Lung Physiology 4: control of breathing

Question 1

is breathing automatic?

Answer 1

yes, no conscious effort for the basic rhythm
Rate and depth under additional influences

Question 2

Types of chemoreceptors?

Answer 2

central and peripheral

Question 3

where are peripheral chemoreceptors found? what nerve afferent is present at each?

Answer 3

Carotid bodies
Bifurcation of the common carotid
(IX) cranial nerve afferents

Aortic bodies
Ascending aorta
Vagal (X) nerve afferents

Question 4

Can low O2 cause hyperventilation?

Answer 4

only at very low levels of oxygen, initially caused by low PACO2

Question 5

name 2 main areas and centres in each that controll basic breathig rythm

Answer 5

respiratory control centres

Pons:
Pneumotaxic and Apneustic Centres

Medulla oblongata:
Phasic discharge of action potentials
Two main groups:
Dorsal respiratory group (DRG)
Ventral respiratory group (VRG)

Question 6

What pulmonary centre is predominantly active during inspiration?

Answer 6

Dorsal respiratory group (DRG)

Answer 7

Each are bilateral, and project into the bulbo-spinal motor neuron pools and interconnect

Question 8

what are the 3 lung receptors? some of their roles? afferent nerves present?

Answer 8

Stretch, J and irritant
Afferents; vagus (X)
Combination of slow and fast adapting receptors
Assist with lung volumes and responses to noxious inhaled agents

Question 9

What pulmonary centre is active during both inspiration and expiration?

Answer 9

Ventral respiratory group (VRG)- more mainly in expiration

Question 10

What is the central pattern generator?

Answer 10

Neural network (interneurons)
Located within DRG/VRG

produces rhythmic synaptic drive for motoneurons controlling respiratory muscles- want to breath

Question 11

process of inspiration

Answer 11

Progressive increase in inspiratory muscle activation
Lungs fill at a constant rate (linear) until tidal volume achieved
End of inspiration, rapid decrease in excitation of the respiratory muscles

Question 12

process of expiration

Answer 12

Largely passive due to elastic recoil of thoracic wall
First part of expiration; active slowing with some inspiratory muscle activity
With increased demands, further muscle activity recruited
Expiration can be become active also; with additional abdominal wall muscle activity

Question 13

what do the central chemoreceptors mainly controll?

Answer 13

primary influence is PaCO2, brain barrier is relatively impermeable to H+

Question 14

what percentage of influence is central receptors vs peripheral receptors?

Answer 14

60% of the influence from PaCO2 is via central receptors
40% of the influence from PaCO2 is via peripheral receptors
though there is significant interaction between the two

Question 15

what do the peripheral chemoreceptors mainly controll?

Answer 15

all ventilatory response to low PaCO2
PaO2, pH

Question 16

where are central chemoreceptors found?

Answer 16

Located in brainstem
Pontomedullary junction
Not within the DRG/VRG complex

Question 17

How do central chemoreceptors work to be able to send signals to respiratory controll centres?

Answer 17

Blood brain barrier relatively impermeable to H+ and HCO3-

therefore CO2 preferentially diffuses into CSF, then drives reaction via carbonic anhydrase to produce here more H+, H+ in turn agonises the receptor causing activation of the respiratory control centre

Question 18

the detection of what gas causes the want to take a breath?

Answer 18

co2 not o2

Question 19

why are patients with chronic hypoxia e.g. copd not experioencing same symptoms as someone who quickly becomed hypoxic

Answer 19

the patients become habituated- body adjusts base level

Question 20

What height dose the death zone begin?

Answer 20

over 8000m above sea level

Question 21

what are the muscle proprioceptors? what’s their role?

Answer 21

present in Joint, tendon and muscles use to breath
neuromuscular sense organs that allow the organs to communicate with the brain

Question 22

where are other airway receptors present?

Answer 22

Nose, nasopharynx and larynx, Pharynx
muscle and airway receptors that provide afferance, vagus is important within this

Question 23

what are afterio-venous malformations?

Answer 23

very rare, shunt blood from right to left side of heart meaning blood not oxygenated - associated with Hereditary hemorrhagic telangiectasis