--- title: "Heart structure & double circulation" description: "Describe the structure of the heart (four chambers, valves, coronary arteries) and explain how it pumps deoxygenated blood to the lungs and oxygenated blood to the body in a double circulatory system" canonical: https://lightmysky.com/learn/science/heart-structure-and-double-circulation-mt_TR2oTy9c2M source: https://lightmysky.com/learn/science/heart-structure-and-double-circulation-mt_TR2oTy9c2M.md retrieved: 2026-11-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Heart structure & double circulation Describe the structure of the heart (four chambers, valves, coronary arteries) and explain how it pumps deoxygenated blood to the lungs and oxygenated blood to the body in a double circulatory system Subject: Science · Area: Organisms & Life Processes · Ages 12 to 13 Page: https://lightmysky.com/learn/science/heart-structure-and-double-circulation-mt_TR2oTy9c2M ## Ready when they can - Identifies the heart's four chambers and describes the receiving role of the atria - Traces the route of blood through the double circulatory system - Explains the role of valves in preventing backflow - Compares arteries, veins, and capillaries ## Lesson: Heart structure & double circulation You have followed blood through arteries, capillaries and veins. Inside the heart are four chambers: two upper atria and two lower ventricles. Each side has one of each. Atria receive blood and help move it into the ventricles. Ventricles pump blood out. In a normally formed heart after birth, a wall called the septum separates the right and left sides. Deoxygenated blood is low in oxygen, not empty of it. Blood returning from the body enters the right atrium through the superior and inferior vena cava, together called the venae cavae. It passes into the right ventricle, which pumps it through the pulmonary arteries to the lungs. At the lungs, oxygen enters the blood and carbon dioxide leaves it. *(drawing: Read left to right, then continue on the next row. This is a route map linking the body, right side of the heart and lungs, not an anatomical drawing.)* Pulmonary veins return oxygen-rich (oxygenated) blood from the lungs to the left atrium, then the left ventricle pumps it through the aorta to the body. Blood returns to the right atrium, enters the right ventricle and goes through pulmonary arteries to the lungs. These linked loops take blood through the heart twice per complete trip: double circulation. The left ventricle's thicker muscle wall produces higher pressure for the body loop than the right produces for the lung loop. *(drawing: Read left to right, then continue on the next row. Oxygen-rich blood returns through pulmonary veins and leaves through the aorta for the body.)* Valves lie between each atrium and ventricle and at the ventricular exits. Working valves open for forward flow and close against backflow. When ventricular pressure rises above atrial pressure, the valve between them closes. Blood can leave through the outgoing artery once its exit valve opens. If the atrium-to-ventricle valve cannot close fully, some blood may leak back into the atrium. Heart valve closure produces the normal lub-dub sounds. Arteries carry blood away from the heart. Their thick muscular, elastic walls withstand higher pressure than veins. Veins return blood at lower pressure; many have valves. Capillaries have walls one cell thick for exchange with tissues. Vessel names describe direction, not oxygen content. Coronary arteries branch from the aorta and supply oxygen and nutrients to heart muscle. **Recap.** The right side pumps to the lungs; the left pumps to the body. Two linked loops form double circulation. Working valves prevent backflow. *This lesson, question bank and flashcards were written for this dataset.* ## Practice 8 questions on this page, each with its working shown. ## Needs first - [The circulatory system](https://lightmysky.com/learn/science/the-circulatory-system-mt_BX4D8cCFtQ) - [Gas Exchange & Breathing](https://lightmysky.com/learn/science/gas-exchange-and-breathing-mt_V9SQS9gLFw) ## Optional connections - [Nutrient Transport in Animals](https://lightmysky.com/learn/science/nutrient-transport-in-animals-mt_YSyjTZfjvv) ## Opens up - [Blood Components and Blood Vessels](https://lightmysky.com/learn/science/blood-components-and-blood-vessels-mt_aWZ2sGXGMn)