Acid-Base Homeostasis (16) Flashcards

1
Q

Acid production

A

Total CO2 25mol/day

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

Plasma [H+] 40nmol/L

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2
Q

Buffering systems

A

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

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3
Q

pH

A

[H+]

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4
Q

Normal pH

A

7.45-7.35

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5
Q

Normal [H+]

A

35-45 nmol/L

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6
Q

[H+]

A

low - alkolotic, high-acidotic

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7
Q

Henderson-Hasselbalch equation

A

H+ + HCO3- H2CO3 CO2 + H2O

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

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8
Q

[H+] homeostasis requires

A

Balance between H+ production and regeneration of HCO3-

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9
Q

Sites of acid-base metabolism

A

Lungs, kidney, GI tract, liver

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10
Q

Tissue gas exchange

A

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

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11
Q

RBC equation

A

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

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12
Q

When does haemoglobin dissociated curve shift right?

A
Right shift
Increased
2,3 diPG
H+ acidosis
Temperature
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13
Q

Kidney

A
  • 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)
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14
Q

GI

A

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

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15
Q

Liver

A

Dominant site of lactate metabolism, only site of urea synthesis

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16
Q

Severe liver failure

A

Metabolic alkalosis, NH4+ toxicity

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

17
Q

Compensatory mechanisms

A

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

18
Q

Normal [H+]

A

36-44 nmol/L

19
Q

Normal Na+

A

132-144 mmol/L

20
Q

Normal K+

A

3.5-5.5 mmol/L

21
Q

Normal Cl-

A

98-108 mmol/L

22
Q

Normal HCO3-

A

21-28 mmol/L

23
Q

Normal urea

24
Q

Normal creatine

25
Metabolic acidosis
Increased H+ formation, acid ingestion, reduced renal H+ excretion, loss of bicarbonate (High H+, low CO2, high O2)
26
Metabolic alkalosis
Generation of bicarbonate by gastric mucosa, renal generation of HCO3- in hypokalaemia, administration of bicarbonate (Low H+, high CO2, low pO2)
27
Consequences of metabolic alkalosis
K+ > cells and urine PO4 > cells Respiratory suppression
28
Respiratory acidosis
CO2 retention due to - inadequate ventilation and perfusion, parenchymal lung disease (High H+, High CO2, Low pO2)
29
Respiratory alkalosis
Increased CO2 excretion - hyperventilation | Low H+, Low pCO2, High pO2
30
Causes of increased H+ formation
Ketoacidosis, diabetic, alcoholic, lactic acidosis, poisoning, inherited organic acidoses
31
Diabetic keto-acidosis
Hyperglycaemia, osmotic diuresis > pre-renal uraemia, hyperketonaemia, increase FFA (all lead to acidosis)
32
Lactic acidosis
Shock or metabolic and toxic causes
33
Normal lactic acid levels
0.9-1.7 mmol/L
34
Acidosis in an alcoholic
NAD+ depletion (thiamine), thiamine deficiency (PDH co-factor), enhanced glycolysis for ATP formation, leto-acids (B-HBD) secondary to counter-regulatory hormones, profuse vomiting
35
In alkalosis
Increased glycolysis, reduced O2 delivery due to shift in O2 dissociation curve, lactate induced vasoconstriction, impaired mitochondrial respiration
36
O2 debt in alkalosis due to
Further anaerobic lactate production, hyperventilation
37
reduced H+ excretion
Renal tubular acidosis, generalised renal failure
38
Renal failure
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%)