Resp. 5 - Control of Ventilation

Question 1

Respiratory Control System

Answer 1

1. Automatic Rhythm
2. Rhythm Adjustment to Changing Demands

– E.g. – metabolic demands ( PO2 , PCO2 and pH)

Question 2

Automatic rhythm used when were not consciously controlling breathing, in tune with

Answer 2

metabolic demands (partial pressure of O2 and CO2 and pH) that will increase or decrease ventilation or the depth of breathing or the rate.

Question 3

Change in partial pressures are monitored by:

Answer 3

• Peripheral Chemoreceptors (PCR)
• Central Chemoreceptors (CCR)

-Drive the CPG (central pattern generator)

Question 4

What does the CPG do?

Answer 4

Increase or decrease ventilation

Question 5

Respiratory and Metabolic Acidosis/Alkalosis:

Answer 5

• Respiratory acidosis →
• Respiratory alkalosis →
• Metabolic Acidosis →
• Metabolic Alkalosis →

Question 6

• Respiratory acidosis →

Answer 6

hypoventilation (CO2 production > CO2 elimination): not only PCO2 ↑ but also H+ concentration ↑

Question 7

• Respiratory alkalosis →

Answer 7

hyperventilation (CO2 production < CO2 elimination): not only PCO2 ↓ but also H+ concentration ↓

Question 8

• Metabolic Acidosis →

Answer 8

↑ in blood H+ concentration independent from changes in PCO2

Question 9

• Metabolic Alkalosis →

Answer 9

↓ in blood H+ concentration independent from changes in PCO2

Question 10

Where are peripheral chemoreceptors located

Answer 10

Carotid and aortic bodies

Question 11

Peripheral Chemoreceptor Sense mostly changes in

Answer 11

arterial PO2 and will also be activated by changes in pH (H+ conc.).

Question 12

• The carotid and aortic bodies sense primarily

Answer 12

hypoxia, which is a low arterial PO2 level

Question 13

Which cells are coupled with blood vessels to monster the levels of O2 levels

Answer 13

The Glomus Cell Is the Chemosensor in the Carotid and Aortic Bodies

Question 14

_______ that are responsible for evoking an increase in ventilation to a decrease in PaO2.

Answer 14

Glomus cells

Question 15

Type I glomus cells -

Answer 15

chemosensitive; drive the response, or the change in ventilation, if there are changes in the arterial PO2.

• Triggered when O2 falls below 60 mmHg.
• sensitive to high conc. of H+ (low pH)

Question 16

Chemical Control of Ventilation- CCR

Answer 16

• Sensitivity to increase in PaCO2(H+)

* Indirectly does sensitive to PaCO2, and directly sensitive to H+ levels.

Question 17

Respiratory Acidosis vs Metabolic Acidosis

Answer 17

Both result in significant responses when viewed by CCR

Respiratory Acidosis: increase in PaCO2 and decrease in pH

Metabolic Acidosis: no change in PaCO2 but decrease in pH

Question 18

Metabolic acidosis Occurs with the production of

Answer 18

acids which are carried in the blood and are not associated with changes in PCO2

Question 19

Metabolic acidosis process

Answer 19

concentration of H+ → activation of PCR (glomus cells in carotid bodies) → increase ventilation → decrease alveolar PCO2 → decrease arterial PCO2 → return of arterial hydrogen ions towards normal levels

Question 20

• H+ stimulates mostly peripheral chemoreceptors because

Answer 20

H+ does not cross easily blood brain barrier (As CO2 does)

Question 21

Respiratory acidosis process

Answer 21

As CO2 crosses the BBB, producing more bicarbonate and H+, the pH will drop making it more acidic, the CCR then respond by increasing ventilation.

Question 22

Dependence of CSF pH on blood pH

Answer 22

• the response for repository acid-base changes is far greater then metabolic acid-base changes because of the H+ easily detected by CCR.
• the reps once for Metabolic acid-base changes is a lot smaller since H+ aren’t diffusible, and wont be detected (small relative change)

Question 23

Dependance of ventilation on CSF pH

Answer 23

Heavily relies on the CCR to monitor pH and increase ventilation when its to acidic.

Question 24

Very importantly for control of metabolism, or acidity of blood. Chngaes in CO2 and H+ on a regulatory pathways are

Answer 24

more important then any changes in O2.

Question 25

A decrease in PO2 < 60 mmHg in the arterial blood will be detected by

Answer 25

PCR, increase ventilation via the respiratory control centres.

Question 26

An increase in PCO2 in the arterial blood will be cause

Answer 26

An increase in H+ (decrease in pH) in both the arterial blood AND the cerebral spinal fluids.

• H+ ions detected by PCR (PCR more sensitive to O2 changes) and will cause an increase in ventilation at the CPG.
• H+ ions detected by CCR and will increase ventilation via CPG.

Question 27

Response to Hypercapnia Mediated by

Answer 27

Response to breathing a gas mixture containing carbon dioxide: acts through central or peripheral chemoreceptors

Question 28

Response to Hypercapnia Mediated by Central chemoreceptors

Answer 28

Increase in inspired CO2 → increase alveolar PCO2 → increase in arterial PCO2 → increase in brain extracellular fluid PCO2 → increase in brain extracellular fluid H+ ion conc. → H+ ions activate central chemoreceptors → CCR increase rate of firing → provide an excitatory drive to the ventral respiratory group → increase ventilation.

Question 29

Response to Hypercapnia Mediated by peripheral chemoreceptors

Answer 29

Increase in inspired CO2e → increase alveolar PCO2 → increase in arterial PCO2 → increase arterial concentration of H+ ions (reduction in pH) → glomus cells (carotid bodies) increase rate of firing and excite the glossopharyngeal nerve→ drive activity in the dorsal and ventral respiratory group, where the Pre- Bötzinger complex and pFRG are located → increase ventilation

Question 30

Activation of the peripheral and central chemoreceptors will activate

Answer 30

respiratory neurons in the medulla which will increase ventilation so the H+ conc. at the level of the periphery (arterial blood pH) and at the level of the brain will return to normal levels

Question 31

A direct increase of ventilation due to high levels of CO2 is always done by the

Answer 31

CCR as they are indirectly sensitive to CO2 and directly sensitive to H+.

Question 32

Integrated Responses to Hypoxia, Hypercapnia and Acidosis

Answer 32

CCR:
– 80 – 90% response to respiratory acidosis

PCR:
– slow
– fast

Question 33

Dependance on PO2

Answer 33

Change in O2 is VERY fast rxn form the glomus cells, increases ventilation

• no response until O2 drops to 50 mmHg
• even though O2 drops to 50, CO2 remains constant at 36 mmHg