Control of ventilation

Question 1

What are the roles of chemoreceptors? (2)

Answer 1

Chemical control of ventilation

Detect changes in arterial pCO2, pO2 and [H+]

Question 2

What are the 2 types of chemoreceptors, where are they located and what do they detect?

Answer 2

Central chemoreceptors: Medulla - [H+] and pCO2

Peripheral chemoreceptors: aortic arch and carotid arteries - pO2 and pH

Question 3

Explain the what happens at the blood brain barrier: (5)

Answer 3

1. Increase of pCO2 causes CO2 to diffuse out of the blood vessel
2. CO2 + H2O H2CO3 HCO3- + H+
3. Increase in H+ extracellular fluid and cerebrospinal fluid. Detected by CCRs and leads to hyperventilation
4. Hypervewntilation decrease pCO2 in blood and CSF
5. Decrease pCO2 = hypoventilation

Question 4

What is the blood brain barrier impermeable and impermeable to?

Answer 4

Impermeable: H+ & HCO3- (ions)
Permeable: CO2

Question 5

What do pCO2 levels indirectly cause?

Answer 5

Indirectly activates CCRs causing a response of hyper or hypoventilation

Question 6

What does the aortic arch detect and what is the result of this?

Answer 6

Arterial O2, CO2 levels

Hyperventilation when O2 decreases below 13.3mmHg (kPa)

Question 7

What does the carotid artery detect?

Answer 7

pH levels

Question 8

What is the priority of responses from a ventilation stimulus?

Answer 8

1. PCO2
2. pH
3. PO2

Question 9

What chemoreceptors are most sensitive to PCO2?

Answer 9

CCRs - levels held within 0.3kPa

Question 10

What chemoreceptors are quickest to detect rapid changes in PCO2?

Answer 10

PCRs - levels held within 1.3kPa

Question 11

Why do we control PCO2?

Answer 11

Avoid acid-base problems

Question 12

How can we increase ventilation? (3)

Answer 12

Decrease pH making it more acidic
Increase CO2
Increase ventilation to remove CO2

Question 13

What chemoreceptors detect changes in PO2?

Answer 13

PCRs - stimulated when levels drop lower than 13.3kPa

Question 14

Why control PO2?

Answer 14

Avoid hypoxia

Question 15

What is neural regulation of ventilation? (2)

Answer 15

Sets the rhythm and pattern of ventilation

Controls respiratory muscles

Question 16

What is chemical regulation?

Answer 16

Detects central and peripheral arterial PCO2 and pH and peripheral PO2

Question 17

Why is neural regulation faster than chemical regulation? (2)

Answer 17

Neural control - dependent on fast acting impulses to and from the CNS
Chemical control - responds to changes in partial pressure of CO2/O2

Question 18

What are the parts in the medulla? (2)

Answer 18

Dorsal respiratory group (above ventral)

Ventral respiratory group

Question 19

What is the role of the dorsal respiratory group? (3)

Answer 19

1. Fibres from DRG innervate the diaphragm and external intercostal muscles
2. Diaphragm contraction and thoracic cavity expansion causes inspiration
3. DRG neurone switch on for 2s and switch off for 3s causing a rhythmic pattern

Question 20

What is the role of the ventral respiratory group? (2)

Answer 20

1. Fibres from VRG innervate the abdominal muscles and internal intercostal muscles
2. Activity enhanced during forced expiration

Question 21

What is involved within the Pons section of the brain? (2)

Answer 21

Pneumotaxic centre (above the medulla)
Apneustic center

Question 22

What is the role of the pneumotaxic centre? (5)

Answer 22

1. Transmit signals to the DRG
2. Role is to limit inspiration
3. Fine tunes breathing - inhibits DRG with impulses
4. Limit the period of inspiration to 2s
5. Prevents over-inflammation of the lungs

Question 23

What is the role of the apneustic centre? (3)

Answer 23

1. responsible for prolonged inspiratory gasps
2. Prolong DRG stimulation
3. Apneusis observed in severe brain injury

Question 24

What is the role of the vagus nerve? (2)

Answer 24

Sends afferent information from lungs to DRG

Role is to prevent over inflation of the lungs by switching off inspiration

Question 25

What are the higher brain centers involved in ventilation? (5)

Answer 25

Cerebral cortex - breathing rate and depth
Hypothalamus - homeostasis, endocrine, thirst
Pons
Medulla
Brainstem

Question 26

What is the role of the cerebral cortex? (3)

Answer 26

1. Stimulates motor neurones of the inspiratory muscles
2. Bypasses the medullary centers when consciously holding breath
3. Limited ability to holds breath - respiratory centers automatically reinitiate breathing when O2 conc in blood reaches critical levels (drowning)

Question 27

What is the role of the hypothalamus?

Answer 27

1. Strong emotions, pain and changes in temp can alter rate and rhythm
2. Apnoea (suspension of breathing) can be induced by anger, pain or decrease in temp
3. Tachypnoea (rapid breathing) can bee induced by excitation or increase in temp

Question 28

What are stretch receptors and where are they located? (4)

Answer 28

• Respiratory reflexes
• located in smooth muscle of trachea and bronchi
• Sensitive to lung expansion
• Stops overinflation of the lungs by short, shallower breaths

Question 29

What are juxtapulmonary receptors? (3)

Answer 29

1. Lie in the alveolar wall between epithelium and endothelium
2. Stimulated by congestion, oedema, histamine
3. Activation results in responses such as apnoea or rapid shallow breathing, bronchoconstriction and mucus secretion

Question 30

What are irritant receptors? (4)

Answer 30

• Respiratory reflexes
• Located between epithelia cells
• Sensitive to irritant gases, smoke and dust
• Activation results in rapid shallow breathing, cough, bronchoconstriction, mucus secretion, augmented breaths