Which hormone is an example of a peptide hormone?

Oxytocin is classified as a peptide hormone because it consists of a short chain of amino acids, specifically nine amino acids, making it a non-steroid hormone. Peptide hormones are generally synthesized in the endoplasmic reticulum and stored in vesicles until they are needed. Once released, they bind to specific receptors on the surface of target cells, triggering a response.

In contrast, testosterone is a steroid hormone derived from cholesterol, which leads to its differing structure and mode of action. Norepinephrine is classified as a catecholamine, a type of amine hormone that is derived from the amino acid tyrosine. Insulin, while also a peptide hormone like oxytocin, is not the answer in this instance because the question specifically identifies oxytocin. Each of these hormones has unique roles and mechanisms in the body, but oxytocin is the best example of a peptide hormone in this context.