Answers to Mastering Concepts Questions
27.1
1. What are the components of blood?
Blood contains plasma, red blood cells, white blood cells, and platelets.
2. What is the location and function of hemoglobin?
Hemoglobin is located within red blood cells, where it binds oxygen and transports it to
the body tissues.
3. What are the functions of white blood cells?
White blood cells start the inflammation response, destroy microbes, and produce
antibodies.
4. Where do red and white blood cells originate?
Red and white blood cells originate in red bone marrow.
5. Describe the process of blood clotting.
Blood clots when a wound causes blood to escape from a vessel. As the vessel constricts,
platelets adhere to the wounded area, forming a plug that helps control blood loss. In the
meantime, exposure of blood to the surrounding tissue activates clotting factors that
trigger clot formation.
27.2
1. Distinguish between open and closed circulatory systems.
Open systems lack a continuous circuit of vessels. The heart pumps blood through short
vessels that empty into open areas in the body, where materials are exchanged with
surrounding cells; a second set of vessels picks up and returns the blood to the heart.
Closed systems have a continuous vessel system through the organism, and nutrients are
exchanged with the tissues across the vessel walls.
2. What is the difference between pulmonary and systemic circulation?
The pulmonary circulation moves blood returning to the heart from the body to the lungs
to exchange gases. The systemic circulation moves oxygenated blood from the heart to
the body tissues to exchange gases and then back to the heart.
27.3
1. What is the cardiovascular system?
The cardiovascular system is the combination of heart, blood, and blood vessels.
2. Describe the relationships among arteries, veins, arterioles, venules, and capillaries.
Arteries are the major vessels that carry blood away from the heart; they branch into
smaller arterioles, which become the network of capillaries where materials are
exchanged between the blood and tissues. The capillaries rejoin to form the venules,
which become the larger veins for returning blood to the heart.
27.4
1. Describe the anatomy of the heart.
The heart has four chambers: two atria on the top and two ventricles on the bottom. The
atria receive blood, and the ventricles pump blood out of the heart. Two valves separate
the atria from the ventricles, and two valves separate the ventricles from the blood vessels
leaving the heart.
2. Describe the path of blood through the heart’s chambers and valves, and through the
pulmonary and systemic circulations.
Blood flows along this pathway: right atrium, right ventricle, to the lungs via the
pulmonary artery, to the capillaries of the lungs (pulmonary circulation), and then back to
the heart via the pulmonary veins. The pulmonary vein empties into the left atrium, from
which blood passes through the left ventricle, and then to the body tissues (systemic
circulation) via the aorta. Blood from the systemic circulation returns to the right atrium,
and the cycle continues. A valve separates each atrium from its neighboring ventricle and
separates each ventricle from the blood vessels leaving the heart.
3. What is the function of heart valves?
Heart valves prevent the backflow of blood.
4. How does heartbeat originate and spread?
The heartbeat originates in the sinoatrial node (pacemaker). It spreads across the atria to
the AV node that sends an electrical signal to the ventricle walls.
5. How does exercise affect the circulatory system?
Exercise affects the circulatory system in several ways. It strengthens the heart, increases
its cardiac output, allows it to pump out a greater volume of blood each minute, and
allows it to increase the rate at which it beats. Exercise can also cause extra blood vessels
to develop within the walls of the heart.
27.5
1. Compare and contrast the structures of arteries, capillaries, and veins.
Arteries, veins, and capillaries are similar in that all are blood vessels and all have an
inner layer of endothelial cells. Capillaries are the smallest vessels, consisting of only a
single layer of endothelial cells. Arteries and veins are much larger. Arteries take blood
away from the heart, whereas veins bring blood to the heart. The force of heart
contractions moves blood in arteries, which have a thicker wall of smooth muscle than do
veins. Skeletal muscle contraction helps return blood to the heart. Large and mediumsized veins of the legs have venous valves that prevent backflow of blood.
2. Trace the path of a red blood cell from the heart to a capillary bed in the foot and back
to the heart.
Left ventricle of heart – aorta – femoral artery – artery to foot – arteriole – capillary bed
in the foot – venule – vein from foot – femoral vein – inferior vena cava – right atrium of
heart
3. Across the human circulatory system, how are blood pressure, blood velocity, and
vessel diameter related?
Blood pressure and velocity are greatest in the largest arteries, and blood pressure is
lowest in the veins. Vessel diameter is smallest in the capillaries, but capillaries have the
greatest cross-sectional area, so blood velocity is lowest in the capillaries.
