Ch. 5 The Integumentary System

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  1. Skin (integument)
    • largest organ of the human body
    • it has two distinct regions:
    • The superficial region is a thick epithelial tissue, the epidermis
    • Deep to the epidermis is the dermis, a fibrous connective tissue
  2. The skin performs a variety of functions: Pg. 104
    • Protection
    • Body Temperature Regulation
    • Excretion
    • Production of Vitamin D
    • Sensory Reception
  3. Epidermis
    • is a keratinized stratified squamous epithelium that contains four distinct types of cells: keratinocytes, melanocytes, tactile epithelial cells, and dendrictic cells 
    • relies on capillaries in the underlying connective tissue (dermis) for its nutrients
  4. Keratinocytes
    • the most abundant epidermal cell, produce keratin, a tough fibrous protein that gives the epidermis its protective properties
    • produces antibiotics and enzymes that detoxify the harmful chemicals to which our skin is exposed
    • they arise from the deepest layer of the epidermis from cells that undergo almost continuous mitosis
  5. 1. Thick Skin
    2. Thin Skin
    • 1. covers the palms and soles, the epidermis consists of five layers, or strata ("bed sheets")
    • 2. covers the rest of the body, only four strata is present
  6. Layers of the Epidermis
    • ↓ Stratum corneum
    • ↓ Stratum lucidum
    • ↓ Stratum granulosum
    • the plasma membranes of the cells thicken so that they become more resistant to destruction=the keratinocytes "toughen up" to make the outer layer the strongest skin region
    • ↓ Stratum spinosum
    • ↓ Stratum basale
  7. Stratum Basale (Stratum germinativum)
    • the deepest of the epidermal layer, is firmly attached to the underlying dermis along a wavy borderline
    • it consists of a single row of cells, mostly stem cells representing the youngest kerinocytes
    • cells divide rapidly, and many mitotic nuclei are visible
  8. Tactile epithelial cells (Merkel cells) Fig. 5.3
    • Hemisphere-shaped
    • associated with a dislike sensory nerve ending and functions as a receptor for touch
  9. Melanocytes Fig. 5.3
    • About 10%-25% of the cells in the stratum basale are spider-shaped melanocytes, which make the dark skin pigment melanin ("black")
    • ↳ melanin is made in membrane-walled granules and then transferred through the cell processes (the "spider legs") to nearby keratinocytes
    • ↓ this melanin clusters on the superficial side of the keritinocytes, thus shielding the cell nuclei from UV rays, which damage DNA and cause cancer
  10. Stratum Spinosim (Spin=spine)
    • is several cell layers thick 
    • mitosis occurs here, but less often than in the basal layer
    • cells of the stratum spinosum contain thick bundles of intermediate filaments, which consist of a tension-resisting protein pre-keratin
  11. Dendritic cells
    • scattered among the keratinocytes of the stratum spinosum
    • these star-shaped cells are part of the immune system 
    • Dendritic cells police the outer body surface, using receptor-mediated endocytosis to take up foreign proteins (antigens) that have invaded the epidermis
    • ↳ then they leave the skin and travel to a nearby lymph node and initiate an immune response to all foreign cells that carry that antigen
  12. Stratum Granulosum (gran =grain)
    How many layers?
    What are keratinocytes abundant with?
    • thin layer, consists of one to five layers of flattened keratinocytes
    • Abundant with pre-keratin intermediate filaments, these cells also contain keratohyalin granules and lamellar granules, thus its name-granular layer
    • Lamellar granules contain a waterproofing glycolipid that is secreted into the extracellular space and plays a major role in slowing water loss across the epidermis
  13. Stratum Lucidum (luci =clear)
    • occurs in thick skin but not in thin
    • appearing through the LM as a thin translucent band, consists of a few rows of flat, dead keratinocytes
    • cells are identical to those at the bottom of the stratum corneum
  14. Stratum Corneum (Horny layer)
    • the most external layer of the epidermis
    • is many cells thick
    • its dead keratinocytes are flat sacs completely filled with keratin because their nuclei and organelles disintegrated upon cell death
    • Both the keratin and and the thickening of the plasma membranes of cells in the stratum corneum protect the skin against abrasion and penetration
    • the glycolipid between its cells keeps this layer waterproof
  15. 1. Dermis
    2. The cells of the dermis are typical of any connective tissue proper:
    3. The typical fiber types:
    4. The dermis has two regions:
    • 1. the second major region of the skin, is a strong, flexible connective tissue 
    • 2. fibroblast, macrophages, mast cells, and scattered white blood cells
    • 3. collagen, elastic, and reticular
    • 4. Papillary dermis and the reticular dermis
  16. Papillary dermis
    ↳ Dermal papillae ("nipples") Fig. 5.4
    • the superficial 20% of the dermis, is areolar connective tissue containing very thin collagen and elastic fibers
    • ↳ includes the dermal papillae, fingerlike projections that extend into the overlying epidermis
    • ↓ these projections increase the surface area for exchange of gases, nutrients, and waste products between these layers
