Video narration
How can one heart deliver supplies to every cell in your body? Think of circulation as a delivery route: blood carries what cells need, then carries waste away. The heart sends blood through blood vessels to the lungs, where it picks up oxygen. It returns to the heart. Here's the key: blood is not making one giant trip. The heart drives two connected loops. First, blood travels from the heart to the lungs and back. Oxygen-rich blood leaves the heart and travels around the body. It delivers oxygen to cells, collects carbon dioxide, and carries that waste back toward the lungs to be breathed out. The heart keeps pumping, so this route repeats nonstop-dropping off oxygen and bringing waste back. So how does one heart reach every cell? Through two connected loops: the heart loads oxygen at the lungs, delivers it to cells, and brings waste back.