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25 Cards in this Set
- Front
- Back
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Where are arterial-blood CO2 sensitive chemoreceptors located?
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CO2 sensitive chemoreceptors are located on the ventro-lateral surfaces of the medulla. These central chemoreceptors actually respond to changes in the pH of the cerebrospinal fluid.
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Where are arterial-blood O2 sensitive chemoreceptors located?
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O2 sensitive chemoreceptors are located in the aortic and carotid bodies.
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How does CO2 act on central chemoreceptors, and why can't H+ ions or bicarbonate?
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The blood-brain barrier prevents H+ or bicarbonate ions from entering the CSF, but CO2 readily crosses, combining with water to make bicarbonate and H+. The hydrogen ions, in turn, irritate central chemoreceptors stimulating inspiration.
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How does the Carotid body communicate to the pontine-medullary respiratory center?
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Via the glossopharyngeal nerve
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How does the Aortic body communicate to the pontine-medullary respiratory center?
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via the Vagus nerve
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What stimulates peripheral chemoreceptors?
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PaO2<55mmHg, PaCO2 > 55mmHg, pH <7.50, Shock, Cyanide poisoning, Nicotine
Peripheral chemoreceptors are not stimulated significantly until the PaO2 falls below 55mmHg or the PaCO2 rises above 55mmHg. O2 and CO2 act synergistically. CO2 isn't as important unless it's a sudden increase i.e. choking(because the central chemoreceptors are more sensitive but slower to respond). |
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What is Kussmaul breathing?
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Breathing caused by acidosis stimulating the peripheral chemoreceptors
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Ventilation caused by peripheral chemoreceptors are only caused when PaO2 drops below 60mmHg-- why is this so insensitive?
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At 60mmHg or above, Hemoglobin is >90% saturated. Stimulating ventilation at this low threshold prevents the respiratory muscles from overworking (and counterproductively using more O2 than they can help deliver to the body).
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What is the molecular mechanism by which peripheral chemoreceptors are stimulated?
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A hemoglobin-like oxygen receptor responds to low PaO2 by closing a potassium channel and depolarizing the cell. A Ca2+ voltage gated channel is opened, Ca2+ influx, dopamine release, stimulation of IX --> Respiratory Centers
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What measure of oxygen are peripheral chemoreceptors sensitive towards?
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Oxygen TENSION, rather than arterial oxygen content.
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If PaCO2 in arterial blood rises by as little as 2mmHg, alveolar ventilation will... ?
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If PaCO2 in arterial blood rises by as little as 2mmHg, alveolar ventilation will just about double
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What factors increases the sensitivity of central chemoreceptors to CO2?
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Progesterone, Aspirin
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What factors decrease the sensitivity of central chemoreceptors to CO2?
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Heroin, COPD
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Describe the respiratory adaptations to someone who climbs a mountain 1) arriving at the top 2) after a few hours at the top 3) after having descended from the mountain
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1) Arriving at the top, the low PaO2(~ 40mmHg) stimulates rapid breathing; however this then lowers PaCO2 and increases the pH of the CSF, which turns OFF the respiratory input from central chemoreceptors.
2) After a few hours, bicarbonate in the CSF is lowered so that the pH is lowered to normal, and the respiratory response to low O2 is then allowed to turn ON, greatly increasing the breathing. 3) After descending, PaO2 returns to normal, and so does PaCO2-- however, you still hyperventilate because the CSF pH falls (no bicarb left!), stimulating breathing. In a few days, CSF bicarb increases and baseline breathing is restored. |
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What is the Hering-Breuer reflex?
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When you breath in, your airways expand and this stretches receptors in the walls that send impulses up the vagus nerve to an inspiratory center in the medulla. This results in a decrease in impulse traffic over the phrenic nerves back to the diaphragm causing it to relax and allowing expiration to take place.
If the vagus is severed --> unusually deep breaths before expiration. |
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What are J receptors?
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Juxtacapillary "J" receptors in the interstitium stimulated by edema fluid or inflammation cause tachypnea.
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What do muscle spindles in intercostal muscles do?
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They adjust the muscle tension to the work needed for adequate ventilation.
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List the basic components of the Pontine-Medullary respiratory center.
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Pons:
Upper 1/3 contains the Pneumotaxic center Lower 2/3 contains the Apneustic center Medulla: Contains the inspiratory and expiratory centers |
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What does the apneustic center do?
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The apneustic center in the lower 2/3 of the pons constantly sends impulses to the medulla to breathe in, breathe in. These impulses are periodically interrupted by the vagus nerve and by a so-called pneumotaxic center in the upper 1/3rd of the pons.
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What are the inputs from the higher brain centers that influence respiration?
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Voluntary hyper/hypoventialtion
Ondine's curse Talking, sighing, laughing, yawning, eating, vomiting, coughing, singing |
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What are inputs from the periphery that influence respiration?
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Cold (diving reflex), Pain, Joints
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What is Cheyne-Strokes respiration, and what causes it?
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When a patient starts taking small breaths, and then increasing larger breaths up to a maximum, before decrescendoing back down to a period of apnea. It is seen in Pts with a combination of neurological damage and congestive heart failure. CO2 rich blood is delayed in reaching the central chemoreceptors, but upon reaching it causes large stimulation of breathing.
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What is Biot's breathing, and when does it occur?
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Biot's breathing consists of a burst of deep breaths, followed by apnea. This type of breathing usually signifies intracranial problems such as hemorrhage or infection.
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What is sleep apnea and what causes it?
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Sleep apnea is repeated periods of apnea while sleeping. This can be caused by a neurological deficit (central apnea) or by an onstruction to airflow (obstructive apnea).
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Definition of apnea
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No airflow for >10 sec
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