Integumentary system

Integumentary system

1. epidermis

   • S. Corneum
     • 25-30 rows of dead keratinocytes without nucleus or organelles. Plasma membrane enclosed "bags" of keratin bundles. Also called "corneocytes"
   • S. Lucidum
     • 4-6 rows of dead cells with orderly keratin bundles. Present only in thick skin (fingertips, palm, soles). Flat and clear appearance.
   • S. Granulosum
     • 3-5 rows of dying cells. Keratohylin converts keratin filaments into organized keratin bundles. Lamellar granules produce a waterproofing lipid secretion into the cells. Stains very dark.
   • S. Spinosum
     • 8-10 rows of keratinocytes with keratin bundles that project into plasma membrane making "spiny" appearance. Keratin linkages form desmosomes at point to point junctions with neighboring cells. Contains arm projections of melanocytes and intraepidermal macrophages (Langerhans cells).
       • Langerhans cells: arise from red bone marrow and migrate to epidermis. Provide immune response against invading microbes and cancerous cells.
   • S. Basale
     • Deepest layer of simple cuboidal/ columnar keratinocytes. Some are stem cells which continually divide. Other cells include melanocytes, tactile disks, and Merkel cells.
       • Melanocyte: produce the pigment melanin. Has a cuboidal body in s. basal with armlike projections of plasma membrane. Contains melanin granules in melanosomes which are transferred to superior cells to shield keratinocyte nuclei from UV damage to DNA.
         • Pheomelanin: yellow-red
         • Eumelanin: Brown - black
       • Merkel cell (tactile epithelial cells): cells in contact with flattened dendrite of sensory neuron called merkel disk. Can sense touch.

2. Dermis: below epidermis. Contains fibroblasts, macrophages, adipocytes, blood vessels, nerves, and glands

   • Papillary
     • Areolar CT with collagen and elastic fibers. 1/4 size of dermis.
     • Makes dermal Papilla
   • Reticular
     • Dense irregular CT (collagen and elastic fibers). Much thicker than papillary
   • Plexus (network) - can dilate or contract to control body temperature
     • Papillary plexus is blood vessel supply to capillary loops which follow contour of epidermis.
     • Cutaneous plexus: boundary b/w reticular and hypodermis layers.

3. Hypodermis/subcutaneous

   • Contains areolar and adipose CT

4. Accessory Regions

   • Hair
     • Hair resides in hair follicles. Root hair plexus (network of nerves) encase follicles and sense movement.
     • Arrector Pili: muscle located b/w the dermis and hair follicle shaft. Causes hair to raise at 90 degree to epidermis "goose bumps" when exposed to emotional and psychological stress.
     • Vellus hair: Peach fuzz on face and arms (more common in women)
     • terminal hair: hair on head, axillal regions, groin. More common in men.
     • Grey hair is from spaces of air in medulla. White hair is from lack of pigment in medulla.
   • Nail

5. Glands

   • Sebaceous glands
     • Branched acinar glands that use holocrine secretion. Secrete sebum (oil) that coats hair shaft in gland, and epidermis from follicles. Used for lubrication and antibacterial . Secretes not on the sole or palm.
   • sweat glands
     • simple coiled tubular; merocrine secretion. Secrete water, ions, uric acid, urea, ammonia, AA, glucose, and lactic acid. Used for thermoregulation and waste elimination.
       • Eccrine: throughout skin, ear drums, lips, nail bed, glanspenis, glansclitoris, labia minor.
       • Apocrine: axilla, groin, areola, bearded region of face. Uses merocrine secretion.
   • eccrine glands
     • More common than apocrine. Found in skin, forehead, palms, and soles. Forms fingerprints. Secretory portion is in deep dermis.
   • ceruminous gands
     • Lubricate, protect, and clean outer ear w/ secretions from sebaceous glands called cerumen or ear wax.