Insulin-like growth factors (IGFs)

Insulin-like growth factors (IGFs) are peptide hormones, mainly made by the liver, that mediate many of growth hormone's growth-promoting effects in Anatomy and Physiology I. They help tissues grow, repair, and build new protein.

What are insulin-like growth factors (IGFs)?

Insulin-like growth factors (IGFs) are hormones in Anatomy and Physiology I that carry out many of the growth effects started by growth hormone (GH). The two main forms you will see are IGF-1 and IGF-2, and IGF-1 is the one most often tied to GH in the adult body. They are called "insulin-like" because their structure is similar to insulin, not because they do the same job in blood sugar control.

Most IGF-1 is produced by the liver after GH binds to receptors there, but other tissues can also make IGFs locally. That local production matters because not every IGF signal is a body-wide hormone signal. Some of it works right at the tissue where it is made, especially in bone, muscle, and other growing or repairing tissues.

Think of GH as the signal that says "grow," and IGFs as one of the main messengers that turns that signal into actual tissue change. IGFs stimulate cells to divide, make proteins, and increase the size of certain tissues. In bone, they support growth at the epiphyseal plates during development. In muscle and many soft tissues, they support repair and anabolic processes, which means building up rather than breaking down.

IGFs fit into the body’s larger homeostasis picture because they do not work in isolation. Their release and effects are tied to nutrition, sleep, stress, and energy availability. If the body is undernourished, for example, GH may still be present, but the liver may produce less IGF-1, so growth slows down. That is why normal hormone levels do not always mean normal growth if the body lacks the raw materials to build tissue.

You will usually learn IGFs when the course connects the endocrine system, metabolism, and tissue growth. They sit at the intersection of cell signaling and organ function, which is a very A&P way of thinking: one hormone signal begins in one gland, gets processed through the liver, and ends with changes in target tissues throughout the body.

Why insulin-like growth factors (IGFs) matter in Anatomy and Physiology I

IGFs matter because they connect the endocrine system to real structural change in the body. A lot of A&P terms sound abstract until you trace the path from a gland to a tissue outcome, and IGFs are a clean example of that chain. Growth hormone does not just "make things grow" on its own. Much of that effect depends on IGF production, especially IGF-1 from the liver.

This term also shows up when you study metabolism and body state. In the fed state, with enough amino acids and energy, the body can support anabolic pathways, protein synthesis, and tissue maintenance. In poor nutrition or chronic illness, IGF production and action can drop, which helps explain slowed growth or weak tissue repair.

IGFs also help you understand why the endocrine system is more than a list of glands. It is a communication network. The hypothalamus and pituitary influence GH, the liver responds by making IGFs, and target tissues respond by growing, dividing, or repairing. That sequence is the kind of cause-and-effect chain A&P questions often ask you to trace.

How insulin-like growth factors (IGFs) connect across the course

Growth Hormone (GH)

GH is the pituitary hormone that signals the liver and other tissues to increase IGF production. If you mix them up, the pathway gets blurry, because GH is the upstream signal and IGFs are major downstream effectors. In many cases, GH rises first, then IGF-1 reflects how strongly the body is actually responding.

Hypothalamus

The hypothalamus sits above the pituitary in the control chain for growth-related hormones. It helps regulate GH release through releasing and inhibiting hormones, which then affects IGF production indirectly. This connection shows how the nervous and endocrine systems work together to control body growth.

Pituitary Gland

The anterior pituitary secretes growth hormone, so it is the gland that starts the classic GH to IGF pathway. If the pituitary does not release enough GH, IGF-1 levels often fall too. That makes the pituitary a useful checkpoint when you are tracing why growth is normal or abnormal.

Absorptive State

IGF activity is easier to support when the body is in the absorptive state, because nutrients are available for building tissue. This is the opposite of a starvation or heavily catabolic situation, where growth-related signaling is less effective. The connection helps explain why growth depends on both hormones and nutrition.

Are insulin-like growth factors (IGFs) on the Anatomy and Physiology I exam?

A quiz item might ask you to trace the path from the hypothalamus to the pituitary to the liver and then to body tissues. When you see a case about slow growth, thin muscle mass, or poor healing, IGFs are one of the hormones you should consider. You may also need to identify IGF-1 as the liver response to growth hormone, not the initial pituitary signal itself.

On diagrams, you might label the liver as the source of most circulating IGF-1 and explain that its release depends on GH. In short-answer questions, the best move is to connect hormone source, target tissue, and effect, rather than just naming the hormone. If the prompt mentions nutrition, sleep, or stress, bring those in as factors that change IGF production and activity.

Insulin-like growth factors (IGFs) vs Growth Hormone (GH)

GH and IGFs are closely linked, but they are not the same thing. GH is made by the anterior pituitary and triggers IGF production, while IGFs, especially IGF-1, are made mainly by the liver and carry out many growth effects in tissues. If you remember only one difference, remember that GH starts the signal and IGFs often do the building.

Key things to remember about insulin-like growth factors (IGFs)

• Insulin-like growth factors (IGFs) are peptide hormones that help the body grow and repair tissues, especially through IGF-1.

• GH from the anterior pituitary stimulates the liver to produce most circulating IGF-1, so IGFs are part of a hormone chain, not a standalone signal.

• IGFs support protein synthesis, cell division, and tissue growth, which is why they matter in bone, muscle, and other developing tissues.

• Because IGF production depends on energy and nutrients, growth can slow down even when hormone signaling is present if the body lacks resources.

• In Anatomy and Physiology I, IGFs are most useful when you are tracing endocrine pathways, explaining growth, or linking hormones to metabolism and homeostasis.

Frequently asked questions about insulin-like growth factors (IGFs)

What are insulin-like growth factors (IGFs) in Anatomy and Physiology I?

IGFs are hormones, mainly produced by the liver, that mediate many of the growth effects of growth hormone. They promote cell growth, tissue repair, and protein synthesis. In A&P, they show up when you are studying the endocrine system, growth, and metabolism.

Are IGFs the same as growth hormone?

No. Growth hormone is made by the anterior pituitary, while IGF-1 is made mainly by the liver after GH stimulation. GH is the upstream signal, and IGFs are major downstream hormones that carry out growth effects in tissues.

How do IGFs affect the body?

IGFs help cells divide, make proteins, and build tissue. They are especially active in growing bones, muscle repair, and other anabolic processes. That is why they are linked to childhood growth and to tissue maintenance in adults.

Why would IGF levels matter in a nutrition or growth question?

IGF production depends on both hormone signaling and enough nutrients to support building tissue. If the body is underfed or stressed, IGF activity can fall and growth may slow. That makes IGFs useful for explaining why hormones alone do not guarantee normal growth.