Animal Hormones
Chemical messengers that coordinate every process in your body — from growth and metabolism to the fight-or-flight response. How the endocrine system works, how it partners with the nervous system, and the glands that keep you alive.
What Are Hormones and How Do They Work?
Hormones are chemical signals secreted by cells of the endocrine system. They travel through the body and activate only target cells — cells that have the right receptors for that specific hormone. No receptor = no response.
Three Modes of Hormone Signaling
Three Chemical Types of Hormones
All hormones fall into one of three chemical categories, and their chemistry determines how they travel, where their receptors are, and how they signal:
Peptide / Polypeptide
Water-soluble. Chains of amino acids.
Travel freely in blood (no carrier needed).
Cannot cross cell membrane.
Receptors: on cell surface.
Examples: insulin, glucagon, ADH, oxytocin