Cardiovascular System: The Heart
Describe how the arrangement of cardiac muscle bundles "squeeze" the blood from the heart.
The muscle bundles of the atria are circular. Contraction of these
bundles forces the
blood inferiorly through the AV valves into the ventricles. The bundles of the ventricles are
arranged as a spiral. These bundles contract in a twisting fashion, beginning at the apex and
wringing the blood superiorly through the semilunar valves of the pulmonary trunk and aorta.
Compare the difference between incompetent and stenotic heart valves.
Incompetent heart valves are valves that do not close properly and
allow blood to leak
past the cusps. In contrast, stenotic heart valves do not open properly because they have become
stiff and rigid as a result of accumulation of calcium deposits. Although both conditions differ in
their cause, their common effect is to weaken the heart and diminish its efficiency.
Describe the function of the cardiac skeleton of the heart.
The cardiac skeleton of the heart anchors the heart valves in
position and prevents their
openings from overdilating as blood flows through. The skeleton also anchors the cardiac muscle
bundles and keeps the heart from tearing itself apart as different chambers contract. Finally, the
cardiac skeleton serves as an electrical insulator that limits spread of the electrical
depolarizations of the atria to the ventricles.
Identify the change in blood flow through the heart in the condition
of a ventricular septal
A ventricular septal defect allows blood to flow directly from the
right to left
ventricles. When this happens, some of the blood from the right atrium has bypassed the
pulmonary circuit and therefore remains deoxygenated. This means that blood pumped from the
left ventricle through the systemic circuit consists of both oxygenated and deoxygenated blood.
Describe the histological features of cardiac cells that allow for coordinated contractions.
Individual cells of the myocardium are connected by intercalated
disks. These disks
have fingerlike projections that interlock with those of the adjacent cell. Within these
interlocking disks, fasciae adherens are desmosome-like structures that transmit the contractile
force of one cell to another. Additionally, gap junctions in the disks allow for the flow of
activating ions (calcium and sodium) between cells so that synchronized contractions occur.