  17. 1. Reticular dermis
    2. What does its extracellular matrix contain?
    3. How did it get its name?
    4. Cleavage lines (tension lines)?
    5. "Stretch Marks"?
    6. Flexure lines?
    • 1. which accounts for about 80% of the thickness of the dermis, is dense irregular connective tissue
    • 2. contains thick bundles of interlacing collagen and elastic fibers that run in many different planes
    • 3. network of collagen fibers (reticulum=network)
    • 4., 5., & 6. Pg. 108
  18. 1. Palms and Sole of the feet
    ↑ Epidermal Ridges (Friction Ridges)
    ↑ Dermal Ridges
    2. Epidermal ridges increase/enchances?
    3. Patterns of these ridges are unique?
    4. Sweat Pores?
    • 1.
    • ↑ these elevate the overlying epidermis into epidermal ridges, which create fingerprints, palmprints, and footprints
    • ↑ On the palms of the hands and the soles of the feet, the dermal papillae lie atop larger mounds called dermal ridges
    • 2. increases friction and enhances the gripping ability of the hands and feet
    • 3. Because they are genetically determined 
    • 4. open along the crests of the friction ridges, they leave distinct fingerprints on almost anything they touch (Fingerprints=sweat films)
  19. Dermal Plexus & Subpapillary Plexus Fig. 5.1
    • Dermal Plexus is located between the hypodermis and the dermis
    • ↳ it nourishes the hypodermis and the structures located within the deeper portions of the dermis 
    • the subpapillary plexus located just below dermal papillae , supplies the more superficial dermal structures, the dermal papillae, and the epidermis
  20. 1. Dermal blood vessels do more than nourish the dermis and overlying epidermis they also?
    2. How much blood can they hold?
    3. Cold day vs Hot day?
    • 1. they also perform a critical role in temperature regulation
    • 2. can hold 5% of all blood in the body
    • 3. when internal organs need more blood or heat, nerves stimulate the dermal vessels to constrict, shunting more blood into the general circulation and making it available to the internal organs
    • on hot days the dermal vessels engorge with warm blood, cooling the body by radiating heat away from it
  21. Hypodermis (Superficial Fascia & Subcutaneous layer)
    • composed of loose areolar connective tissue and adipose tissue (normally predominates)
    • Stores fat 
    • is also an insulator because fat is a poor conductor of heat, it prevents heat loss from the body
    • anchors the skin to the underlying structure
  22. Melanin
    • the most important, is made from an amino acid called tyrosine
    • present in several varieties, melanin ranges from yellow to reddish to brown to black
    • the variations in skin color in humans result from differences in both the amount and type of melanin produced
  23. Carotene
    • is a yellow-orange pigment that the body obtains from vegetable sources such as carrots and tomatoes
    • it tends to accumulate in the stratum corneum of the epidermis and in the fat of the hypodermis
  24. hemoglobin
    • the pink hue of Caucasian skin reflects the crimson color of oxygenated hemoglobin in the capillaries of the dermis
    • because Caucasian skin contains little melanin, the epidermis is nearly transparent and allows the color of blood to show through
  25. Hematoma ("blood swelling")
    • the general term for a clotted mass of escaped blood anywhere in the body
    • Ex. Bruises usually caused by blows, reveal sites where blood has escaped circulation and clotted below the skin
  26. Skin appendages
    include nails, hair, and hair follicles, sebaceous (oil) glands, and sweat glands
  27. Nail Fig. 5.6
    • is a scalelike modification of the epidermis that corresponds to the hoof or claw of other mammals
    • enable us to pick up small objects and scratch 
    • made up of dead, keratinized cells
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Ch. 5 The Integumentary System
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