Keef 1 Flashcards
What are the 3 lines of defense to buffer the blood?
1st line of defense: chemical buffering
2nd line of defense: CO2 by the lungs
3rd line of defense: regulation of acid & bicarb by the kidneys
What do the kidneys do to help buffer?
Conserve bicarbonate when you need it
Make new bicarbonate
Excrete excess bicarbonate (during alkalosis)
Excrete fixed acid
Where is bicarb absorbed in the kidney & @ what percentages when the body is in acidosis?
80% reabsorption in the PCT
15% in the ascending limb of the loop of Henle
5% in the late DCT & cortical & beginning medullary collecting duct
How is bicarb reabsorbed in the PCT?
H+ is secreted into the lumen thru the sodium gradient (Na+ reabsorption). It combines w/ bicarb in the lumen & forms carbonic acid. Carbonic anhydrase makes it into CO2 & H20. The CO2 diffuses into the epithelial cell. Carbonic anhydrase in there turns it back into carbonic acid. This dissociates into H+ & bicarb. The bicarb is reabsorbed thru exchange of Cl- into the cell. The H+ is secreted back into the PCT lumen.
What are the 2 types of cells in the DCT? Which is more prevalent?
principal cells & intercalated cells.
principal cells are more prevalent…
Which of the DCT cells is responsible for acid secretion?
alpha intercalated cells
What are the principal cells of the DCT responsible for?
for aldosterone-sensitive sodium reabsorption
T/F Thru the reabsorption of bicarb there is greater excretion of H+.
False. The H+ is mainly cycled thru as a way of reabsorbing bicarb…but secreted H+ doesn’t equate to excreted H+.
In the PCT how low can the pH become?
6.0
Which membrane in the nephron is particularly low to H+ ions?
The DCT membrane. If the H+ gets in the lumen–>it stays there.
T/F there is no carbonic anhydrase on the membrane of the DCT or inside the cells.
False. They are in the cells, but not on the membranes.
How low can the luminal pH get in the distal nephron?
4.4
When there are already so many hydrogen ions in the lumen of the distal nephron…how do you shove more in there?
you do it thru the hydrogen potassium pump & the hydrogen ion pump. These both put hydrogen ions in the lumen thru ATP consumption.
What is a pretty normal pH for your urine?
~pH=6
In an alkalotic patient…what happens to the H+ in the urine…& the bicarb? Where is the biggest difference in bicarb reabsorption?
H+ in the urine decreases
pH of the urine increases to like 7.5 maybe
79% of the bicarb is reabsorbed in the PCT & then you get maybe 1-2% excretion of bicarb (higher fractional excretion).
What are some important uses of carbonic anhydrase inhibitors, such as Diamox?
Antiglaucoma, diuretics, antiepileptics, mountain sickness, glaucoma, gastric & duodenal ulcers, neurological disorders, osteoporosis
What is the story of carbonic anhydrase inhibitors with mountain sickness?
Go to a high elevation Low pO2 Higher ventilation rate Lower PaCO2 Respiratory Alkalosis Take Diamox Carbonic Anhydrase blocked Bicarb excretion pH returned to normal
What is the drawback of taking Diamox for mountain sickness?
the water will follow the bicarb that is excreted & it will also act as a diuretic…
Osmotic Diuresis
Dehydration may result. Need to take fluids.
What are the 2 methods for eliminating fixed acids?
- titratable acids
2. formation of ammonium
How does the whole titratable acid thing work?
HPO4- becomes H2PO4 when the lumen becomes acidic enough–>this allows it to be excreted.
How does the whole ammonium thing work?
Glutamine is broken down in the epithelial cells of the PCT only into ammonium & bicarb. The bicarb is reabsorbed & the ammonium is secreted into the lumen (exchanged with Na+).
- *then the ammonium is reabsorbed.
- *the ammonia is again secreted in the Collecting Duct & it will form ammonium to be excreted.
- *its actions are determined partially by luminal pH
What does aldosterone do to the cells of the collecting duct?
Principal Cells: causes sodium reabsorption & potassium secretion
Intercalated Cells: causes H+ secretion & in proportion to this bicarb reabsorption
How can you determine the bicarb reabsorption rate?
Bicarb Reabsorption Rate=Bicarb Filtered Load - Bicarb Excretion Rate
**b/c the bicarb excretion is negligible, reabsorption rate = filtered load.
What are the 2 things that the kidneys simultaneously do? How?
Make new bicarbonate
Excrete Acid
**the breakdown of H2CO3
