--- title: "Pulmonary Trunk | Anatomy and Physiology I" description: "Pulmonary trunk in Anatomy and Physiology I: the vessel leaving the right ventricle and splitting into pulmonary arteries that send blood to the lungs." canonical: "https://fiveable.me/anatomy-physiology/key-terms/pulmonary-trunk" type: "key-term" subject: "Anatomy and Physiology I" unit: "Unit 19" --- # Pulmonary Trunk | Anatomy and Physiology I ## Definition The pulmonary trunk is the large vessel that carries deoxygenated blood out of the right ventricle and then splits into the left and right pulmonary arteries. In Anatomy and Physiology I, it sits at the start of pulmonary circulation. ## What It Is The pulmonary trunk is the short, large artery that leaves the right ventricle of the heart in Anatomy and Physiology I. Its job is to carry blood that has already delivered oxygen to the body and send it toward the lungs for reoxygenation. Right after blood is pumped through the pulmonary semilunar valve, it enters the pulmonary trunk. That valve prevents blood from slipping back into the right ventricle when the ventricle relaxes. From there, the trunk quickly divides into the left and right pulmonary arteries, one heading to each lung. A common point of confusion is that the pulmonary trunk is not the same thing as the pulmonary arteries, even though they are directly connected. The trunk is the main vessel coming out of the heart, while the pulmonary arteries are the two branches that carry blood deeper into the lungs. In diagrams, the trunk is usually shown as a short central vessel before the split. Functionally, this vessel is part of pulmonary circulation, the low-pressure loop that moves blood from the heart to the lungs and back again. The blood inside the pulmonary trunk is deoxygenated, which surprises many people because arteries usually carry oxygen-rich blood. In this case, the word artery is based on the direction blood flows away from the heart, not on how much oxygen it contains. The pulmonary trunk matters because it is the first step in getting blood to the alveolar capillaries, where gas exchange happens. Without that quick pathway out of the right ventricle, blood could not reach the lungs efficiently, and the body would not be able to restore oxygen levels or remove carbon dioxide effectively. ## Why It Matters The pulmonary trunk is one of the cleanest ways to trace the path of blood through the heart and lungs. If you can identify it, you can usually keep the entire pulmonary circuit straight: right ventricle, pulmonary trunk, pulmonary arteries, lungs, pulmonary veins, left atrium. That sequence shows up constantly in Anatomy and Physiology I when you study heart diagrams, blood flow, and valve function. It also helps you interpret why the heart has two sides that do different jobs. The right side sends blood to the lungs, and the pulmonary trunk is the first big vessel in that route. It also clears up a major language trap in cardiovascular anatomy. Many students assume an artery always means oxygenated blood, but the pulmonary trunk is a built-in exception that proves the rule is about direction, not oxygen content. Once that clicks, a lot of vessel names become easier to read. In lab, labeling the pulmonary trunk correctly is a quick check that you understand heart orientation, blood flow direction, and the relationship between chambers and vessels. In class discussion or quiz questions, it often shows up in questions about what happens after blood leaves the right ventricle or what vessel branches to each lung. ## Connections ### Right Ventricle The pulmonary trunk begins where the right ventricle ends. When the right ventricle contracts, it pushes blood through the pulmonary semilunar valve and into the trunk. If you are tracing blood flow, the right ventricle is the chamber that feeds the pulmonary trunk, so they are usually studied together in heart diagrams and flow-order questions. ### Pulmonary Arteries The pulmonary trunk splits into the left and right pulmonary arteries. This means the trunk is the parent vessel, and the pulmonary arteries are the two branches that carry blood to each lung. On diagrams, students sometimes label the whole vessel as one thing, but the split is what distinguishes the trunk from the arteries. ### [Pulmonary Circulation](/anatomy-physiology/key-terms/pulmonary-circulation) The pulmonary trunk is the first vessel in pulmonary circulation. That circulation loop moves blood from the right side of the heart to the lungs and then back to the left side of the heart. When you understand the trunk, the rest of the route makes more sense, especially the idea that this loop is for gas exchange, not supplying body tissues. ### [Aortic Valve](/anatomy-physiology/key-terms/aortic-valve) The aortic valve is part of the left side of the heart, while the pulmonary trunk is part of the right side pathway. Comparing them helps you separate