EXAM III: 5C Regulation of Respiration

Question 0

What is the role of the Brainstem is breathing?

Answer 0

• Breathing is an involuntary process that is controlled bny the medulla and pons.
• The frequency of normal involuntary breathing is regulated by 3 groups of neurons or brainstem centers

Question 1

How is volume of air inspired and expired controlled?

Answer 1

• Tightly controlled both with respect to frequency of breaths and to tidal volume
• Breathing is regulated so lungs can maintain the Pa O2 and Pa CO2 within their normal ranges, even under widely varying conditions such as exercise.

Question 2

What are the 3 neurons or brainstem centers that regulate breathing?

Answer 2

1) Medullary respiratory center
2) apneustic center
3) pneumotaxis center

Question 3

In the Medullary Respiratory (Rhythmicity ) center what is primarily responsible for inspiration and generates the basic rhythm for breathing?

Answer 3

Dorsal Respiratory Group (DRG)

Question 4

What 2 brainstem centers are located in the Pons?

Answer 4

1. Pneumotaxic center

2. Apneustic center

Question 5

What is the difference between DRG and VRG and where are they located?

Answer 5

DRG–> in the MEDULLA, to inspiratory muscles (Diaphragm and external intercostals)

VRG–> in the MEDULLA, to expiratory muscles (internal intercostal and others)

Question 6

What is role of CN X in DRG?

Answer 6

Inputs information from peripheral chemoreceptors and mechanorecepts (e.g ling stretch receptors, irritant receptors, J receptors and joint & muscle receptors)

Question 7

What is role of CN IX in DRG?

Answer 7

• Inputs information from peripheral chemoreceptors

- Output from the DRG travels via the phrenic nerve to the diaphragm & external intercostals

Question 8

What is the role of VRG? when is it activated?

Answer 8

• Responsible for expiration
• Not active during normal, quite breathing, when expiration is passive
• Is activated (during exercise) when expiration becomes an active process

Question 9

When happens when the Dorsal Respiratory group is ACTIVE ?

Answer 9

2 seconds–> Diaphragm & external intercostals actively contract–>normal inspiration

Question 10

When happens when the Dorsal Respiratory group is INACTIVE ?

Answer 10

3 seconds–>Diaphragm & external intercostals relax followed by elastic recoil of the lungs–>Normal expiration

Question 11

Where is the Apneustic center located? When is it stimulated?

Answer 11

• Located in the lower Pons
• Stimulates inspiration, producing deep & prolonged inspiratory gasps (apneusis) followed by occasional brief exhalations

-Stimulation of these neurons excites inspiratory center in medulla, and prolonging the contraction of the diaphragm.

Question 12

Where is the Pneumotaxic center located and what does it inhibit ?

Answer 12

• Located in the upper pons
• inhibits inspiration and limits the burst of APs in the phrenic nerve
• limits the size of the TV

Question 13

What is the Role of the Cerebral Cortex?

Answer 13

Commands of cerebral cortex can temporally override the brainstem centers

Example: person can voluntarily hold breath(increase CO2 and decrease O2) or hyperventilate (decrease CO2 and increase O2)

Question 14

Where are the central chemoreceptors and peripheral chemoreceptors located?

Answer 14

• Central chemoreceptors located bilateral in the ventrolateral medulla.
• Peripheral chemoreceptors are in the aortic arch & carotid arteries

Question 15

How is pH, PCo2, and pH affected in the central chemoreceptors and peripheral chemoreceptors ?

Answer 15

In Central: pH is DECREASED and PCO2 increased

In Peripheral: PO2 ( if < 60 mm Hg) is decreased, PCO2 is increased, and pH is DECREASED

Question 16

What is the most potent and most closely controlled chemicals influencing respiration?
What is the Normal arterial number for this chemical?

Answer 16

CO2

-Normally arterial PCo2 is 40 mmHg and maintained within +- 3 mmHg

Question 17

What are the central chemoreceptors of the medulla sensitive to?

Answer 17

-Sensitive to the pH of the CSF–>decreased in pH i=of the CSF produces an increase in breathing rate (hyperventilation)

-H+ does not cross BBB like CO2 does.
-CO2 diffuses from arterial blood into CSF b/c it is lipid-soluble.
-In the CSF, CO2 combines w/ H2O to produce H+ &
\HCO3—>resulting H+ acts directly on the central chemoreceptors

Question 18

What does an increase in PCo2 and H+ stimulate?

