Endocrine and exocrine refer to two different kinds of glands in the body. Both types of gland secrete products in a watery solution. The terms endocrine and exocrine indicate where and how these products are secreted. Exocrine glands release their products onto body surfaces like the skin or into cavities such as those inside the digestive tract. Endocrine glands secrete substances directly into the bloodstream. Exocrine glands tend to be relatively simple and have local effects, while endocrine glands release hormones that travel throughout the body.

Most endocrine and exocrine glands form in the embryo from epithelial tissue. Exocrine glands retain an opening in this tissue called a duct, also made of epithelial tissue, through which they secrete their products. Sweat glands are one such example, as they are located beneath the surface of the skin but secrete sweat onto the skin's surface. Endocrine glands do not form ducts and release their products directly into the blood. Endocrine and exocrine glands can be classified by whether or not they have a duct.

Another difference between endocrine and exocrine glands is that exocrine glands are usually much simpler and easier to categorize than endocrine glands. Although they are often made up of multiple cells, exocrine glands may be as small as a single cell. Goblet cells are single-celled glands in the respiratory tract that produce mucus.

The human body contains many types of exocrine glands that have diverse functions. They include the salivary glands of the mouth, the oil- and sweat-producing glands of the skin, and many others. Some glands that are often thought of as endocrine, such as the liver and pancreas, also have exocrine functions.

Since endocrine glands have no ducts and release their secretions directly, they are often known as ductless glands. Their secretions are called hormones, and send messages to other specific organs. Together they form the endocrine system, which is a system of glands responsible for regulating the functions of many organs of the body, as well long-term processes like growth and digestion. Many endocrine glands play a role in other systems of the body, but some, such as the pituitary gland, belong to no other system.

Hormones affect other cells by targeting specific locations on another cell's outside or inside, which causes changes in the function of the target organ. Important hormones include the sex hormones produced in the female ovaries and the masculine testes. Other endocrine glands include the adrenal glands, the pancreas, and the pineal glands.