The covering of the heart is called pericardium. It is divided into three layers. The outer one is called epicardium.

Vitamin K is a fat-soluble vitamin. It helps in the clotting of blood.

During diastole, the flow of blood from both the atria to the respective ventricle occurs. Diastole means relaxation of the heart chamber.

These cells do not contain mitochondria. Hence, these cannot respire.

The SA node is also known as the sinu-atrial node and is the natural pacemaker of the heart. Initiation of the heartbeat occurs in the SA node.

Macrophages are large-sized cells which are phagocytic in nature and engulf foreign particles, digesting them with the help of their lysosomal enzymes.

Carbon monoxide is more harmful than carbon dioxide as it combines more readily with haemoglobin than carbon dioxide. Hence, it does not allow oxygen to combine with haemoglobin.

The heart wall is made of pericardium which is divided into three layers - epicardium, myocardium and endocardium.

The spleen is the organ which stores blood. It is also called the graveyard of RBCs.

The blood flows from atria to ventricles to arteries and finally to veins. Oxygenated blood is carried through arteries and deoxygenated blood or impure blood is carried through veins.

All veins carry deoxygenated blood, but the pulmonary vein is an exception as it carries oxygenated blood.

The walls of the left ventricle are about three times thicker than the right ventricle as it has to supply the blood more forcefully to the large diameter of aorta.

The heart will go on beating for a short time after it has been entirely removed.

In the human heart, contraction is initiated by a special modified heart muscle known as sinoatrial node. It is located in the right atrium.

Cockroaches have an open circulatory system. In these organisms, the blood does not remain confined to the blood vessels but flows freely in the open spaces of the body cavity and channels.