Question

Explain the following:
(i) Why is the SA node called the pace-maker of the heart?
(ii) Why is there no mixing of deoxygenated and oxygenated blood in the human heart normally?
(iii) Why is the closed circulatory system more efficient than the open system?
(iv) Why does the left ventricle posses a thicker wall than the right ventricle?

Answer 1

(i) Sinoatrial node (SA node) is located in the right atrium. It has the inherent ability to generate a wave of contraction and to control the pace of heartbeat by producing electrical signals much similar to those produced by nerves. Therefore, it is known as the pacemaker of heart.

(ii) Human heart is four chambered, comprising two atria and two ventricles. These chambers are separated by a muscular wall called septum that prevents the mixing up of oxygenated and deoxygenated blood. The wall between the left and the right atria is the inter-atrial septum and the wall between the left and the right ventricle is the inter-ventricular septum. These septa help in preventing the mixing of blood in the right and left parts of the heart.

(iii) The closed circulatory system is more efficient than the open circulatory system as it operates even with a higher blood pressure and uses less blood for higher and faster distribution of oxygen and nutrients. This allows the organism to move, digest and eliminate wastes more quickly. Also, due to the efficient distribution of antibodies, immune responses are much stronger and, therefore, help the body to fight off infection more powerfully.

(iv) The walls of the left ventricle are thicker than those of the right ventricle because it is from this chamber that the blood is pumped with great force through aorta to various other parts of the body.