Questions about the Kidney

[thestrokes14]

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I have a couple of questions about the Kidney as I have been reviewing the material. If you can help with anything, I would really appreciate it!

1. The Kidney is known to regulate the pH of the blood, but I have had read conflicting opinions on the following matter: Are H+ and HCO3- ions reabsorbed into the blood stream, or secreted into the urine? I am confused about which direction the particular ions are going.

2. Does ADH (antidiuretic hormone) need to be present to reabsorb water? Can aldosterone reabsorb water by osmosis without any help from ADH?

3. I have read that urea may be reabsorbed. Is there any reason why it would be beneficial to reabsorb urea?

Thanks!

 

[shffl]

I have a couple of questions about the Kidney as I have been reviewing the material. If you can help with anything, I would really appreciate it!

1. The Kidney is known to regulate the pH of the blood, but I have had read conflicting opinions on the following matter: Are H+ and HCO3- ions reabsorbed into the blood stream, or secreted into the urine? I am confused about which direction the particular ions are going.

2. Does ADH (antidiuretic hormone) need to be present to reabsorb water? Can aldosterone reabsorb water by osmosis without any help from ADH?

3. I have read that urea may be reabsorbed. Is there any reason why it would be beneficial to reabsorb urea?

Thanks!

Here's what I think:

1. You already mentioned that kidney regulates pH of the blood so naturally the kidney will do both reabsorption and excretion according the blood's pH level to regulate it. Which direction? If blood is too acidic as detected via high pCO2, the kidney will act to raise pH by secreting more H+. When the bicarbonate is too high and hence blood is too alkaline, kidney will excrete more bicarbonate to lower the pH to normal level.

2. Yes aldosterone can allow body to reabsorb water via osmosis but I think it's a lot quicker and more efficient when ADH open channels in cells that allows water to be reabsorbed at a much quicker rate.

3. Urea is sometimes reabsorbed through diffusion. Not sure why it may be beneficial though.

 

[Pamplemousse123]

I have a couple of questions about the Kidney as I have been reviewing the material. If you can help with anything, I would really appreciate it!

1. The Kidney is known to regulate the pH of the blood, but I have had read conflicting opinions on the following matter: Are H+ and HCO3- ions reabsorbed into the blood stream, or secreted into the urine? I am confused about which direction the particular ions are going.

2. Does ADH (antidiuretic hormone) need to be present to reabsorb water? Can aldosterone reabsorb water by osmosis without any help from ADH?

3. I have read that urea may be reabsorbed. Is there any reason why it would be beneficial to reabsorb urea?

Thanks!

the benefit to reabsorbing urea has to do something with the counter current exchange system set up by the kidney

 

[thestrokes14]

Here's what I think:

1. You already mentioned that kidney regulates pH of the blood so naturally the kidney will do both reabsorption and excretion according the blood's pH level to regulate it. Which direction? If blood is too acidic as detected via high pCO2, the kidney will act to raise pH by secreting more H+. When the bicarbonate is too high and hence blood is too alkaline, kidney will excrete more bicarbonate to lower the pH to normal level.

2. Yes aldosterone can allow body to reabsorb water via osmosis but I think it's a lot quicker and more efficient when ADH open channels in cells that allows water to be reabsorbed at a much quicker rate.

3. Urea is sometimes reabsorbed through diffusion. Not sure why it may be beneficial though.

Thanks! Concerning my first question, the direction can be implied based on common sense, but I have read that when the blood experiences acidosis (low pH), the kidney reaborbs bicarbonate ions. I have also read that the kidney can secrete H+ ions. Maybe is doesn't really matter; ions could flow in both directions?

 

[shffl]

Thanks! Concerning my first question, the direction can be implied based on common sense, but I have read that when the blood experiences acidosis (low pH), the kidney reaborbs bicarbonate ions. I have also read that the kidney can secrete H+ ions. Maybe is doesn't really matter; ions could flow in both directions?

