Bio 1001 qs - nephron + cartilage

[capn jazz]

Q 649: Decreased sodium flow through which nephron segment is most likely to stimulate the macula densa?
A) renal pelvis
B) proximal convoluted tubule
C) collecting duct
D) renal calyx

Answer: B
According to the passage, the macula densa releases renin when stimulated by low levels of NaCl entering the distal nephron. The nephron is the functional unit of the kidney. Review of the nephron anatomy: the glomerulus --> Bowman's capsule --> proximal convoluted tubule --> Loop of Henle (descending and ascending) --> distal convoluted tubule (this is where the macula densa is located) --> collecting ducts --> minor calyx --> major calyx --> renal pelvis --> out of the kidney into the ureter.

Ummmm... did they mean "distal convoluted tubule" as choice B? I picked collecting duct because it was the only distal part!
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650: A diuretic is a drug that promotes the excretion of water from the body. Which of the listed diuretics is the most likely to exert a particularly powerful effect?

A) spironolactone action in the collecting duct
B) thiazide action in the distal convoluted tubule
C) furosemide action in the loop of Henle
D) mannitol action in Bowman's capsule.

The answer is C. I don't get it. Can someone explain the loop of Henle to me?

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883) When examining hyaline cartilage under a microscope, one expects to find which of the following?
A) canaliculi
B) microscopic blood vessels
C) peptide fibers
D) Volkmann's canals

Answer: B. Cartilage is avascular (!!!) connective tissue that receives all nutrients by simple diffusion. It has no blood vessels or Haversian or Volkmann's canals, which are only found in bone. Collagen is the main peptide found in cartilage.

Bone is very vascular and is constantly being supplied with blood. Canaliculi are microvascular spaces used by osteocytes to maintain nutrient supply to
every bone cell.

Uh, so is the answer C) peptide fibers? Because they explicity reject all the other options!

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[Charles_Carmichael]

I love renal! For your first question, yes, it's true that the distal tublule is where the macula densa is located at, but think about it this way: whatever is left at the end of the proximal tubule will have to flow through the loop of Henle and the distal tubule. So, if low levels of Na+ flow through the proximal tubule and 66% of it is reabsorbed (based on the table that they give), there's still going to be low levels of Na+ in the distal tubule, which comes after the proximal tubule.

It wouldn't make sense to choose collecting duct because we don't know what the incoming Na+ level in the distal tubule was; for example, normal levels of Na+ could have entered the distal tubule but because of aldosterone action, the Na+ levels in the collecting duct are low. So, the answer choice has to be either the distal tubule or some segment before the distal tubule; any segment that occurs after the distal tubule (like all the other answer choices) may have filtrate modified by the distal tubule itself, so you can't go with them.

For your second question, the answer is based off of the table that they give. The table gives how much Na+ and H2O is reabsorbed in different segments of the nephron. Out of the possible answer choices, the loop of Henle reabsorbs the most amount of water (15%) based on the table; that's why a loop diuretic would have the most powerful effect. The distal tubule, according to the table, reabsorbs only 4% of the water that flows through the nephron, and since this is less than in the loop of Henle, this wouldn't be the best choice. They don't give us the data for the collecting duct but we know that some water is not reabsorbed, since some urine will form; this means that the collecting duct reabsorbs less than the 15% remaining (100 - 85 = 15%); so this isn't the right choice either since the loop of Henle reabsorbs more. And a proximal tubule diuretic is not a choice.

For your last question, the answer should be peptide fibers, since collagen is basically a peptide fiber and collagen is abundant in cartilage. I think EK is wrong in that; I'm pretty sure I'm right in two other questions also in the renal section and they're wrong...some of their wording in question stems/answer choices is just plain weird. Hope this helps.

 

[capn jazz]

Thank you so much! It all makes sense now!

 

[Charles_Carmichael]

Thank you so much! It all makes sense now!

You're welcome! I'm such a nerd; I'm just scouring the Q&A forum hoping people would post more physiology/biochem/anything bio-related questions so I don't have to study gen. chem!

 

[dougkaye]

I actually think it's a typo. Not sure if it's in the EK errata but the answer specifically says that NaCl levels in the "distal nephron" are the most relevant for stimulating renin release. It doesn't make must sense to list the distal convoluted tubule as the location of the macula dense, and then to say that the correct answer is the proximal tubule.