Phys: Test 3: Lecture 8. Control Of Ventilation

Front 1

Review: how will arterial PO2, CO2, and pH change in hypoventilation?

Back 1

• PO2 decrease
• CO2 increase
• pH decrease

Front 2

List the components of the ventilatory control system. What kind of system is it?

Back 2

• The ventilator control system is a negative feedback system
• 3 basic elements
o Respiratory control center(feedback controller)
 Respiratory muscles (effector)
• Chemoreceptors (lung receptors) [sensor]

Front 3

What is the main regulated variable by chemoreceptors?

Back 3

PCO2, also respond to inflation of lungs and irritants

Front 4

Describe the location and broad functions of the respiratory control center.

Back 4

• The respiratory control center is located in the medulla and pons
o Medulla integrates the info from the body while the pons modifies patterns for inspiration and expiration
 Thus the pons can modify how the medulla sends signals
• Integrator (medulla) gets info from the cortex, hypothalamus/limbic system, chemoreceptors, lung receptors

Front 5

List the brain regions outside of the respiratory control center that can influence
ventilation. (feed to integrator, 5)

Back 5

cortex, limbic system, hypothalamus, lung receptors, chemoreceptors

Front 6

. List and describe the location and function of the main groups of neurons that are
thought to control inspiration and expiration

Back 6

• Medulla
o Medullary respiratory center
 Causes firing for inspiration/expiration

Front 7

Divisions of the Pons and their functions?

Back 7

o Lower pons: apneustic area
 Prolongs inspiration
o Upper Pons: Pneumotaxic center
 Turns off inspiration
 Good for fine tuning

Front 8

What are the divisions of the medullary respiratory center?

Back 8

• Ventral respiratory group
o Mainly expiration
o Quiescent at rest
 This is because you just relax to exhale, aka turn off dorsal respiratory group

Front 9

Inspiratory 'off-switch' neurons get input from where and send a signal out to what?

Back 9

Inputs:
+ lung stretch receptors, pneumotaxic center, integrator neurons

- from apneustic area

Output: integrator neurons

Front 10

Describe the Hering-Breuer reflex. Explain how lung stretch and irritant receptors
can influence the pattern of ventilation.

Back 10

• Stimulation of lung stretch receptors promotes expiration and
-irritant receptors promote inspiration
• Increase in lung volume inhibits further inspiration, promotes expiration
o Also vice versa
• Only activated during high tidal volumes

Front 11

Describe the locations, stimuli, neuronal pathways and effect of stimulation of
bronchial C-fibers and J-receptors.

Back 11

• J
o Juxtacapillary (right next to)
o Stimulated by engourgment of fluid (edema)
o When stimulated get rapid shallow breathing
• C
o Bronchial
o Respond to chemicals in bronchial circulation
o Inflammation stimulates these receptors
 Partially responsible for restriction seen in asthma
o Again, when stimulated get rapid shallow breathing (due to bronchiole constriction)

Front 12

. List the chemoreceptors in order of their importance for ventilatory control under
normal resting conditions. Describe the locations of chemoreceptors in the body.

Back 12

• 1. Central
o Near ventral medulla
• 2. Peripheral
o Carotid bodies
 At bifurcation of common carotid
o Aortic
 Above and below aortic arch

Front 13

Describe the mechanism of stimulation of central chemoreceptors

Back 13

• Respond to pH of the CSF, which is dependent of PCO2
• Increased CO2 in blood vessel diffuses into ECF
o End up getting H+ in the CSF due to high CO2
 The CSF is not able to buffer the H+ as well as in the ECF, thus it responds more readily to changes in H+ (more sensitive)
• The H+ is what activates the chemoreceptors to increase ventilation

Front 14

Describe the stumuli that activate the peripheral chemoreceptors.

Back 14

• Respond primarilay to hypoxia (important in COPD and arterial hypoemia) (low PO2 in blood)
• Also Respond to arterial PCO2 and pH

Front 15

partially compensated metabolic acidosis will be sensed by what kind of receptor?

Back 15

peripheral chemoreceptors

Front 16

Describe the variation of ventilation with increases in arterial PCO2 or decreases in
arterial PO2. Name the parameter that is most important for the control of ventilation
under normal conditions.

Back 16

• PCO2 is the parameter controlling ventilation

due to the fact that the relationship between PACO2 and ventilation is steep

Front 17

List the factors that reduce the sensitivity of the chemoreceptors to arterial PCO2

Back 17

• Sleep
• Barbiturates
• COPD
• Anesthetics

Front 18

Explain why giving pure oxygen to a patient with severe COPD may decrease
ventilation.

Back 18

• In severe COPD, peripheral chemoreceptors can provide the main drive to breathe (in essence the central chemoreceptors are knocked out)
• When you give them oxygen you increase the arterial PO2
o This abolishes the stimulation of the peripheral chemoreceptors
 Reducing the drive to breathe
• Which can actually enhance the problem

Front 19

Describe the nature of the contribution made by the peripheral chemoreceptors to
the total response to an increase in arterial PCO2.

Back 19

• They respond faster than the central ones (because of their proximity to the lung)
• But they only contribute about 20% of the total response (central will take care of the rest)

Front 20

16. Describe the pattern of breathing in Cheyne-Stokes respiration. Explain how this
pattern can be produced in heart failure by J-receptor and peripheral chemoreceptor
stimulation combined with slowed circulation.

Back 20

o Hypoxemia stimulates peripheral chemoreceptors
o J receptor stimulation due to heart failure (edema)
 Leads to hyperventilation
• Decreased PaCO2
o Due to slowed circulation (because of heart failure) by the time the info hits the chemoreceptor, the receptor will think that breathing is too high and stop it, causing apnea
 Then your body will need to respond to the hypoxia again by hyperventilating
• Vicious cycle
•
• Rapid increase of breathing followed by rapid cessation