4. How does regulation of blood pressure illustrate negative feedback?
When blood pressure is too high, the autonomic nervous system will dilate arterioles in
the skin and decrease the heart rate. These have the net effect of decreasing blood
pressure, bringing it back to normal. In contrast, if blood pressure is too low, the
arterioles in the skin will constrict and the heart rate will increase, with the net effect of
increasing blood pressure. In addition, the body raises or lowers blood volume through
control of the amount of fluid lost through the kidneys.
27.6
1. What is the main function of the respiratory system?
The main function of the respiratory system is to exchange gases with the atmosphere.
2. What is the relationship between the circulatory and respiratory systems?
The respiratory system exchanges gases with the atmosphere, removing CO2 from the
bloodstream and acquiring O2. The circulatory system delivers O2 to cells and picks up
CO2. So, these two systems are partners in gas exchange.
3. List the components of the upper and lower respiratory tracts.
Upper: Nose, pharynx, and larynx. Lower: Trachea and lungs.
4. Describe the relationships among the trachea, bronchi, bronchioles, and alveoli.
The trachea is the windpipe, or passageway to the lungs. The trachea branches into two
bronchi, one leading to each lung. Inside each lung, the bronchi are further divided into
bronchioles. The bronchioles lead to alveolar ducts, which open to the alveoli.
27.7
1. What is the relationship between the volume of the chest cavity and the air pressure in
the lungs?
As the volume of the chest cavity decreases, air pressure in lungs increases; as the
volume of the chest cavity increases, air pressure in lungs decreases.
2. Describe the events of one respiratory cycle.
In inhalation, the diaphragm and skeletal muscles of the chest contract; the rib cage
moves up, and the diaphragm moves down. The volume of the chest cavity increases, air
pressure in the lungs decreases, and air rushes into the lungs. In exhalation, the
diaphragm and skeletal muscles of the chest relax; the rib cage moves down, and the
diaphragm moves up. The volume of the chest cavity decreases, air pressure in the lungs
increases, and air is forced out of the lungs.
3. Define tidal volume and vital capacity.
Tidal volume is the air exchanged with each relaxed breath, and vital capacity is the
maximum volume of air a person can exhale after taking the deepest possible breath.
27.8
1. Describe the direction of O2 and CO2 diffusion in external and internal respiration.
In external respiration at the lungs, CO2 diffuses out of the red blood cells and plasma,
and into the alveoli. O2 moves in the opposite direction. In internal respiration (at the rest
of the body), O2 diffuses out of the blood and into the tissues, while CO2 moves into the
bloodstream.
2. In what forms does blood transport O2 and CO2?
Most O2 is bound to hemoglobin, although about 1% travels as dissolved gas in the
plasma. Most CO2 is carried as bicarbonate ions.
3. How does the brain regulate breathing rate?
Multiple chemoreceptors send information about blood pH and CO2 concentrations to the
brain. Neurons in the medulla integrate this information and regulate the contraction of
rib and diaphragm muscles.
27.9
1. How did researchers use DNA evidence to determine why icefishes have colorless
blood?
They collected DNA from icefishes and from their close relatives that have red blood.
When they sequenced the globin genes from all of the fishes, they discovered that the
globin genes in icefishes are unable to encode normal hemoglobin proteins.
2. Which component of blood is likely to transport most of the oxygen in an icefish?
Most of the oxygen is probably dissolved in the blood plasma.
Answers to Write It Out Questions
1. Maintaining the proper proportions of cells and platelets in the blood is essential for
health. What can happen when the blood contains too few or too many red blood cells?
Too few or too many white blood cells? Too few or too many platelets?
When blood contains too few red blood cells, the body’s ability to deliver O2 to cells is
hampered. When there are too many red blood cells, blood becomes too thick and blood
pressure increases. When blood contains too few white blood cells, the immune system
suffers. When there are too many white cells, then red blood cell formation may be
hindered, causing anemia. If platelet counts are low, an individual may not be able to
stop bleeding when injured. If platelets are too abundant, a blood clot could form inside a
vessel and cut off circulation.
2. Why can a person with type A blood not receive a transfusion of type B blood? If a
person has type O blood, what blood type(s) can he or she receive in a transfusion?
Each blood type has a unique set of markers. If a person with type A blood is given type
B blood, her immune system will recognize the foreign markers and cause the blood to
clump together (agglutinate). A person with type O blood can only receive type O blood.
3. Why is blood clotting that happens too quickly or too slowly dangerous?
Blood that clots too easily or quickly can lead to dangerous clots that plug blood vessels
and may cause death. Blood that clots too slowly can cause an injured person to bleed to
death.
4. One effect of aspirin is to prevent platelets from sticking together. Why do some
people take low doses of aspirin to help prevent a heart attack?
When the platelets don’t easily stick together, the blood doesn’t clot as easily, reducing
the chance that a blood clot will block a vessel leading to the heart.
