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CH 16 Short Answer/ Long Answer
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Terms in this set (13)
What is surfactant? Why is it important?
Surfactant, made by the type II alveolar cells, reduces the surface tension in the
fluid in the alveoli, thereby facilitating inflation and inhibiting collapse of the alveoli. It increases the compliance of the lungs.
Air flow in the respiratory system and blood flow in the cardiovascular system have many similarities—name them.
How are they different?
1. Flow takes place from regions of higher pressure to regions of lower pressure.
2. A muscular pump creates pressure gradients.
3. Resistance to fluid flow is influenced primarily by the diameter of the tubes.
The primary difference is that air is a compressible mixture of gases while blood is a non-
Explain how oxygen and carbon dioxide are transported in the blood.
How does the means of transport relate to the solubility and chemical reactivity of these gases in plasma?
Oxygen is not highly soluble in water, which is the main component of plasma. Less
than 2% is dissolved in plasma, with the remainder bound to hemoglobin.
The iron in the heme portion of the molecule can bind up to four oxygen atoms. Oxygen is not chemically reactive in the body.
Carbon dioxide is more soluble than oxygen, at about 7% dissolved. Carbon dioxide is chemically reactive, combining with water to form carbonic acid, which then dissociates to bicarbonate and hydrogen ion.
Most carbon dioxide is transported in the form of bicarbonate, about 70%, and the remaining 23% binds to amino acids on hemoglobin.
List, compare, and contrast the brain's centers for monitoring and controlling respiration.
Respiratory neurons in the medulla control inspiration and expiration. Neurons in the pons modulate ventilation. The rhythmic pattern of breathing arises from a network of spontaneously discharging neurons. Ventilation is subject to modulation by various chemical factors and by higher brain centers.
List, compare, and contrast the locations and stimuli for respiratory chemoreceptors.
Peripheral chemoreceptors in the carotid and aortic bodies sense changes in oxygen concentration, pH, and PCO2 of the plasma.
Central chemoreceptors monitor cerebrospinal fluid composition and respond to changes in the concentration of CO2 in the cerebrospinal fluid.
Draw a flow chart that shows the components of the reflex in which an increase in blood PCO2 leads to increased ventilation.
Peripheral chemoreceptors in carotid and aortic bodies detect changes in PCO2 and pH.
Central chemoreceptors in the medulla oblongata monitor CO2 in CSF.
Either an increase in PCO2 or decrease in pH will stimulate the receptors, which project to a control center in the medulla oblongata. The control center stimulates somatic motor neurons that control the skeletal muscles involved in ventilation. The effect is increased ventilation, which lowers PCO2 by eliminating CO2, so blood pH
increases because of this shift.
An industrious 10-year-old swimmer has attached an extension to his snorkel tube, so
that he can sit on the bottom of the ocean for a longer period of time, watching the fish of the coral reef. What problems would you expect him to have? Assuming he is successful in breathing this way for a little while, what are some of the differences he will experience compared to normal breathing?
The resistance to air flow increases as a result of adding the extension to the snorkel tube. Assuming he has used an extension of sufficiently large diameter, he is in a shallow location where the total length isn't excessive, and he has the strength and endurance in his respiratory muscles, he may be able to breathe this way for a few seconds longer than he could have held his breath. He will probably notice that he is breathing more deeply and at a higher rate, to maintain ventilation against the higher
resistance. After a few exchanges he will start to hypoventilate, despite his efforts to increase pulmonary ventilation, because the presence of dead airspace in the tube will result
in decreasing PO2 in the alveoli. Dead airspace is a problem if the total volume of air in the
tube is greater than the volume exchanged with each breath.
Hemoglobin binds to and has a much higher affinity for carbon monoxide (CO) than for oxygen. CO is colorless and odorless and can be produced in homes heated by natural gas; victims usually do not realize they are being poisoned and often die in their sleep. Describe the likely changes in a CO poisoning victim.