I'd have to review my notes for these but kidneys can definitely reabsorb bicarbonate while experiencing acidosis. Bicarbonate reacts with H+ to form CO2 and water (expiration of CO2 is another way to deal with acidosis). That's why individuals undergoing acidosis hyperventilates to get rid of those CO2 that are forming. I'm sure ions can flow in both directions depending on the regulation levels.

 

[thestrokes14]

Concerning urea, I have been digging around and I think I may have found an answer as to why it's reabsorbed. It passively diffuses in the proximal convoluted tubule back into the blood stream which maintains an osmolarity concentration gradient that forces water to reabsorb in the descending loop of Henle. It is critical that we don't lose too much water, so this reabsorption of water is key, and urea appears to aid in the osmosis process.

Still, some urea is excreted in our urine as a means of getting rid of nitrogen wastes that occur due to deamination of amino acids.

 

[PiBond]

I have a couple of questions about the Kidney as I have been reviewing the material. If you can help with anything, I would really appreciate it!

1. The Kidney is known to regulate the pH of the blood, but I have had read conflicting opinions on the following matter: Are H+ and HCO3- ions reabsorbed into the blood stream, or secreted into the urine? I am confused about which direction the particular ions are going.

2. Does ADH (antidiuretic hormone) need to be present to reabsorb water? Can aldosterone reabsorb water by osmosis without any help from ADH?

3. I have read that urea may be reabsorbed. Is there any reason why it would be beneficial to reabsorb urea?

Thanks!

1. Under normal conditions, the epithelial cells along the nephron secrete H+ and reabsorb HCO3-. Carbonic anhydrase is present in the epithelial cells along the nephron and catalyzes the production of these two products. This is why urine is normally slightly acidic and our blood is slightly alkaline. Of course, this all can change if the body undergoes a pH imbalance.

2. ADH must be present to reabsorb water at the collecting duct. The collecting duct has variable permeability to water based on the amount of ADH present. Thus in the absence of ADH, the collecting duct is impermeable to water. Aldosterone purely increases the activity (and synthesis) of Na+/K+ pumps, thus resulting in increased Na+ absorption and increased potassium excretion. Water is able to move by osmosis as a result of the insertion of aquaporins caused by ADH.

3. Urea is present in high concentrations in the medulla of the kidney, resulting is a very "salty" and high osmolarity environment. This helps to create hypertonic filtrate at the bottom of the loop of henle (in addition to other ions). In doing so, we take back H20 which gets transported via the vasa recta that runs along side and picks up the water.

Does that make sense?

 

[thestrokes14]

1. Under normal conditions, the epithelial cells along the nephron secrete H+ and reabsorb HCO3-. Carbonic anhydrase is present in the epithelial cells along the nephron and catalyzes the production of these two products. This is why urine is normally slightly acidic and our blood is slightly alkaline. Of course, this all can change if the body undergoes a pH imbalance.

2. ADH must be present to reabsorb water at the collecting duct. The collecting duct has variable permeability to water based on the amount of ADH present. Thus in the absence of ADH, the collecting duct is impermeable to water. Aldosterone purely increases the activity (and synthesis) of Na+/K+ pumps, thus resulting in increased Na+ absorption and increased potassium excretion. Water is able to move by osmosis as a result of the insertion of aquaporins caused by ADH.

3. Urea is present in high concentrations in the medulla of the kidney, resulting is a very "salty" and high osmolarity environment. This helps to create hypertonic filtrate at the bottom of the loop of henle (in addition to other ions). In doing so, we take back H20 which gets transported via the vasa recta that runs along side and picks up the water.

Does that make sense?

Very clear! Thank you very much. For number 2, could aldosterone cause reabsorption of water in the distal tubule (by osmosis) without ADH?

 

[TwoPaddles]

Very clear! Thank you very much. For number 2, could aldosterone cause reabsorption of water in the distal tubule (by osmosis) without ADH?

Edit: nevermind, just saw PiBond's post.
But I don't believe there would be reabsorption since without the presence of ADH the distal tubule is impermeable to water. Whatever is at that point gets diuresed.