controlling water potential Flashcards
Give 2 ways water is lost from the body
From sweat
From excretion
What do the kidneys do
They regulate the water potential of the blood , so the body has the right amount of water
where does the regulation of the water potential of the blood take place in the nephron?
The loop of Henle, DCT, collecting duct
if water potential of the blood is too low…..
Then more water is reabsorbed by osmosis into the blood from the tubules of the nephron , so the urine is more concentrated, so less water is lost during excretion.
if water potential of the blood is too high
Then less water is reabsorbed by osmosis into the blood from the nephron tubules, so urine is more dilute, so less water is lost during excretion.
What are the two limbs that make up the loop of henle?
ascending limb
descending limb
What does a countercurrent multiplier mechanism do?
Reabsorbs water back into the blood
Process: Countercurrent mechanism
- Near the top of the ascending limb
Na+ and Cl- are actively pumped out into the medulla
-But water stays inside the ascending limb, which creates a lower water potential in the medulla - As there is a lower W.P in the medulla than the D.L, water moves out the D.L into the medulla by osmosis.
- filtrate becomes more concentrated as ions cant diffuse out of the D.L ( impermeable to ions)
- water in the medulla is reabsorbed into the blood through the capillary network
- Neat the bottom of the ascending limb, ions diffuse out into the medulla, decreasing the water potential of the medulla
- Increased concentration of ions in the medulla, lowers the water potential of it. SO water moves out of the collecting duct by osmosis, and the water is reabsorbed into the blood through the capillary network
why does water stay inside the ascending limb?
The ascending limb is impermeable to water ( water can not pass through it)
Why is the filtrate more concentrated?
Descending limb is impermeable to ions.
How do you control the volume of water reabsorbed from the collecting duct into the capillaries
By changing the permeability of the collecting duct
What does a longer loop of henle mean?
Means:
- more water can be reabsorbed from the filtrate
- longer A.L- which means more ions are actively pumped out into the medulla, creating a low W.P in the medulla
- Which therefore means, more water moves out of the nephron and collecting duct into the capillaries, giving CONCENTRATED urine ( more yellow)
Do desert animals have linger or smaller loop of henle
Longer loop of henle to save as much water as
possible.
What receptors monitor the water potential of the blood
Osmoreceptors in the hypothalamus
What happens when there is a low water potential in the blood? ( to do with signalling)
- osmoreceptors are stimulated by low W.P in the blood
- The hypothalamus sends nerve impulses to the posterior pituitary gland to release ADH into the blood.
