Lecture 39 Flashcards
pH definition
Partial pressure of H+ in solution
Types of buffers in the body
Chemical
- proteins
- bicarbonate
- ammonia
Physiological
- excretion of acids or bases in the renal system
Renal system use of buffer system
Uses both physiological and chemical processes to regulate blood pH levels
Using HCO3- and H+
Process of buffering of H+ ions into the nephron for excretion
HCO3- forms with H+ Dissociates to form H2O and CO2 Diffuses into the tubular cells Reforms to H2CO3 using carbonic anhydrase Dissociates into HCO3- and H+ H+ enters the filtrate
Process begins again
Renal correction of acidosis
As pH drops, HCO3- is taken up by the kidneys
Secretion of H+ causes excretion of surplus H+ ions
CO2 converted to HCO3-, making the ECF more alkaline (uptake of H+ ions)
What happens when pH is below 4.5 in filtrate
No more H+ ions will be secreted into the nephron
Limits control of pH limiting by HCO3-
NH3 takes up additional H+
Forming NH4+
NH4+ cannot be reabsorbed
Additional H+ will be excreted in form of NH4+
Where does NH3 come from?
Protein metabolism
How to make acidic urine in mild acidosis?
HCO3- forms with H+ ions
Making H2CO3
Absorbed into tubular cells in form of CO2 and H2O
Reforms H2CO3 in tubular cells
HCO3- formed diffuses into blood = alkaline effect
H+ excreted
Acidic urine in severe acidosis?
ECF v acidic
NH3 diffuses into tubular lumen combining with H+
NH4+ excreted in urine
Acidosis symptoms
Cardiovascular dysfunction Confusion CNS depression Seizures Coma if below pH7 Excitable cells of the body harder to stimulate due to CNS depression
Why does acidosis lead to CNS depression and cardiovascular dysfunction?
Plasma proteins less ionised, (more H+ binding to the plasma proteins) less calcium taken up by them
More free calcium blocks Na+ channels
Causing depolarisation of neurones and myocytes harder
Lack of nerve or cardiac action potentials cause coma and cardiac arrest
Causes of acidosis
Respiratory acidosis
Metabolic acidosis
Respiratory acidosis causes and what we’d see
Ventilatory failure
Complications of COPD or Asthma
See ↓ PaO2 ↑ PaCO2 Slightly low pH Raised plasma HCO3- due to renal compensation
Renal injury/disease causing metabolic acidosis
Cause ↓ HCO3- reabsorption
↓ H+ secretion and excretion
Diarrhoea causing metabolic acidosis
More Na+ in filtrate means ↓ H+ secreted
Less HCO3- reabsorbed
Acidosis
