Glands are classified as either endocrine or exocrine.
Endocrine glands do not have direct outlets for its products that is why they are called
ductless glands. The products of these glands are picked up by nearby (mostly fenestrated) capillaries and transported to its target organs through the blood. On the other hand,
exocrine glands have ducts that transport glandular products directly into the external environment such as the alimentary canal and skin.
There are different types of exocrine glands. The complexity ranges from simple cellular glands like goblet cells to compound mixed tubular and acinar glands like the salivary glands.
Tubular glands have their secretory region in the form of tubes while
acinar glands have urn-shaped secretory regions. Mixed glands like the
tubuloacinar glands have both types of secretory regions. The
secretory regions are areas where glandular products are mostly produced while the
excretory ducts are tubules that transport these products toward the external environment.
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| Types of Glands as Shown in Gartner and Hiatt (2007). |
The simplest type of glands are the
goblet cells. As the name implies, these are
unicellular glands that can be found in several areas of the body like the digestive tract, nasal passages and the respiratory tract. These glands produce
mucous secretions to
protect linings from acids and enzymes such as in the digestive tract or to
keep linings moist such as in the respiratory tract.
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| Duodenal Goblet Cell |
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| Tracheal Goblet Cell |
The next type of glands are simple and compound tubular glands. These glands are
