--- title: "Angiotensin-Converting Enzyme | Anatomy I" description: "Angiotensin-converting enzyme (ACE) converts angiotensin I into angiotensin II and helps control blood pressure, fluid balance, and kidney perfusion in Anatomy and Physiology I." canonical: "https://fiveable.me/anatomy-physiology/key-terms/angiotensin-converting-enzyme" type: "key-term" subject: "Anatomy and Physiology I" unit: "Unit 17" --- # Angiotensin-Converting Enzyme | Anatomy I ## Definition Angiotensin-converting enzyme (ACE) is a blood-vessel enzyme that turns angiotensin I into angiotensin II, a stronger vasoconstrictor in the RAAS. In Anatomy and Physiology I, it shows up in blood pressure and kidney regulation. ## What It Is Angiotensin-converting enzyme, or ACE, is the enzyme that finishes a major blood pressure control step in the renin-angiotensin-aldosterone system (RAAS). It converts angiotensin I into angiotensin II, which is the more active molecule that narrows blood vessels and pushes the body to conserve fluid. In Anatomy and Physiology I, ACE usually comes up when you trace how the kidneys, blood vessels, and endocrine signals work together to keep blood pressure stable. The enzyme is found mainly on endothelial cells lining blood vessels, especially in the lungs, so the blood can be modified as it moves through the circulation. Here is the sequence you usually need to know. When blood pressure or blood volume drops, the kidneys release renin. Renin starts the pathway by helping form angiotensin I. ACE then converts that inactive or less active precursor into angiotensin II, which has stronger effects on the cardiovascular system. Angiotensin II raises blood pressure in two main ways. First, it causes vasoconstriction, which increases resistance in the arteries. Second, it signals the adrenal cortex to release aldosterone, and aldosterone makes the distal tubules and collecting ducts keep more sodium, which pulls water back into the bloodstream. ACE does one more thing that matters a lot in physiology classes. It breaks down bradykinin, a vasodilator. That means ACE is not just making a pressor hormone, it is also removing a molecule that would normally help blood vessels relax. So ACE pushes blood pressure upward from both directions, stronger constriction and less dilation. ## Why It Matters ACE shows up in A&P because it connects several body systems in one pathway. You can use it to explain why a drop in kidney perfusion can lead to a whole-body response that changes vessel diameter, blood volume, and filtration pressure. It also helps you make sense of the kidney unit. When renal blood flow falls, the body does not only try to fix the kidney locally. It changes circulating hormones through RAAS, and ACE is the step that turns that signal into angiotensin II, which then affects the heart, vessels, adrenal glands, and distal tubules. This term also helps explain common physiology questions about hypertension and treatment. If ACE activity is high, the body keeps more fluid and maintains tighter vessels, which can raise blood pressure. If ACE is inhibited, less angiotensin II is made, less aldosterone is released, and blood pressure usually falls. You will often see ACE in diagrams, flow charts, and short answer questions that ask you to trace cause and effect. If you can follow the pathway from low blood pressure to renin to ACE to angiotensin II to aldosterone, you can usually explain the logic of the whole response. ## Connections ### Renin-Angiotensin-Aldosterone System (RAAS) ACE is one step inside RAAS, not the whole pathway. RAAS starts when the kidneys sense low perfusion, and ACE helps turn that signal into a stronger hormone response. If you know the full sequence, it is easier to explain why blood pressure, blood volume, and sodium balance all change together. ### [Angiotensin II](/anatomy-physiology/key-terms/angiotensin-ii) ACE makes angiotensin II from angiotensin I, so this is the molecule most directly linked to ACE’s effects. Angiotensin II is the part of the pathway that causes vasoconstriction and helps trigger aldosterone release. If you are asked what ACE does, angiotensin II is usually the next step in your answer. ### Aldosterone Aldosterone comes after angiotensin II in the RAAS chain. ACE does not release aldosterone itself, but it helps create the signal that tells the adrenal cortex to release it. Aldosterone then acts on the distal tubules to increase sodium reabsorption, which raises water retention and blood volume. ### [Distal Tubules](/anatomy-physiology/key-terms/distal-tubules) The