Module 2 of 5

Your Body

Where peptides are made and how they communicate with your cells

Your Body's Peptide Factory

Your body produces hundreds of different peptides that regulate everything from hunger and mood to immune response and blood pressure. Click on different areas to discover what peptides are made where.

Interactive

How Peptides Talk to Cells

Peptides don't enter cells directly. Instead, they act like a key fitting into a lock -- binding to specific receptors on the cell surface to trigger a cascade of signals inside the cell. One peptide molecule can amplify into thousands of downstream effects.

Interactive
Signal amplification: When a single peptide binds its receptor, it can activate hundreds of G-proteins, each of which activates many enzymes, each producing thousands of second messenger molecules. This is why tiny amounts of peptides can have massive effects.

Peptides You Already Know

You encounter peptides every day without realizing it. Here are some of the most important ones your body produces naturally -- and what happens when their levels are disrupted.

Insulin

51 amino acids

Made by the pancreas. Controls blood sugar by telling cells to absorb glucose. Disruption causes diabetes.

Oxytocin

9 amino acids

Made by the hypothalamus. Involved in bonding, trust, and childbirth. Often called the "love hormone."

Endorphins

16-31 amino acids

Made by the pituitary gland. Natural painkillers that produce the "runner's high." Bind to opioid receptors.

GLP-1

30 amino acids

Made by the gut after eating. Signals fullness and regulates blood sugar. Basis for Ozempic and Wegovy.

Melatonin

derived from tryptophan

Made by the pineal gland in darkness. Regulates your sleep-wake cycle. Disrupted by blue light exposure.

Angiotensin

8 amino acids

Made by the liver/kidneys. Controls blood pressure by constricting blood vessels. ACE inhibitors target this pathway.

Three Families of Peptides

Not all peptides do the same job. Your body uses three major families of peptides, each with distinct roles in keeping you alive and healthy.

Hormones
Long-distance messengers -- released into the bloodstream to reach distant organs. Insulin, oxytocin, GLP-1, and growth hormone are peptide hormones. They regulate metabolism, growth, reproduction, and mood.
Neuropeptides
Brain signals -- used by neurons to communicate. Endorphins, substance P, neuropeptide Y, and orexin control pain perception, appetite, sleep, and emotional responses. Often co-released with neurotransmitters.
Antimicrobial
Immune defenders -- kill bacteria, viruses, and fungi directly. Defensins and cathelicidins (like LL-37) punch holes in bacterial membranes. Your skin, gut, and airways produce them as a first line of defense.
Overlap is common: many peptides fall into multiple categories. Oxytocin is both a hormone (released into blood) and a neuropeptide (used in the brain). GLP-1 acts as a gut hormone but also has neuroprotective effects.

Common Questions About Peptides in the Body

Short, sourced answers to the questions people ask most about what peptides do in the body, how they signal cells, and where they come from.

What do peptides do in the body?

Your body produces hundreds of different peptides that act as chemical messengers. They regulate everything from hunger and mood to immune response and blood pressure. Peptides work by binding to receptors on the surface of your cells, triggering signals that tell those cells what to do.

How do peptides signal your cells?

Peptides don't enter cells directly. Instead they act like a key fitting into a lock, binding to specific receptors on the cell surface to trigger a cascade of signals inside the cell. One peptide molecule can amplify into thousands of downstream effects, which is why tiny amounts of peptides can have massive effects.

Where are peptides made in the body?

Peptides are produced all over the body. Insulin is made by the pancreas, oxytocin by the hypothalamus, endorphins by the pituitary gland, GLP-1 by the gut after eating, and angiotensin via the liver and kidneys. Each site releases peptides suited to the job it controls, from blood sugar to blood pressure.

Are peptides hormones?

Some are. Your body uses three major families of peptides: hormones, neuropeptides, and antimicrobial peptides. Peptide hormones like insulin, oxytocin, GLP-1, and growth hormone travel through the bloodstream to reach distant organs. Many peptides overlap categories, though; oxytocin acts as both a hormone and a neuropeptide.

What are some natural peptides in the body?

You encounter peptides every day without realizing it. Common natural ones your body makes include insulin for blood sugar, oxytocin for bonding and childbirth, endorphins as natural painkillers, GLP-1 for fullness and blood sugar, and angiotensin for blood pressure.

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  2. Uvnas-Moberg K et al. "The Role of Oxytocin and the Effect of Stress During Childbirth." Front Psychol. 2021;12:734236. PMID 34777247
  3. Thau L et al. "Oxytocin." StatPearls. 2024. NBK507848
  4. Holst JJ. "Glucagon-like peptide 1: a newly discovered gastrointestinal hormone." Gastroenterology. 1994. PMID 7958701
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  6. Sprouse-Blum AS et al. "Understanding Endorphins and Their Importance in Pain Management." Hawaii Med J. 2010;69(3):70-71. PMID 20397507
  7. Tiwari V et al. "Biochemistry, Endorphin." StatPearls. 2024. NBK470306
  8. Kreymann B et al. "Glucagon-like peptide-1 7-36: a physiological incretin in man." Lancet. 1987;2(8571):1300-4. PMID 7958701

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Practice Exercises

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How They're Used