the two outflow routes of the heart. Both are semilunar valves, but one sends blood to the body through the aorta, and the other sends blood to the lungs through the pulmonary trunk. ## On the AP Exam A diagram ID question may point to the large vessel leaving the right ventricle, and you need to name it as the pulmonary trunk before it branches into the pulmonary arteries. In flow-order questions, you should place it right after the right ventricle and before the lungs. If a prompt asks why an artery carries deoxygenated blood, the pulmonary trunk is the example you use to explain that arteries are named by direction away from the heart, not oxygen content. In a lab practical, you may also need to distinguish the trunk from the separate left and right pulmonary arteries on a heart model or sectional image. ## pulmonary trunk vs Pulmonary Arteries The pulmonary trunk is the single vessel that exits the right ventricle before it splits. The pulmonary arteries are the two branches that carry blood from that split to the left and right lungs. If a question asks for the vessel right after the pulmonary semilunar valve, the answer is pulmonary trunk. If it asks for the branches that go to each lung, the answer is pulmonary arteries. ## Key Takeaways - The pulmonary trunk is the large vessel that carries deoxygenated blood out of the right ventricle. - It quickly divides into the left and right pulmonary arteries, which carry blood to the lungs. - This vessel is part of pulmonary circulation, the heart-to-lungs-and-back loop for gas exchange. - The pulmonary trunk is an artery even though it carries deoxygenated blood, because arteries are named for the direction blood travels away from the heart. - If you can place the pulmonary trunk in the blood flow sequence, heart diagrams and valve questions become much easier to read. ## FAQs ### What is pulmonary trunk in Anatomy and Physiology I? The pulmonary trunk is the major vessel that leaves the right ventricle and carries deoxygenated blood toward the lungs. It then splits into the left and right pulmonary arteries. In heart anatomy, it marks the start of pulmonary circulation. ### Is the pulmonary trunk the same as the pulmonary artery? Not exactly. The pulmonary trunk is the short main vessel leaving the right ventricle, and it then branches into the pulmonary arteries. A lot of students use the terms loosely, but the split is what makes the difference. ### Why does the pulmonary trunk carry deoxygenated blood? Because it is sending blood to the lungs for gas exchange, not to the body tissues. The right side of the heart collects blood that has already delivered oxygen, then sends it through the pulmonary trunk to pick up more oxygen and drop off carbon dioxide. ### How do I identify the pulmonary trunk on a heart diagram? Look for the large vessel leaving the right ventricle before it branches to both lungs. If the diagram shows a central vessel splitting into two branches near the top of the heart, that central part is the pulmonary trunk. It is often shown near the pulmonary semilunar valve. ## Related Study Guides - [19.1 Heart Anatomy ](/anatomy-physiology/unit-19/1-heart-anatomy/study-guide/rkGmPKJ0SjTIT3Kf) ## About This Document Canonical Fiveable pages are available as Markdown at the same path plus `.md`. - [llms.txt](https://fiveable.me/llms.txt): index of Fiveable's sections and URL patterns - [llms-full.txt](https://fiveable.me/llms-full.txt): complete subject and unit listing - [MCP server](https://fiveable.me/mcp): call Fiveable as tools instead of fetching pages (`https://fiveable.me/api/mcp`) - [MCP server for AP teachers](https://fiveable.me/mcp/teachers): a teacher's classes, assignments and AP-rubric grading (`https://fiveable.me/api/mcp/teacher`) ## Structured Data ```json {"@context":"https://schema.org","@graph":[{"@type":"LearningResource","@id":"https://fiveable.me/anatomy-physiology/key-terms/pulmonary-trunk#resource","name":"Pulmonary Trunk | Anatomy and Physiology I","url":"https://fiveable.me/anatomy-physiology/key-terms/pulmonary-trunk","learningResourceType":"Concept explainer","educationalLevel":"AP® / High School","about":{"@id":"https://fiveable.me/anatomy-physiology/key-terms/pulmonary-trunk#term"},"audience":{"@type":"EducationalAudience","educationalRole":"student"},"dateModified":"2026-07-03T02:20:41.765Z","isPartOf":{"@type":"Collection","name":"Anatomy and Physiology I Key Terms","url":"https://fiveable.me/anatomy-physiology/key-terms"},"publisher":{"@type":"Organization","name":"Fiveable","url":"https://fiveable.me"}},{"@type":"DefinedTerm","@id":"https://fiveable.me/anatomy-physiology/key-terms/pulmonary-trunk#term","name":"pulmonary trunk","description":"The pulmonary trunk is the large vessel that carries deoxygenated blood out of the right ventricle and then splits into the left and right pulmonary arteries. 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