Page 497 - Atlas of Histology with Functional Correlations

Keratinocytes are the predominant cell type in the epidermis

Less numerous epidermal cells are the melanocytes, Langerhans cells, and
Merkel cells

MAJOR SKIN FUNCTIONS

Protection through the keratinized epidermis from abrasion and the entrance
of pathogens
Impermeable to water, owing to lipid layer in the epidermis

Body temperature regulation as a result of sweating and changes in vessel
diameters
Sensory perception of touch, pain, pressure, and temperature changes
because of nerve endings

Excretions through sweat of water, sodium salts, urea, and nitrogenous waste
Formation of vitamin D from precursor molecules produced in the epidermis
when exposed to the sun

SKIN DERIVATIVES

Hairs

Develop from the surface epithelium of the epidermis and reside deep in the
dermis
Are hard cylindrical structures that arise from hair follicles
Surrounded by external and internal root sheaths

Grow from the expanded hair bulb of the hair follicle
Hair bulb indented by connective tissue (dermal) papilla that is highly
vascularized

Hair matrix situated above the papilla contains mitotic cells and melanocytes

Sebaceous Glands

Numerous sebaceous glands associated with each hair follicle

Cells in sebaceous glands grow, accumulate secretions, die, and become oily
secretion sebum

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