Renal Physl 18 Flashcards
What takes care of the majority of pH disturbances?
Buffer systems and ventilation
What are the two ways kidneys can alter pH?
- Reabsorption or excretion of H+
* Modifying HCO3- reabsorption or excretion
How is H+ affected by the kidneys during acidosis?
The kidneys secrete H+ into tubule lumen
What are buffers in the kidneys?
Ammonia from amino acids, and phosphate ions (HPO4 2-)
What are large amounts of hydrogen ions trapped as in the kidneys?
NH4+ and H2PO4- which is excreted
What do the buffers in the kidneys help with?
Excretion of H+ excretion by binding to them in the lumen
What do the kidneys generate during the excretion of H+ ions?
Bicarbonate ions from carbon dioxide and water
What can the carbon dioxide and water produced in the kidney do?
Go into the bloodstream and act as a buffer and help increase pH
What happens in the kidneys during alkalosis?
HCO3- is secreted and H+ is reabsorbed to help restore pH
How long do renal response to acidosis or alkalosis take?
24-48 hours
What does the apical Na+-H exchanger do?
Brings sodium into the cell and H+ into the lumen against its concentration gradient
What does the Basolateral Na+- HCO3- symporter do?
Moves Na+ and HCO3- out of the cell and into the interstitium. Using the energy from bicarbonate moving down its concentration gradient
What does H+ ATPase (proton pump) do?
Pumps H+ into the lumen of distal nephron against its concentration gradient
What does the H+ K+ ATPase do?
Pumps H+ into urine in exchange for K+ and can contribute to potassium homeostasis
What does the Na+ NH4+ antiporter do?
Puts NH4+ into the lumen in exchange for Na+
What part of the nephron plays an important role in hydrogen secretion and bicarbonate reabsorption?
The proximal tubule
What happens to most of the bicarbonate that is filtered by the kidneys?
It is reabsorbed to maintain the body’s buffer systems
Which tubule reabsorbs most bicarbonate?
The proximal tubule
What two ways does the proximal tubule reabsorb bicarbonate?
- Filtered bicarbonate is converted into carbon dioxide which is then converted back into bicarbonate for reabsorption
- Using the amino acid glutamine
Why does the proximal tubule need to reabsorb bicarbonate indirectly?
Because there is no apical membrane transporter
How is filtered bicarbonate is converted into carbon dioxide which is then converted back into bicarbonate for reabsorption?
- Hydrogen is secreted from the proximal tubule epithelial cell into the lumen opposite of sodium which is pumped into the cell using the Apical Na+-H+ exchanger (NHE)
- Carbonic anhydrase bound to the apical membrane combines the secreted hydrogen with filtered carbonate to form carbon dioxide in the lumen
- The carbon dioxide then diffuses from the lumen into the tubule cell
- Within the cell carbon dioxides combines with water to form carbonic acid which dissociates to hydrogen and bicarbonate
- The bicarbonate can be transported out of the cell using the Na+ HCO3- symporter which put it into the interstitium
What is the process for bicarbonate reabsorption and H+ excretion using amino acid metabolism?
- Glutamine in the proximal tubule cell is metabolized to alpha ketoglutarate and NH4+ (ammonium ion)
- Ammonium is transported into the lumen in exchange for sodium and is excreted
- Alpha ketoglutarate is further metabolized to form bicarbonate which is transported into the blood along with sodium
What is acid base balance closely regulated by in the distal nephron?
Intercalated cells
What type of cells are the target of aldosterones actions?
Principle cells
What do intercalated cells have a high level of?
Carbonic anhydrase so they can rapidly convert carbon dioxide and water into hydrogen ions and bicarbonate
What does the intercalated cells do to the H+ they produce?
They are pumped out of the cells by the hydrogen ATPase or the hydrogen potassium ATPase
What does the intercalated cells use to move the bicarbonate they produce?
It enters the interstitium by the bicarbonate chloride antiporter
What do Type A intercalated cells do during acidosis?
Secrete hydrogen ions and reabsorb bicarbonate
What do type B intercalated cells do during alkalosis?
Secrete bicarbonate and reabsorb H+ ions
What is different for how type A intercalated cells secrete H+ during acidosis vs the proximal tubule?
The apical hydrogen ATPase and hydrogen potassium ATPase is used rather than the sodium hydrogen antiporter
How do type B intercalated cells reabsorb H+ during alkalosis?
They reabsorb hydrogen ions by transport into the interstitium on the basolateral side of the cell while bicarbonate is secreted into the lumen
