Proximal Tubule and Loop of Henle Flashcards
What do the kidneys reabsorb?
99% fluid and salt
100% glucose and amino acids
50% urea
0% creatinine
What amount of filtered fluid is reabsorbed in the proximal tubule?
80 ml/min
What is iso-osmotic with filtrate?
fluid reabsorbed in the proximal tubule
What is secreted in the proximal tubule?
H Hippurates NTs Bile pigments Uric acid Drugs Toxins
What is reabsorbed in the pT?
sugars amino acids phosphate sulphate lactate
What are the steps involved with tubular reabsorption?
transcellular
paracellular
What are the types of carrier mediated transport?
primary active transport
secondary active transport
facilitated diffusion
What diffuses through lipid bilayer?
O2 and CO2
What diffuses through channels?
Na
What is facilitative diffusion molecule?
glucose
What is reabsorbed through primary active transport?
K and Na through Na-K ATPase - essential for Na reasborption
What is reabsorbed through secondary active transport?
Na and Glucose
What is the iso-osmotic fluid reabsorption across leaky PT due to?
standing osmotic gradient
oncotic pressure gradient
How is glucose absorbed into the tubular epithelial cell?
SGLT
How is water reabsorbed?
through the NaCl osmotic gradient
What is the transport maximum for glucose?
2mmol/min
What is the renal threshold for glucose?
10-12mmol/l
What happens when Tm is reached?
clearance of reabsorbed or secreted substances is not constant
What is Na reabsorption driven by?
Na-K ATPase
What is the osmolarity of the tubular fluid?
300mosmol/l
What is the function of the loop of henle?
generates a cortico-medullary solute concentration gradient
WHat does the solute concentration gradient allow?
the formation of hypertonic urine
How does the loop function?
as a countercurrent multiplier
What is the function of the ascending limb?
Na and Cl reabsorbed in thick ascending limb
impermeable to water
What is the function of the descending limb?
does not reabsorbed NaCl
highly permeable to water
What ensures that NaCl is absorbed into the interstitial fluid?
K recycling
What allows K recycling and Na, Cl reabsorption?
NKCC channel
What blocks the NKCC channel?
loop diuretics
What is the effect of solute being removed in the ascending limb?
tubular fluid is diluted and osmolality of interstitial fluid is raised
How is the osmolality maintained?
interstitial solute cannot enter the descending limb
What does the high osmolality allow?
water to leave descending limb by osmosis
What type of fluid moves into the distal tubule?
200mOsmol/l
What is the osmolarity at the renal pelvis?
1200mosmol/l
What contributes to approx half of the medullary osmolality?
the urea cycle
Where is urea impermeable?
the distal tubule
Where is 50% of urea absorbed?
the collecting duct
Where does urea diffuse passively?
into the loop of henle
What is the purpose of countercurrent multiplication?
to concentrate the medullary interstitial fluid
Why is counter current multiplication important?
to enable the kidney to produce urine of different volume and concentration according to the amounts of circulating ADH
What is the Vu on normal fluid intake?
around 1ml/min
what is the counter current exchanger?
the vasa recta run alongside the long loop of henle of the juxtamedullary nephrons
Where does blood osmolality rise?
as it dips into the medulla - water loss and solute gained
Where does blood osmolality fall?
as it rises back to the cortex - water gained and solute lost
How does the countercurrent system solve the problem of NaCl being washed away by essential blood flow?
vasa recta capillaries follow hairpin loops
vasa recta capillaries freely permeable to NaCl and water
Blood flow to vasa recta is low
What is the function of the countercurrent exchange?
ensures that solute is not washed away
