5C - Regulation of Respiration

Question 1

What three groups of neurons or brainstem centers regulates the frequency of normal, involuntary breathing?

Answer 1

1. Medullary respiratory center
   - 1a. Dorsal respiratory group
   - 2a. Ventral respiratory group
2. Apneutistic center
3. Pneumotaxic center

Question 2

What two subcenters of neurons in the medulla are part of the regulation of normal, involuntary breathing?

Answer 2

1. Dorsal respiratory group

2. Ventral respiratory group

Question 3

What is the Dorsal respiratory group responsible for?

Answer 3

Inspiration and generates the basic rhythm for breathing

Question 4

What three nerves are involved with the dorsal respiratory group?

Answer 4

CN X, CN IX, and Phrenic nerve

Question 5

5c6. What role does CN X play in regards to the dorsal respiratory group?

Answer 5

Inputs info from peripheral chemoreceptors and mechanoreceptors

Ex. Lung stretch, irritant, J, joint, and muscle receptors

Question 6

5c6. What role does CN IX play in regards to the dorsal respiratory group?

Answer 6

Inputs info from peripheral chemoreceptors

Question 7

5c7. What is the ventral respiratory group responsible for?

Answer 7

(Active) expiration

Is not active during normal, quiet breathing, when expiration is passive

Activated when expiration becomes an active process

Question 8

5c8. What muscles are active during normal inspiration via the dorsal respiratory group?

Answer 8

Diaphragm and external intercostals actively contract

Question 9

5c8. What muscles are active during normal expiration via an inactive dorsal respiratory group?

Answer 9

Diaphragm and external intercostals relax followed by elastic recoil of the lungs

Question 10

5c9. Where is the apneustic center located?

Answer 10

Lower pons

Question 11

5c9. What does the apneustic center stimulate?

- What kind of breathing activity is produced?

Answer 11

Stimulates inspiration

• Produces deep and prolonged inspiratory gasps (apneusis), followed by occasional brief exhalations
• Excites the dorsal respiratory group in the medulla, prolonging the period of action potentials in the phrenic nerve, and thereby prolonging the contraction of the diaphragm

Question 12

5c9. The apneustic center utilizes another respiratory center group to stimulate inspiration. What other respiratory center is it?

Answer 12

The dorsal respiratory group in the medulla

This prolongs the period of action potentials in the phrenic nerve, and thereby prolongs the contraction of the diaphragm. - coordinates the speed of inhalation and expiration

Question 13

5c10. Where is the pneumotaxic center located and what is it responsible for?
- What does it limit the size of?

Answer 13

Located in the upper pons

Inhibits inspiration and limits the burst of action potentials in the phrenic nerve - coordinates the speed of inhalation and expiration

Limits the size of the tidal volume

Question 14

5c11. What part of the brain can temporarily override the brainstem centers?
- What’s an example?

Answer 14

Commands from the cerebral cortex can temporarily override

Voluntarily hyperventilation (increasing frequency and volume)

Question 15

5c11. What is hyperventilation?

Answer 15

Increase breathing frequency and volume

• Decreases Pa (CO2), causing arterial pH to increase
• Can produce unconsciousness however

Question 16

5c11. What is hypoventilation?

Answer 16

Decrease breathing frequency and volume

- Decreases Pa (O2) and increases Pa (CO2)

Question 17

5c12. Where are the central chemoreceptors located?

Answer 17

Located bilaterally in the ventrolateral medulla

Participate in chemoreceptor reflexes

Question 18

5c12. Where are the peripheral chemoreceptors located?

Answer 18

Located in the aortic arch and carotid arteries

Participate in chemoreceptor reflexes

Question 19

5c12. What are the stimuli that stimulate central chemoreceptors?

Answer 19

Decrease in pH

Increase in P (CO2)

Question 20

5c12. What are the stimuli that stimulate peripheral chemoreceptors?

Answer 20

Decrease P (O2) - if < 60 mm Hg
Increase P (CO2)
Decrease in pH

Question 21

5c13. Out of all of the chemicals influencing respiration, what is the most potent and most closely controlled?

