Na+(important to note that K+ is being excreted simultaneously)-> Water follows due to osmotic pressure-> Greater blood volume= higher BP)

Not an end all but it is a decent summery of the events that happen.

 

[StudyLater]

I think it matters more that you just know that ADH causes resorption of water at the DCT and collecting ducts via aquaporin channels whereas aldosterone causes resorption of sodium (and water follows due to osmotic pressure) at the DCT.

Yes. SPECIFICALLY the part about aquaporin channels. You need to know they are aquaporin channels. Are you listening to me???? You can't just say water goes back into the collecting ducts. They have to go through the aquaporin channels. This is very, very, VERY important for your exam. 10 questions on this minimum, guaranteed.

 

[El-Rami]

Yes. SPECIFICALLY the part about aquaporin channels. You need to know they are aquaporin channels. Are you listening to me???? You can't just say water goes back into the collecting ducts. They have to go through the aquaporin channels. This is very, very, VERY important for your exam. 10 questions on this minimum, guaranteed.

Also water goes in single-file in the aquaporin channels. Now, I don't know if THAT is too much to know or not, but why not?

 

[StudyLater]

Also water goes in single-file in the aquaporin channels. Now, I don't know if THAT is too much to know or not, but why not?

Holy omgwtfbbq how could I have forgotten!?!?!?!? I'm totes gonna fail. I don't even know why I did this. My parents pressured me into it. I can't be a doc, I'm not good enough! I only got like 85% on my EK exams! *breaks down*

 

[El-Rami]

Holy omgwtfbbq how could I have forgotten!?!?!?!? I'm totes gonna fail. I don't even know why I did this. My parents pressured me into it. I can't be a doc, I'm not good enough! I only got like 85% on my EK exams! *breaks down*

lol. Don't forget the subunits and Km of the transporter. Very, very important.