Hormones are chemicals secreted by one cell group that travel through the
bloodstream to act on targets
Endocrine glands: release hormones within the body, straight into the bloodstream
(e.g. pancreas, ovaries, testes)
Exocrine glands: use ducts (e.g. tear ducts) to secrete fluids such as tears and
sweat outside of the body
Understanding of hormones
Castration (removal of gonads, usually testes), results in behavioural and
physiological changes. Berthold (1849) through experiment has found that
testes release a chemical into the bloodstream that affects male behaviour
and body structure