Ch. 8 West

Question 1

What are the three basic elements of the respiratory control system?

Answer 1

1. Sensors that gather information and feed it to
2. the Central controller in the brain, which coordinates information, and in turn sends impulses to
3. The effectors (respiratory muscles)

Question 2

There are three main groups of neurons in the brainstem (pons and medulla) which are recognized to control breathing. What are they?

Answer 2

1. Medullary respiratory center
2. Apneustic center
3. Pneumotaxic center

Question 3

Where is the medullary respiratory center?

Answer 3

In the reticular formation of the medulla beneath the floor of the fourth ventricle.

Question 4

Where is the apneustic center located?

Answer 4

Lower pons

Question 5

Where is the pneumotaxic center located?

Answer 5

In the upper pons

Question 6

The respiratory major neural output is to ____ nerves but there are also impulses to other respiratory muscles.

Answer 6

Phrenic nerves

Question 7

What is the voluntary portion of the brain in terms of control of breathing?

Answer 7

Mainly the cortex

Question 8

What are the most important receptors involved in the minute-to-minute control of ventilation, and where are they located?

Answer 8

The chemoreceptors located near the ventral surface of the medullar in the vicinity of the exit of the 9th and 10th nerves

Question 9

The composition of the ECF that surrounds central chemoreceptors is altered by CSF, local blood flow, and local metabolism. Which of these seems to be the most important?

Answer 9

CSF

Question 10

How does CSF determine the chemoreceptors impetus to increase ventilation?

Answer 10

Though there’s a BBB, CO2 readily diffuses across it. So when PCO2 increases, CO2 can diffuse into the CSF from the cerebral blood vessels, liberating H+ ions that stimulate the chemoreceptors.

Question 11

How do CO2 levels in the blood regulate ventilation?

Answer 11

Chiefly by its effect on the pH of the CSF

Question 12

Cerebral vasodilation/vasoconstriction occurs secondary to elevated PCO2 levels in the blood

Answer 12

Cerebral vasodilation

Question 13

Does the central chemoreceptor change in response to PO2

Answer 13

NO

Question 14

Why is the CSF subject to greater changes in pH with a smaller volume of CO2?

Answer 14

Because it’s relatively protein-free, meaning there aren’t ample buffers for acid.

Question 15

What compensatory change occurs in the CSF in patients with chronic increase in PCO2?

Answer 15

A compensatory change in HCO3 occurs as a result of transport across the BBB; however, the CSF pH doesn’t usually return all the way to normal. This effect is faster than the renal handling of bicarb in response to acidosis.

Question 16

Where are the peripheral chemoreceptors important in controlling respiration?

Answer 16

In the carotid bodies at the bifurcation of the common carotid arteries and in the aortic bodies above and below the aortic arch

Question 17

Peripheral chemoreceptors respond to:

Answer 17

Respond to decreases in arterial PO2 and pH and increases in PCO2

Question 18

At what PO2 level do the peripheral chemoreceptors begin responding to hypoxemia?

Answer 18

Once the arterial PO2 is less than or equal to 100 mmHg

Question 19

T/F: Peripheral chemoreceptors are responsible for all the increase in ventilation that occurs secondary to arterial hypoxemia.

Answer 19

True

Question 20

Pulmonary stretch receptors main effect:

Answer 20

When the lung is inflated, respiratory frequency slows down due to an increased expiratory phase.

Question 21

Irritant receptors main effect:

Answer 21

Bronchoconstriction and hyperpnea occur in response to inhaled irritants

Question 22

J receptors main effect:

Answer 22

May play a role in the rapid development of tachypnea with pulmonary edema; stimulation of the fibers can lead to rapid shallow breathing, although intense stimulation can cause apnea.

Question 23

Bronchial C fibers main effect:

Answer 23

Respond quickly to chemicals and lead to shallow breathing, bronchoconstriction, and mucus secretion.

Question 24

T/F: Raising the PCO2 raises the ventilatory rate regardless of the patient’s PO2.

Answer 24

True

Question 25

T/F: Because the PO2 can normally be reduced so far without evoking a ventilatory response, the role of this as a hypoxic stimulus in the day to day control of ventilation is small.

Answer 25

True

Question 26

In a patient who is chronically hypercapnic, why is hypoxia the main driver in changes in their ventilation rates and why could giving them a high FiO2 blunt their drive to breathe?

Answer 26

Chronic increase in PCO2, chronic decrease of pH- their brain CSF has equilibrated almost back to normal, and their renal compensation for acidosis has minimized the peripheral pH abnormalities. So, since they are chronically used to CO2 being high, they have lost most of their increase in the stimulus to ventilation from CO2. Under these conditions, arterial hypoxemia is the primary stimulus to additional ventilation beyond the basic rate set by the medullary respiratory center. If this patient is given a high concentration of inhaled oxygen, ventilation may decreased substantially.

Question 27

T/F: A reduction in arterial pH stimulates ventilation.

Answer 27

True- via stimulation of the peripheral chemoreceptors

Question 28

T/F: The strongest response of peripheral chemoreceptors to low PO2 occurs once PO2 has reached 50 mmHg or lower.

Answer 28

True- accelerates at 100, rapidly accelerates after 50