The blood circulation from heart to lungs and back to heart is pulmonary circulation and the circulation between heart to tissue and back to heart is systematic circulation and both are included in double circulation.

Pulmonary circulation
The course of blood from the heart to the lungs and back to the heart is called pulmonary circulation. It is one of the two types of circulation in the body, the other being systemic circulation.

Explanation:
Pulmonary circulation refers to the movement of blood between the heart and the lungs. This circulation is responsible for oxygenating the blood and removing carbon dioxide. It is a vital process that ensures the exchange of gases necessary for respiration.

Course of blood in pulmonary circulation:
1. Deoxygenated blood enters the right atrium of the heart through the superior and inferior vena cava, which collect blood from the upper and lower body respectively.
2. From the right atrium, the blood flows into the right ventricle.
3. The right ventricle then contracts, pumping the deoxygenated blood into the pulmonary artery.
4. The pulmonary artery carries the blood to the lungs.
5. In the lungs, the blood is oxygenated through the process of respiration. Oxygen from the inhaled air diffuses into the blood, while carbon dioxide, a waste product, diffuses out of the blood into the air sacs of the lungs.
6. The oxygenated blood returns to the heart through the pulmonary veins.
7. The pulmonary veins carry the oxygenated blood to the left atrium of the heart.
8. From the left atrium, the blood flows into the left ventricle.
9. The left ventricle then contracts, pumping the oxygenated blood into the aorta, which is the main artery of the body.
10. The aorta branches into smaller arteries, which distribute the oxygenated blood to the different organs and tissues of the body, initiating systemic circulation.

Significance of pulmonary circulation:
Pulmonary circulation is essential for maintaining adequate oxygen levels in the body. It allows for the exchange of gases in the lungs, ensuring that oxygen is supplied to the tissues and carbon dioxide is removed. This process is crucial for cellular respiration, which provides the energy needed for various bodily functions. Without pulmonary circulation, the body would not receive the oxygen it requires and waste products would not be efficiently eliminated.