Physiology 4: Control of Respiration (L6)

Question 1

Name the 2 divisions of respiratory control

Answer 1

• Neural Control

- Chemical Control

Question 2

Where in the brain is the respiratory centre located

Answer 2

The Pons and Medulla Oblongata

In the brainstem

Question 3

Name the 3 respiratory groups in the brain

Give their locations

Answer 3

• Pontine respiratory group (Pons)
• Ventral respiratory group (Medulla oblongata)
• Dorsal respiratory group (Medulla oblongata)

Question 4

Name the 2 parts of the pontine respiratory group

Give their locations

Answer 4

• Pneumotaxic centre (Superior)

- Apneustic centre (Inferior)

Question 5

What is the general function of the medullary respiratory centres?

Answer 5

To generate rhythm

Question 6

Describe the Pre-Botzinger complex

Answer 6

• Part of the ventral respiratory group
• Generates breathing rhythm
• Exhibits pacemaker activity (Rhythmic firing)

Question 7

Describe the dorsal respiratory group

Answer 7

• Stimulated by the Pre-Bötzinger complex
• A medullary respiratory centre
• Fires in bursts to cause contractions of inspiratory muscles

Question 8

Describe the neural process that leads to inspiration and then expiration

Answer 8

• Pre-Bötzinger complex
  generates rhythm
• Excites dorsal respiratory group neurons
• Dorsal respiratory group neurons fire as a burst
• Causes the contraction of inspiratory muscles and the pneumotaxic centre to fire
• Pneumotaxic centre inhibits inspiration
• Dorsal firing stops, inspiratory muscles relax
• Passive expiration

Question 9

What is the consequence of increased dorsal respiratory group neuron firing?

Answer 9

• Excites the ventral respiratory group

- Causing active expiration

Question 10

Describe the ventral respiratory group

Answer 10

• A medullary respiratory centre
• Excited by the increased firing of dorsal respiratory group neurons
• Activate active expiratory muscles

Question 11

Do ventral respiratory group neurons activate active expiratory muscles in normal breathing?

Answer 11

No

Only during active expiration

Question 12

Describe the pneumotaxic centre

Answer 12

• Located in the pontine respiratory group
• Stimulated by dorsal respiratory group neurons
• Its stimulation terminates inspiration
• Prevents apneusis (long inspirations with short expirations)

Question 13

When the pneumotaxic centre is not functioning what condition is observed

Answer 13

Apneusis

Prolonged inspiration, brief expiration

Question 14

Describe the apneustic centre

Answer 14

• Located in the pontine respiratory group
• It fires to excite the ventral respiratory group (prolonging inspiration)
• (Apneustic centre wants apneusis)

Question 15

What is the general function of the pontine respiratory centres?

Answer 15

To modify the rhythm generated by the medulla

Question 16

Describe the neural process that leads to active expiration

Answer 16

• Pre-Bötzinger complex
  generates rhythm
• Excites dorsal respiratory group neurons
• Dorsal respiratory group neurons fire more than normal
• Causes the contraction of inspiratory muscles more than normal (and the pneumotaxic centre to fire)
• Pneumotaxic centre inhibits inspiration
• Increased dorsal group firing activates the ventral resp group, activates active expiratory muscles
• Dorsal firing stops –> inspiratory muscles relax
• Active expiration

Question 17

The respiratory centres are influenced by stimuli received from different places.

List these places

Answer 17

• Higher brain centres (cerebral cortex, hypothalamus)
• Pulmonary stretch receptors
• J receptors
• Temperature
• Adrenaline
• Joint receptors
• Baroreceptors
• Central chemoreceptors
• Peripheral chemoreceptors

Question 18

Describe the function of pulmonary stretch receptors in the lungs in influencing respiratory centres

Answer 18

• In the walls of bronchi and bronchioles
• Activated by large inspiration
• Activation inhibits inspiration
• The Hering-Breuer inflation reflex prevents hyperinflation

Question 19

Describe the function of J receptors in the lungs in influencing respiratory centres

Answer 19

• Juxtapulmonary (J) receptors

Stimulated by:

• Pulmonary capillary congestion
• Pulmonary oedema
• Pulmonary emboli

Question 20

Describe the function of joint receptors in the lungs in influencing respiratory centres

