1. the atrioventricular valves permit blood flow:
a) in one direction only.
b) in both directions.
c) in many directions.
d) in opposite directions on the right and left.
e) from a ventricle to an atrium

2. blood leaves the right ventricle by passing through the:
a) aortic valve.
b) pulmonary valve.
c) mitral valve.
d) tricuspid valve.
e) bicuspid valve.

1. A) in one direction only.

2. B) pulmonary valve.

Explanation:

The heart consists of four cavities: two atria (upper cavities) and two ventricles (lower cavities). Blood passes through a valve before leaving each cavity of the heart. The valves prevent the backward flow of blood. Actually, the valves are fins (leaflets) that act as single-way blood inlets on one side of the ventricle, and as single-way blood outlets on the other side of the ventricle. Normal valves have three fins (leaflets), except the mitral valve, which only has two.

The four valves of the heart are the following:

• The tricuspid valve controls blood flow between the right atrium and the right ventricle.

• The pulmonary valve controls blood flow from the right ventricle to the pulmonary arteries, which transport blood to the lungs to oxygenate it.

• The mitral valve allows oxygen-rich blood from the lungs to pass from the left atrium to the left ventricle.

• The aortic valve allows oxygen-rich blood to pass from the left ventricle to the aorta, the largest artery in the body, which transports blood to the rest of the body.

As the heart muscle contracts and relaxes, the valves open and close, allowing blood flow to the ventricles and atria alternately. The following step-by-step illustration explains the normal operation of the left ventricle valves:

- When the left ventricle relaxes, the aortic valve closes and the mitral valve opens. This allows blood to flow from the left atrium to the left ventricle.

- When the left atrium contracts, more blood flows to the left ventricle.

- When the left ventricle contracts again, the mitral valve closes and the aortic valve opens so that blood flows to the aorta.

When we talk about atrioventricular valves, it means tricuspid valves and  the mitral valve

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