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Structures of the integument
Functions of the integumentary system
- Temperature regulation
- Vitamin D production
- Epidermis: superficial layer of epithelial tissue
- Dermis: deep layer of connective tissue
- -structural strength
- Subcutaneous tissue:
- -not part of skin
- -loose connective tissue that connects skin to underlying muscle or bone
- -Avascular; nourished by diffusion from capillaries of the papillary layer of the dermis
- -Composed of cells arranged into layers, or strata
- -Separated from dermis by basement membrane
Epidermal cell types
- Keratinocytes: most cells. Produce keratin for strength and durability. Give epidermis its ability to resist abrasion and reduce water loss.
- Melanocytes: contribute to skin color. Melanin produced by these cells then trasferred to keratinocytes. Same number of melanocytes in all people.
- Langerhan's cells: part of the immune system
- Merkel's cells: associated with nerve endings, detect light, touch, and superficial pressure
cells of the deeper layers undergo mitosis; as they move toward the surface, older cells slough off
As cells move outward through the layers they fill with keratin, die, and serve as a layer that resists abrasion and forms permeability layer.
Stratum basale (germinitivum)
- Stratum Basale: deepest portion of epidermis and single layer. High mitotic activity and cells become keratinized
- Stratum Spinosum: limited cell division. Desmosomes break apart and new desmosomes form. Additional keratin fibers & lamellar bodies (lipid-filled, membrane bound organelles) form inside keratinocytes...limited cell division takes place in the S.S. Mitosis does not occur in the more superficial strata
- Stratum granulosum: contains keratohyalin (nonmembranebound protein granules). In superficial layers nucleus and other organelles degenerate and cell dies.
- Stratum lucidum: thin, clear zone. Found only in palms and soles.
- Stratum corneum: most superficial. Consists of cornified cells.
Epidermal layers and keratinization
Cells move from deep to superficial
- 1. In the stratum basale, cells divide by mitosis & some of the newly formed cells become the cells of the more superficial strata.
- 2. In the stratum spinosum, keratin fibers and lamellar bodies accumulate.
- 3. In the stratum granulosum, keratohyalin granules accumulate, & a hard protein envelope forms beneath the plasma membrane; lamellar bodies release lipids; cells die.
- 4. In the stratum lucidum, the cells are dead and contain dispersed keratohyalin.
- 5. In the stratum corneum, the dead cells have a hard protein envelop, contain keratin, and are surrounded by lipids.
- -Has all 5 epithelial strata
- -Found in areas subject to pressure or friction (palms, fingertips, soles of feet)
- -fingerprints and footprints. Papillae of underlying dermis in parallel rows.
- -More flexible than thick skin
- -Hair grows here
Callus & Corn
Callus: increase in number of layers in stratum corneum. When this occurs over a bony prominence, a corn forms.
Skin color determined by what 3 factors?
- -Blood circulating through the skin,
- -Thickness of stratum corneum
Skin color: pigments
(Melanin, melanocytes, Albinism, carotene)
- Melanin: provides for protection against UV light. Group of chemicals derived from aa tyrosine. Colored brown to black, may be yellowish or reddish.
- Melanocytes: produces melanin. Processes extend between keratinocytes of the stratum basale and the stratum spinosum.
- Albinism: deficiency or absense of pigment. Production determined by genetics, hormones, exposure to light.
- Carotene: yellow pigment. From vegetables. Accumulates in stratum corneum, in adipose cells of dermis and in subcutaneous tissue.
Skin Color cont.
- Blood circulating through the skin
- -imparts reddish hue and increases during blushing, anger, inflammation
- -Cyanosis: blue color caused by decrease in blood oxygen content
- Thickness of stratum corneum
- -thicker areas can be yellowish
- -Gives structural strength. Connective tissue with many fibers, fibroblasts, macrophages. Some adipocytes and blood vessels.
- -Contains nerves, blood vessels, hair follicles, smooth muscles, glands, and lymphatic vessels.
- -Sensory functions: pain, itch, tickle, temperature, touch, pressure, two-point discrimination.
2 layers of the Dermis
Papillary: superficial. 1/5. Areolar with lots of elastic fibers. Dermal papillae, capillary beds. Fingerprints. Whorls of ridges. Touch receptors (Meissner's), free nerve endings sensing pain
Reticular: deep 4/5. Dense irregular connective tissue. Collagen and elastic fibers. In the figure see: some adipose, hair follicles, nerves, oil glands, ducts of sweat glands, heat sensors.