Below is the video transcript.
“Homeostasis is essential for the health and vitality of living systems. Among the the organs that regulate homeostasis in the body, the kidneys are of great importance. Which of the following is not a homeostatic function of the…?”
Okay, so really, we’re just asked here about what the kidney does, in terms of homeostasis, per se. So it’s not really asking us to dissect anything in detail. A lot of the questions in the MCAT are like that. They generally provide a lot of information that you don’t necessarily need. You just kind of have to focus. So, here, we’re asked about homeostasis, or homeostatic function, and we’re asked about the kidney. So what are some of the functions of the kidney? That’s essentially what we’re being asked here, okay? So, let’s see. Choice A says “renal absorption,” Choice B, renal excretion, C is hormone secretion, and then D is micturition. Okay, so if you recall, let’s take a look.
When we learned about the kidney in physiology classes, we learned that there is of course these different sections and the functional unit is the nephron. So we have, of course, the proximal convoluted tubule. We have Bowman’s capsule. We have the Descending Loop of Henle, because all of this is the Loop of Henle, the ascending portion, and then of course the distal convoluted tubule. And it was a pain to learn what each region does, but here’s a nice little diagram. It says, hey, here’s the nephron. We know that the renal corpuscle is responsible for filtration because, remember, the purpose of the kidney is of course to filter impurities from the body, so of course it filters the blood here. Then we have the proximal. “Proximal” means close, so this is the closer region, closer to the corpuscle where of course the fluid enters or the process begins, and it’s here that we have re-absorption and secretion. Here we see the entrance of things like urea, dopamine. The question doesn’t ask for this great detail, but this is just a quick, you know, refresher. Then we have of course the actual loop, the descending and ascending limbs. We see that water leaves here, salt leaves. And then over here, we also have re-absorption in the distal convoluted tubule and collecting duct regions. So this is really nice. You could probably look at this, pause the screen just to refresh your memory about it. But we do see that the kidney is involved in re-absorption, absolutely. “Filtration” means, of course, separating the impurities and retaining the things that are needed by the body.
So when we return, we see that the answer choices had, of course, absorption, excretion – absolutely, we saw that those things were leaving – and hormone secretion. Now, of course, when we look at the function of the kidney here in terms of when we study it as part of the urinary system or excretory system, we don’t see much about hormone production. But do remember that the kidneys are capable of secreting hormones, okay? Some of them, for instance, are involved in the production of red blood cells during anaemic conditions in the body. So, in addition to the physiological function of the kidney in terms of things that we’ve learned – filtration, pH, and removing impurities – always remember that the kidney is also capable of secreting hormones, okay? So that’s the hormone secretion.
Now, micturition is actually just a fancy way for saying, “releasing urine from the body,” or, “urination.” And so we know that the kidney, even though it is endocrine because it releases hormones…we know that it’s part of the excretory system and it’s involved in filtration, re-absorption and excretion, the kidney is not a part of the micturition. That is something that we associate of course with the bladder and the muscles and the urethra. So, in this case, the correct response is Choice D.