WEEK XV (Control of respiration)

Question 1

What are the two mechanisms that regulate respiration?

Answer 1

• Nervous regulation of respiration
• Chemical regulation of respiration

Question 2

What are the components of Neural control of Respiration?

Answer 2

• Factors that generate the alternating inspiration-expiration rhythm
• Factors that regulate the magnitude of ventilation to match body needs
• Factors that modify respiratory activity for other purposes

Question 3

What centre in the brain stem generates the rhythmic pattern of breathing?

Answer 3

Medullary respiratory center

Question 4

What are the Inspiratory and Expiratory Neurons in the Medullary Center?

Answer 4

• Dorsal Respiratory Group (DRG)
• Ventral Respiratory Group (VRG)

Question 5

What are the properties of the Dorsal Respiratory Group (DRG)?

Answer 5

• Mostly inspiratory neurons
• Descending fibers terminate on motor neurons supplying inspiratory muscles
• When DRG inspiratory neurons fire -> stimulate inspiratory muscles -> INSPIRATION
• When DRG neurons stop firing -> inspiratory muscles relax -> Passive expiration occurs

Question 6

What are the properties of the Ventral Respiratory Group (VRG)?

Answer 6

• Composed of inspiratory and expiratory neurons
  [both inactive during normal quiet breathing]
• Called into play by DRG during increased ventilation demands
• Important in ACTIVE EXPIRATION

Question 7

What is the Pre-Botzinger complex?

Answer 7

• Located in the upper end of the VRG
• Generates basic rhythm of ventilation by displaying pacemaker activity

Question 8

What is the difference between the Pneumotaxic center and the Apneustic center?

Answer 8

PNEUMOTAXIC CENTER
- sends impulses to the DRG to limit the duration of inspiration
- dominates over the apneustic center to regulate normal breathing patterns

APNEUSTIC CENTER
- provides extra boost to the inspiratory drive

Question 9

What is the Hering-Breuer reflex?

Answer 9

A reflex triggered during exercise when tidal volume is large, preventing overinflation of the lungs

[stretch receptors in the small airways send inhibitory signals to the MEDULLARY CENTER to cut inspiration short before overinflation occurs]

Question 10

Ventilation magnitude is adjusted in response to which chemical factors?

Answer 10

• PO2
• PCO2
• H+

Question 11

Arterial PO2 is monitored by which peripheral chemoreceptors?

Answer 11

Carotid bodies and aortic bodies

Question 12

When do the peripheral chemoreceptors respond?

Answer 12

When arterial PO2 falls below 60mmHg

[an important emergency mechanism in dangerously low arterial PO2 states]

Question 13

What do Central chemoreceptors respond to?

Answer 13

Located in the MEDULLA near the respiratory center, they respond to changes in CO2-induced H concentration in the brain extracellular fluid (ECF) resulting from increased PCO2 in the arterial blood

Question 14

What can high levels of CO2 result in?

Answer 14

• Depress entire brain, including the respiratory center
• Depress respiratory neurons instead of further increasing ventilation

Question 15

What is Apnea?

Answer 15

The transient interruption of ventilation with breathing resuming spontaneously. If breathing does not resume, it is called RESPIRATORY ARREST.

[during apnea, a person “forgets to breathe; during dyspnea, a person feels “short of breath”]

Question 16

What is Sudden Infant Death Syndrome (SIDS)?

Answer 16

Also known as “crib death” is a tragic form of sleep apnea that can result in a death of a previously healthy infant

CAUSE:
Not fully understood but is related to immature respiratory control or abnormal lung development or bacterial infection

RISK FACTORS:
- Sleeping position (sleeping on abdomen)
- Exposure to nicotine

Question 17

What is Dyspnea?

Answer 17

Sensation of not getting enough air or feeling “short of breath”

[It is not directly related to chronic changes in arterial PCO2 or PO2]

Question 18

What happens when O2 concentration in blood decreases?

Answer 18

Stimulates the peripheral chemoreceptors -> Transmission of impulses to respiratory centres -> Activation of respiratory centres -> Increases the activities of respiration (RATE + DEPTH) -> Increase alveolar ventilation -> Increases the uptake of O2 -> Increases the level of O2 in blood

Question 19

What happens when CO2 concentration in blood increases?

Answer 19

Stimulates chemoreceptors -> Transmission of sensory impulses to respiratory centres -> Activation of respiratory centres -> Increases the activities of respiration (RATE + DEPTH) -> Increase alveolar ventilation -> Expulsion of CO2 and decreases the level of CO2 in blood