6/11/20131Test next Tues, Covering this,IA. Heart anatomyIB.Heart Physiologyi. Blood flow and heart soundsii. Conduction of action potentialsIC.Heart PathologiesIIA.Vessel anatomyIIB. Vessel physiology(Ch. 18–pp.i.Blood pressure regulationii. Changes during exerciseFigure 18.21At RestLight ExerciseHeavy ExerciseAt rest, cardiac outputaverages around 5.8 L/min.Note the pattern of blooddistribution to major organs,especially the skeletalmuscles, brain, andabdominal viscera.As you begin light exercise, threeinterrelated changes take place:1. Vasodilation occurs, peripheralresistance drops, and blood flowthrough the capillaries increases.2. The venous return increases as skeletalmuscle contractions squeeze bloodalong the peripheral veins. At the sametime, each inhalation creates a negativepressure in the thoracic cavity that pullsblood into the venae cavae from theirtributaries. This mechanism is calledthe respiratory pump.3. Cardiac output rises, primarily due tothe increased venous return.At higher levels of exertion, cardiacoutput increases toward maximallevels, and major changes in theperipheral distribution of blood occur,facilitating blood flow to active skeletalmuscles. Under massive sympatheticstimulation, the vasomotor centersseverely restrict blood flow to“nonessential” organs, such as thedigestive viscera. Although blood flowto most tissues is diminished, bodytemperature rises and skin perfusionincreases to promote heat loss. Onlythe blood supply to the brain remainsunchanged.BrainBrainBrainCardiacoutput =5800 mL/minCardiacoutput =9500 mL/minCardiacoutput =17,500 mL/minKidneyKidneyKidneyAbdominalvisceraAbdominalvisceraAbdominalvisceraSkinSkinSkinOther tissuesOther tissuesOther tissuesSkeletalMusclesSkeletalMusclesSkeletalMuscles750 mL/min750 mL/min750 mL/min250 mL/min350 mL/min750 mL/min600 mL/min600 mL/min1900 mL/min400 mL/min12,500 mL/min900 mL/min1100 mL/min1400 mL/min1100 mL/min1500 mL/min500 mL/min600 mL/min400 mL/min1200 mL/min4500 mL/minFigure 18 Section 3A summary of the sites andmechanisms of cardiovascularregulationVenous ReturnCardiac OutputRegulation (Neural and Hormonal)Arterial Blood PressurePeripheral ResistanceCapillary PressureVenous PressureValves and muscular compressionof peripheral veins play animportant role in maintainingvenous pressure and venous bloodflow. As blood moves toward theheart, the vessels get larger andlarger in diameter, and resistance iscontinuously decreasing.The venous return is the amountof blood arriving at the rightventricle each minute; on average,it is equal to the cardiac output.To maintain cardiac output, theheart must generate enoughpressure to force blood throughthousands of miles of peripheralcapillaries, most scarcely larger indiameter than a single red blood cell.