5. How are open and closed circulatory systems similar? How are they different?
Both types of circulatory systems move blood (or a similar fluid) within an animal’s
body. In an open circulatory system, the blood directly bathes the body’s cells, whereas
in a closed circulatory system, the blood remains confined to vessels and does not come
into direct contact with the cells that it is nourishing.
6. Describe the circulatory systems of fishes and mammals. What is the advantage of
separating the pulmonary and systemic circulatory pathways?
Fish have one circulatory pathway with a two-chambered heart. Mammals have a fourchambered heart that separates the pulmonary and systemic pathways. Separating these
pathways is efficient because it ensures that the systemic circulation receives fully
oxygenated blood.
7. Describe the events that occur during one cardiac cycle.
The heart contracts and relaxes in one cycle. The contraction starts in the atria at the
sinoatrial node (pacemaker). The electrical signals converge and delay at the AV node,
giving the ventricles time to fill with blood. Lastly, the electrical signal spreads through
the ventricles and they contract, pushing blood out of the heart.
8. Make a chart that compares systemic arteries, capillaries, and systemic veins.
Consider the following properties: structure; amount of smooth muscle; presence of
valves; cross-sectional area; blood pressure; blood velocity; direction of blood flow
relative to the heart; O2 content of blood.
Characteristic
Overall structure
Smooth muscle
Valves
Cross-sectional area
Blood pressure
Blood velocity
Direction of flow
Arteries
Thick, muscular
walls
Thick
Absent
Low
Highest
Fastest
Away from heart
O2 content
High
Capillaries
Wall consists of a
single layer of cells
Absent
Absent
High
Low
Slowest
Links arteries with
veins
Low
Veins
Thin walls
Thin
Present
Low
Lowest
Slow
Towards heart
Lowest
9. How do the body’s cells receive nutrients and O2 and dispose of wastes?
The cells receive nutrients and oxygen from the fluid around the cells at the capillary
beds. The oxygen and nutrients move into the cells by diffusion or active transport.
Wastes are eliminated from the cell through diffusion or active transport, and end up in
the fluid surrounding the capillary beds where it moves into the blood to be transported
away.
10. Why is blood pressure highest in the arteries and lowest in the veins?
Pressure on the arteries is high due to their close proximity to the heart, which pumps
blood directly to the arteries. The farther an artery is from the heart, the lower the
pressure. Once the blood reaches the veins, there is little or no help from the heart in
moving the blood. Instead, skeletal muscle contraction propels blood back to the heart;
therefore, the pressure in veins is low.
11. What types of changes in blood vessels would raise blood pressure?
Anything that causes the diameter of blood vessels to decrease – from drugs to the
buildup of fats in arteries – would raise blood pressure.
12. Some of the body’s blood pressure receptors are located in the carotid sinus, where
the carotid artery passes through the neck. If you press lightly on the carotid sinus, what
do you predict should happen to your heart rate? What if you press lightly on a spot just
below the carotid sinus? Hint: Figure 27.13 may help you answer this question.
Pressure on the carotid sinus would cause the receptors to sense an increase in pressure.
This will cause the heart rate to drop to counter the perceived rise in pressure. This drop
in pressure could actually cause a person to pass out. If you press just below the sinus
then less blood will enter the sinus and a drop in pressure will be detected. This will
result in an increase in heart rate to compensate.
13. Describe the interactions between the circulatory system and the respiratory, immune,
digestive, and endocrine systems.
Blood passing through the respiratory system disposes of waste CO2 and picks up O2 to
deliver to the tissues. White blood cells are immune system cells that are carried
throughout the body in blood. Blood passing near the digestive system picks up nutrients
and carries them to the body’s cells. The endocrine system secretes hormones that are
carried in the bloodstream.
14. Name three ways that the circulatory system helps maintain homeostasis.
The circulatory system delivers O2 for cells to use in aerobic respiration, which restores
depleted ATP. Second, the circulatory system removes wastes from the cells, preventing
the buildup of harmful products. Third, hormones circulate in the bloodstream; hormones
maintain homeostasis in many ways.
15. Section 8.7 describes the rationale behind cancer treatments that inhibit the growth of
blood vessels toward a tumor. Why would tumors without a blood supply quit growing
(or even shrink)?
Without a blood supply there would be no oxygen or nutrients delivered to the tumor
cells, and so they could not grow or carry out cellular respiration.
16. What is the function of breathing?
Breathing supplies O2 to the cells for aerobic respiration and removes waste CO2.
17. What is the connection between breathing and cellular respiration?
An organism must inhale to acquire O2 for its cells. The cells need O2 to undergo cellular
respiration. A product of cellular respiration is CO2, which animals dispose of as they
exhale.
