Chapter 9 Flashcards
What cells secrete bicarbonate in the kidney and where are they located?
In the Type B intercalated cells, in the distal nephron
How do kidneys excrete an acid load and replace bicarbonate deficit?
Bicarb is generated from CO2 and water. In this process, hydrogen are also generated which need to be eliminated.
All the filtered bicarbonate is reabsorbed, then the kidneys secrete additional hydrogen ions that attach to bases in the tubular fluid (not bicarb). The new protonated base is excreted.
At the same time, the bicarbonate generated is transported across the basolateral membrane into the blood via anti porters called AE1, replacing the loss of bicarb when the acid load entered the body.
What are the two important steps to restore bicarbonate plasma level?
- Generation of new bicarbonate
- Excretion of hydrogen ions on non bicarbonate bases.
If there were no new bicarb, plasma levels would not be restored, and if hydrogen ions were not excreted, they would recombine with the bicarb just generated.
How is hydrogen excreted and what are the products?
Hydrogen ion is excreted associated with phosphate (filtered bases) but as it is not enough, the rest is excreted as ammonium (ammonia genesis).
Ammonium in small quantities is toxic, the liver converts it in which products?
urea and glutamine –> completion of the catabolism of protein = acid-base neutral.
Where is glutamine released and taken up?
Released by liver and taken up by proximal tubule cells
How can we quantify the amount of acid/base excretion?
Looking at 3 quantities in the urine:
1) Amount of titratable acidity (amount of acid that was taken up by urinary bases other than ammonia).
2) Amount of Ammonium
3) Amount of Bicarbonate
How do the kidneys detect the acid-base status of the body?
kidneys detect intra/extracellular pH and intracellular bicarbonate.
There are pH-dependant membranes receptors that activate G-protein-coupled signaling pathway and pH-dependent ion channels.
Kidneys act as a “pH meters”, bicarbonate detector, and PCO2 detector, and adjust their transport of hydrogen, bicarbonate excretion accordingly.
What are some examples of renal /non renal mechanisms that acidify or alkalinize the blood?
see table
If the PCO2 is low, how do the kidneys compensate it?
By decreasing the plasma concentration of bicarbonate
How do the kidneys respond to acidosis?
Increasing acid excretion and bicarbonate production
What is Fanconi syndrome and to what does it lead?
Impaired transport of substances in the proximal tubule. Lead to proximal RTA (type 2) (renal tubular acidosis).
What is the “Classic distal RTA” (type 1) ?
Defect in acid secretion by type A intercalated cells in the distal nephron.
Which RTA is associated with hypoaldosteronism or pseudohypoaldosteronism? And what is the consequence of this disorder?
Hyperkalemic RTA (type 4).
Metabolic acidosis (hyperkalemia reduces the ability to take up glutamine and synthesize ammonium).
