Chapter 13 - Endocrine Glands
The endocrine system is composed of glands that synthesize and secrete products, called hormones, directly into the blood or lymph rather than through a duct. Hormones are transported throughout the body where they influence only those cells that have receptors for that hormone.
The pituitary is often called the "master gland" of the body because it produces hormones that regulate other endocrine glands, as well as, have direct effects on target tissues.
Differences in the morphology of secretion granules allow identification which hormone is being produced by a cell.
The thyroid gland produces hormones, triiodothyronine (T3) and thyroxine (T4), that primarily influence the metabolic rate and protein synthesis. It is unique in that it stores its hormones extracellularly in large follicles.
Adrenal glands produce a variety of hormones that help regulate metabolism, blood pressure, the response to stress, and other essential functions.