Lecture 9 - Regulation of Body Fluid pH

Question 1

What are sources of H+ ions?

Answer 1

• ingested protein metabolism
• food
• medications
• cell metabolism
• disease
• metabolid intermediate by products

Question 2

What are the buffers systems in the ICF and ECF?

Answer 2

ICF: phosphates, amino acids

interstitium: H₂CO₃ / HCO₃^-
plasma: Hb, plasma proteins and H₂CO₃ / HCO₃^-

Question 3

What is carbonic acid buffer system?

Answer 3

CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃^-

Question 4

What are the three defences in pH?

Answer 4

• chemical buggering - seconds
• respiratory - minutes
• renal - days

Question 5

What are normal aterial blood gas levels?

Answer 5

pH: 7.4

CO₂: 40mmHg

HCO₃^-: 24mmol/L

Question 6

What can H ions react with to be excreted?

Answer 6

HPO₄^2- - but loads is reabsorbed

NH₃ - most removed this way

Question 7

How does H add onto HCO₃^-?

Answer 7

1. Na moves down EC gradient and exchanges with H via antiporter system
2. H combines with filtered HCO₃^- to form carbonic acid
3. this disaccoiated via carbonic anhydrase to form CO2 and H2O
4. CO2 diffuses into PCT cell and recombines with water
5. this combines via carbonic anhydrase to form carbonic acid which disaccoiates into H and HCO3
6. HCO3 can be reabsorbed

Question 8

How does the renal phosphate buffer system work?

Answer 8

• HPO₄^2- + H⁺ forms H₂PO₄^-
• H₂PO₄^- excreted (titratable acid)
• new HCO₃^- generated by renal tubules

same as renal ammonia buffer system

Question 9

Describe respiratory acidosis.

What levels would you expect?

In what cases can it occur?

What can occur for compensation?

Answer 9

low pH as a result of high CO₂

occurs during hypoventilation, lung problems etc

lungs are a problem, so kidneys fix by:

• peripheral chemoreceptors detect
• more renal excretion and secretion of H
• more renal reabsorption and generation of HCO3^-

Question 10

Describe respiratory alkalosis.

What levels would you expect?

In what cases can it occur?

What can occur for compensation?

Answer 10

high pH due to less CO₂

hyperventilation, anxiety, aspirin overdose, pneumonia

lungs are a problem, so kidneys fix by:

• peripheral chemoreceptors detect
• more renal excretion and secretion of HCO3-
• more renal reabsorption and generation of H

Question 11

Describe metabolic acidosis.

What levels would you expect?

In what cases can it occur?

What can occur for compensation?

Answer 11

low pH due to low HCO₃^-

occurs if diarrhoea, ingested aspirin/NSAIDS, accumulation of acid, exercise as lactic acid produced

lungs will hyperventilate to remove CO₂ and kidneys will:

• peripheral chemoreceptors detect
• more renal excretion and secretion of H
• more renal reabsorption and generation of HCO3-

Question 12

Describe metabolic alkalosis.

What levels would you expect?

In what cases can it occur?

What can occur for compensation?

Answer 12

high pH due to less H

result of vomiting, alkaline drugs, excessive intake of fruits

lungs will hypoventilate to retain CO2 and kidneys will:

• peripheral chemoreceptors detect
• more renal excretion and secretion of HCO3
• more renal reabsorption of H