18. The Heart

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 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

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

Mark the following statements as true or false. If a statement is false, correct it to make a true statement.

The heart plays a role in the regulation of blood pressure and secretes the hormone atrial natriuretic peptide.

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

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 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

Describe the pericardium and distinguish between the fibrous and the serous pericardia relative to histological structure and location.

The AV node has fewer gap junctions than the SA node, leading to slower conduction. How does this slower conduction help the heart function?

Which statement best describes intrinsic conduction of the heart?

A newer drug, ivabradine, lowers the heart rate by blocking the nonselective HCN cation channels. Why would this action decrease the heart rate? Would this drug have an effect on pacemaker cells, contractile cells, or both? Explain.

Which structure or structures are most directly responsible for allowing contraction of the ventricles to begin at the apex of the heart rather than in the septum closer to the AV node?