Do You Understand Concept 38.2?
Draw sketches of circulatory systems showing a single and a double
circuit design. Label all of the parts.
Answer:
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?
Answer:
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.
Answer:
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?
Answer:
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.
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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.
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?
Answer:
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?
Answer:
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.
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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