Lecture 20 - Control of Breathing

Question 1

What are the three examples of Local Control of gas transport?

Answer 1

• Vasodilation in response to increased PCO2 in systemic system
• Lung Perfusion (Vasoconstriction in areas of decreased PO2)
• Alveolar Ventilation (Bronchodilation to direct air flow to areas of higher PCO2)

Question 2

Define hypercapnia

Answer 2

High PCO2 in blood

Question 3

Where specifically are the central chemoreceptors found?

Answer 3

Just beneath the ventral surface of the medulla (near the entry of the VIII and XI cranial nerves)

Question 4

Where specifically are the peripheral chemoreceptors found?

Answer 4

Carotid body - at the bifurcation of the carotid arteries
Aortic bodies - above and below the aortic arch

Question 5

Which stimulus(i) do the central chemoreceptors respond to, and what response do they prompt?

Answer 5

Increased PCO2 -> decreased pH (as CSF is only weakly buffered) -> increased ventilation -> decreased PCO2

Question 6

What stimulus(i) do the peripheral chemoreceptors respond to?

Answer 6

Increased PCO2, decreased pH AND decreased PO2 (below 60 mmHg)

Question 7

Which nerves innervate the two peripheral chemoreceptors?

Answer 7

Carotid - carotid sinus nerve (CSN) -> glossopharyngeal
Aortic - vagus nerve

Question 8

What happens to the equilibrium when CO2 increases (and what is the condition called)?

Answer 8

Equation is pushed to right (more acidic) -> respiratory acidosis

Question 9

What happens to the equilibrium when CO2 decreases (and what is the condition called)?

Answer 9

Equation is pushed to left (more alkaline) -> respiratory alkalosis

Question 10

What can result from increased O2 (e.g., breathing oxygen-rich mixtures)?

Answer 10

Generation of free-radicals leading to coma and death

Question 11

Where are Slowly Adapting Stretch Receptors found and what response do they stimulate?

Answer 11

In the visceral pleura, bronchioles and alveoli -> Hering-Beruer Reflex

Question 12

Describe the Hering-Breuer Reflex

Answer 12

The Slowly Adapting Stretch Receptors (bronchopulmonary SRs) detect an overinflation of the lungs -> they increase discharge -> respiratory centres are inhibited

Question 13

Where are Rapidly Adapting Stretch Receptors found and what response do they stimulate?

Answer 13

In airway epithelia, close to mucosa -> cough reflex

Question 14

Describe the function of Rapidly Adapting Stretch Receptors

Answer 14

They are irritant receptors - in response to noxious gases, smoke/dust, cold air etc. they increase discharge -> bronchoconstriction (cough reflex)

Question 15

Where are C-fibres receptors found?

Answer 15

In the alveoli wall (close to capillaries) and conducting airways (bronchial mucosa)

Question 16

Describe the function of C-fibre receptors

Answer 16

In response to chemical/mechanical stimuli (e.g., left heart failure -> engorgement of pulmonary capillaries) they increase discharge -> bronchoconstriction, rapid shallow breathing, mucus secretion

Question 17

What are the OVERALL functions of the respiratory centres found in the pons and medulla?

Answer 17

Medulla - rhythmicity centre -> controls automatic breathing
Pons - pneumotaxic and apneustic centres -> modify firing pattern of medullar centres

Question 18

What are the two groups found in the rhythmicity centre and which neurons are found in each?

Answer 18

Dorsal Respiratory Group (DRG) - I (inspiratory) neurons
Ventral Respiratory Group (VRG) - E (expiratory) + I neurons

Question 19

What is the function of the apneustic centre?

Answer 19

Promotes Inspiration by stimulating I neurons

Question 20

What is the function of the pneumotaxic centre?

Answer 20

Inhibits apneustic centre -> stop inhalation and promote exhalation