--- title: "Ductus Arteriosus | Anatomy and Physiology I" description: "Ductus arteriosus is the fetal vessel that shunts blood from the pulmonary artery to the aorta, then closes after birth in Anatomy and Physiology I." canonical: "https://fiveable.me/anatomy-physiology/key-terms/ductus-arteriosus" type: "key-term" subject: "Anatomy and Physiology I" unit: "Unit 28" --- # Ductus Arteriosus | Anatomy and Physiology I ## Definition The ductus arteriosus is a temporary fetal blood vessel that connects the pulmonary artery to the aorta, letting blood bypass the lungs before birth. In Anatomy and Physiology I, it is a main part of fetal circulation and the newborn transition. ## What It Is In Anatomy and Physiology I, the ductus arteriosus is a temporary vessel in fetal circulation that sends blood from the pulmonary artery into the aorta instead of through the lungs. Before birth, the lungs are filled with fluid and are not doing gas exchange, so most blood needs a different route. That route matters because the fetus gets oxygen from the placenta, not from breathing air. Blood coming from the right side of the heart is directed away from the high-resistance fetal lungs and into the systemic circulation. The ductus arteriosus is one of the shortcuts that makes that possible. Think of it as part of the fetal bypass system. The right ventricle pumps blood into the pulmonary trunk, but because the pulmonary vessels are still constricted in utero, a large portion of that blood passes through the ductus arteriosus and enters the aorta. From there, it can be carried toward the placenta and the rest of the body. This vessel works closely with the foramen ovale. The foramen ovale shunts blood between the atria, while the ductus arteriosus shunts blood between major arteries. Together, they keep fetal blood moving through the body without forcing it through lungs that are not ready to function yet. After birth, the first breaths change everything. Oxygen in the lungs rises, pulmonary vascular resistance falls, and blood flow through the lungs increases. As that happens, the ductus arteriosus normally constricts and closes within the first days of life, becoming the ligamentum arteriosum later on. If it stays open, the result is patent ductus arteriosus, or PDA. That means blood can keep flowing between the aorta and pulmonary artery after birth, which can overload the lungs and affect normal circulation. In class, this is usually tied to fetal circulation diagrams, newborn transition, and congenital heart defects. ## Why It Matters The ductus arteriosus matters because it shows how the fetal cardiovascular system is built for life before birth, not after. If you can trace this vessel on a diagram, you can explain why fetal blood does not need to pass through the lungs and how circulation changes at delivery. It also connects structure to function, which is a big theme in Anatomy and Physiology I. The ductus arteriosus is not just an extra tube, it is a response to fetal conditions like fluid-filled lungs, placental oxygenation, and high pulmonary resistance. That makes it a great example of how the body adjusts to its environment. This term also shows up when you study newborn transition and congenital defects. When closure does not happen normally, PDA can create a left-to-right shunt after birth, which changes pressure and flow patterns. Being able to explain that shift helps you move from memorizing names to actually reading circulation as a process. It is also a useful comparison term. Once you know what the ductus arteriosus does, the foramen ovale, pulmonary artery, and fetal circulation make much more sense as part of the same system instead of separate facts. ## Connections ### Fetal Circulation The ductus arteriosus is one of the main shortcuts in fetal circulation. It works alongside other shunts so blood can move efficiently before the lungs are active. If you are tracing blood flow in the fetus, this vessel is part of the path that redirects blood away from gas exchange in the lungs and toward the placenta. ### [Foramen Ovale](/anatomy-physiology/key-terms/foramen-ovale) The foramen ovale and ductus arteriosus are often taught together because both bypass fetal lungs, but they do it in different places. The foramen ovale shunts blood between atria, while the ductus arteriosus shunts blood from the pulmonary artery to the aorta. Together they create the fetal pattern of circulation. ### [Pulmonary Artery](/anatomy-physiology/key-terms/pulmonary-artery) The ductus arteriosus branches off the pathway carrying blood from the heart to the lungs. In the fetus, blood entering the pulmonary artery does not need to stay in