Respiratory Physiology - Control of Ventilation

Question 1

Respiratory control system

Answer 1

Negative feedback system

Question 2

Rhythm controllers in the brainstem:
Medulla oblongata

Answer 2

Dorsal respiratory neuron group - inspiration

Ventral respiratory neuron group - expiration

Pre-Botzinger Complex - pattern generator, also ventral

Question 3

Rhythm controllers in the brainstem:
Pons

Answer 3

Apneustic centre - excitatory function

Pneumotaxic centre - can inhibit inspiration

Question 4

Effectors

Answer 4

Respiratory muscles:
1) Diaphragm
2) Intercostal muscles
3) Abdominal muscles
4) Accessory muscles

Question 5

Sensors

Answer 5

Central chemoreceptors

Peripheral chemoreceptors

Lung receptors

Other receptors

Question 6

Chemoreceptor definition

Answer 6

Specialised tissue that responds to change in chemical composition of the blood / fluid

Question 7

Central chemoreceptor

Answer 7

Responds to pH in extracellular fluid (which is similar to CSF pH)

Blood brain barrier prevents certain molecules from diffusing out of blood vessel (eg H+ and HCO3- ions)

More CO2 -> drop in pH -> stimulates central chemoreceptor

Question 8

pH of CSF

Answer 8

~ 7.32

Question 9

Buffering of CSF

Answer 9

Low buffering power due to low protein content

Bicarbonate in CSF controlled by choroid plexus

Question 10

Peripheral chemoreceptor sites

Answer 10

Carotid body - at bifurcation of common carotid artery

Aortic body chemoreceptors (less important than carotid body chemoreceptors)

Also note baroreceptors but they are more relevant for cardiovascular physiology

Question 11

Carotid body chemoreceptors

Answer 11

Responds to arterial pH, PCO2 and PO2

1/5th of response to drop in pH / rise in CO2 comes from peripheral chemoreceptors (compared with central chemoreceptor)

Type 1 and Type 2 glomus cells
Type 1 glomus cells have high dopamine levels in them

Little response from carotid body in normoxia

Question 12

Lung receptors

Answer 12

Pulmonary stretch receptors (aka slowly adapting pulmonary stretch receptors)

Irritant receptors (aka rapidly adapting pulmonary stretch receptors)

J receptors (juxta-capillary receptors)

Bronchial C fibres

Question 13

Hering-Breuer reflex

Answer 13

Seen with pulmonary stretch receptors

As lung is inflated, it will prevent further expansion of the lung

Question 14

Irritant receptors

Answer 14

Stimulated by irritants eg smoke / smog, cold air
Also some response to stretch

Causes bronchoconstriction

Involved in asthma

Question 15

J receptors

Answer 15

In alveolar wall close to capillaries

Cause rapid shallow breathing

Eg. with pulmonary oedema, pulmonary fibrosis

Question 16

Bronchial C fibres

Answer 16

Similar to J receptors but supplied by bronchial vascular system

Question 17

Other receptors

Answer 17

Nose and upper airway

Joint and muscle

Gamma system

Arterial baroreceptors

Pain and temperature

Question 18

Gamma system

Answer 18

Involved in sensation of dyspnoea

Question 19

Response to CO2

Answer 19

Primary factor controlling ventilation

Response to CO2 is reduced during sleep so PCO2 rises slightly whilst asleep

Question 20

Ventilation response to PO2

Answer 20

PO2 has to drop quite far before notable change in ventilation occurs

No role under normoxic conditions

Response is increased if PCO2 is also raised

Important for high altitude and certain chronic lung disease

Question 21

Ventilation response to reduced blood pH

Answer 21

Sensed by peripheral chemoreceptors

Important for metabolic acidosis

If severe reduction in pH, central chemoreceptors may be stimulated

Question 22

Ventilation response to exercise

Answer 22

Ventilation increases but mechanism unclear

In moderate exercise, blood gases remain normal

Question 23

Types of sleep apnoea

Answer 23

Obstructive

Central

Question 24

Obstructive sleep apnoea

Answer 24

Airway obstruction from tissue

Sleep deprivation leads to daytime somnolence and cognitive impairment

Question 25

Central sleep apnoea

Answer 25

Respiratory depression during sleep

Recognised by absence of respiratory efforts