Lecture 20: Renal Acid-Base

Question 1

Define acid and base

Answer 1

Acid: compounds that release H+ ions.

Bases: compounds that accept H+

Question 2

Distinguish btw volatile and nonvolatile acids and give examples

Answer 2

Volatile: CO2. Can enter gaseous phase. Excreted from the lungs.

Nonvolatile: fixed acids. Sulfuric acid. Phosphoric acid. Excreted from kidneys

Question 3

Define pH and know the normal pH range of venous and arterial blood.

Answer 3

pH: -log[H+]. P Stands for -log:.

Venous: 7.35
Arterial: 7.4

Question 4

Define equilibrium constant for the dissociation reaction and explain what pKa refers to:

Answer 4

Ka is the equilibrium constant for the dissociation rxn. Where the [ ] ends up at equibrium.

PKa= P stands for -log…..dissociation constant.

Question 5

List the major system in the body that regulate pH

Answer 5

Chemical acid-base buffer systems of the body fluids

Respiratory center.

Kidneys.

Question 6

Define “buffer” and list the important buffer systems in the body.

Answer 6

A substance that can reversible bind H+

3 important buffer systems:
Bicarbonate buffer
Phosphate buffer
Proteins as buffers-not covered..

Question 7

Tell which buffer system is the most important extracellular system.

Answer 7

Bicarbonate buffer system

Question 8

Explain how the bicarbonate buffer system works when a strong acid or a strong base is added

Answer 8

Strong acid: increasing [H+], it’ll combine w. Bicarb and will dissociate to CO2 and water–leads to formation of weak acid.

Strong base: NaOH combines w/ carbonic acid. Forms NaHCO3 + water. Formation of a weak base.

Question 9

Identify the organ that primarily regulates the bicarbonate buffer system

Answer 9

Lungs and kidneys

Mainly kidneys though because [bicarb] is regulated in kidneys

Question 10

Distinguish btw metabolic acid-base disorders and respiratory acid-base disorders *****

Answer 10

Metabolic: change in [bicarbonate] in extracellular fluid

Respiratory:change in [pCO2] in extracellular

Question 11

How does the normal operating pH point for bicarbonate buffer system compare to its pKa?

Answer 11

pH of 6.1 occurs when [ ] of bicarbonate and CO2 are equal

Since it is at equilibrium pH=pKa

Therefore, 6.1 is our pK
6.1=pK
PK=6.1

Question 12

Describe the phosphate buffer system and explain why it is more important as a buffer in the kidney tubular fluids.

Answer 12

Plays role in buffering renal tubular fluid and intracellular fluids Strong acid is replaced by an additional amount of a weak acid and pH change is minimal.

Why its important as buffer in kidney tubular fluids:

• usually becomes greatly [ ]ed in the tubules.
• lower pH of the tubular fluid brings the operating range of the buffer closer to the pK of the buffer system.

Question 13

What is the primary method for removing nonvolatile acids?

Answer 13

Renal excretion

Question 14

What must happen before filtered bicarbonate is reabsorbed?

Answer 14

Bicarbonate must react w/ secreted H+ ion to form carbonic acid before it can be reabsorbed.

Question 15

List the 3 mechanisms by which the kidneys regulate extracellular Hydrogen ion:

Answer 15

1. Kidneys reabsorb filtered bicarbonate ions.
2. Kidneys can secrete H+ ions.
3. Kidneys can produce new bicarbonate ions.

Question 16

Where in the kidney tubules does H+ secretion and bicarbonate reabsorption occur?

Answer 16

H+ Secretion: 2ndary active transport in almost all parts of the tubules except the ascending and descending thin limbs of the loop of henle.
-primary active H+ secretion begins in the late distal tubules in the intercalated cells and involves H-transporting ATPase. SLide 29

bicarbonate reabsorption: proximal tubule(85%), thick ascending loop of henle, collecting duct. Almost all reabsorbed.

Question 17

Describe the mechanism by which bicarbonate ion is reabsorbed:

Answer 17

Bicarbonate and water combine to form carbonic acid. Then it is dissociated to CO2 and water.

Diffuses into tubular cell and new carbonic acid molecule then dissociates to bicarbonate and H+ ion

Bicarbonate then diffuses though basolateral membrane into the interstitial fluid and then into the. Blood

Carbionic anhydsrase is req’d

Question 18

What role is played by carbonic anhydrase?

Answer 18

formation of carbonic acid from CO2 and water.

Question 19

Explain why the bicarbonate ion returned to the extracellular fluid is not the same as that filtered into the tubular lumen

Answer 19

The bicarbonate ion taken up by the pericapillary tubules is formed from the dissociation of carbonic acid into H+ ion and bicarbonate ion. Thus, it is not the same bicarbonate ion that was filtered into the tubular lumen.

Question 20

Explain how bicarbonate ion is normally titrated against H+ and how incomplete titration can be used to correct acidosis or alkalosis
***

Answer 20

Normally, each time a H+ ion is formed in the tubular epithelial cells.
In metabolic acidosis, new bicarbonate ion is added to the extracellular fluid.
In metabolic alkalosis, bicarbonate are removed from extracellular fluid by renal excretion.

Question 21

What is the role of intercalated cells in H+ transport, and where are these cells found?

Answer 21

Intercalated cells: active transport resulting in H+ ion secretion

In late distal renal tubules

Question 22

What is the lower limit of pH that can be achieved in normal kidneys?

Answer 22

4.5

Question 23

Explain how excess H+ is generated

Answer 23

Excess loss of bicarbonate ions is the same as adding H+ ions into the extracellular fluid

This is b/c (CO2) H+ has less HCO3 to combine w. In tubular cells to make carbonic acid to then return bicarbonate to the extracellular..

Simple answer: excess loss of bicarbonate

Question 24

What limits the amount of free H+ that can be excreted

Answer 24

Only a small part of the excess H+ secreted in excess of the filtered bicarbonate ion can be excreted in ionic form in the urine b/c the minimal urine pH is ~4.5 (H+ [ ] =0.03 mEq/L

Question 25

What buffers are important in allowing larger amounts of H+ to be excreted?

Answer 25

Phosphate buffer and ammonia buffer system

Question 26

How does the excretion of excess H+ lead to the formation of new bicarbonate ions?

Answer 26

B/c H+ are excreted by the phosphate buffer system and ammonia buffer system, more CO2 is secreted into tubular cells from the renal interstitial fluid. This combines w/ water and forms carbonic acid (carbonic anhydrase)
This occurs w/ HCO3 coming from gluatmine as well in ammonia buffer system

Question 27

Describe the renal handling of excess base

Answer 27

Reduction in extracellular fluid H+ ion [ ] leads to alkalosis.
–kidneys can correct this by failing to reabsorb all the filtered bicarbonate ion.

This is the same as adding H+ ion to extracellular (thus, fluid pH returns to normal)

Question 28

Explain how the action of the respiratory system can produce acidosis/alkalosis and how the respiratory system can compensate for acid-base disturbances

Answer 28

Decrease [HCO3]= metabolic acidosis

• primary*kidneys will add new bicarbonate
• lungs: increased ventilation rate.

Resp alkalosis: decrease inCO2
-caused by hyperventilation.
Compensation: reduce plasma bicarbonate [ ] caused by renal excretion of bicarbonate