Physiology V

Question 1

How is breathing controlled?

Answer 1

By centers in the brains them so that PaCO2 and PaO2 are maintained

Question 2

What four components control breathing?

Answer 2

1) chemoreceptors for O2 and Co2
2) Mechanoreceptors in the lungs and joints
3) Involuntary control centers for breathing in the brain stem (medulla and pons)
4) Respiratory muscles

Question 3

How else can breathing be controlled?

Answer 3

commands from the cerebral cortex (e..g breath holding) that override the brains stem

Question 4

The frequency of involuntary breathing is controlled by what three groups of neurons (aka brain stem centers)?

Answer 4

• medullary respiratory center
• apneustic center (lower pons)
• pneumotaxic center (upper pons)

Question 5

What is the medullary respiratory center composed of?

Answer 5

• inspiratory center (dorsal)

- expiratory center (ventral)

Question 6

What does the inspiratory center control?

Answer 6

basic rhythm for breathing by setting the frequency of inspiration

Question 7

What CNs control the inspiratory center?

Answer 7

glossopharyngeal and vags

Question 8

How does the inspiratory center transmit its signals? To where?

Answer 8

to the diaphragm via the phrenic nerve

Question 9

When is the expiratory center activated?

Answer 9

only during exercise (not normally)

Question 10

What is apneusis?

Answer 10

an abnormal breathing pattern with prolonged inspiratory gasps

Question 11

What does the pneumatic center do?

Answer 11

turns off inspiration

Question 12

How is hyperventilation self-limited?

Answer 12

Because giving off so much Co2 will cause a person to pass out

Question 13

The brain stem controls breathing based on input of what sources of data?

Answer 13

PaO2, PaCO2, and arterial pH

Question 14

Central chemoreceptors (the most important mechanism for minute to minute control of breathing) communicate directly with what?

Answer 14

the inspiratory center

Question 15

Brain stem chemoreceptors are also very sensitive to changes in _____

Answer 15

pH of cerebrospinal fluid directly (and indirectly to changes in arterial PCo2)

Question 16

Why are central chemoreceptors so sensitive to Co2?

Answer 16

Co2 is permeable across the BBB (unlike HCO3- and H+) and thus enters the extracellular fluid of the brain and the CSF. Once in the CSF, CO2 is converted to H+ and HCO3- and the brain stem chemoreceptors can sense change in the pH via added H+. Since the central chemoreceptors are close to the inspiratory center, they can quickly promote hyperventilation

Question 17

Where are peripheral chemoreceptors for H+, O2, and CO2 located?

Answer 17

in the carotid bodies at the bifurcation of the carotids and in the aortic bodies on the aortic arch

Question 18

Are peripheral chemoreceptors very sensitive to changes in PO2?

Answer 18

No, only when it drops below 60mm Hg does the breathing rate increase (steep and linear)

Question 19

Are PERIPHERAL chemoreceptors more or less sensitive to changes in PaCO2 than to changes in PaO2?

Answer 19

Less. Central is WAY more important

Question 20

Changes in arterial pH are sensed where?

Answer 20

ONLY in the carotid BODIES (not in the aortic bodies)

Question 21

In addition to chemoreceptors, what other receptors are involved in breathing?

Answer 21

• lung stretch receptors
• joint and muscle receptors
• irritant receptors
• juxtacapillary receptors

Question 22

How do lung stretch receptors work?

Answer 22

distention of the airways initiates the Hering-Brruer reflex, which decreases breathing rate by PROLONGING expiratory time

Question 23

How do joint and muscle receptors work?

Answer 23

detect limb movement and instruct inspiratory center to increase the breathing rate

Question 24

When are joint and muscle receptors most important?

Answer 24

early exercise

Question 25

How do J receptors work?

Answer 25

Engorgement of pulmonary capillaries with blood and increases in interstitial fluid volume may activate these receptors and increase breathing rate

Question 26

What causes dyspnea in CHF?

Answer 26

J receptors cause a decrease in breathing rate (to match V/Q) that leads to rapid shallow breathing

Question 27

What happens to physiologic dead space during exercise?

Answer 27

it decreases

Question 28

T or F. PaO2 and PaCO2 remain constant during strenuous exercise

Answer 28

T. NOTE: The current hypothesis is that the MEAN remains the same but oscillations in their values may occur which may stimulate chemoreceptors

Question 29

T or F. Pulmonary resistance decreases during exercise

Answer 29

T. As a result V/Q ratios throughout the heart become more similar, producing a decrease in physiologic dead space

Question 30

Which way does the o2-Hb dissociation urge shift during exercise?

Answer 30

right

Question 31

How does arterial pH change at high altitude?

Answer 31

increases (respiratory alkalosis) due to hyperventilation

Question 32

How does Hb conc change at high altitude?

Answer 32

increases due to increased RBC concentration

Question 33

How does 2,3-DPG conc change at high altitude?

Answer 33

increase

Question 34

How does pulmonary vascular resistance change at high altitude?

Answer 34

increases due to hypoxic vasoconstriction

Question 35

Why does hyperventilation occur at high altitude?

Answer 35

hypoxemia below 60 mm Hg stimulates peripheral chemoreceptors

Question 36

Note about breathing at high altitude

Answer 36

The drop in PaCO2 that results from hyperventilation and the resulting increase in pH will inhibit central and peripheral chemoreceptors and offset the increase in ventilation rate initially

Question 37

Why does hyperventilation occur again within a couple days at altitude?

Answer 37

HCO3- excretion increases and leaves the CSF and the pH of the CSF decreases toward normal so hyperventilation will resume

Question 38

How can the respiratory alkalosis that occur at altitude be treated?

Answer 38

carbonic anhydrase inhibitors like acetazolamide

Question 39

T or F. Right ventricular hypertrophy may occur at altitude

Answer 39

T. Because of hypoxic vasoconstriction of pulmonary arteries

Question 40

A tool for determining the cause of hypoxemia is ____.

Answer 40

A-a gradient

Question 41

T or F. The A-a gradient is normal in altitude caused hypoxemia

Answer 41

T.