Kidneys Flashcards
outline the process of ultrafiltration
afferent (incoming) arteriole has larger diameter than efferent (outgoing)
so high pressure glomerular capillaries
forces plasma & molecules with Mr below 69,000 out through fenestrations of capillary wall
then it would go through basement membrane & podocytes into bowmans capsule
how is the distal convoluted tubule adapted to maximise reabsorption
Selective Reabsorption:
- epithelial cells have many microvilli to maximise surface area
- epithelial cell membranes contain Na+-glucose/aminoacid cotransporter proteins
- convoluted (coiled) to maximise distance travelled by filtrate therefore maximise reabsorption of useful molecules back into blood
outline what happens in PCT
- Na+ actively pumped out epithelial cell into lumen of PCT so conc. of cytoplasm decreases
- Na+ accompanied by an amino acid/glucose diffuses back into epithelial cell via cotransport proteins = secondary active transport
- water follows in by osmosis
- glucose/amino acids diffuse into the blood
what happens in descending limb of loop of henle
descending limb permeable to water & ions
ascending limb impermeable to water but permeable to ions
in descending limb: water leaves by osmosis, so ion conc. increases down the medulla. Na+ & Cl- diffuse into DL as they are actively transported out AL
in thin (lower part of) ascending limb; Na+ & Cl- diffuses out down conc. gradient as it Is permeable in thick (upper) ascending limb; Na+ & Cl- is actively transported out
explain the nature & purpose of the countercurrent multiplier mechanism of the loop of henle
because it is a loop:
maximises diffusion of solutes out of the limb as the fluids travel in opposite directions (@ top of DL where water potential highest, the conc. of medulla is lowest so still steep gradient
when water potential decreases down the DL, the conc. of medulla is highest (lowest WP) so still steep conc. gradient
what is the purpose of the loop on henle?
to lower the medulla fluid water potential so that water leaves collecting duct by osmosis (the amount is controlled by ADH therefore aquaporins in collecting duct walls)
define osmoregulation
Maintaining a constant water potential of the blood, despite changes in the level of water and salt intake.
what happens if WP of blood goes below optimum range
osmoreceptors in hypothalamus detects
more ADH released by posterior pituitary gland- travels through blood & binds to receptors on collecting duct walls
more aquaporins inserted into collecting duct walls
less permeable to water
less water reabsorbed
= small volume conc. urine
blood WP increased back to normal range
what happens if WP of blood goes above optimum range
osmoreceptors in hypothalamus detects
less ADH released by posterior pituitary gland- travels through blood & binds to receptors on collecting duct walls
less aquaporin vesicles fuse with membrane
less aquaporins inserted into collecting duct walls; less permeable to water
less water reabsorbed into blood; more leaves as uring
= large volume of dilute urine
blood WP decreases back to normal range
what happens to WP as you descend the medulla and why?
gets lower so water can be reabsorbed from collecting duct, then go into the blood which has even lower WP, by osmosis (how much depends on level of aquaporins, then it re-enters capillaries by osmosis)
why does urea conc. increase as you proceed the nephron?
water leaves so its relative amount to water increases; there isn’t actually more urea than started with.
why does the conc. of glucose & amino acids decrease as you proceed the PCT?
selective reabsorption back into blood so leaves the filtrate
what may cause low blood WP & high blood WP?
Low WP= salt intake or lots of sweating
High WP= drinking too much water or cool day so not sweating
define glomerular filtration rate and how is it impacted by kidney failure?
how much fluid enters nephron from glomerulus per min
reduces with kidney failure
4 causes of kidney failure
diabetes mellitus (type1/2)
heart failure
infection
hypertension (high BP)
