Section I • Histology and Cell Biology
ChapterSummary
• The integument consistsand sebaceousofthe skin glands,(epi ermishairs,andanddermnailss).andIt isassociatthe largestd appendages (sweat
organ in the body. The epidermis is devoid of blood vessels and contains a stratified squamous epithelium derived primarily from ectoderm. It is composed of 5 layers in thick skin: stratum basale, which is a proliferative layer of columnar/cuboidal cells, showing mitotic activity; stratum
spinosum, which is a multilaminar layer of cuboidal/polygonal cells; stratum granulosum, which has more flattened polygonal cells containing basophilic granules; stratum lucidum, which is a thin, eosinophilic layer of squamous cells; and stratum corneum, which is a thick layer containing anucleate keratinized cells. All 5 layers contain various amounts of keratin.
The epidermis contains 4 cell types:
Keratinocytes, which produce keratin
Melanocytes derived from neural crest cells that produce melanin
Langerhans cells, which are antigen-presenting cells
Merkel cells, associated with nerve fibers.
The dermis is a connective tissue layer mainly of mesodermal origin. Other layers are the dermis-epidermal junction and hypodermis. The latter contains adipocytes.
Sweat glands may be eccrine or apocrine. These are compared in Table 1-12-1.
•Sebaceous glands are branched holocrine acinar glands that discharge their secretions onto hair shafts within hair follicles. They are absent in the palms and soles.
•Hair is comprised of keratinized epidermal cells. Hair follicles and the associated sebaceous glands are known as pilosebaceous units.
•Nails are modified stratum corneum of the epidermis and contain hard keratin. Cells continually proliferate and keratinize from the stratum basale of the nail matrix.
