Ischemia of kidney medulla

[medInUSA]

Just something I was wondering about ever since first learning it.

The anatomy of the nephron renders certain tubular segments susceptible to ischemic injury. Although the kidney recieves 20% of cardiac output, the renal medulla normally exists on the brink of hypoxia, due in part to the high metabolic activity required for transport precesses and low blood flow to the segment. For this reason it so easily damaged be ischemia.
Evolutionarily speaking what could possibly be the advantage of keeping the medulla with such little oxygen? Anyone have any ideas?

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[beastmaster]

Lowering blood flow is one of the mechanisms the medulla uses to produce a gradient that can concentrate urine. Too much blood flow disrupts the gradient, and vice versa (loop diuretic improves flow). I guess you can say that evolution struck a happy balance.

It's called "countercurrent exchange" you can google it.

 

[Bertelman]

I don't really care to revisit renal physio long enough to understand your question, more less piece together a response. On the evolution side, however, I would suggest that not all mechanisms in our body have been optimized to perform in an ideal state. Some have been asked to "step it up" and perform in the best possible conidtions available. This is likely the case with what you are describing. There are many responsibilities placed on kidneys, and therefore must be compromises in some of its capabilities and resources.

This actually sounds like a great question to ask a prof. I suggest maybe at the end of class, when everyone else is ready to leave.

 

[medInUSA]

Bertleman, lol

I actually used to do that alot, But now I learned to keep my mouth shut and not to ask the questions in class. (one of the most important pieces of advice I would give to med students who are just starting up)

 

[Droopy Snoopy]

Might as well ask why the brain or heart are kept within minutes or seconds of serious hypoxic damage. Although in this case my guess is instead of making the system better, evolution just gave us an extra kidney.

 

[fakin' the funk]

Evolutionarily speaking what could possibly be the advantage of keeping the medulla with such little oxygen? Anyone have any ideas?

The medulla only becomes hypoxic and ischemic in conditions that we humans have only in the past 50 years invented the technology to even witness.

For millions of years, when humans experienced severe trauma or sepsis, they died quite promptly. Ask that caveman from the Geico commercials about renal ischemia and see if he cares.

 

[exmike]

Just something I was wondering about ever since first learning it.

The anatomy of the nephron renders certain tubular segments susceptible to ischemic injury. Although the kidney recieves 20% of cardiac output, the renal medulla normally exists on the brink of hypoxia, due in part to the high metabolic activity required for transport precesses and low blood flow to the segment. For this reason it so easily damaged be ischemia.
Evolutionarily speaking what could possibly be the advantage of keeping the medulla with such little oxygen? Anyone have any ideas?

Actually, the renal cortex is the region of high metabolic demand since the PCT and DCT are packed with Na/K pumps. The thin descending and ascending limbs are in the medulla - neither participate significantly in active transport.

btw. ive noticed a steady stream of basic questions that you could probably learn by reading your textbook or syllabus. Wouldn't it be more a more effective learning strategy if you actually studied it first, then came to the board with informed questions that might educate us all?

 

[Church]

For millions of years, when humans experienced severe trauma or sepsis, they died quite promptly. Ask that caveman from the Geico commercials about renal ischemia and see if he cares.

Renal ischemia... so easy, a caveman could die from it?

 

[fakin' the funk]

Renal ischemia... so easy, a caveman could die from it?

(Sitting on the shrink's couch) "It's my mom...I'll put her on speakerphone."

 

[medInUSA]

Actually, the renal cortex is the region of high metabolic demand since the PCT and DCT are packed with Na/K pumps. The thin descending and ascending limbs are in the medulla - neither participate significantly in active transport.

btw. ive noticed a steady stream of basic questions that you could probably learn by reading your textbook or syllabus. Wouldn't it be more a more effective learning strategy if you actually studied it first, then came to the board with informed questions that might educate us all?

One mistake, part of the thick ascending limb is in the medulla, and it is especially susceptible to hypoxia (accoridng to goljan). Also you can look on the diagram of the nephron i 1st aid.

 

[exmike]

One mistake, part of the thick ascending limb is in the medulla, and it is especially susceptible to hypoxia (accoridng to goljan). Also you can look on the diagram of the nephron i 1st aid.

i didnt mention the TAL did i? all i said was that the cortex has greater metabolic demand than the medulla because of the convoluted tubules.