18. The Heart

Name the elements of the intrinsic conduction system of the heart in order, beginning with the pacemaker

What is the important function of this conduction system?

The activity of the heart depends on intrinsic properties of cardiac muscle and on neural factors. Thus:

a. Vagus nerve stimulation of the heart reduces heart rate

b. Sympathetic nerve stimulation of the heart decreases time available for ventricular filling

c. Sympathetic stimulation of the heart increases its force of contraction

d. All of the above

The cells of the conducting system differ from the contractile cells of the heart in that:

(a) Conducting cells are larger and contain more myofibrils

(b) Contractile cells exhibit pacemaker potentials

(c) Contractile cells do not normally exhibit autorhythmicity

(d) Both a and b are correct

The autonomic centers for cardiac function are located in:

(a) The myocardial tissue of the heart

(b) The cardiac centers of the medulla oblongata

(c) The cerebral cortex

(d) All of these structures

Trace the normal pathway of an electrical impulse through the conducting system of the heart.

What effect does sympathetic stimulation have on the heart? What effect does parasympathetic stimulation have on the heart?

What role do the chordae tendineae and papillary muscles play in the normal function of the AV valves?

If the papillary muscles fail to contract:

(a) The ventricles will not pump blood

(b) The atria will not pump blood

(c) The semilunar valves will not open

(d) The AV valves will not close properly

(e) None of these happen

The refractory period of cardiac muscle is much longer than that of skeletal muscle. Why is this a desirable functional property?

After Randy was diagnosed with stomach cancer, nearly all of his stomach had to be removed. Postoperative treatment included regular injections of vitamin B12. Why was this vitamin prescribed, and why were injections specified?

How does the heart's ability to contract differ from that of other muscles of the body?

Identify the structures in the following diagram of a sectional view of the heart.

a. ___

b. ___

c. ___

d. ___

e. ___

f. ___

g. ___

h. ___

i. ___

j. ___

k. ___

l. ___

m. ___

The serous membrane covering the outer surface of the heart is the:

(a) Parietal layer of the serous pericardium

(b) Endocardium

(c) Myocardium

(d) Visceral layer of the serous pericardium

The simple squamous epithelium covering the heart valves is the:

(a) Epicardium

(b) Endocardium

(c) Myocardium

(d) Endothelium

Describe the three distinct layers that make up the heart wall.