Week 13

Question 1

Why is acid-base regulation so important

Answer 1

pH has a strong influence on nearly all enzymes and many other proteins `

Question 2

What are the 3 primary systems that determine H+ concentration

Answer 2

1. The chemical acid-base buffer systems in body fluids
2. The respiratory centers control breathing and CO2 excretion
3. The kidneys control the excretion of acidic or alkaline urine

Question 3

Bicarbonate Buffer System

Answer 3

CO2 + H2O = H2CO3 = HCO3- + H+
- catalyzed by Carbonic Anhydrase
- Changes in CO2 and H+ concentrations causes shifts in equilibrium

Question 4

How can the bicarbonate buffer system be quantified?

Answer 4

Henderson- Hasselbalch Equation

Question 5

Respiratory control of acid-base balance

Answer 5

• Increases in ventilation increase CO2 excretion leading to decrease in pH
• Increases in arterial PCO2 and/or H+ concentrations stimulate alveolar ventilation through chemoreceptors
• Ventilatory response to increased CO2/H+ limits the magnitude of arterial pH change

Question 6

How would impairment in lung function, such as in severe emphysema, affecting extracellular pH?

Answer 6

Increase in pH due to less gas exchange capacity

Question 7

Renal Control of Acid-base balance

Answer 7

• Control rates of H+ and HCO3- excretion
• H+ secretion and HCO3- reabsorption occur in all parts of the tubules except the thin loop of henle
• Both HCO3- reabsorption and/or H+ secretion act to reduce extracellular H+ in the body

Question 8

How does H+ secretion in the proximal to early distal tubule act on pH

Answer 8

• can only reduce pH in the tubular lumen to 6.7
• this is because Na+/H+ exchange becomes electrochemically unfavorable at low pH

Question 9

How does secretion of H+ in the late distal tubule and collecting duct

Answer 9

• Use apical H+ ATPase which can reduce lumenal pH down to 4.5

Question 10

What is the effect of PCO2 in extracellular fluid on pH

Answer 10

• Increased PCO2 in the extracellular fluid is a key signal increasing H+ secretion and HCO3- reabsorption

Question 11

Respiratory Acidosis or Alkalosis

Answer 11

Extracellular pH disturbance caused by abnormal rates of respiratory CO2 excretion
- generally compensated for by the kidneys

Question 12

Metabolic Acidosis or alkalosis

Answer 12

All other types of extracellular pH disturbance besides those due to abnormal CO2 excretion
- Generally compensated for by the respiratory system