Can you answer why the pulmonary artery shown in figure is blue in colour ?

Name the following :

(i) Contraction phase of heart.

(ii) The structure that holds the heart valves in position.

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 …………… .

Name the two major circulations of blood in the human body.