BIO 202
Chapter 18: The Endocrine System
Section 18.1: Hormones Are Chemical Messengers
● The endocrine glands and several other hormone-secreting organs and tissues together
all form the endocrine system
○ All are connected by the cardiovascular system
○ All also are tied directly to the nervous system
● Endocrine glands secrete hormones directly into the bloodstream
○ Rather than through ducts to the surface of the gland
● Some organs and tissues also secrete hormones but are not considered glands
○ Kidneys, stomach, liver, skin, ovaries/testes, heart, small intestine
● Organs and tissues communicate with cells using hormones as chemicals messengers