Acid-Base Homeostasis (16)

Question 1

Acid production

Answer 1

Total CO2 25mol/day

Unmetabolised acids 50 mmol/day (urine, sulphuric acid, phosphoric acid)

Plasma [H+] 40nmol/L

Question 2

Buffering systems

Answer 2

Hb, bicarbonate, phosphate, proteins, ammonia, organic acids

Question 3

pH

Answer 3

[H+]

Question 4

Normal pH

Answer 4

7.45-7.35

Question 5

Normal [H+]

Answer 5

35-45 nmol/L

Question 6

[H+]

Answer 6

low - alkolotic, high-acidotic

Question 7

Henderson-Hasselbalch equation

Answer 7

H+ + HCO3- H2CO3 CO2 + H2O

pH = pK + log ([HCO3-]/[pCO2] x a)

Question 8

[H+] homeostasis requires

Answer 8

Balance between H+ production and regeneration of HCO3-

Question 9

Sites of acid-base metabolism

Answer 9

Lungs, kidney, GI tract, liver

Question 10

Tissue gas exchange

Answer 10

CO2 non-polar, easily pass into RBC, if acidify RBC changes shape and releases O2 > lungs

Question 11

RBC equation

Answer 11

H+Hb+O2 > HbO2 > H+ + HCO3 (CO2/Cl-)

Question 12

When does haemoglobin dissociated curve shift right?

Answer 12

Right shift
Increased
2,3 diPG
H+ acidosis
Temperature

Question 13

Kidney

Answer 13

• Bicarbonate is lost (active Na+/H+ pump)
• Regeneration of bicarbonate in renal tubule
• Distal tubercle under aldosterone control - regulates salt and water (Na+ secreted, K+ absorbed)

Question 14

GI

Answer 14

Stomach secretes [H+], pancreatic juice [HCO3-]

Question 15

Liver

Answer 15

Dominant site of lactate metabolism, only site of urea synthesis

Question 16

Severe liver failure

Answer 16

Metabolic alkalosis, NH4+ toxicity

NH4+ + oxo-glutamate X>X glutamine
NH4+ + CO2 X>X urea and H+

Question 17

Compensatory mechanisms

Answer 17

Respiratory, renal bicarbonate regeneration, hepatic shift between urea synthesis and ammonia excretion

Question 18

Normal [H+]

Answer 18

36-44 nmol/L

Question 19

Normal Na+

Answer 19

132-144 mmol/L

Question 20

Normal K+

Answer 20

3.5-5.5 mmol/L

Question 21

Normal Cl-

Answer 21

98-108 mmol/L

Question 22

Normal HCO3-

Answer 22

21-28 mmol/L

Question 23

Normal urea

Question 24

Normal creatine

Question 25

Metabolic acidosis

Answer 25

Increased H+ formation, acid ingestion, reduced renal H+ excretion, loss of bicarbonate (High H+, low CO2, high O2)

Question 26

Metabolic alkalosis

Answer 26

Generation of bicarbonate by gastric mucosa, renal generation of HCO3- in hypokalaemia, administration of bicarbonate
(Low H+, high CO2, low pO2)

Question 27

Consequences of metabolic alkalosis

Answer 27

K+ > cells and urine
PO4 > cells
Respiratory suppression

Question 28

Respiratory acidosis

Answer 28

CO2 retention due to - inadequate ventilation and perfusion, parenchymal lung disease
(High H+, High CO2, Low pO2)

Question 29

Respiratory alkalosis

Answer 29

Increased CO2 excretion - hyperventilation

Low H+, Low pCO2, High pO2

Question 30

Causes of increased H+ formation

Answer 30

Ketoacidosis, diabetic, alcoholic, lactic acidosis, poisoning, inherited organic acidoses

Question 31

Diabetic keto-acidosis

Answer 31

Hyperglycaemia, osmotic diuresis > pre-renal uraemia, hyperketonaemia, increase FFA
(all lead to acidosis)

Question 32

Lactic acidosis

Answer 32

Shock or metabolic and toxic causes

Question 33

Normal lactic acid levels

Answer 33

0.9-1.7 mmol/L

Question 34

Acidosis in an alcoholic

Answer 34

NAD+ depletion (thiamine), thiamine deficiency (PDH co-factor), enhanced glycolysis for ATP formation, leto-acids (B-HBD) secondary to counter-regulatory hormones, profuse vomiting

Question 35

In alkalosis

Answer 35

Increased glycolysis, reduced O2 delivery due to shift in O2 dissociation curve, lactate induced vasoconstriction, impaired mitochondrial respiration

Question 36

O2 debt in alkalosis due to

Answer 36

Further anaerobic lactate production, hyperventilation

Question 37

reduced H+ excretion

Answer 37

Renal tubular acidosis, generalised renal failure

Question 38

Renal failure

Answer 38

Reduced volume of nephrons, increased bicarbonate loss, reduced NH4+ excretion, NH4+ to liver for urea and H+ synthesis, only fraction of NH4+ derived from glutamine (normal approx 100%)