A. Structure and Location: These exocrine glands occur in all thin skin, most often in association with hair follicles into which their ducts empty, but are most numerous in the skin of the face, forehead, and scalp. In hairless skin, they open directly onto the surface. Their acinar secretory portions contain many large lipid-filled cells that appear pale-staining and foamy.
B. Function: The acinar cells of sebaceous glands fill with lipid droplets containing a mixture of triglycerides, waxes, squalene, and cholesterol and its esters. Their nuclei become pyknotic, and the cells eventually burst, releasing their contents and other cell debris (together termed sebum) into the ducts. The entire cell is shed, a type of secretion known as bolocrine secretion. The oily sebum moves through the ducts and into the hair follicle. It covers the hair and moves out onto the surface. Here, it lubricates the skin and may have some antibacterial or antifungal effects. The secretory activity of these glands, which begin functioning at puberty, is continuous and is increased by androgens.
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