Answer 21

CO2

Arterial P(CO2) is normally 40 mmHg and is maintained within 3 mmHg by a sensitive homeostatic mechanism, mainly mediated by central chemoreceptors that monitor rising CO2

Question 22

5c14. What are central chemoreceptors in the medulla particularly sensitive to?

Answer 22

The pH of the CSF

Question 23

5c14. What does a decrease in pH of CSF produce?

Answer 23

Produces hyperventilation - an increase in breathing rate

Question 24

5c14. Physiologically, why would it make sense for chemoreceptors that monitor CSF to be more sensitive to CO2 instead of oxygen?

Answer 24

CO2 can diffuse from arterial blood into CSF because it is lipid-soluble and readily crosses the BBB

Question 25

5c14. What chemical equation summarizes the equilibrium that is maintained for CO2 levels?

Answer 25

CO2 + H2O H2CO2 H + HCO3

Question 26

5c14. Based on CO2 equilibrium levels, increases in PCO2 and H+ will lead to what?

Answer 26

Will stimulate breathing, in order to return arterial P(CO2) towards normal

Question 27

5c14. Based on CO2 equilibrium levels, decreases in PCO2 and H+ will lead to what?

Answer 27

Will decrease breathing, in order to return arterial P(CO2) towards normal

Question 28

5c15. Which chemoreceptors are sensitive to arterial O2?

How sensitive is the body to arterial P O2 levels?

Answer 28

Peripheral chemoreceptors

Arterial PO2 must drop substantially, to at least 60 mmHg in order for ventilation to increase

Question 29

5c16. Decreases in arterial PO2 will stimulate peripheral chemoreceptors to do what?

Answer 29

Increase breathing rate, but they must decrease to <60 in order to stimulate breathing

Question 30

5c16. Increases in arterial PCO2 stimulate peripheral chemoreceptors to do what?

Answer 30

Increase breathing rate, however the peripheral chemoreceptor response is not as important as the central chemoreceptor response to CO2 (and H).

Question 31

5c16. Increase in arterial H stimulate peripheral chemoreceptors to do what?

Answer 31

Increase breathing rate

Question 32

5c16. What is hypoxic drive?

Answer 32

When arterial P(CO2) levels become chronically elevated (due to emphysema and chronic bronchitis) and chemoreceptors become accustomed to the constant high P(CO2) levels, the body will turn to P(O2) levels monitored by peripheral chemoreceptors to regulate breathing.

Question 33

5c16. Why do we need to be careful with oxygen levels in gas mixtures administered to patients with respiratory distress?

Answer 33

Any excess inspiration of oxygen can cause peripheral chemoreceptors to slowdown breathing and elevate P(CO2) as a consequence (oxygen toxicity).

Question 34

5c19. In addition to chemoreceptors, what other receptors provide input to the brainstem and are involved in regulating breathing?

Answer 34

1. Lung stretch receptors
2. Irritant receptors
3. Joint and muscle receptors

Question 35

5c20. Where are lung stretch receptors found?

Answer 35

Smooth muscle of the airways

Question 36

5c20. How does the body respond when lung smooth muscle is excessively stretched?

Why?

Answer 36

The lung stretch receptors will send impulses to the brainstem and decrease breathing frequency.

This is to prevent over-expansion of the lung (defensive mechanism)

Question 37

5c21. What are irritant receptors?
- Location
- What do they monitor
- What nerve to send impulses?

Answer 37

They are located between epithelial cells lining the airways.

They monitor noxious chemicals and particles

They send impulses via the vagus nerve

Question 38

5c21. When irritant receptors are stimulated, what happens?

Answer 38

They cause a reflex constriction of bronchial smooth muscle and an increase in breathing rate.

Question 39

5c22. When we exercise, our body actually increases its oxygen intake even before we need it. What are two components that explain this?

Answer 39

1. Anticipation of exercise - via SNS
2. Activation of stretch receptors (propriocentors) in skeletal muscle and joints.
   - This is detected via the brainstem and results in increased rate and depth of respiration.