Acid-Base Balance

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  • Created by: Becca
  • Created on: 27-12-13 19:40
What is the link between [H+] & pH?
Increase [H+] -> Decrease pH -> ACIDOSIS. Decrease [H+] -> Increase pH -> ALKALOSIS
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Which organs are involved in maintaining the pH of the body?
Lungs & kidneys (maintain acid-base balance through reabsorption/excretion of [HCO3-] and secretion of [H+])
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What are the normal values for pH, pCO2 & [HCO3-]?
pH: ~7.4, pCO2: 5.3 kPa & [HCO3-]: 24 mmol/L
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What do respiratory acid-base disorders result from?
Primary changes in blood pCO2. If pCO2>5.3 -> acidosis, kidneys compensate (slow response) by excretion of H+, plasma [HCO3-], increasing NH4+ & [H2PO4-] in urine. If pCo2 alkalosis, kidneys compensate (slow response) by excretion of [HCO3-]
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What do metabolic aicd-base disorders result from
Changes in plasma [HCO3-]. If acidosis, lungs respond by ventilation (immediate) to lower pCO2 (not sustainable, chronic will become acidaemia). If >24 -> alkalosis, lungs decrease ventilation to increase pCO2, poor compensation due to hypoxia
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What are the sources of H+ gain?
From CO2 in tissue (aerobic respiration), metabolism of protein and other organic molecules, due to loss of HCO3- in diarrhoea & urine
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What are the sources of H+ loss?
H+ + HCO3- -> H2O + CO2 (CO2 excreted through lungs), utilisation of H+ in metabolism of organic anions, loss of H+ in vomitus & urine
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What are the 3 mechanisms of pH homeostasis?
Buffers (intra & extracellular phosphates and proteins including Hb), ventilation and renal regulation of H+ and HCO3- (slow)
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How do the kidneys contribute to the homeostasis of extracellular [H+]?
Excreting or reabsorbing H+ (phosphate/ammonia buffers) and regulating plasma [HCO3-] (excretion of filtered HCO3-/addition of new HCO3- to blood)
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What is the plasma [H+] in alkalaemia? How do the kidneys compensate?
Low plasma [H+]. Kidneys compensate by inhibiting H+ secretion (decrease HCO3- reabsorption), so excreting HCO3- in urine -> increases plasma [H+]
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What is the plasma [H+] in acidaemia? How do the kidneys compensate?
High plasma [H+]. Kidneys compensate by increasing H+ secretion (excreted in urine) & adding HCO3- to blood -> decreases plasma [H+]
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What is involved in HCO3- reabsorption
HCO3- is completely filterable, reabsorption involves H+ secretion, 1 HCO3- reabsorbed:1 HCO3- filtered (no net gain of HCO3-, doesn't correct acidosis, excreted in urine->net loss in alkalosis). HCO3- is also reabsorbed at thick ascending limb & CD
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Via what process is new HCO3- (excretion of H+) added to the blood?
Via ammoniagenesis (glutamine metabolism) in proximal tubule. Glutamine -> new HCO3- -> blood. And glutamine -> NH4+ -> generate NH3/H+ or trapped to act as a buffer, H+ stimulates NH4+ production (acidosis, increase urine [NH4+], slow)
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What happens during diffusion trapping/ammonium trapping?
NH4+ produced & secreted by proximal epithelium (ammoniagenesis). Early in nephron, most secreted H+ ions used to reabsorb bicarbonate (important in LDT/CD). NH4+ reabsorbed by thick limb into medullary interstitium, exits as NH4+ & NH3 -> excreted
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Card 2

Front

Which organs are involved in maintaining the pH of the body?

Back

Lungs & kidneys (maintain acid-base balance through reabsorption/excretion of [HCO3-] and secretion of [H+])

Card 3

Front

What are the normal values for pH, pCO2 & [HCO3-]?

Back

Preview of the front of card 3

Card 4

Front

What do respiratory acid-base disorders result from?

Back

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Card 5

Front

What do metabolic aicd-base disorders result from

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