The plateau in the cardiac action potential is primarily due to:
1. slow outward diffusion of ${\mathrm{K}}^{+}$
2. fast inward diffusion of ${\mathrm{Cl}}^{-}$
3. fast outward diffusion of ${\mathrm{Ca}}^{2+}$
4. slow inward diffusion of ${\mathrm{Ca}}^{2+}$

Artificial pacemakers can be used to treat a patient suffering from:
1. a myocardial infarction
2. atherosclerosis
3. a third degree AV node block
4. mitral stenosis

Lymph does not contain:

The lymph eventually enters the circulation by draining into two specific ___________.
1. arteries
2. arterioles
3. capillaries
4. veins

The fraction of an anticoagulated blood sample called the "buffy coat" contains
1. red blood cells
2. white blood cells
3. platelets
4. white blood cells and platelets

The cause of “aplastic anemia" would be:
1. lack of iron content or iron absorption from the diet
2. destruction of the bone marrow, perhaps by chemicals in the environment or chemotherapy
3. high altitude
4. inadequate vitamin B₁₂ absorption from the diet because the intrinsic factor is absent

Thrombocytes:
1. have a life span of about 60 days
2. are also called megakaryocytes
3. release a chemical called serotonin that constricts blood vessels
4. are not involved in hemostasis

The rarest white blood cells are:

What is true regarding pulmonic and aortic semilunar valves in the human heart?
1. They prevent the backflow of blood from the ventricles into the atria
2. They are open during the relaxation phase of the ventricles
3. They are held tightly closed by papillary muscles and chordae tendineae
4. They regulate the passage of blood from the ventricles into the pulmonary artery and the aorta

Which of the following causes the second heart sound [dub]?
1. opening of the AV valves at the start of diastole
2. closing of the AV valves at the start of systole
3. opening of the semilunar valves at the start of systole
4. closing of the semilunar valves at the start of diastole