the lung circulation, so the ductus arteriosus sends much of it into the aorta instead. That link is why the pulmonary artery matters in fetal shunting. ### [Atrial Septum](/anatomy-physiology/key-terms/atrial-septum) The atrial septum is where the foramen ovale sits, so it is part of the same newborn transition story. The atrial septum separates the atria, while the ductus arteriosus handles a separate bypass at the arterial level. Looking at both helps you separate the heart's atrial shortcut from the arterial one. ## On the AP Exam A lab quiz or image ID question may ask you to point out the ductus arteriosus on a fetal circulation diagram and explain the direction of blood flow. You might also get a short-answer prompt about what happens after the first breath, where you need to connect rising oxygen levels, lower pulmonary resistance, and closure of the vessel. In a case question, watch for a newborn with a persistent shunt after birth and identify PDA as failure of the ductus arteriosus to close. If you are asked to compare fetal and postnatal circulation, use this term to show how blood bypasses the lungs before birth and then reroutes through them after birth for oxygenation. ## ductus arteriosus vs Foramen Ovale These are both fetal shunts, so they get mixed up a lot. The ductus arteriosus connects the pulmonary artery to the aorta, while the foramen ovale is an opening between the right and left atria. One bypasses the lungs at the arterial level, the other at the atrial level. ## Key Takeaways - The ductus arteriosus is a temporary fetal vessel that carries blood from the pulmonary artery to the aorta. - It helps bypass the lungs before birth because fetal lungs are not the main site of gas exchange. - After birth, increased oxygen and decreased pulmonary resistance usually trigger closure of the ductus arteriosus. - If it does not close, the result is patent ductus arteriosus, or PDA. - This term is easiest to remember as part of the fetal circulation system, along with the foramen ovale. ## FAQs ### What is the ductus arteriosus in Anatomy and Physiology I? The ductus arteriosus is a fetal blood vessel that connects the pulmonary artery to the aorta. It lets blood bypass the lungs before birth, when the lungs are not yet doing gas exchange. In newborn circulation, it normally closes soon after birth. ### Why does the ductus arteriosus close after birth? After the first breaths, oxygen levels rise and the pulmonary vessels open up, so pressure in the lungs drops. That makes it unnecessary for blood to bypass the lungs. The vessel constricts and later becomes the ligamentum arteriosum. ### What is the difference between the ductus arteriosus and the foramen ovale? Both are fetal shunts, but they route blood in different places. The ductus arteriosus connects the pulmonary artery to the aorta, while the foramen ovale lets blood pass between the atria. They work together to keep blood away from the fetal lungs. ### What happens if the ductus arteriosus stays open? If it remains open after birth, it is called patent ductus arteriosus, or PDA. Blood can keep moving between the aorta and pulmonary artery, which can overload the lungs and disrupt normal circulation. This is a common congenital heart defect example in fetal circulation units. ## Related Study Guides - [28.3 Fetal Development ](/anatomy-physiology/unit-28/3-fetal-development/study-guide/9VWtVO6TlVol3Zg7) - [28.5 Adjustments of the Infant at Birth and Postnatal Stages ](/anatomy-physiology/unit-28/5-adjustments-infant-birth-postnatal-stages/study-guide/Go04YK5yLiBAXVS2) - [20.6 Development of Blood Vessels and Fetal Circulation ](/anatomy-physiology/unit-20/6-development-blood-vessels-fetal-circulation/study-guide/P7hzmuTAzmqbuO6c) - [19.5 Development of the Heart ](/anatomy-physiology/unit-19/5-development-heart/study-guide/TbeMMLg8CcS41duk) ## 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/ductus-arteriosus#resource","name":"Ductus Arteriosus | Anatomy and Physiology I","url":"https://fiveable.me/anatomy-physiology/key-terms/ductus-arteriosus","learningResourceType":"Concept explainer","educationalLevel":"AP® / High School","about":{"@id":"https://fiveable.me/anatomy-physiology/key-terms/ductus-arteriosus#term"},"audience":{"@type":"EducationalAudience","educationalRole":"student"},"dateModified":"2026-07-03T02:20:38.182Z","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/ductus-arteriosus#term","name":"ductus arteriosus","description":"The ductus arteriosus is a temporary fetal blood vessel that connects the pulmonary artery to the aorta, letting blood bypass the lungs before birth. 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