Tag: heart, blood vessels and cardiac cycle

• The SA node is the heart's natural pacemaker. 
• The SA node is a muscular tissue where electrical impulses are generated for the rhythmic contractions of the heart.
  
  Hence, option D is correct.

Pulmonary circulation carries blood to and from the lungs. They include the pulmonary artery (aorta) and its branches to the capillaries in the lungs, as well as the veins, that drain those capillaries. The pulmonary arteries carry blood low in oxygen from the right ventricle, while the pulmonary veins carry blood high in oxygen from the lungs into the left atrium. This circuit functions to eliminate carbon dioxide from the blood and replenish its supply of oxygen.

Myogenic contraction refers to a contraction initiated by the myocyte cell itself.

The sinoatrial node (SAN) can generate the maximum number of action potentials, i.e., 70 - 75 beats/min, and is responsible for initiating and maintaining the rhythmic contractile activity of the heart. Therefore, it is called as the pacemaker of the heart.

The Purkinje fibers are specialised conducting fibres present in the inner ventricular walls of the heart. They help in the contraction of the ventricles and thus maintain the rhythmicity of the heart. 

The bundle of His is a group of muscle cells that transmits the electrical impulses from AV node to the ventricle wall via Purkinje fibres. 

Arteries carry blood oxygenated blood away from the heart. While the veins carry deoxygenated blood towards the heart.

Arteries carry oxygenated blood away from the heart.  Pulmonary artery carries the de-oxygenated blood from the right ventricle to the lungs for oxygenation.

The bundle of His is the upper end of the electrical path,which through the Purkinje fibres allows the electrical signal to activate the ventricles and thus to pump the blood.

Under the normal conditions heart rate has an inverse relation with the size of the animal.