Lecture 25 Flashcards
Reabsorption of Bicarbonate, Na+ & H+ Ions: What reabsorbs Na+ and secretes H+?
- Na+ antiporters
- PCT cells produce the H+ & release bicarbonate ion to the peritubular capillaries
- important buffering system
***For every H+ secreted into the tubular fluid,
one filtered bicarbonate eventually returns to the blood
secretion =
blood to tubule
reabsorption =
tubule to blood
Passive Reabsorption in the 2nd Half of PCT: Electrochemical gradients produced by
symporters & antiporters causes passive reabsorption of other solutes
What passively diffuses into peritubular capillaries?
Cl-, K+, Ca+2, Mg+2 and urea
What promotes osmosis in PCT?
Passive Reabsorption in the 2nd Half of PCT-
VERY permeable because of aquaporin-1 channels
Ammonia (NH3) is a
- poisonous waste product of protein deamination in the liver
- most is converted to urea which is less toxic
Both ammonia & urea are
filtered at the glomerus & secreted in the PCT
PCT cells do what?
deaminate glutamine in a process that generates both NH3 and new bicarbonate ion.
Bicarbonate diffuses into what?
-the bloodstream
-
during acidosis more what is generated?
bicarbonate
Reabsorption in the Loop of Henle:
- Tubular fluid
- Sets the stage for independent regulation of both volume & osmolarity of body fluids
Tubular fluid has PCT that does what?
-reabsorb 65% of the filtered water so chemical composition of tubular fluid in the loop of Henle is quite different from plasma
Osmolarity of tubular fluid is close to that of blood because why?
Since many nutrients were reabsorbed as well
Symporters in the Loop of Henle: Thick limb of loop of Henle has
Na+ K- Cl- symporters that reabsorb these ions
Symporters in the Loop of Henle: K+ leaks through
K+ channels back into the tubular fluid leaving the interstitial fluid and blood with a negative charge
Symporters in the Loop of Henle: Cations do what?
passively move to the vasa recta
Reabsorption in the DCT: 1. Removal of Na+ and Cl- continues in
the DCT by means of Na+ Cl- symporters
Reabsorption in the DCT: 2. Na+ and Cl- then reabsorbed into
peritubular capillaries
***DCT is major site
where parathyroid hormone stimulates reabsorption of Ca+2
***DCT is not very permeable to
water so it is not reabsorbed with little accompanying water
Reabsorption & Secretion in the Collecting Duct: By end of DCT,
95% of solutes & water have been reabsorbed and returned to the bloodstream
***Reabsorption & Secretion in the Collecting Duct: 2 Cell types in the collecting duct make the final adjustments
- Principal cells
2. Intercalated cells
***Principal cells do what?
reabsorb Na+ and secrete K+
***Intercalated cells do what?
reabsorb K+ & bicarbonate ions and secrete H+ (buffering, ex. pH)
Actions of the Principal Cells: 1st step
Na+ enters principal cellsthrough leakage channels
Actions of the Principal Cells: 2nd step
Na+ pumps keep theconcentration of Na+ inthe cytosol low
Actions of the Principal Cells: 3rd step
Cells secrete variableamounts of K+, to adjustfor dietary changes in K+intake
-down concentration gradient due to Na+/K+ pump
Actions of the Principal Cells: 4th step
Aldosterone (hormone) increases Na+ and water reabsorption & K+ secretion by principal cells by stimulating the synthesis of new pumps and channels
Secretion of H+ and Absorption of Bicarbonate by Intercalated Cells: 1st Step =
Proton pumps secrete H+ into tubular fluid
-can secrete against a concentration gradient so urine can be 1000 times more acidic than blood
Secretion of H+ and Absorption of Bicarbonate by Intercalated Cells: 2nd Step =
Cl-/HCO3- antiporters move bicarbonate ions into the blood
-intercalated cells help regulate pH of body fluids
Secretion of H+ and Absorption of Bicarbonate by Intercalated Cells: 3rd Step =
Urine is buffered by HPO4 2- and ammonia, both of which combine irreversibly with H+ and are excreted
-get rid of waste w/o destroying body
