1Hormones are chemical messengers secreted by glands. 2Exocrine glands secrete fluids through ducts, while endocrine glands secrete hormones directly into the bloodstream. 3The pituitary gland plays an important role in puberty and growth. 4Epinephrine, triggering the 'fight or flight' response, is produced by the adrenal glands, which sit on top of the kidneys. 5Most glands that secrete hormones operate using feedback mechanisms. When hormone concentrations are high, the gland will produce less of the hormone. 6Many cells produce chemicals called prostaglandins, hormone-like substances that impact inflammation and reproduction 7The gland that helps regulate growth, body temperature, and the level of calcium in the blood is called the thyroid gland. 8 Steroid hormones are lipids, while nonsteroid hormones are made from amino acids. Steroid hormones are lipid soluble; they are able to pass through target cell membranes, but most nonsteroid hormones cannot do that and bind to receptors on cell surface membranes. Also, synthetic steroids can interact with the steroid receptors, but they may be weaker or stronger than natural steroids. Both types require certain proteins in order to fulfill their function.