Integumentary System
Skin consists of the epidermis (keratinized stratified squamous epithelium) and the dermis (dense irregular connective tissue). Cells of the epidermis include keratinocytes, melanocytes, langherhan’s cells, and merkel’s cells. Epidermal derivatives include hair follicles and hair, sweat (sudoriferous) glands, sebaceous glands, nails, and mammary glands.
Attachment of the epidermis and the dermis is enhanced by increased interface between them. They are represented by fingerlike protrusions called dermal papillae that project into the undersurface of the epidermis. Papillae are complemented by epidermal ridges or rete ridges/pegs (which appear to project into the dermis). The dermis contains two layers:
- Papillary layer, which is more superficial and consists of loose connective tissue just beneath the epidermis. It is thin and includes dermal papillae and epidermal ridges. It contains blood vessels and nerve processes, where the nerves may enter the epidermis.
- For the nerve supply, free endings means they lack investment of a connective tissue or a Schwanna cell sheath. The function with multiple sensory modalities, including fine touch, heat, cold, and surrounding and attaching to the outer root sheath of hair follicles (especially useful in whiskers of cats or rodents).
- Encapsulated endings possess a connective tissue or Schwann cell sheath. These include pacinian corpuscles, meissner’s corpuscles, ruffini endings, and krause end bulbs.
- Skin appendages are derived from down-growth of epidermal epithelium during development. Hair follicles and hair, sebaceous glands (produce sebum), eccrine sweat glands (produce sweat), and apocrine sweat glands (produce serous secretion = sex attractant). The eccrine sweat glands are simple, coiled, and tubular, and have a darker staining cuboidal epithelium. The myoepithelial cells are at the basal surfaces of the secretory cells.