1. Select the correct statement about cardiac output. A. A slow heart rate reduc

Question

1.         Select the correct statement about cardiac output.

A.         A slow heart rate reduces stroke volume and force of contraction.

B.         Decreased venous return will result in increased stroke volume.

C.         If a semilunar valve were partially obstructed, the stroke volume in the affected ventricle would be decreased.

D.         Stroke volume increases if the filling decreases.

E.         a and c

2.        Which one of the following is not a factor in determining the flow rate of blood in a particular vessel

A.        viscosity of the blood in the vessel

B.        length of the blood vessel

C.        radius of the vessel

D.        a and c

E.         thickness of the vessel

Briefly explain the significance of venous return and how does it affect the cardiac output.

Explanation / Answer

Slow heart rate reduces stroke volume and force of contraction

Stroke volume is the volume of blood pumped by the ventricles with each heartbeat.

b. incorrect

increase in venous return increases ventricular load and stroke volume

c. correct

when semilunar valve is blocked, it leads to the decrease in the blood volume in the respective ventricle. This results in reduced stroke volume

however, if the semilunar valve is incompetent, it allows blood to flow from aorta into the left ventricle. This results in greater filling of blood in ventricle and eventually higher stroke volume.

D. incorrect

filling and leaving should be same.

A and C are correct.

2. E

Five factors that effect blood flow are

Viscosity of blood, length and diameter of blood vessel, volume of blood, compliance and cardiac output

3. venous return is the blood that flows back to heart. In normal conditions, venou return is equal to cardiac output. Venous return is determined by the following equation,

(Pv-Pra)/Rv

Pv is the venous pressure; Pra is the right atrial pressure; Rv is the vascular resistance

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