Salt/Water + Acid/Base Balance

Question 1

What is volatile and non-volatile acid? ()

Answer 1

All acids produced by the body are non-volatile (fixed acid) except from those produced from CO2 – i.e. carbonic acid (H2CO3), which is volatile

Question 2

How much hydrogen and CO2 are produced by the body in 24 hours? ()

Answer 2

In 24 hours the body produces 40-80mmol H+ by metabolic processes, which is excreted in urine. In addition, >15,000mmol CO2 is produced during aerobic oxidation, and this is excreted by the lungs

Question 3

How is pH regulated by the lungs? (7)

Answer 3

pH is dependent on H+
CO2 from tissue is transported into RBCs where it combines with water to form carbonic acid
Carbonic acid then split into H+ and HCO3- (bircarb)
Reactions controlled by carbonic anhydrase
Bicarbonate exchanged for Cl- into circulation (dissolves in plasm)
Process reverses in order to deliver CO2 to alveoli for expiration
Breathing controlled by respiratory centre in the medulla

Question 4

How is pH regulated by the kidneys? (1)

Answer 4

Control pH by excreting non-volatile acids + by reabsorbing bicarb (mostly in PCT)

Question 5

Cause of resp. acidosis (5)

Answer 5

High pCO2, high H+, low pH due to not blowing off enough CO2
Cx = airway obstruction (COPD, bronchitis, asthma), resp centre depression (morphine), pulmonary diseases (pneumonia), NM disease (MND)
Can be acute or chronic

Question 6

Cause of resp. alkalosis (3)

Answer 6

Low pCO2, low H+, high pH due to blowing off too much CO2

Cx = hypoxia (high altitude, anaemia, pulmonary oedema) - increased resp drive, voluntary hyperventilation

Question 7

Cause of metabolic acidosis ()

Answer 7

Due to increased production/decreased removal of H+ (other than those derived from CO2), increase HCO3- excretion
Cx = increased acid production (diabetic ketoacidoss

Question 8

Cause + management of metabolic alkalosis ()

Answer 8

C

Question 9

What is the rough distribution of water in the body? (4)

Answer 9

Water accounts for ~60% body weight:

• 2/3 ICF
• 1/3 ECF
• 8% plasma

Question 10

How is body water content regulated in the body? ()

Answer 10

d

Question 11

What are the clinical features of hyperkalaemia? ()

Answer 11

Cx: ↑intake (oral – spironolactone/parenteral), ↓excretion (renal failure, aldosterone deficiency)
CPx: ventricular fibrillation + cardiac arrest

Question 12

What are the clinical features of hypokalaemia? ()

Answer 12

Cx: ↓intake (oral/parenteral), ↑excretion (diuretics, renal failure, ↑RAAS, Cushing’s)
CPx: neuromuscular (hypotonia + weakness, constipation, confusion, depression), cardiac (arrythymias, ECG changes), renal (polyuria, polydipsia) metabolic (alkalosis)

Question 13

What is osmolality? (2)

Answer 13

A measure of no. of dissolved particles in a fluid, mainly due to Na+
I.e. conc. of substances in a sample