Question

1. What are the four mechanism responsible for

returning blood to the heart? How does each of

these work? Why dont' arteries need these?

2. What are the two factors that regulate blood flow

to the tisse?

a) If blood pressure gradient increases, does

more or less blood flow to the tissue?

b) If resistance increases, does more or less

blood flow to the tissue?

3. What phase of the cardiac cycle does systolic

blood pressure correspond to? What avout

diastolic pressure?

Answer 1

1.The four mechanisms responsible for the returning blood to heart are -

a.Muscle contraction mechanism- The muscle contraction (muscle pump mechanism)actively helps in returning the blood to heart.The contraction of muscles causes the blood flow through the distal valve and obstruct the flow into the muscles due to closing of proximal valve during contraction.

b.Muscle relaxation mechanism - The muscle relaxation (muscle pump mechanism)causes proximal valves to open and fill into the venous part.During this time,the distal valves initailly remains close and get opened up by the filling of the blood into the venous segment.

c.Respiratory mechanism - The increasing the rate of respiration ,accelerated by the force of respiration increases the cardiac output and thus increases the returning blood to heart.It occurs through the lowering of the atrial pressure.

d. Thoracic pump action - During inspiration,the intrapleural pressure becomes negative and thus promotes the chest wall and lung expansion,superior and inferior vena cava and cardiac chambers.

The arteries doesn't need such mechanism ,because when heart contract ;it automatically pushes the vessels wall and creates the high pressure which helps in the blood flow through arteries to the tissues.