According to Central Virginia Community College, endocrine glands secrete hormones into their internal environment and lack ducts. By contrast, exocrine glands secrete substances, such as wax, saliva and enzymes, into their external environment via ducts. The University of Leeds explains that both types of glands are comprised of secretory epithelial cells. During the course of development, some exocrine glands lose their ducts and become endocrine glands.
The endocrine system plays an important role in coordinating the body’s various systems. These glands accomplish this by creating and secreting hormones, which function as chemical messengers for the body. Because endocrine glands secrete hormones directly into the bloodstream, they can affect organs located far from themselves. The adrenal glands, parathyroid, thyroid and pituitary glands are examples of endocrine glands. The University of Leeds explains that the pineal gland is one other example of an endocrine gland, and it is located in the brain. The pineal gland is a photoreceptive organ, and produces melatonin, which influences day and night cycles.
Sebaceous glands and sweat glands are two types of exocrine glands, according to the University of Leeds. Because they secrete substances through a duct, they do not have a significant effect on distant organ systems.