Physiology 8 (easy)

Question 1

Normal plasma pH

Answer 1

7.4

Question 2

Normal [HCO3]p

Answer 2

25 mmol/l

Question 3

Normal arterial PCO2

Answer 3

40mmHg

Question 4

Compensation vs correction of an A-B disturbance

Answer 4

Compensation is the restoration of pH irrespective of what happens to [HCO3-]p and PCO2

Correction of an A-B disturbance is restoration of pH and [HCO3-]p and PCO2 to normal

Question 5

Give examples of when CO2 is retained by body

Answer 5

Chronic bronchitis
Chronic emphysema
Airway restriction (bronchial asthma, tumour)
Chest injuries
Respiratory depression

Question 6

PCO2 and H+

Answer 6

PCO2 drives H+ secretion by the kidney

therefore, CO2 retention stimulates H+ secretion into the filtrate

Question 7

Why does [HCO3]p rise in respiratory acidosis?

Answer 7

Rises because of a) the disorder (see equation) and b) as a result of renal compensation

-correction requires lowering pCO2 by restoration of normal ventilation

Question 8

Causes of respiratory alkalosis

Answer 8

Low inspired PO2 at altitude (hypoxia stimulates peripheral chemoreceptors, hyperventilation lowers PCO2)
Hyperventilatio (fever, brainstem damage)
Hysterical overbreathing

Question 9

What is metabolic acidosis?

Answer 9

Excess H+ from any source other than CO2

Question 10

Causes of metabolic acidosis

Answer 10

Ingestion of acids or acid-producing foodstuffs

Excessive metabolic production of H+ (e.g. lactic acid during exercise or ketoacidosis)

Excessive loss of base from the body (e.g. diarrhoea – loss of HCO3-)

Question 11

Causes of metabolic alkalosis

Answer 11

Loss of HCl from the stomach (vomiting)

Ingestion of alkali or alkali-producing foods
(e.g. Ingestion of NaHCO3 as an antacid, though not a problem with modern antacids)

Aldosterone hypersecretion
(causes stimulation of Na+/H+ exchange at the 	apical membrane of the tubule; acid secretion)