Physiology 5 Flashcards
Plasma buffer system equation?
HCO3- + H+ H2CO3
What is the first line of defence in terms of protecting against acidosis/alkalosis?
Buffers
What are the relative concentrations of bicarbonate and carbonic acid?
26mM 3uM
what is the equation which controls the amount of carbonic acid in the blood?
CO2 + H2O H2CO3 Equalibirum is far towards CO2 Very slow reaction Needs carbonic anhydrase Particularly high in RBCs
What enzyme converts carbonic acid?
Carbonic anhydrase
What is the effective buffer system between?
Bicarbonate and carbon dioxide (dray out equation)
What is the pK of CO2 and HCO3-?
6.1
What would be the ideal pK of a buffer?
7.4
What organ controls bicarbonate?
Kidneys
Henderson-Hasselbalch equation:
pH = pK + log {[base]/ [acid]}
What is the role of the lungs in altering pH?
Alter pCO2 through changes in ventilation
What is the role of the kidneys in altering pH?
–Alter HCO3- by changes in production & excretion –Alter pH by changes in H+ excretion
Aside from buffers what else can buffer the blood?
Plasma proteins
Phosphate (HPO4/H2PO4)
Heamoglobin (very high buffering ability)
Buffering is just a temporary solution
What reaction takes place with CO2 in the RBC?
CO2 + H2O H2CO3 (Carbonic anhydrase)
What acids to the kidneys deal with?
Sulphuric and phosphoric acids from proteins and lipids.
Lactic acid from anaerobic metabolism
Keto acids from fatty acids
Why does the kidney need to deal with acids?
There are a number of non-volatile acids (i.e. cannot breath them out). Relatively a lot less than CO2
How much acid to the kidneys deal with each day?
70 mmol of strong acid per day
What is the hallmark of a metabolic acidosis?
Decrease in a bicarbonate level
What happens with regard to pH with prolonged diarrhoea?
Metabolic acidosis due to loss of bicarbonate
What happens with vomiting with regard to pH?
Metabolic alkalosis
What is the anion gap?
If we add Na and K HCO3 and Cl It is found that the gap is about 10mmol
What is the most important contribution to the anion gap?
Proteins
What causes a high anion gap?
• Lactic acidosis (lactic acid) • Diabetic ketoacidosis (keto-acids) • Renal failure
What are the renal compensations in an alkalosis?
Reduced acid excretion Excretion of bicarbonate
What is the renal response to acidosis?
Increased acid secretion Increased HCO3 re-absorption and production
How is bicarbonate reabsorbed?
Proton secretion into the tubule
Where are hydorgen ions secreted?
Proximal tubule Distal tubule Collecting duct
Steps bicarbonate reabsorption and acid excretion
Na+/H+ antiport secretes H+
H+ in filtrate combines with filtered HCO3- to form CO2
CO2 diffuses into cell and combines with water to from H+ and HCO3-
H+ is secreted again and excreted
HCO3- is reabsorbed
Glutamate is metabolized to ammonium ion and HCO3-
NH4+ is secreted and excreted
HCO3- is reabsorbed
What happens to secreted hydrogen ions?
There is a lot of carbonic anhydrase and will convert it into water and produce a CO2
