There are three types of circulation within the body: pulmonary circulation, systemic circulation, and coronary circulation. Your circulatory system carries the oxygen and nutrients necessary to your cells and also picks up the carbon dioxide molecules and other waste products as blood flows through your system.
Pulmonary circulation is the process of the blood moving from the heart to the lungs (to become oxygenated) and back to the heart again. Deoxygenated blood in your body leaves the circulation system as it enters the right atrium of the heart through your superior and inferior vena cava. The blood is pumped through your tricuspid valve and into the right ventricle. The right ventricle is the chamber in your heart that moves the deoxygenated blood from your heart to your lungs.
The blood is then pumped through your pulmonary valve into your pulmonary artery. The main pulmonary artery splits into two arteries – one for each lung. Once the blood is at the lungs, it travels through capillary beds located on the alveoli (little sacs in the lungs that process the pulmonary gas exchange). Once there, the carbon dioxide is removed and oxygen is added during respiration (or breathing). The oxygenated blood will then leave your lungs through the pulmonary veins, where it will return to your heart’s left atrium. The blood moving into the left atrium essentially marks the end of the pulmonary circuit.
Systemic circulation can be broken into two phases – bringing vital organs and tissues the necessary oxygen and nutrients to function and then bringing the oxygen-depleted blood back to the heart to be re-oxygenated. Once the pulmonary circuit is complete and the oxygenated blood has been delivered to the aorta, the aorta branches into other major arteries within the upper body before ultimately passing through your diaphragm. From your diaphragm, the major arteries will branch into smaller arteries, arterioles, and then eventually tiny capillaries.
As the blood travels through your circulatory system, your body is simultaneously diffusing carbon dioxide and waste from the cells into the bloodstream and oxygen is diffusing from the blood into the cells. The blood that is oxygen-depleted continues to flow through the capillaries which eventually merge into venules and then veins, and finally the vena cava. From the vena cava, the blood will flow into the right atrium of the heart, starting the pulmonary circuit once again.
In your main circulatory process, oxygenated blood is brought to vital organs to provide oxygen and nutrients. The heart pumps blood to the lungs to become oxygenated and then immediately to the aorta to be delivered to the rest of your body. However, at some point, the heart needs to take in the oxygen and nutrients as well.
After the blood has been oxygenated and returned to the heart via the left atrium, the aortic pressure increases, forcing blood into the coronary (meaning ‘of the heart’) arteries and into the musculature of the heart. The heart receives the oxygen and nutrients and then the oxygen-depleted blood returns to the right atrium via your coronary veins.