Renal Lectures 6 and 7

Question 1

What in the diet contributes to H+ input?

Answer 1

Fatty acids and amino acids

Question 2

What in the metabolism contributes to H+ input??

Answer 2

CO2 (+ H2O) - forms carbonic acid
Lactic acid
Ketoacids

Question 3

How does ventillation affect H+ output?

Answer 3

Volatile acids - CO2 (+ H2O) - forms carbonic acid

Question 4

How do the kidneys affect H+ output?

Answer 4

Fixed acids (H+)

Question 5

What buffers are involved in plasma pH?

Answer 5

Bicarbonate in ECF
Proteins, hemoglobin, phosphates in cells
Phosphates and ammonia in urine

Question 6

Normal plasma pH

Answer 6

7.38-7.42

Question 7

Alkalosis

Answer 7

Above 7.45

Question 8

Acidosis

Answer 8

Below 7.35

Question 9

Carbonic acid (H2CO3) formation (hydration reaction)

Answer 9

From CO2 and H2O, catalyzed by the enzyme carbonic anhydrase.

Question 10

Carbonic acid dissociates spontaneously to bccome

Answer 10

bicarbonate and H+

Question 11

Alkalodic

Answer 11

Usually alkalosis. You rely on kidneys to get rid of bases, as meat promotes acidosis.

Question 12

Effect of vomiting on GI system pH

Answer 12

Lose acidic stomach content, bicarbonate bicarbonate left over

Question 13

Lower gut - acidosis or alkalosis

Answer 13

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

Question 14

Upper gut - acidosis or alkalosis

Answer 14

Alkalosis becomes H+ needed in stomach lumen, so other HCO3 from H2CO3 goes into interstial fluid and crosses wall to blood vessel

Question 15

Effect of diarhea on GI system pH

Answer 15

Acidosis because bicarbonate used tp neutralize feces for secretion, lots of H+ left over

Question 16

Henderson-Hasslebeck eqn.

Answer 16

For: HA H+ + A-
We use:
pH=pK +log[A-]/[HA]

Question 17

What does it mean if pH = pK

Answer 17

There is an equal concentration of acid and HA and A-.

Question 18

A good buffer

Answer 18

pK matches pH so it comprises binding and giving up of H+.

Question 19

What is the pH and pK of carbonic acid as a buffer

Answer 19

pK=6.1
pH=7.4
Use PCO2 (about 40mmHg) and [HCO3-] (12mmol)
pH = 6.1 + log [HCO3-]/0.03*PCO2

Question 20

Does the kidney ever lose bicarbinate

Answer 20

100% of filtered bicarbonate is reclaimed by the kidney - none exits in urine.
80% in PT, 15% in TAL, 5% in CCD

Question 21

Explain how the proximal tubule reclaims filtered HCO3-

Answer 21

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.

Question 22

Explain how the distal tubule reclaims filtered HCO3-

Answer 22

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.

Question 23

How is new bicarbonate generated using buffers?

Answer 23

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.

Question 24

Where is NH4 produced?

Answer 24

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.

Question 25

What happens if the kidney doesn’t excrete the NH4+ into urine?

Answer 25

It goes to the liver and is converted to urea. This generates H+ which requires HCO3- to buffer. By consuming HCO3-, it negates the synthesis of new HCO3- by the synthesis of NH4+.

Question 26

Why does ammonia have to go to the liver?

Answer 26

It needs to be detoxified; urea is the non-toxic form.

Question 27

Assuming the ammonia doesn’t go to the liver, what happens in the proximal tubule?

Answer 27

Two molecules of NH4+ are generated and two molecules of 2HCO3-. Both HCO3- go through basolateral membrane into blood while 2NH4 is separated into H+, NH3, and NH4+. The H+ is used for Na+/H+ antiport. The NH4+ can also be antiported in the same antiporter. The NH3 can diffuse across and combines with the pumped H+ to make NH4+ in the urine. NH4+ can be reabsorbed and secreted again throughout the TAT and CD.

Question 28

Respiratory acidoses

Answer 28

Respiration increases PCO2

Correction: More HCO3- reabsorption to compensate.

Question 29

Respiratory alkalosis

Answer 29

Respiration decreases PCO2

Correction: Less HCO3- reabsorption to compensate.

Question 30

Metabolic acidosis

Answer 30

Metabolism decreases HCO3-

Correction: Hyperventilation and more HCO3- reabsorption.

Question 31

Metabolic alkalosis

Answer 31

Metabolism increases HCO3-

Correction: Hypoventilation and more HCO3- secretion.

Question 32

Respiratory Acid-Base relation

Answer 32

pH and [HCO3-] move in opposite directions

pH and PCO2 move in opposite directions

Question 33

Metabolic Acid-Base relation

Answer 33

pH and [HCO3-] move in same direction

pH and PCO2 move in same directions

Question 34

More dangerous - mixed acidosis or mixed alkalosis?

Answer 34

Acidosis

Question 35

Mixed respiratory acidosis and metabolic alkalosis

Answer 35

No pH change but serious issue with HCO3- and CO2 level