Answer 18

Breathing and decreased PCo2 & H+ inhibit breathing –>The reyslting hyperventilation or hypoventilation then returns the arterial PCO2 toward normal

Question 19

What is the influence of PO2?

Answer 19

• The peripheral chemoreceptors are sensitive to arterial O2
• Under normal conditions , the effect of declining PO2 on ventilation is slight & mostly limited to enhancing the sensory of peripheral receptors to increased PCO2.

Question 20

How does a decreased arterial PO2 affect the peripheral chemoreceptors ?

Answer 20

It stimulates the perip chemoreceptors and increases breathing rate–>PO2 MUST DECREASE to <60 mmHg before breathing is stumulated

-When its less than 60, breathing rate is sensitive to PO2

Question 21

How does a increased arterial PO2 affect the peripheral chemoreceptors ?

Answer 21

Stimulates peripheral chemoreceptors and increases breathing rate.

***However the response of the peripheral chemoreceptors to CO2 is less important then the response of the central chemoreceptors to CO2 (or H+)

Question 22

How does a increased arterial H+ affect the peripheral chemoreceptors ?

Answer 22

Stimulates them directly, independent of changes in PCO2.

Question 23

How is arterial P CO2 affected with people who retain CO2 because of emphysema and chronic bronchitis?

Answer 23

Arterial P Co2 is chronically elevated and as a result chemoreceptors adapt to this chemical stimulus.

Question 24

What is the Hypoxic drive?

Answer 24

A declining PO2 acting on the oxygen-sensitive peripheral chemoreceptors provides the principal respiratory stimulus

Question 25

How is oxygen mixtures administered to respiratory distress patients?

Answer 25

The gas mixtures, are only slightly enriched with O2 b/c inspiration of pure oxygen would slow their breathing, further elevating elevating their PCO2

Question 26

What 2 things happen when PCO2 rises above normal (hypercapnia)?

Answer 26

1) Hypercapnia is sensed by peripheral chemoreceptors –> Afferent neurons carry information to the brainstem–>Medullary rhythmically center receives the information–>Efferent neurons carry information to the inspiratory muscles–>Inspiratory muscles contract more forcefully and more freq. (hyperventilation) –>Arterial pCO2 decreases back towards normal
2) CO2 enters into the CSF from arterial blood–>In CSF, CO2 is converted into H+ via the carbonic anhydrase rxn–> DECREASED pH is sensed by central chemoreceptors

Question 27

What are the effects of Hypoxia on ventilation?

Answer 27

Arterial PO2 falls below 60mmHg *Hypoxia (rare)–> Hypoxia is sensed by peripheral chemoreceptors–>Afferent neurons carry information to the CNS–> Medullary rhythmicity center receives the information–>Efferent neurons carry info to inspiratory muscles –> Inspiratory muscles contract more freq (hyperventilation)–>Arterial PO2 elevates back towards normal

Question 28

What other factors provide input to the brainstem for breathing?

Answer 28

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

Question 29

What is the Lung Stretch receptors (Herring-Breurer REFLEX) ?

Answer 29

• Lung stretch receptors are found in the smooth muscle of the airways
• When excessively stretch receptors send impulses to brainstem which produces a decrease in breathing freq.

Question 30

What is the importance of these lung stretch receptors?

Answer 30

This is a protective reflex to prevent over expansion of the lung. NOT used during NORMAL breathing but increased when labored breathing associated w/ vigorous exercise or climbing

Question 31

What are irritant receptors? Where are they located?

Answer 31

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

-Receptors for noxious chemicals and particles are located between epi cells lining airways
-Information from these receptors travels to the brainstem via vagus nerve
-

Question 32

What are the Joint and Muscle receptors? What are the 2 components involved in the increased respiration that follows the increased oxygen requirement?

Answer 32

• 1st is “anticipation of exercise” activation of SNS
• 2nd activation of stretch receptors (proprioceptors) in skeletal muscle and joints.

**Results in increased rate & depth of respiration. Effect is rapid, and shows an “added value” to stretching before exercise !