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Lecture 11

BSC 215 Lecture Notes - Lecture 11: Acne Vulgaris, Sebaceous Gland, Earwax


Department
Biological Sciences
Course Code
BSC 215
Professor
Jason Pienaar
Lecture
11

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Accessory Organs of the Skin
The following accessory organs (skin derivatives) are embedded in the skin:
Hairs are elongated filaments of keratinized epithelial cells that arise and emerge
from the skin of mammals. Hair is composed of the following structures:
o The hair shaft is the portion of the hair that is visible on the surface of the skin.
o The hair root is the portion of the hair that penetrates the skin (epidermis and
dermis).
o The hair follicle is the sheath that surrounds the hair in the skin.
o The bulb is the base of the hair follicle.
o The matrix is the bottom of the hair follicle (located within the bulb). Here, cells
are actively dividing, producing new hair cells. As these cells differentiate, they
produce keratin and absorb melanin from nearby melanocytes. As younger cells
are produced below them, the more mature cells are pushed upward, where they
eventually die. The keratin they leave behind contributes to the growth of the hair.
The color of the hair is determined by the pigments absorbed from the
melanocytes.
o The arrector pili is a smooth muscle that is attached to the hair follicle. When the
muscle contracts, the hair becomes erect; in humans, “goose bumps” are
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