1625915643-5d53d156c9525bd62bd0d3434ecdc231 (843955), страница 99
Текст из файла (страница 99)
In respiratory sinus arrhythmia, which occurs primarily ininfants and children, heart rate is increased during inspiration andreduced during expiration. This is caused by increased venousreturn during inspiration, causing stretch of low pressure atrialbaroreceptors and reflexive increase in heart rate.E. Activation of the sympathetic nervous system (SNS) will produceall of the listed effects. Effects on the heart (increased heart rate andcontractility) involve binding of adrenergic neurotransmitter to β1receptors; constriction of arteries and veins is produced by bindingof the adrenergic transmitter to α1 receptors.B.
The force–velocity relationship for cardiac muscle revealsan inverse relationship between velocity of contraction and afterload (force of contraction). With increased contractility, themaximum velocity of contraction (Vm, which occurs at zero afterload), is increased, as is the maximum force of contraction.Maximum force of contraction occurs during isometric contraction,at the x-intercept of the force–velocity relationship, where velocityis zero.Answers17. B. The vascular function curve represents the relationship betweencentral venous pressure and cardiac output when central venouspressure is the dependent variable; the cardiac function curve represents the relationship when cardiac output is the dependent variable. The intersection of the two curves is at the normal, restingcardiac output and central venous pressure at equilibrium (approximately 5 L/min cardiac output and central venous pressure (CVP)of approximately 2 mm Hg).18.
C. Nitric oxide release by endothelial cells produces vasodilation ofthe vessel by relaxing underlying smooth muscle. This effect is mediated by the second messenger cGMP, which reduces free intracellular Ca2+, producing the smooth muscle relaxation. Dilation ofarterial vessels results in higher capillary hydrostatic pressure downstream. Nitric oxide also inhibits adhesion of platelets to the vascular wall.19.
A. In many tissues and organs, if blood flow is increased due tohigher perfusion pressure, the expected elevation in flow will befollowed by a return in blood flow toward the basal rate. Accordingto the myogenic hypothesis, this autoregulation involves smoothmuscle constriction in response to elevated transmural pressure (inother words, in response to stretch).20. D.
β2 receptor binding produces vasodilation, whereas α1 and α2receptor binding are associated with vasoconstriction. β1 receptorsare found in the heart, where the main effects mediated by thesereceptors are increased heart rate, contractility, and conductionvelocity.21. A. Arterial baroreceptors respond to high arterial pressure (andthus, stretch) by sending afferent nerve impulses to the central cardiovascular center, resulting in reduced sympathetic efferent activityand increased parasympathetic activity. In addition to high pressures, the baroreceptors also respond to pulse pressure.22. C.
Left coronary artery flow is highest during early diastole. Flowis low during systole, due to compression of myocardial vessels bythe contracting myocardium. As the heart relaxes, this compressionis released, and this, combined with the effects of vasodilator metabolites which build up in the myocardium during the low flow ofsystole, results in a large increase in left coronary artery blood flowin early diastole.Section 4: Respiratory Physiology1. A.
A rise in pulmonary artery pressure produces passive distensionof vessels in the pulmonary microcirculation and opening of somevessels that were previously collapsed (recruitment).2. D. Spirometry measures changes in lung volume (tidal volume,expiratory reserve volume, inspiratory reserve volume, vitalcapacity, inspiratory capacity), but cannot measure total lung capacity, residual volume, or functional residual capacity. To determinethese three values, one of them must be measured indirectly,for example by nitrogen washout, helium dilution, or bodyplethysmography.3.
C. In the standing position, both ventilation and perfusion of thelung are greatest in the bottom portion and poorest in the upperportion of the organ. However, the vertical gradient for perfusionis much greater than the gradient for ventilation. Therefore, theventilation-to-perfusion ratio is highest toward the top of the lung.The ratio approaches infinity in areas of dead space and zero in areasof shunt.4. B. Diffusion of a gas through a membrane is a passive process thatfollows Fick’s law. It is directly related to the partial pressure gradient, directly related to surface area, directly related to the diffusionconstant of the gas, and inversely related to membrane thickness.5.
