25. Excretion of waste products Flashcards
Where does most of the reabsorption in the nephron take place?
Proximal convoluted tubule
What does the loop of Henle cause urine to become?
- Become more concentrated as it produces a concentration gradient in the surrounding medullary tissue
- Urine is hyper osmotic to the blood
What are the three parts of the renal tubule?
- Thin descending limb
- Thick ascending limb
- Thin ascending limb
What does the thick ascending limb do?
Actively pumps out NaCl
Is the thick ascending limb permeable to water?
No, the thick ascending limb is impermeable to water so water does not follow
What does NaCl that has been actively pumped out by the thick ascending limb do?
It raises the solute concentration in the surrounding interstitial fluid of the renal medulla
Are there aquaporins in the thick ascending limb?
No aquaporins at this point
What is the thin descending limb permeable to?
Highly permeable to water but not to Na+ or Cl-
Where does water move in the thin descending limb?
- Water exits the descending loop by osmosis because the surrounding interstitial fluid tissue is more concentrated
How does the concentration of the renal fluid in the descending limb change?
It becomes more concentrated
In the distal convoluted tubule, what is the concentration of the renal fluid like?
The renal fluid is less concentrated that the interstitial fluid
What is reabsorbed at the distal convoluted tubule?
- Reabsorption of salts, amino acids
- Some water moves out by osmosis
Compare the concentration of the renal fluid with the interstitial fluid at the distal convoluted tubule?
Renal fluid becomes isosmotic with interstitial fluid
What happens at the collecting duct?
As the renal fluid moves down the collecting duct it become highly concentrated as water is drawn out due to the high solute concentration in the interstitial fluid of the medulla
What is the major solute in the renal fluid of the collecting duct?
Urea
Where does urea movement occur?
- Some urea leaks from the collecting duct into the interstitial fluid of the medulla adding to increased osmotic concentration in renal medulla
- Urea diffuses back into the ascending limb and is returned to the collecting duct
What does ADH do?
Also known as vasopressin, ADH controls the permeability of the collecting duct to water, thereby controlling the amount of water reabsorbed from urine
How does ADH control permeability to water?
It stimulates the expression of aquaporin 2 which is a water channel in the collecting duct cell membranes
What makes people thirsty?
When the brain receives signals that
- The amount of water in the body is too low or
- Some elements in the blood such as sodium are too concentrated
What detects the rise in blood osmolarity?
Osmoreceptors detect increased osmolarity and stimulate ADH release
What do the osmoreceptors stimulate and what does this do?
They stimulate the hypothalamus
Causes release of ADH in the bloodstream
What does ADH do in the kidney?
Increases water permeability of the collecting duct and distal tubule
What does increased water permeability do?
Reabsorption of water helps maintain blood volume and blood pressure
What detects a rise in blood pressure?
Stretch receptors in the aorta and carotid artery detect increases in blood pressure and inhibit ADH release causing a fall in blood pressure
