Renal Lectures 6 and 7 Flashcards
What in the diet contributes to H+ input?
Fatty acids and amino acids
What in the metabolism contributes to H+ input??
CO2 (+ H2O) - forms carbonic acid
Lactic acid
Ketoacids
How does ventillation affect H+ output?
Volatile acids - CO2 (+ H2O) - forms carbonic acid
How do the kidneys affect H+ output?
Fixed acids (H+)
What buffers are involved in plasma pH?
Bicarbonate in ECF
Proteins, hemoglobin, phosphates in cells
Phosphates and ammonia in urine
Normal plasma pH
7.38-7.42
Alkalosis
Above 7.45
Acidosis
Below 7.35
Carbonic acid (H2CO3) formation (hydration reaction)
From CO2 and H2O, catalyzed by the enzyme carbonic anhydrase.
Carbonic acid dissociates spontaneously to bccome
bicarbonate and H+
Alkalodic
Usually alkalosis. You rely on kidneys to get rid of bases, as meat promotes acidosis.
Effect of vomiting on GI system pH
Lose acidic stomach content, bicarbonate bicarbonate left over
Lower gut - acidosis or alkalosis
Acidosis because gain of H+ in blood vessel (don’t want chyme to be acidic anymore) and HCO3- is secreted into gut, leaving H+ behind from H2CO3 in interstitial fluid
Upper gut - acidosis or alkalosis
Alkalosis becomes H+ needed in stomach lumen, so other HCO3 from H2CO3 goes into interstial fluid and crosses wall to blood vessel
Effect of diarhea on GI system pH
Acidosis because bicarbonate used tp neutralize feces for secretion, lots of H+ left over
Henderson-Hasslebeck eqn.
For: HA H+ + A-
We use:
pH=pK +log[A-]/[HA]
What does it mean if pH = pK
There is an equal concentration of acid and HA and A-.
A good buffer
pK matches pH so it comprises binding and giving up of H+.
What is the pH and pK of carbonic acid as a buffer
pK=6.1 pH=7.4 Use PCO2 (about 40mmHg) and [HCO3-] (12mmol) pH = 6.1 + log [HCO3-]/0.03*PCO2
Does the kidney ever lose bicarbinate
100% of filtered bicarbonate is reclaimed by the kidney - none exits in urine.
80% in PT, 15% in TAL, 5% in CCD
Explain how the proximal tubule reclaims filtered HCO3-
The HCO3+ that is filtered recieves H+ when Na+ crosses into the interstial space in exchange for H+. They combine in the tubular fluid to H2CO3, and using CA, become H2O and CO2. These can now be absorbed, and will recombine to form carbonic acid. They will dissociate into bicarbonate and protons in the cell. The protons will exits again via the exchanger whilt the bicarbonate will channel across into the blood.
Explain how the distal tubule reclaims filtered HCO3-
Tubular fluid, which contains HCO3-, will recieve H+ via ATPase pumps. Makes H2CO3 and into CO2 and H2O. Will diffuse into the secreting cell and use carbonic anhydrase to become carbonic acid and then protons and bicarbonate again. Protons pumped back across into tubular fluid, HCO3- channeled into blood.
How is new bicarbonate generated using buffers?
Filtered HPO42- and SO42- are buffers in the filter, that combine with H+ to make H2PO4 and HSO4-. These are titratable acids in the urine. Meanwhile, H2O and CO2 are absorbed from the blood into the cell, combines with carbonic anhydrase to make HCO3-, and then diffuses into blood.
Where is NH4 produced?
In the kidneys via the metabolism of glutamine, which also makes HCO3-. However, the formation of new HCO3− via this process depends on the kidneys’ ability to excrete NH4+ in urine.
