Acid Base Balance

Question 1

Peripheral chemoreceptors

Answer 1

are found in the neck in the bifurcation of the common carotid artery (called carotid bodies) and in the thorax at the arch of the aorta (called aortic bodies)

Question 2

Central chemoreceptors

Answer 2

are found in the medulla

Question 3

Changes in pCO2 & Chemoreceptors

Answer 3

Peripheral chemoreceptors respond to an increase in arterial H+ concentration due to increase in pCO2

At the same time, increase in brain pCO2 that leads to an increase in brain extracellular H+ concentration that stimulates central chemoreceptors

Both central and peripheral chemoreceptors stimulate medullary inspiratory neurons to increase ventilation

Question 4

Other changes in pH

Answer 4

Non-CO2 dependent changes in pH e.g. increase in lactic acid

H+ do not quickly pass across the blood brain barrier so primarily only activate the peripheral chemoreceptors

Reverse happens if there is a decrease in [H+] (e.g. vomiting) and depression of peripheral chemoreceptor firing

Question 5

Bicarbonate regulation in kidneys

Answer 5

Bicarbonate is completely filtered at the renal corpuscles and significant amounts are reabsorbed in the proximal collecting duct, loop of henle and cortical collecting duct
Collecting duct can also secrete HCO3-

Question 6

Collecting duct

Answer 6

Acidosis: pH too low
Kidney excretes H+ and reabsorbs HCO3-= hypoventilation

Alkalosis: pH too high
Kidney excretes K+ and HCO3- ; reabsorbs H+= hyperventalation

Question 7

Renal Response to Acidosis

Answer 7

Sufficient H+ is secreted to reabsorb the filtered HCO3-
More H+ is secreted and adds new HCO3- in the plasma due to non-bicarbonate urinary buffers
Tubular glutamine metabolism and ammonium secretion are increased and adds new bicarbonate to the plasma

Net result: More new HCO3- added to blood and plasma bicarbonate is increased = compensates for acidosis

Question 8

Renal Response to Alkalosis

Answer 8

Amount of H+ secretion is not enough to reabsorb all the filtered bicarbonate so this is excreted in urine
Little or no excretion of H+ on nonbicarbonate buffers
Decreased Tubular glutamine metabolism and ammonium excretion
Type B intercalated cells secrete bicarbonate ions
Net result: Plasma bicarbonate is decreased and compensates for alkalosis