distal tubules are one of the places where the RAAS signal becomes a kidney response. After ACE helps generate angiotensin II and aldosterone is released, the distal tubules reabsorb more sodium and water is kept with it. That link is why ACE matters for both circulation and renal physiology. ## On the AP Exam A quiz item might ask you to put the RAAS steps in order or identify what happens when ACE is blocked. You should be able to trace the pathway from low blood pressure to renin release, then to ACE making angiotensin II, then to vasoconstriction and aldosterone-driven sodium retention. In a case question about hypertension, ACE is the clue that connects vessel tone to kidney fluid handling. In a lab, you may be asked to interpret a diagram of the pathway or explain why an ACE inhibitor lowers blood pressure and can reduce strain on the heart. ## angiotensin-converting enzyme vs Angiotensin II ACE and angiotensin II are related, but they are not the same thing. ACE is the enzyme that makes angiotensin II from angiotensin I. Angiotensin II is the hormone that actually narrows blood vessels and triggers aldosterone release, so if a question asks for the effector molecule, the answer is angiotensin II, not ACE. ## Key Takeaways - ACE is the enzyme that converts angiotensin I into angiotensin II in the RAAS pathway. - In Anatomy and Physiology I, ACE matters because it links kidney perfusion, blood vessel tone, and fluid balance. - Angiotensin II raises blood pressure by causing vasoconstriction and by stimulating aldosterone release. - ACE also breaks down bradykinin, so it reduces a natural vasodilator at the same time it promotes constriction. - If you can trace ACE in the RAAS sequence, you can explain many blood pressure and kidney regulation questions. ## FAQs ### What is angiotensin-converting enzyme in Anatomy and Physiology I? Angiotensin-converting enzyme (ACE) is the enzyme that changes angiotensin I into angiotensin II. In A&P I, it usually appears in the RAAS pathway, where it helps the body raise blood pressure and conserve fluid when blood volume or perfusion drops. ### What does ACE do to blood pressure? ACE increases blood pressure by helping produce angiotensin II, which constricts blood vessels and stimulates aldosterone release. It also breaks down bradykinin, a vasodilator, so the overall effect pushes pressure upward. ### Is ACE the same as angiotensin II? No. ACE is the enzyme, while angiotensin II is the hormone made by that enzyme. A common mistake is mixing up the step that makes the signal with the signal itself. ### Why do ACE inhibitors lower blood pressure? ACE inhibitors block the conversion of angiotensin I to angiotensin II. With less angiotensin II, there is less vasoconstriction and less aldosterone release, so the body holds onto less sodium and water and blood pressure drops. ## Related Study Guides - [17.6 The Adrenal Glands ](/anatomy-physiology/unit-17/6-adrenal-glands/study-guide/o7QQ9urw5EOcLtdx) ## 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/angiotensin-converting-enzyme#resource","name":"Angiotensin-Converting Enzyme | Anatomy I","url":"https://fiveable.me/anatomy-physiology/key-terms/angiotensin-converting-enzyme","learningResourceType":"Concept explainer","educationalLevel":"AP® / High School","about":{"@id":"https://fiveable.me/anatomy-physiology/key-terms/angiotensin-converting-enzyme#term"},"audience":{"@type":"EducationalAudience","educationalRole":"student"},"dateModified":"2026-07-03T02:20:36.799Z","isPartOf":{"@type":"Collection","name":"Anatomy and Physiology I Key Terms","url":"https://fiveable.me/anatomy-physiology/key-terms"},"author":{"@type":"Organization","@id":"https://fiveable.me/editorial#content-team","name":"Fiveable Content Team","url":"https://fiveable.me/editorial","parentOrganization":{"@id":"https://fiveable.me/#organization"},"member":[{"@type":"Person","name":"Amanda DoAmaral","sameAs":["https://www.linkedin.com/in/adoamaral"]},{"@type":"Person","name":"Becky Bahr","sameAs":["https://www.linkedin.com/in/becky-bahr-b52743132"]}]},"publisher":{"@type":"Organization","name":"Fiveable","url":"https://fiveable.me"}},{"@type":"DefinedTerm","@id":"https://fiveable.me/anatomy-physiology/key-terms/angiotensin-converting-enzyme#term","name":"angiotensin-converting enzyme","description":"Angiotensin-converting enzyme (ACE) is a blood-vessel enzyme that turns angiotensin I into angiotensin II, a stronger vasoconstrictor in the RAAS. 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