Central chemoreceptors

Question 1

where are the central chemoreceptors located?

Answer 1

they are situated near the ventral surface of the medulla near the exit of CNIX and CNX

Question 2

what is a chemoreceptor?

Answer 2

a chemoreceptor is a receptor that responds to a change in the chemical composition of the blood or other fluid around it

Question 3

what are the central chemoreceptors surrounded by?

Answer 3

the brain ECF ie CSF

Question 4

what is the composition of the brain ECF govered by?

Answer 4

• CSF
• local blood flow
• local metabolism

Question 5

what is the CSF separated from the blood by?

Answer 5

the blood brain barrier

Question 6

what molecules is the blood brain barrier impermeable and permeable to?

Answer 6

impermeable - H+ and HCO3-
permeable to Co2

Question 7

what occurs if arterial/blood CO2 rises?

Answer 7

• if arterial CO2 rises, CO2 will diffuse across the BBB into the CSF, which liberates H+ ions
• this will cause an decrease in PH (ie more acidic)
• this stimulates the central chemoreceptors to fire - which sends signals to the medullary inspiratory neurons to increase ventilation

Question 8

what stimulus do the central chemoreceptors not respond to?

then what receptors respond to this stimulus?

Answer 8

changes in arterial O2
* the peripheral receptors respond to an arterial O2 reduced to 60mmHg

Question 9

As a result of an increase in arterial CO2, hyperventilation occurs… what happens to the CO2 in blood as a result of this response?

Answer 9

• the hyperventilation will decrease the PCO2 in the blood as more CO2 is being expired
• therefore less CO2 will diffuse into the CSF, then the PH of the CSF will return to normal

Question 10

what happens to CO2 in chronic lung disease such as emphysema?

Answer 10

• CO2 is retained
• this results in an increase in arterial CO2, an increase in CO2 diffusion into CSF and a decrease in CSF PH
• there is a HCO3- compensation which reduces [H+] and increases PH to normal
• accompanied by abnormally low ventilation

Question 11

what molecule compensates for long term changes in CSF PH?

Answer 11

HCO3-

Question 12

what is the exact PH of the CSF?

Answer 12

7.32 (slightly more acidic than blood)

Question 13

during rest and exercise, how much does arterial CO2 change?

Answer 13

changes only by 3mmHg

Question 14

other than the central chemoreceptors, what other chemoreceptors respond to elevations in the arterial PCO2?

Answer 14

peripheral chemoreceptors - however only accounts for approx 10-30%

Question 15

Describe the sequences of responses/events of the periperal chemoreceptors to a change in H+ which is not related to CO2

ie lactic acid

Answer 15

• increase in production of lactic acid eg during exercise
• increase in arterial [H+]
• causes an increase in firing of the peripheral chemoreceptors - which increases the contractions of the respirtory muscles
• increase in ventilation - which decreases alveolar PCO2 and therefore arterial PCO2
• return of arterial [H+] to normal

Question 16

what 3 stimuli cause firing of the peripheral chemoreceptors?

Answer 16

• decrease in arterial PO2
• increase in the** production of non CO2 acids** eg lactic acid
• increase in arterial PCO2