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Tubular Mechanisms


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PCT is what?
Proximal convoluted tubule
in the PCT, what is:
100% Glucose/Amino acids
70% Water, Na, and K+
Secreted: 100% PAH
What happens to filtrate osmolarity at the PCT?
It does not change.
What are the 4 steps of reabsorption in the PCT?
1. Na/K pump makes [Na] low inside PCT cells; Na is reabsorbed.
2. Na reabsorption makes Glucose/AA move into PCT cell up conc. gradient
3. They move into capillary via facilitated diffusion.
4. Water follows them and gets reabs by SIMPLE diffusion (to maintain osmolarity).
what type of transport is
-Na reabsorption
-Glu/AA reabsorption from lumen to PCT cell
-Sodium is primary active transport
-Glu/AA is secondary - uses the energy from Sodium's transport.
what is the brush border membrane, and where is it?
the membrane on the inside of the PCT lumen, with increased surface area for enhanced reabsorption.
What are the 4 (really 5) steps of secretion in the PCT?
1. Na/K pump makes low [Na] inside the PCT cell
2a. Na moves from blood to cell.
2b. a-ketoglutarate moves into cell using energy from #2
3. a-ketoglu moves BACK down its conc. gradient into blood, 4. Allows PAH to move UP its conc. gradient. into PCT cell.
Type of transport when using a-ketoglu's energy to move PAH from blood to PCT cells:
Tertiary active transport (because a-ketoglu used Na's energy in the first place).
What occurs in the
-Descending loop of Henle
-Ascending loop of Henle

What general part of the kidney is this?

Asc: Na and Cl are reabsorbed - no water!

-In the renal medulla.
What are the 3 step of reabsorbption in the Asc loop?
1. Na/K pump makes [Na] low inside PCT cells.
2. Na moves in from lumen, Cl also but UP its conc. gradient.
3. Water STAYS in the lumen; the filtrate becomes hypotonic to the outside.
Why is H2O not reabsorbed in the ascending loop?
b/c membrane is impermeable, due to TIGHT JUNCTIONS between the cells of the membrane.
What happens to the ISF during reabsorpn of NaCl in asc loop?
Becomes concentrated - if it's a juxtamed. nephron, this allows for urine concentration.
What occurs in the distal convuluted tubule (DCT)?
-same processes as in the ascending loop - reabsorption of NaCl, but not water.
-Tubule fluid becomes 50 mOsm - more hypotonic.
when NaCl are reabsorbed, what types of conc. gradients are being fought?
Na isn't - moves DOWN conc. grd.

Cl is - moves UP its conc. grad.
what is the distal nephron composed of?
-Distal Convoluted Tubule (DCT)
-Collecting Duct
What occurs in the collecting duct?
Fine tuning of the filtrate by HORMONE ACTION.
what hormones are responsible for finetuning the filtrate in the collecting duct?
-ADH (antidiarrh. hormone)
How does Aldosterone work in the collecting duct?
Steroid action produces more Na/K pumps; causes increased -Sodium reabsorptn
-Potassium secretion.
How does ADH work in the collecting duct?
Makes membrane H2O-permeable, thus increased H2O reabsorptn.
a. Low ADH makes dilute urine.
b. High ADH = it concentrated.
how does ADH affect urine volume?
High ADH = small amounts of concentrated urine.

Low ADH = large amounts of dilute urine.
What does Alcohol do to ADH?
well you pee a lot so you have large amts of dilute urine so ADH is low = alcohol inhibits its formation.

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