The SA node is the normal pacemaker of the human heart because its cells
1. spontaneously generate electrical signals about 70 to 80 times per minute.
2. are located in the interventricular septum.
3. generate electrical signals only when stimulated by sympathetic fibers.
4. are not in contact with other cells of the heart.

If the SA node is not functional in a human being, his ECG would not show:
1. P wave
2. QRS complex
3. ST segment
4. T wave

What causes the opening of tricuspid and bicuspid valves?
1. Atrial pressure greater than pressure in the ventricles.
2. Ventricular pressure greater than pressure in the arteries.
3. Arterial pressure greater than pressure in the ventricles.
4. Ventricular pressure greater than pressure in the atria.

What happens during the isovolumetric relaxation of the cardiac cycle?
1. the atria contract and pump blood into the ventricles.
2. the ventricles contract and pump blood into the blood vessels.
3. both atria and ventricles are relaxed.
4. the ventricles contract but ventricular pressure is lower than arterial. pressure

The semilunar valves close at the beginning of

How would the blood pumped per minute by the left ventricle compare with that pumped by the right ventricle?
1. normally greater than that of the right ventricle.
2. probably lower than the right ventricle if the person has systemic edema.
3. probably lower than the right ventricle if the person has pulmonary edema.
4. probably higher than the right ventricle if the person has pulmonary edema.

Under normal physiological conditions a higher cardiac output can be achieved by a higher:
1. extracellular ${\mathrm{K}}^{+}$ concentration
2. blood pressure in the systemic circulation
3. venous return
4. parasympathetic tone

Vagotomy [cutting of vagus nerve] would lead to:
1. reduced heart rate
2. increased heart rate
3. reduced strength of contraction
4. increased secretion of acetylcholine

The cardiovascular system is located in:
1. cerebral cortex
2. thalamus
3. basal nuclei
4. medulla oblongata

The liquid portion of the blood with fibrinogen and some of the clotting proteins removed is
1. plasma.
2. platelets.
3. plasma proteins.
4. serum