Acid-Base balance Flashcards
What is the normal pH range for blood?
7.35-7.45
What pH levels are fatal?
Less than 6.8 or greater than 8
How can methanol poisoning lead to metabolic acidosis?
It produces excess formic acid
What is a buffer?
A solution that can resist pH change upon the addition of an acid or a base; they are able to neutralise small amounts of added acid or base and this maintains the pH of the solution
What are the three major chemical buffer systems in the body?
Bicarbonate, protein (haemoglobin and albumin) and phosphate
In order to maintain acid-base what must the kidney do?
Reabsorb all filtered bicarbonate and excrete the daily acid load
How and where does the kidney reabsorb filtered bicarbonate?
In the PCT the nephron reabsorbs all of the filtered bicarbonate through the action of carbonic anhydrase (can only be absorbed in ionic form, HCO3-)
How and where does the kidney reabsorb filtered bicarbonate?
Active excretion of H+ occurs in the distal tubule
Where are renal intercalated cells found?
In the collecting duct
What is the function of renal intercalated cells?
They have a reversed polarity and can react to acidosis or alkalosis by increasing or decreasing the ratio of H+ excretion to HCO3- reabsorption
What is the function of alpha intercalated cells?
They secrete H+ and reabsorb bicarbonate in response to acidosis
What is the function of beta intercalated cells?
Secrete bicarbonate and reabsorb H+ in response to alkalosis
What is the anion gap?
The anion gap is the difference between the measured cations and the measured anions: ([Na+] + [K+]) − ([Cl−] + [HCO3−])
What is the common cause of normal gap metabolic acidosis?
Increased loss of bicarbonate or ineffective renal H+ excretion; caused by laxative abuse or diarrhoea
Outline the cause of normal gap metabolic acidosis
Loss of bicarbonate is counteracted by increased chloride uptake (hyperchloraemia) to remain electroneutrality and therefore anion gap is unchanged
What is the common cause of elevated gap metabolic acidosis?
Increased in unmeasured anions due to increased organic acid production in the body
What is the common cause of low metabolic gap acidosis?
This is almost always as a result of hypoalbuminaemia and this can be caused by haemorrhage, nephrotic syndrome, intestinal obstruction and liver cirrhosis
How do ionised drugs differ to unionised drugs in terms of ability to permeate membranes?
Unionised have a low polarity and a high lipid solubility and therefore can easily permeate membranes, whereas ionised drugs are poorly lipid soluble and highly polar so struggle to permeate membranes.
What is the Henderson-Hasselbach equation?
pH = pKa + log [conjugate base/acid]
What are the common causes of respiratory acidosis and how is it compensated?
This is largely due to CO2 retention and therefore is seen in hypoventilation (COPD etc.) and the kidney compensates by increasing H+ secretion and HCO3- reabsorption
What are the common causes of respiratory alkalosis and how is it compensated?
This is due to increased CO2 loss as in hyperventilation (anxiety and altitude) and the kidney compensates by increasing HCO3- loss and retaining H+
What are the common causes of metabolic alkalosis and how it is compensated?
This is caused by a loss of acid or a gain of base and is seen in vomiting, hypokalaemia or ingestion of HCO3- and the respiratory system stimulates decreased breathing rate to retain more CO2
