Tubular Mechanisms
Terms
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- PCT is what?
- Proximal convoluted tubule
-
in the PCT, what is:
-Absorbed
-Secreted -
Absorbed:
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).
3.
3. -
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? -
Desc: WATER IS REABSORBED.
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?
-
-Aldosterone
-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.