Renal pH regulation Flashcards
Buffer system
- Defintion
- Examples
A system that resists small changes in pH by adding or removing H+.
Examples in the body:
- Carbonic acid/ Bicarbonate
- Proteins
- Phosphate
Respiratory regulation of pH
The lungs are able to excrete acid by breathing out CO2.
CO2 is a potential acid excreted by making H2CO3 first.
Peripheral chemosensors detect pH and alter ventilation:
- Low pH= hyperventilation to excrete more CO2.
- High pH= hypoventilation to increase [H+]
pH range control
pH is kept within narrow limits to provide optimum conditions for enzymatic activity.
Blood pH is maintained at:
7.35-7.45
<7.35= acidaemia >7.45= alkalemia
Average Urine pH
Around 6
- Due to excretion of H+ in the urine to maintain pH.
Average blood carbonate concentration
24 mM
Average blood CO2 concentration
40 mmHg
Average plasma and urine osmolarity
Osmolarity is the the total number of solute particles per litre
Plasma- 280mOsm/kg water
Urine- 600mOsm/kg
Urine osmolarity differs depending on the hydration status so can range from 50-1200.
- The higher the osmolarity the more dehydrated
Renal regulation of acidosis
More H+ is secreted into urine whilst more bicarbonate is reabsorbed into the blood.
Secretion of H+ is inhibited when urine pH falls below 4.5.
At the proximal tubule:
- H+ is secreted into the tubule via Na+/H+ ATPase.
- H+ is generated in cells by the dissociation of carbonic acid.
- HCO3- is reabsorbed at the basolateral membrane through a bicarbonate pump.
At the intercalated cells of the distal tubule and collecting duct:
- Bicarbonate is reabsorbed via bicarbonate/Cl- exchange.
- H+ is secreted via Na+/H+ ATPase.
- More HCO3- is generated from amino acids in the intercalated cells.
Causes of respiratory acidosis
Inadequate ventilation
- Can be acute
- Can be chronic (COPD, bronchitis)
Examples:
- Asphyxia
- Hypoventilation
- Advanced astha
- Severe emphysema
Causes of metabolic acidosis
Caused by anything that is not respiratory, but increases pH.
Examples:
- Loss of bicarbonate from diarrhea/vomitting
- Loss of bicarbonate in urine
- Loss of bicarbonate in non-gastric fluids
- Increase in non-volatile acids, like lactate—> due to inadequate oxygen delivery to tissue
- Ingestion of acidic drugs like aspirin
- Untreated diabetes mellitus leading to ketoacidosis
Body response to acidosis
Arterial and CSF chemoreceptors detect drop in pH.
Stimulates respiratory centre= hyperventilation of lungs to loss more CO2.
Kidneys:
- Excrete more H+ in urine.
- Reabsorb and generate more HCO3- in the blood.
Other buffer systems accept H+ ions.
These mechanism helps to decrease the concentration of H+ in the blood.
Body response to alkalosis
Arterial and CSF chemoreceptors are inhibited.
- Inhibits respiratory center in medulla causing hypoventilation in lungs.
Kidneys:
- Reabsorbs more H+ into the blood.
- Secrete more bicarbonate into urine.
Other buffer systems release H+ into the blood.
Treatment of respiratory acidosis
Restoration of ventilation- excretes more CO2.
Treating underlying disease that causes acidosis.
Administering IV lactate which in converted into HCO3- in the blood.
Treatment of metabolic acidosis
Administering IV lactate- converted into bicarbonate in the blood
Administering isotonic HCO3- solution.
Treatment of respiratory alkalosis
Treating underlying disease causing alkalosis.
Breathing into paper- increases p(CO2)
Administering IV Cl- Increases HCO3- secretion
