Physiology 4+5: Proximal tubule and Loop of Henle Flashcards
what % of urea is reabsorbed by the kidney tubules
50%
what % of creatinine is reabsorbed by the kidney tubules
0%
what % of fluid, salt, glucose and amino acids are reabsorbed by the kidney tubules
fluid + salt = 99% / glucose + amino acids = 100%
what does the glomerular filtrate contain
ions and solutes but no RBC’s or plasma proteins
what osmolarity is the filtrate when it enters AND leaves the proximal tubule
iso-osmotic at 300mosmol/l
what % of substances are reabsorbed in the proximal tubule PT
66% of sodium and water
what substances are reabsorbed in the PT (7)
sugar, amino acids, phosphate, sulphate, lactate, water, potassium
what substances are secreted in the PT (6)
H+, neurotransmitters, bile, drugs, toxins, hippurates
what 2 ways can substances be reabsorbed from the tubules
transcellular or paracellular
what is primary active transport
energy directly required to carry against a concentration gradient
what is secondary active transport
transport is coupled to concentration gradient of an ion (usually Na)
what is facilitated diffusion
passive transport down a concentration gradient with a transporter
how is Na reabsorbed from the lumen into the tubular epithelial cell in the PT (3)
cotransport with glucose and amino acids and also counterport (anti port) with H+ being secreted into the lumen
hows Na transported from the tubular epithelial cell to the per tubular capillaries in the PT
via NaKATPase at the basolateral membrane (3Na out and 2 K in)
how does the reabsorption of Na also drive H20 and Cl reabsorption
standing osmotic gradient where water follows sodium by water and the oncotic drag of the peritubular plasma
how is glucose reabsorbed in the PT
con transport with Na out of lumen and then facilitated diffusion at basolateral membrane
when does glucose reabsorption stop in the PT
at the transport maximum when all the cotransporters are fully saturated - 2 mol/min
what is the function of the loop of henle
generates portico-medullary solute concentration gradient to create concentrated urine
how is countercurrent flow created in the loop of Henle
descending (first) and ascending (second) limb travel in opposite direction
what does the ascending limb (2nd) loop of henle reabsorb
Na and Cl - very little/ no water follows
what is the difference between transport in the thick upper part of the ascending limb and the lower thinner part
upper part is active transport and lower part is passive
what does the descending limb (1st) of the loop of Henle reabsorb
water - no active salt reabosrption
how is Na and Cl reabsorbed in the thick ascending loop of henle
triple-cotransporter of K, Na and Cl called TALH (K then leaks back into lumen filtrate)
1) Solute is removed from the lumen in the ______ limb and ____ cannot follow, making the filtrate ___tonic with a ___ osmolarity
ascending, water, hypo, low (it is diluted)
2) Tubular fluid becomes diluted and causes the interstitial fluid between the ascending and descending limb to become ___ tonic as the solute cannot renter the tubules
hyper (is concentrated)
3)due to the high osmolarity in the interstitial ___ leaves the ____ limb by ___
water, descending, osmosis, greater
4) the tubular fluid in the descending limb becomes ___tonic and has a ___ osmolarity due to water following it’s concentration gradient and leaving the filtrate
hyper, high (concentrated)
5) what happens to the water after it has diffused out the descending limb into the hypertonic interstitium
it is reabsorbed into capillaries
how does the urea cycle affect the medullary osmolarity
adds solute to the interstitial which adds to the medullary osmolarity
in the loop of Henle, which is a larger gradient vertical or horizontal?
vertical
why is the counter current multiplication in the loop of henle useful in regards to ADH levels
kidneys can still produce concentrated urine despite varying ADH levels
what is the vasa recta
arterioles and venules that run the length of the kidney
what is the purpose of the vasa recta
water and solute is absorbed into the blood supply instead of being washed away in the medulla