Integumentary System

Functions: Interface between organism and environment

1. Protective barrier to bacteria and chemicals
2. Selective barrier to certain energy forms - heat, UV, visible light & infrared
3. Detection of stimuli - touch, pressure, pain & temperature
4. Helps regulation of body temperature, body water content & body salts
5. Synthesis of vitamin D (from steroid) by UV

Which of the following cells or tissues are involved in each of the above functions?

Epidermis

Stratified squamous epithelium, thickness depends on body location, layers 1 & 5 always present

1. Stratum germinativum (basale) - basal layer attached to basement membrane
   1. stem cells undergo mitosis & replace lost or damaged cells
   2. contains Merkel cells - touch receptor
   3. forms ridges that extend down into dermis & are responsible for contours of skin surface (fingerprints etc)
2. Stratum spinosum - 8-10 cell layers
   1. cells connected by desmosomes
   2. some mitosis
   3. contain Langerhans cells - respond to invading microorganisms
3. Stratum granulosum - 3-5 cell layers
   1. start producing proto-keratin & organelles begin to degenerate
4. Stratum lucidum - 3-5 cell layers
   1. no nuclei or organelles
   2. proto-keratin is being converted into keratin
5. Stratum corneum - 15-30 cell layers
   1. flattened dead cells filled with keratin which are water-resistant
   2. surface cells are constantly lost

Dermis

Connective tissue, contains blood & lymph vessels, and nerve receptors

1. Papillary layer - superficial, looser collagenous connective tissue with elastic & reticular fibers, blood supply provides nutrients & gases for epidermis, form dermal papillae
2. Reticular layer - deep, dense irregular connective tissue

Subcutaneous (hypodermis)

Loose areolar & adipose connective tissue, indistinct boundary with dermis, also has nerve receptors, serves as insulation & padding

Epidermal derivatives

Epidermal structures that may extend down into dermis

1. Hair - cylinders of keratinized cells
   1. Follicle - tube of epidermis embedded in dermis, shows alternating periods of growth (2-5 yrs) & rest (short)
   2. Root - papilla containing artery & vein, matrix of mitotic cells that differentiate & keratinize
   3. Shaft - outer dead keratinized cells, layer of elongated cells, center of large cells with air spaces (sheen & color tone)
   4. Arrector pili muscle - smooth muscle, erects hair, reflex
2. Sebaceous gland - arise from hair follicle walls, branched alveolar glands, secrete & store sebum (lipid), lubricates skin surface, under nervous & endocrine control
3. Sweat glands - coiled tubular glands, wide distribution (~3000/in² on palm)
   1. produces watery secretion containing Na, Cl, K, Ca, Mg & urea, under neural & hormonal regulation. (odor is bacterial action)
   2. Thermoregulation - rise in blood temperature stimulates sweat reflex, starts at forehead & neck, then back & back of hands (merocrine sweat glands)
   3. Emotional stimulation - sweat appears mainly on palms & soles (apocrine glands)
4. Nails - protect tips of fingers & toes
   1. Nail plate - hard compressed keratinized cells
   2. Nail matrix - germinative epidermis, cells divide, keratinize & elongate
   3. Nail bed - skin under nail is firmly attached to plate, if plate is torn off the nail bed tears too, both grow back from matrix
5. Pigmentation
   • Carotene: orange-yellow pigment accumulates in epidermal cells
   • Melanin - brown pigment produced by melanocytes

Melanocytes - found in stratum germinativum

• secrete melanin in vesicular melanosomes which are transferred into keratinocytes
• coloration (skin, hair, eyes) is result of activity level of melanocytes since number present is about the same in all races.
• activity is genetically controlled but also affected by UV and hormonal changes
• function is to filter out UV to prevent folate breakdown, to neutralize free radicals, & protect DNA