Physiology V Flashcards
How is breathing controlled?
By centers in the brains them so that PaCO2 and PaO2 are maintained
What four components control breathing?
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
How else can breathing be controlled?
commands from the cerebral cortex (e..g breath holding) that override the brains stem
The frequency of involuntary breathing is controlled by what three groups of neurons (aka brain stem centers)?
- medullary respiratory center
- apneustic center (lower pons)
- pneumotaxic center (upper pons)
What is the medullary respiratory center composed of?
- inspiratory center (dorsal)
- expiratory center (ventral)
What does the inspiratory center control?
basic rhythm for breathing by setting the frequency of inspiration
What CNs control the inspiratory center?
glossopharyngeal and vags
How does the inspiratory center transmit its signals? To where?
to the diaphragm via the phrenic nerve
When is the expiratory center activated?
only during exercise (not normally)
What is apneusis?
an abnormal breathing pattern with prolonged inspiratory gasps
What does the pneumatic center do?
turns off inspiration
How is hyperventilation self-limited?
Because giving off so much Co2 will cause a person to pass out
The brain stem controls breathing based on input of what sources of data?
PaO2, PaCO2, and arterial pH
Central chemoreceptors (the most important mechanism for minute to minute control of breathing) communicate directly with what?
the inspiratory center
Brain stem chemoreceptors are also very sensitive to changes in _____
pH of cerebrospinal fluid directly (and indirectly to changes in arterial PCo2)
Why are central chemoreceptors so sensitive to Co2?
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
Where are peripheral chemoreceptors for H+, O2, and CO2 located?
in the carotid bodies at the bifurcation of the carotids and in the aortic bodies on the aortic arch
Are peripheral chemoreceptors very sensitive to changes in PO2?
No, only when it drops below 60mm Hg does the breathing rate increase (steep and linear)
Are PERIPHERAL chemoreceptors more or less sensitive to changes in PaCO2 than to changes in PaO2?
Less. Central is WAY more important
Changes in arterial pH are sensed where?
ONLY in the carotid BODIES (not in the aortic bodies)
In addition to chemoreceptors, what other receptors are involved in breathing?
- lung stretch receptors
- joint and muscle receptors
- irritant receptors
- juxtacapillary receptors
How do lung stretch receptors work?
distention of the airways initiates the Hering-Brruer reflex, which decreases breathing rate by PROLONGING expiratory time
How do joint and muscle receptors work?
detect limb movement and instruct inspiratory center to increase the breathing rate
When are joint and muscle receptors most important?
early exercise
How do J receptors work?
Engorgement of pulmonary capillaries with blood and increases in interstitial fluid volume may activate these receptors and increase breathing rate
What causes dyspnea in CHF?
J receptors cause a decrease in breathing rate (to match V/Q) that leads to rapid shallow breathing
What happens to physiologic dead space during exercise?
it decreases
T or F. PaO2 and PaCO2 remain constant during strenuous exercise
T. NOTE: The current hypothesis is that the MEAN remains the same but oscillations in their values may occur which may stimulate chemoreceptors
T or F. Pulmonary resistance decreases during exercise
T. As a result V/Q ratios throughout the heart become more similar, producing a decrease in physiologic dead space
Which way does the o2-Hb dissociation urge shift during exercise?
right
How does arterial pH change at high altitude?
increases (respiratory alkalosis) due to hyperventilation
How does Hb conc change at high altitude?
increases due to increased RBC concentration
How does 2,3-DPG conc change at high altitude?
increase
How does pulmonary vascular resistance change at high altitude?
increases due to hypoxic vasoconstriction
Why does hyperventilation occur at high altitude?
hypoxemia below 60 mm Hg stimulates peripheral chemoreceptors
Note about breathing at high altitude
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
Why does hyperventilation occur again within a couple days at altitude?
HCO3- excretion increases and leaves the CSF and the pH of the CSF decreases toward normal so hyperventilation will resume
How can the respiratory alkalosis that occur at altitude be treated?
carbonic anhydrase inhibitors like acetazolamide
T or F. Right ventricular hypertrophy may occur at altitude
T. Because of hypoxic vasoconstriction of pulmonary arteries
A tool for determining the cause of hypoxemia is ____.
A-a gradient
T or F. The A-a gradient is normal in altitude caused hypoxemia
T.
