Control of Breathing - Lecture 20

Question 1

How is breathing controlled?

Answer 1

○ Establish automatic rhythm
○ Adjust the rhythm to accomodate changes

Question 2

What changes need to be accommodated?

Answer 2

○ Metabolic: arterial blood gases and pH
○ Mechanical: postural changes
○ Episodic non-ventilatory behaviours: speaking, sniffing, eating

Question 3

What are examples of local control of gas transport?

Answer 3

○ PO2 and PCO2 in active tissue
○ Lung perfusion
○ Alveolar ventilation

Question 4

How is delivery of oxygen and removal of carbon dioxide does in active tissue?

Answer 4

○ Increase blood flow through reflex vasodilation
○ Deliver more oxygen
○ Remove more carbon dioxide

Question 5

How is lung perfusion controlled?

Answer 5

○ If there is a decreased partial pressure of oxygen:
- decreased blood flow and vasoconstriction
- direct blood to areas of higher PO2

Question 6

How is alveolar ventilation controlled?

Answer 6

○ Increase in PCO2 increases air flow through bronchodilation
○ Direct airflow to areas of higher PCO2

Question 7

What sensors are responsible in central control of ventilation?

Answer 7

○ Central chemoreceptors
○ Peripheral chemoreceptors
○ Mechanoreceptors

Question 8

What is the function of central chemoreceptors?

Answer 8

○ Detect changes in pH
○ Detect hypercapnia (high CO2 levels)
○ No effect of hypoxia

Question 9

What is the function of peripheral chemoreceptors?

Answer 9

○ Hypoxia
○ Hypercapnia
○ Change in pH

Question 10

What is the function of mechanoreceptors?

Answer 10

○ Respond to stretch in lungs
○ Rapidly adapting receptors
○ Slowly adapting receptors
○ C-fibres receptors
○ All 3 are innverated by the vagus nerve

Question 11

When does the partial pressure of oxygen become a problem for respiratory system?

Answer 11

When it falls below 60mmHg

Question 12

Where is the anatomical location of the central chemoreceptors?

Answer 12

○ Just beneath the ventral surface of the medulla
○ Close to entry of cranial nerves

Question 13

What innervates the peripheral chemoreceptors?

Answer 13

○ Carotid body: innervated by carotid sinus nerve (branch of glossopharyngeal nerve)
○ Aortic bodies: innervated by the vagus nerve

Question 14

What is respiratory acidosis?

Answer 14

When pH is less than 7.35

Question 15

What is respiratory alkalosis?

Answer 15

pH>7.45

Question 16

What happens if PO2 is too high?

Answer 16

Generate free radicals leading to coma and death

Question 17

What does the slowly adapting receptor do and where is it found?

Answer 17

○ Found in visceral pleura, bronchioles and alveoli
○ Respond to over-inflation -> discharge (hering-breuer reflex) -> inhibition of respiratory centres

Question 18

What does rapidly adapting receptor do and where is it found?

Answer 18

○ In airway epithelia (close to mucosa)
○ Irritant stimuli -> increase in discharge -> bronchoconstriction (coughing reflex)
○ Protect the airway
○ Initially fire rapidly but then soon decrease their firing rate

Question 19

What does the C-fibres receptors do and where is it found?

Answer 19

○ In the alveoli walls (close to the capillaries) and conducting airways (bronchial mucosa)
○ Chemical/mechanical stimuli (left sided heart-failure) -> increases discharge -> bronchoconstriction (rapidly shallow breathing and mucus secretion)

Question 20

What is the rhythmicity centre (medulla)?

Answer 20

○ Controls automatic breathing (quiet breathing)
○ Interact neurons that fire either during inspiration or expiration

Question 21

What is the pneumotaxic and apneustic centre (pons)

Answer 21

○ Modify firing pattern of medullary centres
○ Regulate respiratory rate and depth of respiration

Question 22

How does the rhythmicity centre work?

Answer 22

○ I neurons in DRG -> Regulates activity of phrenic nerve -> set rhythm & stimulate the muscles of quiet inspiration
○ E neurons in VRG -> Passive process -> activity inhibits I neurons

Question 23

How does pneumotaxic and apneustic centres work?

Answer 23

Apneustic:
○ Promotoes inspiration -> stimulates the I neurons
○ Increases intensity of inhalation during respiratory cycle
Pneumotaxic:
○ Inhibits apneustic centre -> stop inhalation & promote exhalation
○ Neither are essential for quiet breathing