Science · Body foundations
Cardiovascular System
Estimated time includes reading and one quiz. Take the time you need.
Start here: key ideas
- The right heart sends blood to the lungs; the left heart sends blood to the body.
- Valves keep blood moving one way.
- Arteries carry blood away, veins carry blood back, and capillaries exchange materials.
- The heart’s electrical system coordinates contraction.
What you’ll be able to do
- Trace blood through the heart, lungs, and body.
- Explain how conduction, pressure, and valves work together.
- Compare arteries, veins, and capillaries.
- Match blood components with oxygen transport, defense, clotting, and fluid transport.
Trace one drop of blood through two circuits, then match each structure to its job.
Optional review
If you’d like to review the basics, visit Anatomical Orientation, Organization, and Homeostasis. You can start this lesson without completing those first.
Two circuits, one continuous route
Start with one big loop. Blood from the body enters the right heart. The right heart sends it to the lungs. Blood then enters the left heart. The left heart sends it back to the body. An atrium is an upper chamber that receives blood. A ventricle is a lower chamber that pumps blood out. The ventricles have thicker walls because they push blood away from the heart. The left ventricle is thickest because it pumps through the whole body.
Now add the exact route: body → venae cavae → right atrium → tricuspid valve → right ventricle → pulmonary valve → pulmonary arteries → lung capillaries → pulmonary veins → left atrium → mitral valve → left ventricle → aortic valve → aorta → body. In the lungs, blood releases carbon dioxide and gains oxygen. The septum separates the two sides of the heart.
The heart-to-lung route is the pulmonary circuit. The heart-to-body route is the systemic circuit. Arteries always carry blood away from the heart, and veins always carry blood toward it. That rule is about direction, not oxygen. Pulmonary arteries carry low-oxygen blood to the lungs, while pulmonary veins carry oxygen-rich blood to the heart.
Trace the pulmonary and systemic circuits
Start with the big loop: body → right heart → lungs → left heart → body. Then find the chambers and vessels along that route. Arteries carry blood away from the heart; veins bring it back. Those names describe direction, not oxygen content.
Trace the pulmonary and systemic circuits — OpenStax College, Anatomy & Physiology (2014 CC BY archive). CC BY 3.0. Original source image reproduced unchanged; explanatory caption added.
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