384
Chapter 12
SECTION B CLINICAL TERMS
4. Draw a ventricular muscle cell action potential. Describe the
changes in membrane permeability that underlie the potential
changes.
5. Contrast action potentials in ventricular muscle cells with SA-
node action potentials. What is the pacemaker potential due to,
and what is its inherent rate? By what mechanism does the SA
node function as the pacemaker for the entire heart?
6. Describe the spread of excitation from the SA node through
the rest of the heart.
7. Draw and label a normal ECG. Relate the P, QRS, and T waves
to the atrial and ventricular action potentials.
8. Describe the sequence of events leading to excitation-
contraction coupling in cardiac muscle.
9. What prevents the heart from undergoing summation of
contractions?
10. Draw a diagram of the pressure changes in the left atrium, left
ventricle, and aorta throughout the cardiac cycle. Show when
the valves open and close, when the heart sounds occur, and
the pattern of ventricular ejection.
11. Contrast the pressures in the right ventricle and pulmonary
trunk with those in the left ventricle and aorta.
12. What causes heart murmurs in diastole? In systole?
13. Write the formula relating cardiac output, heart rate, and
stroke volume; give normal values for a resting adult.
14. Describe the effects of the sympathetic and parasympathetic
nerves on heart rate. Which is dominant at rest?
15. What are the major factors infl uencing force of contraction?
16. Draw a ventricular function curve illustrating the Frank-
Starling mechanism.
17. Describe the effects of the sympathetic nerves on cardiac
muscle during contraction and relaxation.
18. Draw a pair of curves relating end-diastolic volume and stroke
volume during different levels of sympathetic stimulation.
19. Summarize the effects of the autonomic nerves on the heart.
20. Draw a fl ow diagram summarizing the factors determining
cardiac output.
isovolumetric ventricular
contraction
374
isovolumetric ventricular
relaxation
375
laminar fl ow
377
L-type calcium channel
370
mitral valve
365
myocardium
365
pacemaker potential
370
papillary muscle
365
pericardium
365
preload
379
pulmonary valve
366
Purkinje fi ber
369
P wave
371
QRS complex
371
refractory period (of cardiac
muscle)
373
right and left bundle
branches
369
sinoatrial (SA) node
368
stroke volume (SV)
375
systole
373
tricuspid valve
365
T-type calcium channel
370
T wave
371
venous return
380
ventricular ejection
374
ventricular fi lling
375
ventricular function curve
379
angina pectoris
382
artifi cial pacemaker
371
atrial fi
brillation
377
AV conduction disorders
371
cardiac angiography
382
echocardiography
382
ectopic pacemaker
370
heart failure
382
heart murmur
377
hypertrophic
cardiomyopathy
382
insuffi ciency
377
prolapse
365
septal defect
377
stenosis
377
SECTION B REVIEW QUESTIONS
1. List the structures through which blood passes from the
systemic veins to the systemic arteries.
2. Contrast and compare the structure of cardiac muscle with
that of skeletal and smooth muscle.
3. Describe the autonomic innervation of the heart, including the
types of receptors involved.
SECTION C
The Vascular System
The functional and structural characteristics of the blood ves-
sels change with successive branching. Yet the entire cardio-
vascular system, from the heart to the smallest capillary, has
one structural component in common: a smooth, single-celled
layer of endothelial cells, or endothelium, which lines the inner
(blood-contacting) surface of the vessels. Capillaries consist
only of endothelium, whereas all other vessels have additional
layers of connective tissue and smooth muscle. Endothelial
cells have a large number of active functions. These are sum-
marized for reference in
Table 12–4
and are described in rel-
evant sections of this chapter and others.
We have previously described the pressures in the aorta
and pulmonary arteries during the cardiac cycle.
Figure 12–29
illustrates the pressure changes that occur along the rest of
the systemic and pulmonary vascular systems. Text sections
dealing with the individual vascular segments will describe
the reasons for these changes in pressure. For the moment,
note only that by the time the blood has completed its journey
back to the atrium in each circuit, virtually all the pressure
originally generated by the ventricular contraction has dissi-
pated. The reason pressure at any point in the vascular system
is lower than that at an earlier point is that the blood vessels
offer resistance to the fl ow from one point to the next.
Arteries
The aorta and other systemic arteries have thick walls contain-
ing large quantities of elastic tissue. Although they also have
smooth muscle, arteries can be viewed most conveniently as
elastic tubes. Because the arteries have large radii, they serve as
low-resistance tubes conducting blood to the various organs.
Their second major function, related to their elasticity, is to act
as a “pressure reservoir” for maintaining blood fl ow through
the tissues during diastole, as we will describe next.
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