Answer 20

• Stimulated by joint movement (usually in exercise)

NB: (joint receptors ARE NOT J-receptors)

Question 21

Describe the function of baroreceptors in the lungs in influencing respiratory centres

Answer 21

Decreased bp causes an increased respiratory rate

Question 22

Describe the Hering-Breuer inflation reflex

Answer 22

• Pulmonary stretch receptors detect excessive inspiration
• Signal to respiratory centres
• Inhibit inspiration

Question 23

List factors that may increase ventilation during exercise

Answer 23

• Joint receptor stimulation
• Adrenaline release
• Cerebral cortex
• Increase temp (hypothalamus)
• Accumulation of carbon dioxide and hydrogen ions

Question 24

Describe how a cough is stimulated

Answer 24

• Airway irritation or chemical detection
• Nerve impulse to cough centre in the medulla
• Stimulates a cough

Question 25

Is chemical control of respiration a negative or positive feedback control system?

Answer 25

-ve feedback control system

Question 26

Name the 2 types of chemoreceptors

Answer 26

- Peripheral Chemoreceptors | - Central Chemoreceptors

Question 27

Describe peripheral chemoreceptors

Answer 27

- Found in the carotid bodies and aortic bodies - Sense the blood gas tensions of oxygen and carbon dioxide - Senses the [hydrogen ions] in the blood

Question 28

What are the carotid bodies and aortic bodies?

Answer 28

Carotid: - Regions of peripheral chemoreceptors in the carotid arteries Aortic: - Regions of peripheral chemoreceptors in the aora

Question 29

Describe central chemoreceptors

Answer 29

- Located near the medullary surface | - Responds to [hydrogen ions] in the cerebrospinal fluid (CSF)

Question 30

Define blood gas tension

Answer 30

The partial pressure of a gas dissolved in the blood

Question 31

Give the acronym for the partial pressure of a gas in: - Arteries, veins, capillaries, alveoli

Answer 31

Artery - a Alveoli - A Vein - v Capillary -c (include this as subscript between the "P" and The formula of the gas)

Question 32

The cerebrospinal fluid is separated from blood by what?

Answer 32

- The blood-brain barrier

Question 33

Describe the permeability of the blood-brain barrier to: - Hydrogen ions - Bicarbonate ions - CO2

Answer 33

Relatively impermeable: - Hydrogen ions - Bicarbonate ions Easily Diffuses: - CO2

Question 34

Describe the buffering ability of cerebrospinal fluid

Answer 34

Less than blood As it has less protein

Question 35

Describe the effect of arterial hypercapnia on: - Peripheral chemoreceptors - Central chemoreceptors

Answer 35

Peripheral Chemoreceptors: - Weak Stimulation Central Chemoreceptors: - Poor buffering in the CSF allows the readily diffused CO2 to generate hydrogen ions - These H ions dominantly stimulate (dominant control of ventilation)

Question 36

Describe the effect of arterial hypoxia on: - Peripheral chemoreceptors - Central chemoreceptors

Answer 36

Peripheral Chemoreceptors: - Stimulated if PO2 < 8kPa - Called the hypoxic drive of respiration Central Chemoreceptors: - Severe hypoxia depresses the respiratory centres

Question 37

Describe when the hypoxic drive of respiration occurs

Answer 37

- Not during normal respiration - If PO2 falls below 8kPa - Important if chronic CO2 retention (COPD), or at high altitudes

Question 38

Define the hypoxic drive of respiration

Answer 38

The stimulation of peripheral chemoreceptors by a low PO2

Question 39

What are the acute responses to hypoxia?

Answer 39

- Hyperventilation | - Increases cardiac output

Question 40

What are the chronic responses to hypoxia? Describe the purpose of these changes

Answer 40

- Red blood cell production (better oxygen carrying capacity) - Increased 2,3-bisphosphoglycerate in RBCs (oxygen offloaded more readily at tissue) - More capillaries (better difusion) - More mitochondria (more efficient oxygen use) - Kidneys conserve acid (arterial pH decrease)

Question 41

Describe the effect of arterial H ions on: - Peripheral chemoreceptors - Central chemoreceptors

Answer 41

Peripheral Chemoreceptors: - Stimulation (important in acid-base balance) Central Chemoreceptors: - No effect (H ions can't cross the blood brain barrier)