18. An earthworm prefers moist soil. Why does this animal die if it dries out on a
sidewalk?
The earthworm needs to keep its epidermis moist to facilitate gas exchange across its
body surface.
19. How is air cleaned, warmed, and humidified before it reaches the lungs?
Large particles are cleaned from inhaled air by hairs in the nose or sneezing reflexes,
while smaller particles and bacteria are trapped in mucus and destroyed by the enzymes.
Air is also humidified by the mucus and warmed by the rich blood supply in the nose.
20. Trace the path of an O2 molecule from the time it enters the nose to the time it reaches
a respiring cell at the tip of your finger.
Oxygen in air travels through the nose, through the larynx, and into the trachea. It then
travels through a bronchus, bronchiole, and alveolar duct into an individual alveolus. The
oxygen molecule then diffuses across the alveolar wall and into a red blood cell inside a
capillary. The red blood cell will travel through the left side of the heart, through the
aorta, and out to the cells of the finger tip. The oxygen will diffuse across the capillary
bed to the respiring cell.
21. Describe the events that happen during inhalation and exhalation.
During inhalation, the skeletal muscles of the diaphragm and rib cage contract, expanding
the lungs. This drops the air pressure in the lungs, drawing in the air. When the muscles
relax to their original positions, the lungs contract back in size, raising pressure, and air
exits the lungs.
22. What is the difference between tidal volume and vital capacity? What does each
measurement indicate about lung function?
Tidal volume is the air contained in a relaxed breath. It represents the efficiency of the
lungs at rest. Vital capacity is a much larger volume of air drawn from a maximum
inhalation-exhalation cycle. It represents the maximum amount of air a person can access
with one breath.
23. Explain the diffusion gradients for O2 and CO2 at alveoli and at body cells.
CO2 diffuses out of the red blood cells and plasma and into the alveoli of the lungs. O2
moves in the opposite direction. In the rest of the body, O2 diffuses out of the blood and
into the tissues, while CO2 moves into the bloodstream.
24. How does blood transport most of the CO2 produced by the body’s cells? In what
other ways is CO2 transported?
About 5-10% of CO2 travels as dissolved gas in the plasma, and 23% travels on
hemoglobin. The remaining 70% of CO2 travels in the plasma as bicarbonate ions.
25. One recommended treatment for anxiety-related hyperventilation (overbreathing) is to
breathe into a paper bag for several minutes. After several breaths, how does the
composition of air inside the bag compare with that in the atmosphere? How would
breathing air from the bag help relieve hyperventilation? How might it be dangerous to
breathe into a paper bag for more than a few minutes?
Exhaling into a paper bag causes the CO2 concentration in the bag to increase relative to
the concentration in the atmosphere. Rebreathing the contents of the bag raises the
blood’s CO2 content and restores the normal breathing rate. If this is done for too long,
however, the CO2 in the body would rise too high and the O2 would decline, which could
be lethal.
Answers to Pull It Together Questions
1. How do the pulmonary and systemic circulatory pathways fit into this concept map?
“Heart” connects with the phrase “delivers blood to lungs via the” to “Pulmonary
circulation”. “Heart” connects with the phrase “delivers blood to the rest of the body via
the” to “Systemic circulation”.
2. What other substances are in blood besides those listed in this concept map?
Besides what is listed in the concept map, nutrients (like glucose), waste products (like
urea), dissolved gases (like carbon dioxide), and hormones (like insulin) are all found in
the blood.
3. What are the functions of red and white blood cells?
Red blood cells have one main function: to deliver O2 to the body’s tissues and remove
CO2 from them. White blood cells are very different; they are part of the immune
system. They patrol the body for invasive materials and pathogens.
4. Add the following terms to this concept map: diaphragm, alveolus, interstitial fluid,
brain, hemoglobin, O2, CO2.
“Diaphragm” connects to the phrase “contracts to allow air to move into the” to “Lungs”.
“Alveolus” connects with the phrase “is an air sac within the” to “Lungs”. Alveolus also
connects with the phrase “delivers” to “O2” and connects with the phrase “removes” to
“CO2”. “Interstitial fluid” connects with the phrase “is derived from “Plasma”. “Brain”
connects with the phrase “regulates contraction of” to “Heart” and to “Diaphragm”.
“Hemoglobin” connects with the phrase “carries O2 in” to “Red blood cells”.
5. Describe the relationships among the parts of the upper and lower respiratory tracts.
Air moves from the nose to the pharynx and larynx, which together make up the upper
respiratory tract. From the larynx, air moves to the trachea, which branches into two
bronchi. One bronchus leads to each lung.