Difference between Pulmonary and Systemic Circulation

By: | Updated: May-28, 2019

The body is made up of circulatory systems that serve as pathways for blood-carrying vessels. These systems are subdivided into two major parts: pulmonary and systemic circulation. Although they are both powered by the heart, they assume different roles in the body.

Summary Table

Pulmonary CirculationSystemic Circulation
Mainly responsible for supplying oxygen and releasing carbon dioxide to and from the heartMainly responsible for moving blood from the heart to the cells of the body, and vice versa
Composed of the pulmonary trunk (also called pulmonary artery) and the pulmonary veinsComposed of the aorta and the superior and inferior vena cava
Carries deoxygenated blood from the right ventricle to the lungs via the pulmonary trunkCarries oxygenated blood from the left ventricle to the cells of the body via the aorta
Transports oxygenated blood from the lungs to the left atrium via the pulmonary veinsTransports deoxygenated blood from the body to the right atrium via the superior and inferior vena cava
Uses the right ventricle and the left atrium as pathways for deoxygenated and oxygenated blood, respectivelyUses the left ventricle and the right atrium as pathways for oxygenated and deoxygenated blood, respectively

Definitions

pulmonary and systemic circulation
A diagram of both pulmonary and systemic circulation

Pulmonary circulation is a part of the circulatory system responsible for forming a circuit of vessels that transport blood between the heart and the lungs.

Systemic circulation, on the other hand, forms a closed circuit between the heart and the rest of the body. It aids in transporting oxygenated blood, which carries nutrients, to different tissues.

Pulmonary vs Systemic Circulation

These two systems have one major similarity: they are both closed circuit systems that transport blood to and from the heart. But while they play equally-important roles in the body, there is a huge difference between pulmonary and systemic circulation.

Function

The pulmonary and systemic circulation work harmoniously to maintain homeostasis, but they do so differently. Pulmonary circulation is mainly responsible for supplying oxygen and releasing carbon dioxide to and from the heart, while systemic circulation moves oxygenated blood from the heart to the cells of the body, enabling these cells to absorb nutrients and excrete waste. As oxygen is absorbed, deoxygenated blood is transported back to the heart via systemic circulatory pathways.

Transport Vessels

Pulmonary circulation involves blood-carrying vessels such as the pulmonary trunk (also called pulmonary artery) and the pulmonary veins. Systemic circulation, on the other hand, is facilitated by the aorta and the superior and inferior vena cava. The superior vena cava carries blood from the upper parts of the body, while the inferior vena cava is responsible for blood transport from the lower parts of the body.

Circulatory Pathways

Pulmonary circulation works by forming a closed circuit of blood-carrying vessels between the heart and the lungs. To supply the blood with the oxygen it needs, deoxygenated blood exits the heart via the right ventricle and the pulmonary trunk. Structurally, the pulmonary trunk is split into two main branches that carry blood to the left and the right lungs. These branches are further subdivided into smaller branches that can reach pulmonary air sacs (also called alveoli) and capillaries – the main site for oxygen absorption and carbon dioxide release. The oxygen-rich blood is then transported to the pulmonary veins, which open up to the left atrium of the heart.

Systemic circulation uses a completely different circulatory pathway. As the system begins, the heart pumps oxygenated blood, which uses the left ventricle and the aorta (the main artery of the body) as a pathway. The movement of oxygen-rich blood towards arterioles and capillary beds facilitates cellular nutrient absorption and waste excretion. Then, the deoxygenated blood, which now carries cellular waste materials, drains into veins and is transported back to the right atrium via the superior and inferior vena cava.

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