Chemical Control

Question 0

Describe the effects of plasma pH of hyper- and hypoventilation

Answer 0

Hyperventilation - high pH = respiratory alkalosis (decreased HCO3-)
Hypoventilation - low pH = respiratory acidosis (increased HCO3-)

Question 1

Define the terms ‘hypoxia’, ‘hypercapnia’, ‘hypocapnia’, ‘hyperventilation’ and ‘hypoventilation’

Answer 1

Hypoxia - decreased pO2
Hypercapnia - increased pCO2
Hypocapnia - decreased pCO2
Hyperventilation - increased ventilation with no change in metabolism
Hypoventilation - decreased ventilation with no change in metabolism

Question 2

Describe the general effects of acute hyper- and hypoventilation

Answer 2

Hyperventilation - respiratory alkalosis, low HCO3-, dizziness, lightheaded, shortness of breath
Hypoventilation - respiratory acidosis, high HCO3-, low oxygen

Question 3

Define the terms ‘metabolic acidosis’, ‘metabolic alkalosis’, ‘compensated metabolic acidosis’, ‘compensated metabolic alkalosis’

Answer 3

Metabolic acidosis - tissues produce acid that reacts with HCO3
Metabolic alkalosis - increased plasma HCO3
Compensation - change in ventilation/renal

Question 4

Describe the acute affects upon ventilation of falling inspired pO2, increases in inspired pCO2, falls in arterial plasma pH

Answer 4

Falling inspired pO2 –> hyperventilation, increased heart rate, diversion of blood flow to brain/kidney
Increases in inspired pCO2 –> hyperventilation
Falls in arterial plasma pH –> hyperventilation

Question 5

Describe the location and function of the peripheral chemoreceptors, their role in the ventilatory system and other responses to hypoxia

Answer 5

Location - carotid sinus, aortic arch
Function - detect changes in arterial pO2
Decreased pO2 = increased breathing and heart rate, diversion of blood flow to brain and kidney

Question 6

Describe the location and function of the central chemoreceptors, their role in the ventilatory system to changes in arterial pCO2, and their roles in the cerebrospinal fluid, blood brain barrier and choroid plexus in that response

Answer 6

Location - medulla oblongata
Function - detect changes in pH of CSF
CO2 can cross the BBB to directly change the pH of the CSF
This change in pH is detected by central chemoreceptors which changes ventilation
CSF [HCO3-] controlled by choroid plexus cells (long term)
Persisting changes in pH are corrected by choroid plexus cells
Changing CSF [HCO3-] can reset control system e.g. during persistent hypoxia