Figure 11–2 is an anterior view of the heart. Identify each numbered structure and write its name in the corresponding numbered space below the figure. Then. in the relationship CO= HR x SV, CO stands for __?. Cardiac Output for the normal resting heart, the value of HR and SV are ___? 75 beats/ minute and 70 ml/. In the relationship CO = HR x SV, HR stands for ___. Heart Rate. In the relationship CO = HR x SV, SV stands for ___. Stroke Volume. The normal average adult.
True True or False: The pumping action of the healthy heart ordinarily maintains a balance between cardiac output and venous return. True Which term does not belong: Papillary muscles, Aortic semilunar valve, Tricuspid valve, Chordae tendinae Aortic semilunar valve Which term does not belong: Venules Why do veins need valves but arteries do not? Veins need valves to create pressure to pump the blood to the heart.
Name two events occurring within the body that aid in venous return. Tunica Intima Which type of Tunica is the bulky middle coat, that contains a smooth muscle and elastin?
Tunica Media Which type of Tunica provides a smooth surface to decrease resistance to blood flow? Tunica Intima Which type of Tunica is the only tunica of capillaries? Tunica Intima Which type of Tunica is also called the adventitia? Tunica Externa Which type of Tunica is the only tunica that plays an active role in blood pressure regulation? Tunica Media Which type of Tunica is the supporting, protective coat? Tunica Externa Describe the physical characteristics of an artery.
It has no valves, and it has small lumen.
Describe the physical characteristics of a vein. It has valves, and it has big lumen. Describe the physical characteristics of a capillary. It is only a thin wall of tunica intima. The fetus is given oxygen and nutrients by maternal blood. The lungs are mostly used for oxygenation, so it's not needed yet.
Since there is no valve at the entrance to the right atrium, the pressure in the right atrium is necessarily the same as the pressure in the veins at the entrance to the right atrium.SV, Preload, Afterload, Venous Return, EDV & ESV.
This pressure in the large veins at the entrance to the right atrium is called the central venous pressure. In other words, the central venous pressure is the same at the right atrial pressure, and this is the pressure that determines the filling of the right ventricle and thus its end-diastolic volume.
The central venous pressure always is only a few mm Hg, but nonetheless it does change enough to significantly affect the stroke volume. In particular, posture changes this pressure and that is the factor with which we are here most concerned. The Effect of Posture on Stroke Volume Recall how voluminous and thin-walled the superior and inferior vena cava are. You probably were able to put two fingers into the superior vena cava of the pig heart. When a person is lying down, the large veins in the chest are plump with blood.
And because these veins are stretched, the pressure in them is higher than when they contain less blood. Consequently, when lying down, the central venous pressure is relatively high, the end-diastolic volume is relatively high and thus the stroke volume is comparatively high. But this changes when we stand. The pressure in the large veins in the legs increases greatly.
For example, one meter below the heart, the effect of gravity adds about 74 mm Hg of pressure. This causes the distensible, voluminous veins to expand, and blood pools in the leg veins. This reduces the blood in the central veins, and the central venous pressure drops. Because these central veins are very compliant structures, pressure cannot increase again in them until blood flows back into the thorax. The Effect of Muscle Contraction on Stroke Volume Lying down, of course, is one factor that would increase the amount of blood in the veins in the thorax and thus the central venous pressure.
However, another important factor is muscle contraction.
If the standing person begins walking, the contractions of the leg muscles squeeze on the leg veins, thereby forcing blood from those veins up into the thorax. This is called muscle pumping. Thus, as a standing person begins walking, the end-diastolic volume and thus the stroke volume increase.
Muscle pumping works on the veins, but not the arteries, because veins are large, highly compliant and the larger ones have valves. In other words, contracting skeletal muscles serve as auxillary pumps, squeezing blood back into the central veins.
Why have Such Distensible Veins? Given that the veins are so large and compliant, you might wonder why we are put together this way. It allows blood to move around substantially in the veins, altering central venous pressure and thus stroke volume.
Free Biology Flashcards about A&P Heart & Blood
The reason is that it allows us to function despite significant changes in extracellular fluid volume and thus blood volume. A person can lose a liter or more of blood or extracellular fluid through hemorrhage or diarrhea and still easily maintain arterial blood pressure.
As volume is lost, the distensible veins simply contrict, compensating for the lost volume. Likewise, an increase in extracellular fluid volume is accommodated by distension of the veins.
Regulation of Cardiac Output
The central venous pressure is hardly affected. This would lead to a disaster fairly quickly if not corrected.
If this continued for 20 minutes, one liter of blood would be transferred from your systemic circulation into you pulmonary circulation. Pressures throughout your pulmonary circulation would begin increasing and fairly soon you would "drown" from pulmonary edema. Why doesn't this happen? As soon as a fairly small amount of blood is transferred from the systemic to pulmonary circulation, the pressure in the pulmonary veins and left atrium increases a little.
This increases the filling of the left ventricle, and the resulting increase in its end-diastolic volume increases the stroke volume, correcting the problem. This is why even tiny differences in the pumping of the two ventricles are soon corrected.