C. In the middle portion of the lung, zone 2, alveolar pressure fallsbetween pulmonary arterial and venous pressures, and the ventilation and perfusion are approximately balanced, resulting in a ratioof approximately 1.3736. B. Functional residual capacity (FRC) is lung volume after expiration in normal, quiet breathing. At this point, mechanical forces arein balance, with outward elastic recoil pressure of the chest wallbalancing the inward elastic recoil pressure of the lung.7. C. In the respiratory system as a whole, the greatest resistance toflow occurs in the medium-sized airways (fourth to eighth generation).
Proceeding down the airways, the diameter of airwaysdecreases while the number of tubes increases rapidly. Taking intoconsideration both factors, the resistance is greatest in the mediumsized bronchi (in aggregate).8. A. With progressively greater effort, peak air flow is increasedduring expiration, but along the downward slope of the expiratoryflow-volume curves, airflow is effort-independent.9.
B. Severe COPD is characterized by emphysema, with increasedcompliance of the lung and decreased elastic recoil of the lung. Asa result of the decreased elastic recoil, the equal pressure point formsearly during expiration, resulting in trapping of air, and ultimatelycausing increased total lung capacity, functional residual capacity,and residual volume. In pulmonary function tests, expiratory flowrate and FEV1 are reduced as a result.10. A.
The presence of surfactant at the air-fluid interface of alveoli andsmall airways results in lower surface tension and therefore increasedpulmonary compliance, reducing the work of breathing. Surfactantcontains the phospholipid dipalmitoyl phosphatidyl choline. Surfactant deficiency is responsible for respiratory distress syndrome ofthe newborn.11. A. An increase in hematocrit will result in a proportional rise in theamount of oxygen bound to hemoglobin in blood. At 100 mm HgPO2, hemoglobin is saturated with oxygen, and an increase in PO2will only result in a minor rise in oxygen content by raising the smallamount of dissolved oxygen.
Likewise, because hemoglobin in arterial blood is normally nearly saturated with oxygen, increased alveolar ventilation will have very little effect on oxygen content. Anincrease in 2,3-DPG or a fall in blood pH will shift the oxyhemoglobin dissociation curve to the right, resulting in a fall in boundoxygen.12.
C. The pH is below the normal level of 7.4, indicating acidosis;because PCO2 is elevated, this is a case of respiratory acidosis (highPCO2 is the cause of the low pH).13. D. In acute adaptation to high altitude, hypoxemia stimulatesrespiratory rate. Heart rate is also elevated. 2,3-DPG is elevated inblood, resulting in right-shift of the oxyhemoglobin dissociationcurve, causing oxygen to more readily dissociate from hemoglobinat the tissue level. Renal compensation will result in elevated plasmabicarbonate level. In the long term, however, increased hematocrit(higher red blood count [RBC] and hemoglobin concentration inblood) is an important compensatory mechanism, resulting inincreased oxygen carrying capacity of blood.14.
B. Central chemoreceptors respond mainly to changes in arterialPCO2, which diffuses readily into the cerebrospinal fluid (CSF) andalters CSF pH, resulting in stimulation of respiration when arterialPCO2 is elevated. The blood-brain barrier is largely impermeable toHCO3− or H+. Peripheral chemoreceptors respond to changes inarterial PO2 and also pH and PCO2.15. D. The initial, rapid adjustment of respiration during exercise iscaused by input from proprioceptive afferents from joint receptorsto the respiratory center in the brain, collaterals to the respiratorycenter from motor pathways for muscle activation, as well as additional, undefined factors.
The additional elevation of respirationduring continuing exercise is caused by feedback systems involvingchemoreceptors and changes in body temperature.Section 5: Renal Physiology1. C. The clearance of inulin (Cin) is equated with the glomerularfiltration rate, because inulin is freely filtered, is not reabsorbed or3742.3.4.5.6.7.8.9.10.11.12.13.14.15.16.Answerssecreted, and all filtered inulin is excreted. Thus, if the clearance ofa freely filtered substance is less than Cin, it means that overall therewas reabsorption (however, it does not determine whether secretionmight also have occurred).C.
![](https://s.studizba.com/z.php?f=/templates/si/i/noavatar.png&w=100&h=100&t=1"){kind=avatar}
