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

Can you answer why the pulmonary artery shown in Fig. 7.6 is blue in colour?

Name the following:

(i) Contraction phase of the 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 backflow 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.