A-19

Appendix F

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heart, forces blood out of the ventricles andtoward their outflow vessels—the aorta andpulmonary trunks. The aorta and pulmonarytrunks are located at the base of the heart.Ectopic foci cause various regions of theheart to contract at different times. Ectopicaction potentials in the ventricles cause theareas in which the action potentials developto contract independently of all other areasof the ventricles. As a result, the coordinatedcontraction of ventricular cardiac muscle isinterrupted, and pumping effectiveness isreduced. The normal filling and emptyingof the ventricles during the cardiac cycleis also interrupted.A drug that prolongs the plateau of cardiacmuscle cell action potentials prolongsthe time each action potential exists andincreases the refractory period. Therefore,the drug slows the heart. A drug that shortensthe plateau shortens the length of time eachaction potential exists and shortens therefractory period. Therefore, the drug canallow the heart rate to increase further.Endurance-trained athletes have a decreasedresting heart rate because their cardiac mus-cle undergoes hypertrophy in response toexercise. The hypertrophied cardiac musclecauses the stroke volume to increase sub-stantially. The increased stroke volume issufficient to maintain an adequate cardiacoutput and blood pressure even though theheart rate is slower.The two heartbeats occurring closelytogether can be heard through the stetho-scope because the heart valves open andclose normally during each of the heart-beats even if they are close together. Thesecond heartbeat, however, produces agreatly reduced stroke volume becausethere is not enough time for the ventriclesto fill with blood between the first andsecond contractions. Thus, the preload isreduced. Because the preload is reduced,the second heartbeat has a greatly reducedstroke volume, which fails to produce anormal pulse. The pulse deficit results fromthe reduced stroke volume of the second ofthe two beats that are very close together.Atrial contractions complete ventricularfilling, but they are not primarily responsiblefor ventricular filling. Therefore, even ifthe atria are fibrillating, blood can still flowinto the ventricles, and ventricular contrac-tions can occur. As long as the ventriclescontract rhythmically, the heart can pumpan adequate amount of blood, even thoughthe atria are not effective pumps. However,if the ventricles fail to contract forcefullyand rhythmically, they cannot functionas pumps. Thus, the stroke volume will

become too low to maintain adequate bloodflow to tissues. Therefore, atria transplantsare not essential but ventricle transplants are.9. An ECG measures the electrical activityof the heart and would not indicate a slightheart murmur. Heart murmurs are detectedby listening to the heart sounds. The boymay have a heart murmur, but the motherdoes not understand the basis for makingsuch a diagnosis.10. When both common carotid arteries areclamped, the blood pressure within theinternal carotid arteries drops dramatically.The decreased blood pressure is detected,and the baroreceptor reflex increasesheart rate and stroke volume. The result-ing increase in cardiac output causes theincrease in blood pressure.11. Venous return declines markedly inhemorrhagic shock because of the lossof blood volume. With decreased venousreturn, stroke volume decreases (Starlinglaw of the heart). The decreased stroke vol-ume results in a decreased cardiac output,which produces decreased blood pressure.In response to the decreased blood pressure,the baroreceptor reflex causes an increasein heart rate in an attempt to restore normalblood pressure. However, with inadequatevenous return, the increased heart rate isnot able to restore normal blood pressure.

Chapter 21

1. a. aorta, left coronary artery, circumflexartery, posterior interventricular arteryor aorta, right coronary artery, posteriorinterventricular arteryb. aorta, brachiocephalic artery, rightcommon carotid artery, right internalcarotid artery or aorta, left commoncarotid artery, left internal carotid arteryc. aorta, brachiocephalic artery, rightsubclavian artery, right vertebral artery,basilar artery or aorta, left subclavianartery, left vertebral artery, basilar arteryd. aorta, left or right common carotidartery, left or right external carotid arterye. aorta, left subclavian artery, axillaryartery, brachial artery, radial or ulnarartery, deep or superficial palmar arch,digital artery (on the right: the brachio-cephalic artery would be included)f. aorta, common iliac artery, external iliacartery, femoral artery, popliteal artery,anterior tibial arteryg. aorta, celiac artery, common hepatic arteryh. aorta, superior mesenteric artery,intestinal branchesi. aorta, left or right internal iliac artery2. a. great cardiac vein, coronary sinus oranterior cardiac vein

b. transverse sinus, sigmoid sinus, internaljugular vein, brachiocephalic vein,superior vena cavac. retromandibular vein, external jugularvein, subclavian vein, brachiocephalicvein, superior vena cavad. deep: vein of hand, radial or ulnar vein,brachial vein, axillary vein, subclavianvein, brachiocephalic vein, superiorvena cava superficial: vein of hand, radial or ulnarvein, cephalic or basilic vein, axillaryvein, subclavian vein, brachiocephalicvein, superior vena cavae. deep: vein of foot, dorsalis veins offoot, anterior tibial vein, popliteal vein,femoral vein, external iliac vein,common iliac vein, inferior vena cava superficial: vein of foot, great saphe-nous vein, external iliac vein, commoniliac vein, inferior vena cava; or veinof foot, small saphenous vein, poplitealvein, femoral vein, external iliac vein,common iliac vein, inferior vena cavaf. gastric vein or gastroepiploic vein,hepatic portal vein, hepatic sinusoids,hepatic vein, inferior vena cavag. renal vein, inferior vena cavah. hemiazygous vein or accessoryhemiazygous vein, azygous vein,superior vena cava3. A superficial vessel is easiest, such as theright cephalic or basilic vein. The catheteris passed through the cephalic (or brachial)vein and the superior vena cava to the rightatrium. Because the pulmonary veins arenot readily accessible, dye is not normallyplaced directly into them. Instead, the dye isplaced in the right atrium using the proce-dure just described. The dye passes from theright atrium into the right ventricle, the pul-monary arteries, the lungs, the pulmonaryveins, and the left atrium. If the catheter hasto be placed into the left atrium, it can beinserted through an artery, such as the femo-ral artery, and passed via the aorta to the leftventricle and then into the left atrium.4. The resistance to blood flow is less in thevenae cavae for two reasons: First, thediameter of one vena cava is greater than thediameter of the aorta; second, an increaseddiameter of a blood vessel reduces resistanceto flow (Poiseuille’s law). In addition, thereare two venae cavae, the superior vena cavaand the inferior vena cava, but only oneaorta. The blood flow through the aortaand the venae cavae is about equal, but thevelocity of blood flow is much higher inthe aorta than it is in the venae cavae.5. According to Laplace’s law, as the diam-eter of a blood vessel increases, the force