Mention the phase of heart beat in which both the atrio-ventricular valves are closed.

Fill in the blanks

(i) The …………… have thin and less muscular …………… , and have …………… to prevent back flow of …………… .

(ii) …………… carry blood to an organ and break up into …………… ending in capillaries.

(iii) Walls of capillaries consist of a single layer of squamous …………… cells.

(iv) The substances to and from the tissues diffuse through the walls of …………… .

From where to where do the following blood vessels carry blood?

(i) Pulmonary artery

(ii) Renal artery

(iii) Posterior vena cava

(iv) Hepatic vein

(v) Hepatic portal vein

Define portal vein.