Integumentary System

• Skin has three layers: epidermis (outermost), dermis (middle layer), hypodermis/subcutaneous tissue (deepest).
• Epidermis consists of stratified squamous epithelium with five layers: stratum basale, spinosum, granulosum, lucidum, corneum.
• Keratinocytes produce keratin, which provides strength to the skin.
• Dermis


  layer of dense connective tissue that makes up the dermis, contains fibroblasts, fat cells, and microphages
• Papillary dermis


  The superficial layer, lying deep to the epidermis, highly vascular
• Reticular dermis


  the deep layer, forming a thick layer of dense connective tissue, constitutes the bulk of the dermis.
• Stratum basale


  is the deepest epidermal layer and attaches the epidermis to the basal lamina, below which lie the layers of the dermis.
• Stratum spinosum


  is spiny in appearance due to the protruding cell processes that join the cells via a structure called a desmosome. The desmosomes interlock with each other and strengthen the bond between the cells. 
• Stratum granulosum


  has a grainy appearance due to further changes to the keratinocytes as they are pushed from the stratum spinosum. The cells (three to five layers deep) become flatter, their cell membranes thicken, and they generate large amounts of the proteins keratin, which is fibrous, and keratohyalin, 
• Stratum lucidum


  is a smooth, seemingly translucent layer of the epidermis located just above the stratum granulosum and below the stratum corneum. This thin layer of cells is found only in the thick skin of the palms, soles, and digits. The keratinocytes that compose the stratum lucidum are dead and flattened
• Stratum corneum


   is the most superficial layer of the epidermis and is the layer exposed to the outside environment. This dry, dead layer helps prevent the penetration of microbes and the dehydration of underlying tissues, and provides a mechanical protection against abrasion for the more delicate, underlying layers
• Shaft of the hair


  Portrudes above the surface of the skin, whereas the root and hair bulbs are below the surface.
• Hard cortex


  located between the hair cuticle and medulla and is the thickest hair layer
• Hair follicle


  is the extension of the epidermis deep into the dermis, and for tissue repair
• Anagen (growth phase)


  Nourishment of hair follicle via blood supply, enables hair growth.
• Catagen (transition phase)


  Hair follicle detaches from nourishing blood supply.
• Telogen (resting phase)


  Without nourishment the hair dies and falls out
• Arrector pili


  Smooth muscle cells associated with each hair follicle.
• Hair erector muscle


  a tiny muscle connected to each hair follicle and the skin.
• Sebaceous glands


  are simple, branched acinar glands. They produce sebum, an oily, white substance, rich in lipids.
• Eccrine sweat gland


  simple, coiled tubular glands located in almost every part of the skin and are most numerous in the palms and soles.
• Apocrine sweat glands


  simple, coiled tubular glands that produce a thick secretion rich in organic substances. It can be found in the axillary and genitalia.
• Nail


  a thin plate, consisting of layers of dead stratum corneum cells.
• eponychium or cuticle


  stratum corneum that extends throughout the body.