Skin - Epidermis The stratifi ed squamous epithelial epidermis is the superfi cial layer of the skin. This cellular layer and its derivatives — hairs,

nails, and glands — is the most recognizable part of our anatomy. It can range in thickness from a .10 mm (0.0039 in) on the eyelids to 1.5 mm (0.059 in) on the palms and soles. Keratinocytes are the primary cells of the epidermis. They proliferate from the stratum basale and differentiate as they push toward the surface, where they eventually form dead cells fi lled with the protein keratin. Also present in the basal layer are melanocytes that produce the brown pigment melanin to protect the skin from the ultraviolet radiation from the sun.

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Skin - Dermis The connective tissue dermis sits deep to the epidermis where it forms the strong binding layer of the skin. The zone of interface

between the dermis and epidermis is an intricate peg and socket-like arrangement between the two layers. The dermal pegs are called dermal papillae. This arrangement has multiple functions. It assures that the two layers are strongly united, it increases the surface area to improve the blood supply to the avascular epidermis, and it increases the contact surface for sensory receptors. On the palms and soles the arrangement of the dermal papillae creates the friction ridges we call fingerprints.

Dense irregular connective tissue of stratum reticulare

Section of dermis, 200x

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Skin - Glands Like hairs, glands arise as invaginations of the epidermis into the dermis during embryonic and fetal life. The three prominent glands of the skin are the sebaceous

gland, the eccrine sweat gland, and the apocrine sweat gland. The sebaceous and apocrine sweat glands typically empty into a hair follicle, whereas the eccrine sweat gland empties onto the surface of the epidermis.

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Sebaceous gland

Section of dermis, 200x

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Apocrine sweat gland

Section of thin skin, 200x

Eccrine sweat gland

Section of dermis, 200x

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