--- title: "IGF-1 | Anatomy and Physiology I" description: "IGF-1 is a liver-made hormone that carries out many growth hormone effects, boosting protein synthesis, cell growth, and muscle and bone development in A&P." canonical: "https://fiveable.me/anatomy-physiology/key-terms/igf-1" type: "key-term" subject: "Anatomy and Physiology I" unit: "Unit 10" --- # IGF-1 | Anatomy and Physiology I ## Definition IGF-1, or insulin-like growth factor 1, is a hormone made mostly by the liver in response to growth hormone. In Anatomy and Physiology I, it explains how the body promotes tissue growth, especially in muscle and bone. ## What It Is IGF-1, or insulin-like growth factor 1, is a hormone in Anatomy and Physiology I that links growth hormone signaling to actual tissue growth. GH tells the body to grow, but IGF-1 is one of the main hormones that helps carry out that message in cells, especially in muscle, bone, and other tissues. Most IGF-1 is produced by the liver after growth hormone stimulates it, although some tissues also make smaller local amounts. That means IGF-1 can act like an endocrine signal when it travels through the blood, and it can also act more locally where it is made. Either way, its job is to encourage cells to grow, divide, and make more protein. A simple way to picture it is this: growth hormone rises, the liver responds, and IGF-1 helps turn that signal into tissue change. In muscle, IGF-1 supports protein synthesis and helps amino acids get used for building and repair. In bone, it supports growth and remodeling, which is why it shows up in discussions of development and recovery. IGF-1 is tied to anabolism, so it is associated with building up body tissues rather than breaking them down. That is why it is often discussed next to resistance training, muscle hypertrophy, and recovery after exercise. When a class talks about hypertrophy, IGF-1 is part of the cellular explanation for why repeated training can make muscle fibers bigger over time. Its level is not fixed. Growth hormone, nutrition, and physical activity all influence IGF-1. For example, if nutrition is poor, the body may have trouble making as much IGF-1 even if growth hormone is present. That helps explain why growth is not just about one hormone, but about the whole body environment that lets the signal work. In this course, the big idea is not just that IGF-1 exists, but that it is one of the body’s growth messengers. It sits at the intersection of endocrine control, tissue repair, and exercise adaptation, so you use it to explain how hormones affect real changes in muscle and bone structure. ## Why It Matters IGF-1 matters because it connects hormone signaling to the body changes you can actually see in Anatomy and Physiology I. If you are trying to explain why tissues grow, heal, or adapt to exercise, IGF-1 gives you the mechanism behind the change. It also helps you separate general growth signaling from the specific cellular work that happens afterward. Growth hormone starts the process, but IGF-1 helps drive protein synthesis, cell proliferation, and differentiation. That makes it useful anytime you are explaining muscle hypertrophy, bone development, or tissue repair. You will also see IGF-1 when the course brings up exercise and muscle performance. Resistance training can increase IGF-1 signaling, which is one reason repeated loading leads to stronger, larger muscles over time. If you can trace that chain from exercise to hormonal response to tissue adaptation, you are already using the term the way A&P expects. It is also a good term for connecting structure and function. IGF-1 is not just a hormone floating around in the bloodstream. It is part of the body’s homeostatic and growth systems, and it helps explain why nutrition, activity level, and hormone balance all affect how body tissues develop and recover. ## Connections ### [Growth Hormone (GH)](/anatomy-physiology/key-terms/growth-hormone-gh) GH is the upstream signal that stimulates the liver to produce most IGF-1. If you are tracing a pathway in A&P, GH comes first and IGF-1 carries out many of the growth effects. That makes the two terms easy to confuse, but they are not identical. GH is the signal, while IGF-1 is one of the main messengers that helps the body build tissue. ### [Anabolism](/anatomy-physiology/key-terms/anabolism) IGF-1 supports anabolic processes by promoting protein synthesis and cell growth. When you see a question about building