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Activity 42.1 How Is Mammalian Heart Structure Related
to Function?
1. Diagram and describe the path a red blood cell takes from a capillary in your big toe to
your heart and back to your big toe. At each point in the pathway, indicate whether the
red blood cell is most likely picking up or losing oxygen. Indicate also the relative blood
pressure that part of the path is likely to have. Include all of the following terms in your
diagram.
aorta
venules
veins
arteries
arterioles
capillaries
right atrium
left atrium
right ventricle
left ventricle
coronary arteries
heart
internal organs (for example, lungs,
digestive tract)
skeletal muscle
2. The degree of musculature differs in these chambers of the heart: atria, right ventricle,
left ventricle.
a. Draw the heart and its
chambers, including
differences in musculature.
b. Explain why the
differences in
musculature might
exist by explaining
the normal functions
of each chamber.
The walls of the atria,
both right and left, are
fairly thin, indicating
little musculature. Blood
flows through the atria
into the ventricles.
When the atria contract,
they push the blood they
contain only a few
centimeters into the
ventricles. This overfills the ventricles and
helps initiate the ventricular contraction. The
right ventricle pumps its
contents to the lungs.
The left ventricle pumps
its contents out the aorta
and to the rest of the
body. The difference in
musculature of the two
ventricles is correlated
with the amount of
effort required to move
the blood through the
circulatory pathway
associated with each
ventricle.
c. Include in your
description the
functions of the SA
node (pacemaker), the
AV node, and the AV
and semilunar valves.
The signal from the SA
node (also called the
pacemaker) triggers the
contraction of the atria.
This signal is delayed at
the AV node, which allows
the atria to empty before
the ventricles are signaled
to contract.
The atrioventricular (AV)
valves lie between the atria
and the ventricles. These
are one-way valves that
prevent blood from
flowing back into the atria
when the ventricles
contract.
The semilunar valves lie
between the left ventricle
and the aorta and between
the right ventricle and the
pulmonary artery.
These are also one-way
valves that prevent blood
from flowing backward
into the ventricles.
3. While in utero, the wall between the two ventricles of the human fetal heart is not
complete. An opening, the foramen ovale, allows blood from the two ventricles to mix.
Normally, at birth, this hole seals over and the two ventricles are separated from each
other. What would be the consequences to the infant if this hole did not seal over at birth?
If the foramen ovale did not seal at birth, oxygenated blood from the lungs (left ventricle)
would mix with deoxygenated blood from the body (right ventricle). This condition is
called “blue baby syndrome.” The blood going to the body carries less oxygen than
normal. As a result, the baby turns blue during times of higher metabolic activity, which
require greater amounts of oxygen input per unit time.
4. One of the most common congenital defects of the cardiovascular system is called
“transposition of the great arteries.” In infants who have this defect, the pulmonary artery
exits from the heart where the aorta should and the aorta exits where the pulmonary
artery should. All other circulatory connections are normal.
a. Diagram and describe the circulation of blood in an infant who has this genetic defect.
When the positions of the aorta and pulmonary artery are reversed, two separate
circulatory systems are set up. One pumps the blood from the left side of the heart via the
pulmonary artery to the lungs and back via the pulmonary vein to the left side of the
heart. The other pumps the blood from the right side of the heart via the aorta to the body
and back to the right side of the heart via the anterior and posterior vena cava.
b. What type of treatment would such an infant need?
Unless something is done immediately, the infant will die. An operation to reverse the
arteries takes a relatively long time. In the short term, the physician opens the foramen
ovale to allow at least some oxygen to be pumped to the body.