Glandular tissues produce chemical substances. According to the Davidson College Biology Department, many glandular tissues secrete hormones, but others secrete substances such as sebum, saliva and vaginal lubrication. There are two categories of glandular tissue. Endocrine tissue releases substances into the bloodstream, and substances secreted by exocrine tissues travel through ducts to reach the body's outer surface or interior cavities such as the mouth and vagina.
The University of Leeds Histology Guide states that endocrine glands include the adrenal glands, thyroid, thymus and pituitary glands. Secretions made by these glands pass directly into the bloodstream. Exocrine secretions, such as those produced by the sweat, salivary and mammary glands, pass through ducts to reach their final destination.
Exocrine glandular tissue produces one of three secretion types. Sebaceous tissue produces sebum, a white, oily substance that lubricates the skin and traps moisture beneath its surface. The ducts through which sebum passes are called pores. Mucous tissues secrete heavy, viscous liquids such as the mucosal lining of the stomach. Mucous tissues are vital because they protect other delicate tissues from harsh substances such as stomach acid. The third type of exocrine glandular secretions is serous fluids, which are thin and watery. Saliva is an excellent example, although it also contains tiny amounts of mucous. Serous fluid is also an important component of blood.