Glands - What Are Glands - Types Of Glands - Merocrine Glands - Apocrine Glands - Holocrine Glands

In this video we look at the different types of glands in the body. We discuss the structure of glands and how they are classified.
Transcript/notes
Glands are multicellular organs or individual cells that secrete substances for use in the body. Most glands are made up of epithelial tissue and their secretions include mucin, hormones, electrolytes, enzymes and waste products.

Glands can be divided into 2 groups, endocrine glands and exocrine glands.

Endocrine glands secrete their products, mainly hormones, directly into the blood stream or interstitial fluid that surrounds cells. Some endocrine glands include the adrenal, thyroid and pituitary glands.

Exocrine glands typically secrete their products into a duct or onto a surface, such as the skin, not into the bloodstream. Exocrine glands can be unicellular or multicellular. Unicellular exocrine glands do not contain ducts, and the mulicellular glands do contain a duct system.

An example of a unicellular exocrine gland is the goblet cell, which can be found in epithelial tissue and secretes mucin which forms a mucus layer coating certain tissue areas, such as the passageway in the trachea in the respiratory system.

Multicellular exocrine glands can be classified in 2 different ways, by their form, or by their secretion method.

Let’s look at classification by form. There are 2 different forms, simple glands which have a single duct, and compound glands which have branching ducts. There are also 2 different forms of the sectetory portion of the gland, tubular, where the diameter of the duct and secretory portion are similar and acinar or alveolar, where the secretory portion of the gland forms a sac like shape.
So, there are simple straight tubular, coiled tubular, simple branched tubular which still has only one duct making it a simple gland, and simple acinar, and simple branched acinar, again, only 1 duct.

And for compound glands with more than one duct, there are compound tubular, compound acinar and compound tubuloacinar with both tubular and acinar regions.

Now for classification by secretion method, in which there are 3 basic types; merocrine, apocrine and holocrine.

Merocrine glands release their secretions through the process of exocytosis where secretory vesicles are released through the plasma membrane of the cell, without damaging the cell itself. The salivary glands are an example of merocrine glands.

Apocrine glands actually pinch off a portion of the cell to release their secretory products. The cell repairs itself and continues to release its products in the same manner. Mammary and some sweat glands are examples of apocrine glands.

The third type is holocrine glands. In holocrine glands cells accumulate a secretory product and the entire cell ruptures to release the product. The ruptured cells are replaced by other epithelial cells through cell division. Some examples of holocrine glands. Examples of holocrine glands include certain glands in the skin and in the eyelids.

We will cover the structure and functions of individual glands in future videos.

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