AAMC Bio Pack 1 Q#1

[Dr.Qball]

Hello, already starting to question my understanding of Biology with this question. The question states that "The sodium pump would be most active in cells with which of the following structures?" A) Veins B) Loop of Henle C) Lungs D) Bone marrow

My reasoning was it would be veins because the circulating blood would have some glucose and the skeletal muscles will ACTIVELY pump sodium and use the sodium pump to use glucose as a secondary transport. And I never would of thought it would be the Loop of Henle because I thought it had more to do with PASSIVE diffusion of water (so why would there be any pumps for sodium?) and had nothing to do with the sodium pump.

Some clarification would be greatly appreciated. Also thinking about it the Convoluted Tube would make the most sense because I know that part of the kidney has to do with ACTIVE transport of Sodium and Potassium.

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[sazerac]

Hello, already starting to question my understanding of Biology with this question. The question states that "The sodium pump would be most active in cells with which of the following structures?" A) Veins B) Loop of Henle C) Lungs D) Bone marrow

My reasoning was it would be veins because the circulating blood would have some glucose and the skeletal muscles will ACTIVELY pump sodium and use the sodium pump to use glucose as a secondary transport. And I never would of thought it would be the Loop of Henle because I thought it had more to do with PASSIVE diffusion of water (so why would there be any pumps for sodium?) and had nothing to do with the sodium pump.

Some clarification would be greatly appreciated. Also thinking about it the Convoluted Tube would make the most sense because I know that part of the kidney has to do with ACTIVE transport of Sodium and Potassium.

There isn't any guarantee that the vein is in a muscle. Veins are pretty passive tubes.

You might want to review your physiology textbook, or the Wikipedia article on loop of Henle has a good section on physiology. Philosophically, energy needs to be spent to establish and maintain the gradient.

 

[NextStepTutor_3]

If I understand your thought process correctly, you were thinking that the tissue (like skeletal muscle) surrounding the veins would need to take in glucose from the blood, and that this could be accomplished using secondary active transport, moving sodium and glucose at the same time. The problems with this are that:

- transport of nutrients from the blood to the tissues largely occurs in capillaries, not veins. This is the same with gas exchange; capillary walls are so much thinner than venous walls, and this allows exchange to happen fairly easily.

- the question asked about "the sodium pump," by which it was referring to the sodium-potassium ATPase. This pump sends sodium ions OUT of the cell while bringing potassium ions IN. Since you mentioned secondary active transport, I assume you were thinking about some form of sodium-glucose transporter, which isn't what the question was asking about. Also, even if skeletal muscle did use secondary active transport to bring in glucose from the blood, the transporter involved would be on the membrane of the muscle cell - not on venous cells.

Definitely go back and review the loop of Henle - it's absolutely related to sodium transport, not just to water reabsorption. Sodium is actively pumped out of the thick ascending limb; this is very important if you are to understand the countercurrent multiplier system/concentration gradient in the medulla. Once you understand this function, you'll see that the loop of Henle was the "direct" answer here, which the MCAT is typically looking for (as opposed to an answer that required more convoluted reasoning).

Overall, great question on an important topic (membrane transport)! And good luck studying!

 

[Dr.Qball]

Thank you for the responses! I'm glad I am using the question packs to see what I am weak on. With reading the Wiki of the Loop of Henle and Next step tutor answers it makes it more than clear that both the medulla and cortex of the kidney has ATPase to actively make a concentration gradient. As a disclaimer I never took A&P and had to self teach with review books so it is one of my weaker topics but this definitely clears some things up.

 

[sazerac]

Thank you for the responses! I'm glad I am using the question packs to see what I am weak on. With reading the Wiki of the Loop of Henle and Next step tutor answers it makes it more than clear that both the medulla and cortex of the kidney has ATPase to actively make a concentration gradient. As a disclaimer I never took A&P and had to self teach with review books so it is one of my weaker topics but this definitely clears some things up.

No problem. I don't usually send people to Wikipedia, but your question was so basic that there wasn't much to do besides refer to a reference source.

If you can find a copy of Exam Krackers Audio Osmosis, it is a good lecture series that summarizes what you'll need to know for physiology (and a lot of other topics) in bite sized chunks. Also, there is a web based program called Interactive Physiology that covers those topics as well, and it is very interactive which helps with the learning.

Good luck!

 

[Groggs]

Hello, already starting to question my understanding of Biology with this question. The question states that "The sodium pump would be most active in cells with which of the following structures?" A) Veins B) Loop of Henle C) Lungs D) Bone marrow

My reasoning was it would be veins because the circulating blood would have some glucose and the skeletal muscles will ACTIVELY pump sodium and use the sodium pump to use glucose as a secondary transport. And I never would of thought it would be the Loop of Henle because I thought it had more to do with PASSIVE diffusion of water (so why would there be any pumps for sodium?) and had nothing to do with the sodium pump.

Some clarification would be greatly appreciated. Also thinking about it the Convoluted Tube would make the most sense because I know that part of the kidney has to do with ACTIVE transport of Sodium and Potassium.

I finished up the bio Qpack 1 yesterday. I'm assuming you saw this on wiki, but from my understanding part of the ascending limb of the loop of henle engages in active to transport using the sodium potassium pump. Khan academy has some great videos on the renal system that really helped me.