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51 Cards in this Set
- Front
- Back
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How does the pneumotaxic center in the brainstem regulate respiration?
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Regulates depth of inspiration. High output increases frequency
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How does the ventral respiratory group (expiration and inspiration) regulate respiration?
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Increases Va with exercise
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How does the dorsal respiratory group (inspiration) regulate respiration?
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Tidal "quiet" breathing. Passive expiration
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How do the vagus and glossopharygneal nerves regulate respiration?
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Stretch receptors (Herin-Breuer reflex)
Chemoreceptors (brain; carotid and aorta) |
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What do the sensory neurons in the brain, aorta and carotid detect?
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Changes in blood composition and stimulate or inhibit the intrinsic pattern.
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What does the respiratory center in the medulla have that controls respiration?
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Has spontaneously active "pattern generator" nerves that give rise to the intrinsic breathing rhythm of the respiratory muscles
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What types of signals do the pattern generating neurons in the respiratory center of the medulla generate?
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Generate a "ramp" signal from inspiratory neurons. If all inputs to the respiratory center are cut off the pattern of breathing follows this signal - increase in lung volume over a long period of time and a decrease in lung volume all at once.
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How is the intrinsic ramp signal modified during normal breathing?
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By inputs from the lungs (stretch receptors), higher brain centers (emotion, anticipation of exercise) and chemoreceptors (blood gas composition).
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What would happen if the inputs of stretch receptor signals in the lungs were cut from the respiratory center in the medulla?
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A deeper level of inspiration will be produced
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How will athletic training alter alveolar ventilation?
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Athletic training will increase alveolar ventilation and the sensitivity of the respiratory center to increased arterial PCO2. The increase is able to anticipate the level of activity based on motor memory.
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How does blood gas composition control ventilation?
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The most sensitive chemosensory neurons detect a lowering of pH due to an increase in PCO2
pH sensitive neurons are located in the medulla |
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What do chemosensitive neurons in the medulla detect?
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Elevated PCO2
Lowered pH |
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How will a change in PCO2 affect the CSF and why?
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A change in PCO2 will produce a greater reduction of pH in CSF because it is less well buffered
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What is "Cheyne - Stokes Breathing" and what causes it?
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Episodic breathing with periods of apnea.
Patients with reduced blood flow may have a delayed transport of blood from the lungs to the brain. This will allow brain PCO2 to rise and cause a burst of ventilation that lowers PCO2 and ventilation. It may result from a variety of conditions in which respiratory control is diminished |
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What will a small increase in arterial PCO2 result in?
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Will lower pH of the CSF bathing chemosensitive cells of the medulla and stimulate Va cells
Then will cause a large increase in ventilation. NOTE: There is lower sensitivity during sleep that can lead to sleep apnea |
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What does hyperventilation result in?
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Lowers alveolar and thus arterial PCO2.
Snorkeling divers often hyperventilate to stay underwater longer. A suppression of the "inspiratory drive" via the pH sensitive neurons is occurring. This can result in "shallow water blackout" if ventilation is suppressed long enough that arterial PCO2 falls too low. |
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What is the output of the carotid and aortic bodies at normal PO2 values and what happens as PO2 decreases?
Under normal condition what is the primary factor regulating ventilation? |
Low at normal PO2 values and increases rapidly at PO2 below normal alveolar values.
Under normal conditions, PCO2 is the primary factor regulating ventilation. |
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What is hemoglobin?
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Hemoglobin is the protein that carries oxygen and is found in red blood cells. It consists of four subunits = 2 alpha, beta dimers. Each subunit is associated with a heme group that attracts and reversibly binds oxygen. The vast majority of oxygen carried by the blood is bound in the lungs to hemoglobin and unbound at the tissues.
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What does oxygen binding hemoglobin cause?
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Rotates one pair of alpha/beta subunits to increase oxygen binding affinity
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What does 2,3 BPG do in hemoglobin?
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Interacts with the beta subunits to decrease oxygen binding affinity.
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What results in the lungs when reduced blood returns from the tissues?
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A given degree of reduction of PO2 below 40 mmHg results in a greater amount of O2 unloading to support increased metabolic activity.
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How is the affinity of hemoglobin for oxygen measured?
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Measured as the partial pressure at which the hemoglobin is half saturated = The P50. The lower the P50 the greater the affinity, like that for the Km of an enzyme catalyzed reaction.
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How much oxygen per gram is hemoglobin (Hb) able to bind?
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1.34 ml 02/gram
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What is the normal Hb level in the blood and what is the oxygen binding capacity that results?
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Normal Hb in blood 15 g/100 ml which gives an oxygen binding capacity of 20 ml O2/100 ml of blood (=20 volumes %)
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What is the status of hemoglobin (saturated/unsaturated) at alveolar PO2?
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Hb is near saturation (HbO2)
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What is the status of Hb (saturated/unsatruated) at tissue PO2?
