wait-loss
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#1
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Can someone check if this is right please?
And if there's a way to remember everything...

The nephron is the functional unit in the kidney.
Blood capillaries form a knot called the glomerelus
This is surrounded by the Bowman's capsule
The arteriole leasing into the capsule (Afferent) is larger than the vessels in the capsule/ leaving the capsule (Efferent)
This creates pressure (filtrate pressure) forcing fluid out of the capillaries
Red blood cells and proteins remain in the blood cells as they have a RMM of 69,000 or above

85% of the fluid is reabsorbed in the proximal convoluted tubule
In the descending limb the water potential of the fluid is decreased by the addition of salts and removal of water
In the ascending limb salts are removed - water potential increases
In the collecting duct water is removed again to ensure a low water potential.

So essentially, salt from the ascending limb moves into the descending limb, into the capillary taking water with it?
I'm confused with the stuff in bold or the stuff that happens inbetween the PCT and DCT
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Hype en Ecosse
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Report 7 years ago
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(Original post by wait-loss)
Can someone check if this is right please?
And if there's a way to remember everything...

The nephron is the functional unit in the kidney.
Blood capillaries form a knot called the glomerelus
This is surrounded by the Bowman's capsule
The arteriole leasing into the capsule (Afferent) is larger than the vessels in the capsule/ leaving the capsule (Efferent)
This creates pressure (filtrate pressure) forcing fluid out of the capillaries
Red blood cells and proteins remain in the blood cells as they have a RMM of 69,000 or above
This is all right, except I'm not sure about the RMM figure - don't know it off the top of my head.

85% of the fluid is reabsorbed in the proximal convoluted tubule
In the descending limb the water potential of the fluid is decreased by the addition of salts and removal of water
In the ascending limb salts are removed - water potential increases
In the collecting duct water is removed again to ensure a low water potential.

So essentially, salt from the ascending limb moves into the descending limb, into the capillary taking water with it?
I'm confused with the stuff in bold or the stuff that happens inbetween the PCT and DCT
This is mostly right - I'm not sure that salts are added to the descending limb (I've never heard of it and it wouldn't make much sense), as the tubular epithelium in the descending limb has a very low permeability to salts.

What's going on in the bolded:

Salt is removed from the ascending limb into the medullary interstitium - this makes the interstitium very salty, which then pulls water out of the descending limb. The salt doesn't get sent from the ascending into the descending (this would just make a useless loop), rather the salt is used to set up an osmotic gradient to draw the water out of the descending limb.
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Dynamo123
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Report 7 years ago
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(Original post by wait-loss)
Can someone check if this is right please?
And if there's a way to remember everything...

The nephron is the functional unit in the kidney.
Blood capillaries form a knot called the glomerelus
This is surrounded by the Bowman's capsule
The arteriole leasing into the capsule (Afferent) is larger than the vessels in the capsule/ leaving the capsule (Efferent)
This creates pressure (filtrate pressure) forcing fluid out of the capillaries
Red blood cells and proteins remain in the blood cells as they have a RMM of 69,000 or above

85% of the fluid is reabsorbed in the proximal convoluted tubule
In the descending limb the water potential of the fluid is decreased by the addition of salts and removal of water
In the ascending limb salts are removed - water potential increases
In the collecting duct water is removed again to ensure a low water potential.

So essentially, salt from the ascending limb moves into the descending limb, into the capillary taking water with it?
I'm confused with the stuff in bold or the stuff that happens inbetween the PCT and DCT
The stuff you wrote is right. As for the stuff in bold, we must remember that we are supposed to concentrate the urine to minimalize water loss. It is better to start with the second part of the loop of henle, the ascending part. This is impermeable to water, and actively pumps ions into the tube. As a result of this, the descending loop, which is permeable to water, allows water to move out via osmosis as well. Now although water is outside, there is still a lot of salt outside as well. This now passively moves in the descending limb. And again when this concentrated fluid goes to the ascending limb, the salt is actively secreted, and the process begins again.

You can read more about this here:

http://www.s-cool.co.uk/a-level/biol...and-the-kidney
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