formation of urine- reabsorption

what are the 2 surfaces in the kidney tubule

• apical surface

• basolateral surface

what is the kidney tubule lined with

• epithelium

• tight junctions

basolateral surface in the kidney tubule

• where epithelial cells sit

• faces the body, serosal side

apical surface in kidney tubule 

in contact with tubular lumen 

what are there different thing of in different parts of the tubule 

different transporter in different parts of the tubule to perform differing roles 

where are the NaK-ATPases found in the kidney tubule 

• basolateral surface 

• plays a critical role throughout

where does most tubular reabsorption occur

in the proximal tubule

what is the percentage of water and Na+ reabsorbed in the proximal tubule

60-70%

when Na+ moves into the lumen does it go up or down the gradient

down

when glucose, amino acids, phosphates, or lactates move into the lumen do they move up or down the gradient 

up 

when glucose, amino acids, phosphates, or lactates move out of the lumen do they move up or down the gradient 

down 

what is the passive transporter used in the movement of glucose in and out of the lumen 

• SGLT-2 —> in

• GLUT-2 —> out 

what way does water move in the tubular lumen

follows osmotically via the paracellular route

what happens in the proximal tubule

• Na+ moves out and K+ moves in via Na+K+-ATPase

• leak channels move K+ out of the cell

• carbonic anhydrase converts water and CO2 into carbonic acid which splits into a proton and a bicarbonate ion

• bicarbonate ion can move out of the cell and into the blood

• Na+ can move in and H+ moves out via an Na+ H+ exchanger

• proton moves into tubular fluid making urine acidic

• proton joins bicarbonate ion to make carbonic acid, carbonic anhydrase converts to water and CO2 and they move into lumen

is there a higher gradient in the outer medulla or inner medulla

inner medulla

what does the descending limb contain

• aquaporins

• allow water to pass through

what is the descending limb permeable to

water

what is the ascending limb permeable to

• NaCl

• impermeable to water

• no aquaporins and tight junctions are tight 

• water cant move back in 

• dilution of tubular fluid 

what happens in the ascending limb of Henles loop

• Na+ moves out of cell to blood and K+ moves in via NaK- ATPase

• Na, K, and Cl move into cell from lumen via a NKCC2 transporter 

• Cl leaves cell to blood through channels 

what is the distal tube highly impermeable to

water

what happens in the distal tubule

• Na+ moves out of cell into blood and K+ moves in via NaK-ATPase

• Na and Cl move in from lumen and K leaves cell to go to lumen via NCC transporter

how does water move through in the collecting ducts

through aquaporins (not paracellular)

what does the collecting duct pass through

• the medulla

• high osmolarity

where does the regulation of formation of dilute or conc. urine occur

• mainly in collecting duct

• controlled by hormones

what does the collecting duct allow for

reabsorption of final bit of H2O

what happens in the collecting tubule 

• H2O moves in and out of cell through aquaporins- ADH increases the number of aquaporins

• Na+ moves in through a channel and out of cell with K+ moving in through NaK-ATPase

• aldosterone stimulates synthesis of ATPase

what does ADH in the collecting duct do

increases permeability and increases reabsorption of water

how is aldosterone formed

• renin formed into angiotensinogen 

• angiotensinogen formed into angiotensin 1

• angiotensin 1 formed into angiotensin 2

• angiotensin 2 formed into aldosterone