muscle, repairing tissue, or increasing bone mass, anabolic activity is usually part of the answer. IGF-1 is one of the hormones that pushes the body toward that building state instead of breakdown. ### Muscle Hypertrophy Muscle hypertrophy is the increase in muscle fiber size, and IGF-1 is part of the cellular explanation for why it happens. After resistance training, IGF-1 signaling helps support protein buildup and recovery inside muscle cells. So hypertrophy is the outcome, while IGF-1 is one of the signals that helps make the outcome possible. ### [sarcopenia](/anatomy-physiology/key-terms/sarcopenia) Sarcopenia is age-related loss of muscle mass and function, which is almost the opposite of the growth pattern IGF-1 supports. Lower anabolic signaling, including changes in IGF-1 activity, can make muscle maintenance harder over time. Comparing the two helps you see how growth signals and tissue loss are both part of muscle physiology. ## On the AP Exam A quiz question might ask you to trace what happens after growth hormone is released, and you would identify IGF-1 as the hormone that mediates many of the growth effects in tissues. In a short-answer prompt, you might explain why resistance training can increase muscle size by linking exercise, IGF-1, and protein synthesis. In a lab or case question, you might interpret a scenario where poor nutrition limits growth even when growth hormone is present, because IGF-1 production depends on the body having enough resources to build tissue. If you see bone growth, muscle repair, or anabolic signaling in a diagram, IGF-1 is often part of the pathway to label. ## IGF-1 vs Growth Hormone (GH) GH and IGF-1 work together, but they are not the same thing. GH is released by the pituitary gland and stimulates the liver to make IGF-1, which then carries out many of the growth effects in body tissues. If a question asks for the hormone that directly promotes growth in muscle and bone, IGF-1 is often the better answer. ## Key Takeaways - IGF-1 is a hormone that helps the body build and repair tissues, especially muscle and bone. - Most IGF-1 is made by the liver after growth hormone stimulates it, so it sits downstream of GH in the growth pathway. - IGF-1 supports protein synthesis, cell proliferation, and differentiation, which makes it an anabolic signal. - Resistance training and good nutrition can support IGF-1 activity, which is why it comes up in muscle hypertrophy and recovery. - If you are tracing a hormone pathway in Anatomy and Physiology I, IGF-1 is the link between a growth signal and the actual tissue response. ## FAQs ### What is IGF-1 in Anatomy and Physiology I? IGF-1, or insulin-like growth factor 1, is a hormone that helps the body grow and repair tissues. In A&P, it is usually discussed as a major mediator of growth hormone effects, especially in muscle and bone. ### Is IGF-1 the same as growth hormone? No. Growth hormone is the signal released by the pituitary, and IGF-1 is one of the hormones made in response, mostly by the liver. They work in the same growth pathway, but they are different hormones with different jobs. ### How does IGF-1 affect muscle growth? IGF-1 supports protein synthesis, amino acid uptake, and cell growth in skeletal muscle. That is why it shows up in explanations of muscle hypertrophy and recovery after resistance training. ### Why does nutrition affect IGF-1? The body needs enough energy and building materials to make growth signals work well. Even if growth hormone is present, poor nutrition can reduce IGF-1 production or weaken its effects, which can slow tissue growth and repair. ## Related Study Guides - [10.6 Exercise and Muscle Performance ](/anatomy-physiology/unit-10/6-exercise-muscle-performance/study-guide/CuEehw3kp5PMkVYC) ## 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/igf-1#resource","name":"IGF-1 | Anatomy and Physiology I","url":"https://fiveable.me/anatomy-physiology/key-terms/igf-1","learningResourceType":"Concept explainer","educationalLevel":"AP® / High School","about":{"@id":"https://fiveable.me/anatomy-physiology/key-terms/igf-1#term"},"audience":{"@type":"EducationalAudience","educationalRole":"student"},"dateModified":"2026-07-03T02:20:39.382Z","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/igf-1#term","name":"IGF-1","description":"IGF-1, or insulin-like growth factor 1, is a hormone made mostly by the liver in response to growth hormone. 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