Homeostasis: osmoregulation

Question 1

Ultrafiltration:

Answer 1

Blood enters the kidneys through the renal artery at high pressure
Renal artery divides into afferent arteriole then glomerulus and then efferent arteriole
Pressure gradient- efferent arterioles are narrower than afferent arterioles- water and small, soluble molecules forced out of capillary to form the glomerular filtrate, into the bowman’s capsule
larger molecules like proteins left behind as they are too large

Question 2

What resists the movement of the filtrate? (E-C)

how is this reduced? P

Answer 2

capillary endothelial cells
epithelial cells of the renal capsule

pondocytes have spaces between them- allow filtrate to pass beneath them

Question 3

Selective reabsorption steps:

how is the PCT adapted:3

Answer 3

Active transport of Na+ out of epithelial cells lining PCT into capillaries where they are carried away
Sets up a diffusion gradient for Na+ to diffuse back into epithelial cells from PCT
Co transport of Na+ and glucose from PCT to epithelial cells through co transport carrier proteins

microvilli provide a large surface area to reabsorb substances
infoldings provide large surface area for diffusion into blood capillaries
high density of mitochondria to provide ATP for active transport

Question 4

Which limb is permeable to water, which isnt?

Loop of Henle Steps:

Answer 4

Descending-narrow and permeable
Ascending- thick and impermeable

1) Na+ actively transported out of ascending limb of loop of Henle- requires ATP- creates a low water potential in the interstitial space
2) Water cannot leave through ascending limb as impermeable, but does leave by osmosis out the descending limb- enters capillaries by osmosis and carried away
3) filtrate progressively loses water as it moves down the descending limb
4) at the bottom of the loop, Na+ diffuse out and as it moves up actively transported, so water potential of filtrate increases as you ascend

Question 5

DCT and Collecting duct:

Answer 5

DCT: microvilli and mitochondria to reabsorb material by active transport
make final adjustments to water and salts and to control pH
Collecting duct: runs parallel to loop of Henle- as you descend, decreased water potential- water leaves collecting duct by osmosis.

Question 6

Hormones is osmoregulation:

Answer 6

osmoreceptors in the hypothalamus lose water by osmosis- shrink- detect fall in water potential
causes hypothalamus to produce hormone ADH which is secreted into the blood by the pituitary gland
ADH binds to receptor proteins on the cell surface membrane of the collecting duct
activates enzyme phosphorylase- causes vesicles containing aquaporins to fuse with the membrane- increases permeability- more water leaves collecting duct by osmosis

osmoreceptors detect rise in water potential
send ENI to pituitary gland to stop sending ADH