Glandular tissue is tissue that is designed to secrete something. It is one of the major forms of epithelial tissue, which is the tissue that lines and covers most of the body, from the skin to the inside of the stomach. There are several different kinds, differentiated by how they function.
One type is endocrine tissue, the material found in the endocrine glands. Endocrine glands produce hormones, which are chemical messengers that travel throughout the body to mediate and control various functions. An example of an endocrine gland is the thyroid, a gland found in the neck that produces thyroid hormone. This type of glandular tissue is capable of producing secretions that can enter the bloodstream, allowing them to be distributed to many different areas inside the body.
Exocrine tissue makes secretions that are designed to travel through the tissue to the surface along tube-like structures, having an impact in the immediate surrounding area. These glands do not make chemical messengers; they produce secretions like breast milk, sweat, and mucus. For instance, the salivary glands are made up of exocrine tissue that produces saliva, an oral fluid designed to lubricate the mouth and begin the process of breaking down food. This tissue has a localized effect, in contrast with the whole-body effects produced by endocrine tissue.
Paracrine glands produce chemical signals that are sent to neighboring cells through a process of diffusion. These glands are sometimes classified as a subset of exocrine glands, and they produce and secrete growth and clotting factors.
As with other types of tissue found in the body, glandular tissue can start to grow out of control, producing cancer. This occurs when a single cell's DNA becomes disrupted and the signals that tell it to slow or stop reproducing are scrambled. The body is very adept at identifying cells that have been damaged, but sometimes it misses a cancerous cell and the cell is allowed to multiply and divide, creating a growth.
When cancer involves glandular tissue found in the endocrine glands, it can result in overproduction of the hormones that those glands make. A variety of symptoms related to hormonal imbalances can appear as the body responds to the flood of chemicals. Diagnosis and treatment of such cancers can be complicated by the hormone imbalance, and a biopsy of the suspected gland is needed to identify cancerous cells and determine where they originated.