Session 4- Neural and Chemical Control of Breathing

Question 1

where are the brain resp centres

Answer 1

bilaterally in the brainstem on the medulla oblongata and pons

Question 2

where are the dorsal resp group

Answer 2

dorsal surface of teh medulla

Question 3

where are the ventral resp groups

Answer 3

ventral-lateral surface of the medulla

Question 4

where is the pneumotaxic centre of neurons

Answer 4

dorsally on the pons

Question 5

what sets the basic rhythm of breathing

Answer 5

dorsal repiratory group neurons on the medulla sending inspiratory neuron action potentials to spinal nerves innervating the diaphragm and external intercostal msucles

Question 6

how can ventilation be adjusted

Answer 6

the brainstem recieves infor about how expanded the lungs ar from stretch receptors located in the walls of brinchi and bronchioles

transmitted via the vagus nerve

Question 7

what are chemoreceptors

Answer 7

monitor parameters of arterial blood or brain ECF and send this information to the brainstem respiratory centres

monitor

• conc of H+ (pH)
• pressure of CO2

Question 8

what do central chemoreceptors monitor

Answer 8

PaCo2

pH

Question 9

what do peripheral chemoreceptors monitor

Answer 9

PaO2
PaCO2- less than central
pH

via cranial nerves 9 and 10

Question 10

Hypoxaemia

Answer 10

falls in arterial pO2 below normal in blood

Question 11

what can hypoventilation lead to

Answer 11

removal of CO2 is less rapid than its production
alveolar pCO2 rises so dissolved CO2 rises more than HCO3- producing a fall in plasma pH

RESPIRATORY ACIDOSIS

Question 12

how does the kidney respond to hypoventilation

Answer 12

reducing excretion of HCO3- thus increasing plasma HCO3- and restoring the HCO3-/dissolved CO2 ratio

if pH becomes near normal- partial compensated resp acidosis
if pH becomes normal- full compensated resp acidosis

Question 13

what can hyperventilation lead to

Answer 13

removal of CO2 is more rapid than its production

alveolar CO2 falls , plasma pH rises - Respiratory Alkalosis

Question 14

how does the kidney repsond respiratory alkalosis

Answer 14

excreting HCO3- so that the ratio of [HCO3-:Dissolved CO2] returns to normal and therefore pH is restored

pH near normal- partial compensation
pH normal- full compensation

Question 15

what is metabolic acidosis

Answer 15

if excessive acid is formed in the body the [HCO3-] in the blood is used up to buffer this acid and the [HCO3-] in the blood drops

pH of the blood falls

Question 16

what is metabolic alkalosis

Answer 16

if there is excess {HCO3-} in the plasma

blood pH is corrected by elevaating pCO2

Question 17

what are peripheral chemoreceptors

Answer 17

located in the carotid bodies and aortic bodies

respond to changes of pO2 pCO2 pH

Question 18

how is info carried from the carotid bodies

Answer 18

via the glossopharyngeal nerve

Question 19

how is info carried from the aortic bodies

Answer 19

via the vagus nerve

Question 20

what is the main response of peripheral chemoreceptors to O2 changes

Answer 20

carotid and aortic bodies ar stimulated by aderease in oxygen

they do not significantly repsond to slight changes in pO2 and only respond to significant falls in po2

They increase minute ventilation

Question 21

what is the main response of peripheral chemoreceptors to co2

Answer 21

the carotid and aortic bodies arent sensitive to PaCO2
unless large changes

central chemorecpetors are the main repsonders

Question 22

what are central chemoreceptors

Answer 22

located on the ventral surface of the medulla and exposed to brain extracellular fluid

they respond to a drop in brain extracellular fluid pH which occurs when the arterial PaCO2 rises

Question 23

how is the movement of HCO3- into and out of the CSF determined

Answer 23

cells of the choroid plexus which pump HCO3-

Question 24

what happens when PaCo2 remains altered for any length of time

Answer 24

the activity of choroid plexus serves to reset the central chemoreceptors so that they are no longer sensitive to the existing pCO2 and only respond if the pCO2 rises further

Question 25

how do you analyse an ABG

Answer 25

1) look at the pH- if it is showing acidaemia look at the pCO2 if it is elevated then it is a resp cause therefore resp acidosis, if it is not elevated look at bicarb if if it is low then metabolic acidosis
2) if the pH shows alkalaemia look at pCO2 if low then resp cause so resp acidosis, if not low look at bicarb if elevated then metabolic cause
3) if there si full compensation the pH will be in the normal range and only partial of the pH remains abnormal