18. The Heart

Cardiac muscle cells are joined by structures called:

a. T-tubules.

b. tight junctions.

c. sarcoplasmic reticulum.

d. intercalated discs.

The portion of the intrinsic conduction system located in the superior interventricular septum is the:

a. AV node

b. SA node

c. AV bundle

d. Subendocardial conducting network

More than one choice may apply.

Using the figure, identify the most external part of the pericardium.

Draw a diagram of the heart showing the three layers composing its wall and its four chambers. Label each. Show where the AV and semilunar valves are, and name them. Show and label all blood vessels entering and leaving the heart chambers.

Name three different factors that increase heart rate.

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 ______ is the primary pacemaker of the heart.

a. Atrioventricular node

b. sinoatrial node

c. Purkinje fiber system

d. Atrioventricular bundle

The AV node delay:

a. Allows the atria and ventricles to depolarize and contract as a unit.

b. Allows the two ventricles to depolarize and contract separately.

c. Allows the atria and ventricles to depolarize and contract separately.

d. Speeds up the impulse transmission from the atria to the ventricles.

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.