Wednesday, December 19, 2012

Answers to Chapter 38 DYUC and ATC

Do You Understand Concept 38.2?

Draw sketches of circulatory systems showing a single and a double circuit design. Label all of the parts.

Refer to textbook art on pages 748 and 750.

Why can a mammalian circulatory system have different pressures in the pulmonary and the systemic circuits, and why do you think this is important?

Although the pulmonary and the systemic circuit are in series, they are separated by the heart, which provides a separate pump for each. The right ventricle pumps blood through the pulmonary circuit, and the left ventricle pumps blood through the systemic circuit. This anatomy enables the heart to create a higher pressure in the aorta than in the pulmonary artery, which is important because the total length of blood vessels, and hence the total resistance, is greater in the systemic circuit.

Do You Understand Concept 38.3?

A red blood cell is flowing through the superior vena cava. List all of the heart chambers, valves, vessels, and organs it will pass through before it leaves the heart in the aorta.

The blood cell will enter the right atrium, flow through an atrioventricular valve into the right ventricle and be pumped through the pulmonary valve into the pulmonary artery, flowing to the lung. After oxygenation, the blood cell will return to the heart via the pulmonary vein and enter the left atrium. It will pass through another atrioventricular valve into the left ventricle and be pumped into the aorta, passing through the aortic valve.

Why do the atria contract before the ventricles? What would happen if they contracted at the same time?

The atria contract when an action potential spreads through gap junctions. They are not coupled through these junctions to the ventricles. Instead, the atrioventricular node generates another action potential when its cells are depolarized and conducts it via the bundle of His to the ventricles. If the chambers contracted at the same time it would be possible for blood to flow in the wrong direction.

Do You Understand Concept 38.4?

List the major components of blood (liquid and cellular) and state their functions.

Plasma is the liquid, extracellular matrix of blood and contains water and solutes, such as nutrients, ions, waste products, hormones, gases, and clotting proteins. Cellular components of blood include: erythrocytes, or red blood cells, which carry respiratory gases; leukocytes, or white blood cells, of the immune system; and platelets, which are involved in blood clotting.

Some competitive cyclists have admitted using erythropoietin as an illegal performance-enhancing drug. How can erythropoietin enhance performance?

Erythropoietin enhances the blood's capacity for carrying oxygen by extending the life of existing red blood cells as well as by stimulating development of new ones in the bone marrow.

Do You Understand Concept 38.5?

In which vessels of the circulatory system does the blood move most rapidly? In which does it move most slowly? Why?

Blood moves most rapidly through the arteries due to higher pressure after ventricular contraction and the elastin and smooth muscle fibers that can stretch and withstand this pressure. Blood moves most slowly through capillaries due to their tiny size and the huge quantity of capillaries, resulting in both lower blood pressure and allow for exchange of material with the interstitial fluid.

Compare and contrast the structure of the walls of arteries, capillaries, and veins. How does the structure of the wall relate to each vessel’s function?

Arterial walls contain elastin fibers and smooth muscle fibers that accommodate the high pressure and also propel the blood forward through elastic recoil. Capillaries are very permeable to allow for exchange with the interstitial fluid. Veins have no elastin layer due to the low pressure and rate of flow through them, but may have one-way valves to prevent backflow of blood.

Certain parasitic worms can block lymph vessels. Suppose the lymph vessels draining a leg were completely blocked by a parasite infestation. What do you think would happen to the leg? Explain your answer.

Lymph capillaries take up excess fluid in the capillary beds and then pass the fluid into larger lymphatic vessels that return it to the heart.. If this system were blocked, the lymph would remain in the capillary beds, and the leg would swell as the fluid accumulated.

Occasionally soldiers or guards standing at attention and not moving will faint. Why do you think that occurs? How could they avoid that embarrassing situation?

Fainting can be due to not enough oxygen circulating in the blood. Soldiers who don't move might increase blood flow returning to the heart by flexing skeletal muscles in their legs to compress the veins. They also might exhale completely and inhale deeply to take in more highly oxygenated air.

Do You Understand Concept 38.6?

What three factors determine the mean arterial pressure?

Mean arterial pressure is equal to the product of the heart rate, the stroke volume, and the total peripheral resistance.

If blood pressure gets too high, will angiotensin levels go up or down? What about ADH levels? Explain your answer.

If blood pressure becomes elevated, angiotensin levels will fall because its function is to raise MAP and blood flow to some organs by constricting arterioles throughout the body. ADH levels would also fall so that kidneys would lower their reabsorption of water, decreasing blood volume and thus pressure.

Apply the Concept for Chapter 38

Concept 38.1 A Beating Heart Propels the Blood, p. 752
1. Systole is the duration of contraction of the ventricles, and it would extend from point B to point D.

2. Diastole is when the ventricles are relaxing and filling, and it would extend from point D through B.

3. The blood pumped each cycle is the difference between the end systolic volume and the end diastolic volume—or 70 ml.

4. The first heart sound occurs when the atrioventricular valves shut at the beginning of systole—point B. The second heart sound is when the aortic valve shuts at the end of systole, at point D.

5. The aortic valve would open at point C, when the pressure in the ventricle exceeds the back pressure in the aorta.

Concept 38.2 Blood Circulates in Arteries, Capillaries, and Veins, p. 758

1. There is no sound at the high cuff pressure because the arteries into the arm are totally occluded by the pressure. As the cuff pressure falls, it will eventually fall below the maximum arterial pressure, and at that time the arterial pressure will squeeze some blood into the artery. The sound is due to the starting and stopping of that flow.

2. When the cuff pressure falls below the lowest arterial pressure, the blood will flow continuously through the artery and no periodic sound will be heard.

3. The cuff pressure at which the tapping sounds are first heard (120 mm Hg) is closest to the systolic pressure and the cuff pressure at which the periodic sounds cease (60 mm Hg) is closest to the diastolic pressure.

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