Answer: CO will gradually displace O2 on hemoglobin molecules. While this increases O2 unloading in tissues, it will significantly decrease O2 loading in lungs, therefore hypoxia will result. Victims gradually lose consciousness as the brain tissues become hypoxic.
Write the chemical equation catalyzed by the enzyme carbonic anhydrase. Suppose the concentration of H+ is increased by an outside force in a solution that had been at equilibrium. According to the law of mass action, what must happen to the CO2 concentration to reestablish equilibrium after this disturbance? What must happen to the concentration of bicarbonate?
Answer: CO2 + H2O↔H2CO3↔ H+ + HCO3- Carbon dioxide concentration will increase as the reaction is shifted to the left. Bicarbonate concentration will decrease.
Which is typically more important in regulating the respiratory system, PO2 or PCO2? Explain your answer and briefly discuss the receptors involved. Give examples of situations in which each of those factors changes enough to stimulate a reflex. How and why are these factors related to each other?
Answer: PCO2 is the more important factor. For PCO2, there are central and peripheral receptors that respond to CO2 as well as to CO2-related pH. These receptors are very sensitive to routine changes in PCO2 and pH, such as those associated with an increase in physical activity. Peripheral chemoreceptors have been identified for O2, but these respond only to dramatic changes in PO2, such as those associated with high altitude or disease. Because CO2 is produced as a by-product of aerobic (oxygen-consuming) metabolism, an increase in CO2 is associated with a corresponding decrease in O2.
Timmy is a cantankerous toddler who has just threatened that he will hold his breath
until Mom gives him some chocolate. His mother refuses to be manipulated and watches in amusement as Timmy stubbornly refuses to breathe. To her horror, Timmy loses consciousness and collapses onto the floor. Her cousin, who is enrolled in a course for emergency medical technical (EMT) training, is visiting, and tells her there is no need to call for an ambulance. Why did Timmy lose consciousness? Should his mother trust her instincts and call for help and begin CPR, or should she listen to her well-meaning but young and inexperienced cousin? Explain.
Answer: Timmy loses consciousness due to hypoxia in his brain. There is no need for alarm, because the loss of consciousness indicates mainly that cerebral activity has decreased. The parts of the brain involved in respiratory control are in the brain stem. As long as Timmy was awake and determined, his cerebral signals were able to inhibit brain stem control of pulmonary ventilation. Once he loses consciousness, however, the respiratory control areas are released from inhibition and he starts breathing again. Soon normal oxygen content in the brain will be restored, and Timmy will wake up.
Cary deliberately hyperventilates for several minutes before diving into a swimming pool. Shortly after he enters the water and begins swimming, he blacks out and almost drowns. What caused this to happen?
Answer: Hyperventilation causes a decrease in the alveolar PCO2, and more carbon dioxide is eliminated from the body than during normal breathing. The loss of large amounts of carbon dioxide upsets the body's normal drive for ventilation, and Cary does not feel the urge to breathe as he swims. As the exercising muscles use oxygen, a state of hypoxia develops. This results in insufficient amounts of oxygen reaching the brain, causing Cary to lose consciousness.
Define hyperventilation and explain what may cause it. Is the increased ventilation that occurs while exercising an example of hyperventilation? Explain your answer. How are PO2 and PCO2 affected by hyperventilation? Can breathing into a paper bag remedy hyperventilation or is this just unfounded folk medicine? Explain.
Answer: Hyperventilation is an increase in alveolar ventilation that exceeds metabolic demand. A person can deliberately hyperventilate, or it may occur as a result of emotional stress or high altitude. Strictly speaking, the increase in ventilation during exercise is necessary to meet increased metabolism and is therefore not hyperventilation. PO2 is increased and PCO2 is decreased during hyperventilation, because more O2 is inhaled and more CO2 is exhaled; this produces abnormally low PCO2. Hyperventilation can be remedied by a paper bag treatment, because rebreathing exhaled air will increase PCO2 in the body back to normal.
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