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Flashcards in packet 25 Deck (19)

Na+ antiporters reabsorb Na+ and secrete H+
-PCT cells produce the H+ & release bicarbonate ion to the peritubular capillaries
-important buffering system

Reabsorption of Bicarbonate, Na+ & H+ Ions


on test as fill in the blank

Reabsorption of Bicarbonate, Na+ & H+ Ions

For every H+ secreted into the tubular fluid, one filtered bicarbonate eventually returns to the blood


-Electrochemical gradients produced by symporters & antiporters causes passive reabsorption of other solutes

-Cl-, K+, Ca+2, Mg+2 and urea passively diffuse into the peritubular capillaries

-Promotes osmosis in PCT (especially permeable due to aquaporin-1 channels

Passive Reabsorption in the 2nd Half of PCT



blood to tubule



tubule to blood


Ammonia (NH3) is a poisonous waste product of protein deamination in the liver
--most is converted to urea which is less toxic

secretion of NH3 and NH4 in PCT


Both ammonia & urea are filtered at the
--PCT cells deaminate glutamine in a process that generates both NH3 and new bicarbonate ion.

glomerus and secreted in the PCT


Bicarbonate diffuses into the bloodstream during __ where more bicarbonate is generated



--Tubular fluid
--Sets the stage for independent regulation of both volume & osmolarity of body fluids

Reabsorption in the Loop of Henle


--PCT reabsorbed 65% of the filtered water so chemical composition of tubular fluid in the loop of Henle is quite different from plasma

--since many nutrients were reabsorbed as well, osmolarity of tubular fluid is close to that of blood

tubular fluid in Reabsorption in the Loop of Henle


--Thick limb of loop of Henle has Na+ K- Cl- symporters that reabsorb these ions

--K+ leaks through K+ channels back into the tubular fluid leaving the interstitial fluid and blood with a negative charge

--Cations passively move to the vasa recta

symporters in the loop of henle


--Removal of Na+ and Cl- continues in the DCT by means of Na+ Cl- symporters

--Na+ and Cl- then reabsorbed into peritubular capillaries

Reabsorption in the DCT


major site where parathyroid hormone stimulates reabsorption of Ca+2
---not very permeable to water so it is not reabsorbed with little accompanying water



--By end of DCT, 95% of solutes & water have been reabsorbed and returned to the bloodstream

--Cells in the collecting duct make the final adjustments

Reabsorption & Secretion in the Collecting Duct


two types of cells in the collecting duct make the final adjustments

principal cells
intercalated cells


reabsorb Na+ and secrete K+

principal cells


reabsorb K+ & bicarbonate ions and secrete H+

intercalated cells


actions of principal cells
**micro essay?

1. Na+ enters principal cellsthrough leakage channels

2. Na+ pumps keep theconcentration of Na+ inthe cytosol low

3. Cells secrete variableamounts of K+, to adjustfor dietary changes in K+intake
--down concentration gradient due to Na+/K+ pump

4. Aldosterone 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

actions of intercalated cells
**micro essay

1. Proton pumps (H+ATPases) secrete H+ into tubular fluid
--can secrete against
a concentration
gradient so urine
can be 1000 times
more acidic than

2. Cl-/HCO3- antiporters move bicarbonate ions into the blood
--intercalated cells
help regulate pH of
body fluids

3. Urine is buffered by HPO4 2- and ammonia, both of which combine irreversibly with H+ and are excreted