What happens during exercise? |
At tissue PO2 only 20-25% of the HBO2 has dissociated to deliver O2 to the tissues.
During more exercise more oxygen is released (larger a-v difference) |
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How much oxygen is carried in solution?
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Very small amount of oxygen is actually carried in solution
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How does carbon dioxide presence in tissues affect Oxygen affinity to Hb?
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Carbon dioxide produced by the tissues produces H+ (From H2CO3) that causes a right shift of the curve with a smaller slope and decreased affinity, to increase O2 unloading. This is reversed at the lungs to facilitate O2 loading.
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What does lowering the pH from 7.4 - 7.2 result in?
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Results in the release of O2 from oxyhemoglobin, seen as a right shift of the oxyhemoglobin dissociation curve. Raising the CO2 partial pressure also favors the release of O2 from oxyhemoglobin.
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What is the regulation of oxygen binding by hydrogen ions called?
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Bohr effect after Christian Bohr
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What does the increase in temperature result in with respect to oxygen and CO2 transfer in Hb?
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Increasing temperature also favors unloading as does the presence of 2,3 bisphosphoglycerate (BPG), a metabolite of the glycolytic pathway.
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How does the Bohr effect alter the loading or unloading of O2?
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Functionally, the Bohr effect facilitates O2 loading at the lungs and unloading at the tissues
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What are the steps of O2/CO2 exchange in the RBC?
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1. Association of CO2 and H2O catalyzed by carbonic anhydrase in the RBC.
2 + 3. H+ arising from dissociation of H2CO3 binds to Hb to decrease O2 affinity and facilitates O2 unloading and delivery to the tissues. 4. HCO3- leaves RBC in exchange for Cl- entry, called the chloride shift. |
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How does low PCO2 in alveolar air affect the equilibrium?
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Shifts equilibrium which associates H+ and HCO3-, raises pH and increases O2 affinity to facilitate O2 loading by Hb.
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What is unique about fetal hemoglobin and RBCs?
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Fetal hemoglobin has a steeper slope indicating a greater affinity so the fetus can load oxygen from the maternal circulation. Fetal RBCs have a higher oxygen affinity than that of maternal red blood cells because fetal Hb does not bind 2,3-BPG as well as maternal Hb does.
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What role does the umbilical vein play in fetal gas exchange?
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Umbilical vein carries fetal blood that equilibriates with the maternal blood in the placenta
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What is myoglobin?
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Myoglobin, a monomer, has a high 02 affinity which allows oxygen transfer to tissues. It is particularly abundant in skeletal muscle tissue of diving animals.
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Aside from transporting oxygen what else can hemoglobin transport?
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Hemoglobin can also transport nitric oxide so that an area of vasodilation can spread with the circulation.
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What is carbon monoxide?
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Carbon monoxide has an extremely high affinity for Hemoglobin and competes for O2 binding. Thus, a small amount of carbon monoxide can be fatal.
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What are the three forms of carbon dioxide carried by the blood and in which form is it carried most?
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1. Dissolved 7%
2. Carbamino CO2 23% 3. Bicarbonate 70% Carried most as bicarbonate |
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What is the Haldane effect?
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The unloading of O2 at the tissues facilitating the formation of carboxy hemoglobin (HBCO2)
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What does hyperventilation result in?
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Lowers alveolar PCO2 and thus the PCO2 returning to the heart and systemic circulation = hypocapnia
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What does an increase in PCO2 result in?
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Carbonic acid formation and acidosis
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What is the concentration of H2CO3 a direct function of?
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PCO2
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At what pH is arterial pH maintained?
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pH 7.4
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What provides information regarding acid base imbalances?
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The dissociation equation for carbonic acid
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What regulates PCO2 and thus carbonic acid concentration?
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Alveolar ventilation
Increased Va will decrease ECF PCO2 and reduce the concentration of carbonic acid in the plasma. |
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How is the [HCO3-] maintained?
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At 23-25 mM by renal tubular reabsorption.
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What leads to metabolic acidosis with respiratory alkalosis?
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Metabolic acidosis results from fatty acids and ketone bodies that accumulate during starvation or diabetes. The addition of acid (fatty acids and ketones) will be buffered by HCO3- that becomes lowered as it buffers H+ and becomes H2CO3. This can be compensated by increasing Va to lower PCO2, a condition termed metabolic acidosis with compensatory respiratory alkalosis.
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What leads to respiratory alkalosis with compensatory metabolic acidosis?
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With chronic exposure to altitude, the depressed PCO2 due increased Va, is compensated by a decrease in plasma/ECF bicarbonate due to decreased HCO3- reabsorption by the kidneys
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What physiological factors cause altitude sickness?
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At high altitude the ambient PO2 declines so that alveolar PO2 is depressed and respiration becomes driven by O2 demand. Hyperventilation to get sufficient oxygen reduces PCO2 so PO2 is the primary factor that stimulates Va.
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