--- title: "Atrial Natriuretic Peptide | Anatomy I" description: "Atrial natriuretic peptide is a heart hormone that lowers blood volume and pressure by promoting sodium loss, water loss, and vasodilation in Anatomy and Physiology I." canonical: "https://fiveable.me/anatomy-physiology/key-terms/atrial-natriuretic-peptide" type: "key-term" subject: "Anatomy and Physiology I" unit: "Unit 17" --- # Atrial Natriuretic Peptide | Anatomy I ## Definition Atrial natriuretic peptide (ANP) is a hormone released by atrial myocytes in the heart when blood volume or atrial pressure rises. In Anatomy and Physiology I, it shows how the heart helps regulate blood pressure and fluid balance. ## What It Is Atrial natriuretic peptide, or ANP, is a hormone made by the atria of the heart when those chambers stretch from extra blood volume. In Anatomy and Physiology I, you usually meet it as part of the body’s homeostatic response to high blood pressure or excess fluid. The heart is not just a pump here, it also acts as an endocrine organ. The trigger matters. When the atrial walls detect more stretch, atrial myocytes release ANP into the bloodstream. That signal tells the kidneys and blood vessels that the body has more fluid than it needs. Instead of keeping salt and water, the body starts getting rid of them. ANP makes the kidneys excrete more sodium, and water follows sodium. That process is called natriuresis, and it lowers blood volume. Less volume in the bloodstream means less pressure against vessel walls, so blood pressure falls too. ANP also causes vasodilation, which widens blood vessels and reduces resistance to blood flow. ANP also pushes back against the renin-angiotensin-aldosterone system, or RAAS. RAAS normally raises blood pressure by conserving sodium and water and tightening vessels. ANP has the opposite effect, so it acts like a brake when the cardiovascular system is under too much volume or pressure. A useful way to think about ANP is as the heart’s “too much fluid” signal. If blood volume is high, the atria stretch, ANP rises, and the kidneys and vessels respond by lowering volume and pressure. That feedback loop is a clean example of how the cardiovascular, urinary, and endocrine systems work together to keep internal conditions stable. ## Why It Matters ANP shows up anywhere your course connects the cardiovascular system to homeostasis. It is a strong example of secondary endocrine function, because the heart is doing more than moving blood. It is also a clear model of negative feedback, since the hormone is released when pressure is high and acts to bring pressure back down. This term also helps you make sense of blood pressure regulation beyond the nervous system. A&P often compares fast neural control, like sympathetic vasoconstriction, with slower hormonal control, like ANP and RAAS. If you can explain ANP, you can explain why the body does not rely on just one system to regulate circulation. It also shows up in kidney physiology because sodium handling and water balance are tied together. If you know why sodium loss leads to water loss, the meaning of natriuresis becomes a lot easier to trace. That makes ANP useful in diagrams, short-answer questions, and case studies about fluid overload, hypertension, or heart strain. ## Connections ### Natriuresis ANP causes natriuresis, which means the kidneys excrete more sodium in urine. Water follows sodium, so this effect lowers blood volume as well as blood pressure. When you see a question about ANP, look for the sodium first, because that is the start of the volume drop. ### Vasodilation ANP relaxes blood vessels, which decreases peripheral resistance and helps lower pressure faster. This matters because ANP does not act only through the kidneys. It works on vessels too, so the blood pressure drop comes from both less fluid and wider vessels. ### Renin-Angiotensin-Aldosterone System (RAAS) RAAS and ANP are functional opposites. RAAS raises blood pressure by conserving sodium and water and promoting vasoconstriction, while ANP lowers pressure by doing the reverse. In A&P, these two systems are often paired to show how the body balances circulation. ### [Atrial Cardiomyocytes](/anatomy-physiology/key-terms/atrial-cardiomyocytes) Atrial cardiomyocytes, also called atrial myocytes, are the cells that release ANP when the atria stretch. This connects heart muscle structure to hormone secretion. If you are identifying where ANP comes from, the atrial muscle cells are the source to remember. ## On the AP Exam A quiz item might ask you to predict what happens when atrial pressure rises. The move is to trace the chain: atrial stretch triggers ANP release, ANP increases sodium and water excretion, blood volume falls, and blood pressure drops. If the question includes the kidneys, look for natriuresis. If it includes blood vessels, look for vasodilation. In a case study about edema, hypertension, or fluid overload, ANP is one of the hormones you would mention as part of the body’s attempt to restore balance. You may also see it in diagrams of endocrine organs, where you need to recognize that the heart can function as a secondary endocrine organ. A strong answer connects the trigger, the target organs, and the final effect on pressure. ## Atrial Natriuretic Peptide vs Brain Natriuretic Peptide ANP and brain natriuretic peptide are easy to mix up because both lower blood volume and pressure by promoting sodium loss and vasodilation. The difference is their main source: ANP comes from the atria of the heart, while brain natriuretic peptide is named for, and associated with, different cardiac tissue. If a question asks where the hormone is released from, that source is the clue. ## Key Takeaways - Atrial natriuretic peptide is a hormone released by the atria of the heart when they stretch from increased blood volume. - ANP lowers blood pressure by making the kidneys excrete more sodium and water, a process called natriuresis. - It also causes vasodilation, so blood flows through wider vessels with less resistance. - ANP opposes RAAS, which means it helps shut down the body’s blood-pressure raising signals when volume is too high. - In Anatomy and Physiology I, ANP is a clean example of the heart acting as both a pump and a secondary endocrine organ. ## FAQs ### What is atrial natriuretic peptide in Anatomy and Physiology I? Atrial natriuretic peptide is a hormone released by the atria of the heart when they are stretched by increased blood volume. It helps lower blood pressure by increasing sodium and water loss in the kidneys and by relaxing blood vessels. ### What triggers ANP release? ANP is released when atrial myocytes detect increased stretch from extra blood volume or pressure. That stretch signal tells the heart that the body needs to get rid of salt and water, not hold onto them. ### How does ANP lower blood pressure? ANP lowers blood pressure in two main ways. It causes natriuresis in the kidneys, which reduces blood volume, and it causes vasodilation, which lowers resistance in the blood vessels. ### Is ANP the same as RAAS? No. ANP and RAAS do opposite jobs. RAAS raises blood pressure by conserving sodium and water and narrowing vessels, while ANP lowers pressure by promoting sodium loss, water loss, and vasodilation. ## Related Study Guides - [17.10 Organs with Secondary Endocrine Functions ](/anatomy-physiology/unit-17/organs-secondary-endocrine-functions/study-guide/5SR4qT8SbPFoWPuD) - [20.4 Homeostatic Regulation of the Vascular System ](/anatomy-physiology/unit-20/4-homeostatic-regulation-vascular-system/study-guide/XLUICLfbbikLC8t1) ## 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/atrial-natriuretic-peptide#resource","name":"Atrial Natriuretic Peptide | Anatomy I","url":"https://fiveable.me/anatomy-physiology/key-terms/atrial-natriuretic-peptide","learningResourceType":"Concept explainer","educationalLevel":"AP® / High School","about":{"@id":"https://fiveable.me/anatomy-physiology/key-terms/atrial-natriuretic-peptide#term"},"audience":{"@type":"EducationalAudience","educationalRole":"student"},"dateModified":"2026-07-03T02:20:36.800Z","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/atrial-natriuretic-peptide#term","name":"Atrial Natriuretic Peptide","description":"Atrial natriuretic peptide (ANP) is a hormone released by atrial myocytes in the heart when blood volume or atrial pressure rises. 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