Question

Blood moves into and then out of a heart chamber because 1. the veins and arteries constrict and dilate to propel and attract blood. 2. it moves along its pressure gradient, and that gradient depends on contraction and relaxation during the cardiac cycle. 3. it is under constant pressure, but its movement is dictated by the control of valve openings and closures. 4. All of the choices are correct.

Answer 1

I honk number 4 because Blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium of the heart. ... As the ventricle contracts, blood leaves the heart through the pulmonic valve, into the pulmonary artery and to the lungs where it is oxygenated.