Lecture 9 - Breathing Control

Question 1

Why is taking in oxygen necessary?

Answer 1

requirement for generating ATP through oxidative phosphorylation

Question 2

what is a by-product of respiration?

Answer 2

CO2

Question 3

What is minute ventilation

Answer 3

breathing frequncy x tidal volume

10 breaths in a minute x 500 ml = 5L per minute

Question 4

Why is minute ventilation less than 500 ml?

Answer 4

due to the dead space in the upper airways

reduces 500 ml to around 350ml which is alveolar minute ventilation at rest

Question 5

what happens to o2 consumption during rest?

Answer 5

can increase to more than 10 fold

Question 6

What happens to breathing at a higher altitude?

Answer 6

less O2 in the air so need to work harder to maintain O2 supply

Question 7

How does disease affect breathing?

Answer 7

compromise gas exchange or delivery

Question 8

Give examples of diseases that compromise gas exchange or delivery

Answer 8

Pulmonary diseases - emphysema
cardio - heart and vasculature
sleep apnoea
opioid depression of breathing
conditions of chronic hypercapnia - require oxygen sensing

Question 9

Describe control of respiratory output

Answer 9

factors/sensors providing information to the respiratory centre act as an input to the respiratory centre and act as output to target muscles controlling ventilation

Question 10

What is the function of the pons and the medulla

Answer 10

medulla is the primary centre

pons: regulates medulla

Question 11

Dorsal respiratory group

Answer 11

Contains neurones which fire during inspiration

Question 12

Ventral respiratory group

Answer 12

contain mixed neurones some fire during inspiration and some during expiration

Question 13

What happens to the Ventral and dorsal respiratory group during exercise?

Answer 13

there is reciprocal inhibition during exercise. Inspiratory nerve activity is high and expiratory nerve activity is low and they alternate between high and low in a dna shape

Question 14

What role does the pons play in stimulating respiratory activity

Answer 14

Stimulates the Apneustic and pneumotaxic centre

Question 15

What depresses inspiratory activity?

Answer 15

hypoxia, wide variety of therapeutic drugs (opiates, barbirates and anaesthetics) and inhibition of blood supply

Question 16

What are the main centres providing information to the respiratory centre?

Answer 16

1. Voluntary - higher centers (cerebral cortex control over breathing
2. Automatic - respiratory centres in medulla regulated by pons

Question 17

What are the factors providing information to the respiratory centre causing negative activity?

Answer 17

stretch receptors in the lungs

irritant receptors in the lungs (trachea)

Question 18

What are the factors providing information to the respiratory centre causing positive activity?

Answer 18

Peripheral chemoreceptors in aorta and carotid artery - detect decrease in O2, increase in CO2 and H+
Central chemoreceptors - increase in CO2 and H+
Receptors in muscles and joints

Question 19

Describe the higher brain centre influences

Answer 19

Cortical (Cortex) - voluntary hyperventilation - hypocapnia (low CO2) - Alkalosis
voluntary breath holding - hypoxia (low O2) - unsustainable

Hypothalmic - emotions - anger, anxiety - hyperventilation
Sensory reflexes - pain and cold - gasping and hyperventilation

Question 20

How do pulmonary stretch receptors function

Answer 20

afferent fibres from smooth muscles of bronchi and trachea run in the vagus nerve to the respiratory centre in the medulla
so as inspiration progresses, the dorsal respiratory group that increases inspiration is inhibited and VRG is stimulated (expiration)

Question 21

What is Hering-Breuer lung inflation reflex

Answer 21

it is a reflex that prevents overinflation of the lung

limits breathing frequency (f) x tidal volume (Vt)

Question 22

How to irritants/cough receptors affect respiration?

Answer 22

receptors through airways when stimulated initiate explosive expiration - cough
afferent fibres from these receptors run in the vagus to the respiratory centre
irritant receptors also found in upper airways and nose. Stimulation leads to hyperpnoea and airway constriction which can lead to coughing or sneezing

Question 23

What does local anaesthetics do to reflexes?

Answer 23

They prevent them when passing endotracheal and nasogastric tubes into patients

Question 24

What factors affect muscle/joint receptors and proprioreceptors?

Answer 24

muscle spindles rich in intercostals, few in diaphragm
activated by stretch associated with contraction of breathing, but spindles in exercising muscles
proprioceptors in joints also relay information about activity induced motion which can influence ventilation

Question 25

What role do baroreceptors play in neural modulation?

Answer 25

detect change in blood pressure and can influence ventilation (increase in BP leads to lower ventilation and vice versa)

Question 26

What role do Juxtacapillary receptors play in neural modulation

Answer 26

lie close to capillaries around the alveolar walls. they are activated by traumas such as pulmonary oedema, fluid in the alveoli, inflammatory agents, pneumonia. Their activation triggers increased ventilation

Question 27

What are central chemoreceptors?

Answer 27

specialised regions close to the medulla respiratory centres, but also close to a rich blood supply.
sensitive to CO2 and H+.
h+ cannot cross the blood-brain barrier, but CO2 can, which informs about H+ levels:
rise in CO2 or a rise in H+ stimulates chemoreceptors and increases ventilation

Question 28

What and where are peripheral chemoreceptors?

Answer 28

located in carotid and aortic bodies
sensitive to hypoxia and hypercapnia (high CO2)
and acidosis (high H+)

Question 29

Type of peripheral chemoreceptor

Answer 29

glomus cell which is a primary detector of hypoxia

Question 30

How does the glomus cell initiate action potentials to the respiratory centre

Answer 30

hypoxia triggers ca2 influx into glomus cells via depolarisation (like nerve terminal). the Ca2+ triggers release of neurotransmitters which initiate action potentials in the afferent nerve
Dopamine: one transmitter released, but excitation is from ATP and acetylcholine