3.1.2 Regulation of Ventilation

Question 1

What type of cells control the rate of breathing?

Answer 1

Pacemaker cells in the respiratory center of the medully spontaneously fire, initiating inspiration

Question 2

How would increasing CO2 levels affect ventilation in a patient with low PAO2 compared to one that has normal PAO2?

Answer 2

As it happens with the response to low O2, the response to high CO2 is influenced by the PO2 levels. When the patient hyperventilates in response to high CO2, PO2 increases. This effect is not very marked, because the sensitivity of the peripheral chemoreceptorss at those high PO2 levels is relatively low. On the other hand, if low O2 is added to high CO2, the response is much larger. Curve b was obtained by maintaining PAO2 at a low level; for any given PCO2, ventilation is higher in curve b; in addition, the slope is steeper, so a given increase in PCO2 produces a larger ventilatory response when PO2 is low.

Question 3

How will increasing CO2 in the inspired air effect ventilation?

Answer 3

CO2 is a powerful stimulant of ventilation, the response is linear and a small change in PCO2 produces a very marked increase in ventilation. When you hold your breath, the stimulus that makes you start breathing again is the accumulation of CO2; during breath-holding, PO2 does not decreases sufficiently to reach the steep zone of the curve where ventilation increases markedly; on the other hand, an increase in PACO2 of 2-3 mm Hg produces vigorous ventilatory response.

Question 4

Answer 4

B

Question 5

What is the role of the central controller in the feedback system?

Answer 5

A central controller placed in the central nervous system, receives information gathered by receptors. The information collected by the receptors is processed and signals are sent to the effectors, the respiratory muscles, which will change the ventilatory rate. The change in ventilation, in most cases, will tend to decrease the magnitude of the signal sensed by the receptor. This is a typical negative feedback system

Question 6

What are they?

Answer 6

Question 7

Answer 7

D

Question 8

What is the location of the peripheral chemoreceptors?

Answer 8

These are referred to as the carotid and aortic bodies.

Question 9

What are the peripheral chemoreceptors sensitive to?

Answer 9

Decrease in pH

Increased PaCO₂

Decrease in PO₂

Question 10

What is the effect of breathe-holding on PaCO2 levels?

Answer 10

The increase in PaCO2 is similar to the decrease in PaO2. However, the effect of CO2 in ventilation is much greater than the effect of O2. So what makes you resume your breathing is the change on PCO2, and not the drop in PO2.

Question 11

How do the T-1 glomus cells respond to hypoxia?

Answer 11

Release of catecholamines

Question 12

Answer 12

A

Question 13

How does the firing rate of peripherial chemoreceptors respond to different levels of PO2?

Answer 13

These are the only receptors that sense changes in blood PO2

The rate of firing of the peripheral chemoreceptors increases as PO2 decreases. The response is non-linear, with firing rate increasing sharply at PO2 ~ 60-80 mmHg.

The stimulus is the PO2, not the O2 content or O2 saturation of Hb.

Question 14

What would happen to ventilation in response to decrease PO2 levels, if the CO2 levels are kept constant?

Answer 14

For any given PO2, ventilation is higher at the higher, constant PCO2; also the slope of the curve increases: a drop in PO2 produces a larger increase in ventilation when PCO2 is maintained constant. Curves obtained at constant PCO2 are called isocapnic hypoxic ventilatory response curves, and provide acurate information on the response to reduced inspired O2.

Question 15

The rate of firing in the respiratory center determines? The intensity determines?

Answer 15

The rate of firing determines the respiratory rate

The intensity of the firing determines the tidal volume

Question 16

Answer 16

D

Question 17

Answer 17

Question 18

What provides the peripheral chemoreceptors with O2?

Answer 18

Because the blood flow is so high to peripheral chemoreceptors, the oxygen needs of these cells are supplied entirely by dissolved O2 in the blood.

Question 19

In normal breathing what are the effects of changes in PaO2 or PaCO2 on minute ventilation?

Answer 19

Question 20

Answer 20

E

Question 21

Answer 21

4

Question 22

Answer 22

7

Question 23

Answer 23

A

Question 24

Describe the flow of CO2 and H+ between the CSF, brain ISF, and blood vessels.

Answer 24

Question 25

How will peripheral chemoreceptors respond to a decrease in pH or an increase in CO2?

Answer 25

Like the central chemoreceptors they will increase their rate of firing in response to decreased pH or increased CO2

Question 26

How will the rate of firing in peripheral chemoreceptors be affected by changes in Hb content?

Answer 26

Changes in Hb content will not affect the firing of the peripheral chemoreceptors

Question 27

What is the response of a person had a decrease in their PO2, and what would the compensatory mechanism result in?

Answer 27

Decrease in PAO2 would cause an increase in ventilation, caused by stimulation of the peripheral chemoreceptors.

Increased ventilation would cause PCO2 levels to drop and create an alkalosis. The lowered PCO2 and increased pH, would decrease the level of stimulation of the central chemoreceptors as well as decreasing the levels of stimulation to the peripheral receptors.

So, while the low PO2 tends to increase the ventilation, this increase is attenuated to some extent by the resulting low PCO2 and high pH.

Question 28

How does the blood flow to the peripheral chemoreceptors compare to that of the cerebral blood flow?

Answer 28

Blood flow to the peripheral chemoreceptors is tremendously high - 2000 mL per gram per minute

Cerebral blood flow - approx 50 mL per gram per minute

Question 29

Answer 29

B