Download STRUCTURE OF THE SKIN

STRUCTURE OF THE SKIN
-Composed of two kinds of tissues
1. EPIDERMIS: Outer layer; made up of stratified squamous epithelium capable
of keratinizing: becoming hard and tough
Five Layers of Epidermis
1. Stratum corneum: Horny layer
2. Stratum lucidum: Clear layer (Only present in certain areas)
3. Stratum granulosum: Granular layer
4. Stratum spinosum: Prickly layer
5. Stratum basale (germanitivum): Basal layer
2. DERMIS: Underlying layer; made up of dense fibrous connective tissue;
elastic fibers; epithelial tissue; smooth muscle & nervous tissues; & blood
* SUBCUTANEOUS TISSUE: (Hypodermis) Below dermis; mainly adipose
- Not considered part of skin, but anchors skin to underlying organs and
acts as shock absorber and insulates deeper tissues
*EPIDERMIS: Avascular
-Deepest cell layer known as STRATUM GERMINATIVUM (BASALE): Lies
closest to the dermis
-These cells are constantly growing; millions of cells produced daily
-They are the only cells that receive constant nourishment (through diffusion)
-These cells continue to move away from dermis and become part of more superficial
layers: STRATUM SPINOSUM, STRATUM GRANULOSUM and STRATUM
LUCIDUM
-These layers become increasingly flatter and full of keratin and finally these cells
die
-The outermost layer is the STRATUM CORNEUM:
20 – 30 cell layers thick
-It accounts for three-quarters of epidermal thickness
-Cells are dead and shingle-like
-Completely filled with keratin, therefore referred to as cornified
-Keratin is a water-repellent protein
*Keratin’s abundance in stratum corneum provides a protective “overcoat”
-Stratum corneum rubs and flakes off slowly and steadily
*Get “new” epidermis every 35 – 45 days
*MELANIN: A pigment which ranges in color from yellow to brown to black
*Produced by special cells in stratum basale called MELANOCYTES: Found
chiefly in stratum granulosum
-When skin is exposed to sunlight, this stimulates melanocytes to produce more
melanin, thus tanning occurs
-The stratum basale cells eat the pigment and as it accumulates within them,
melanin forms a protective pigment “umbrella” over superficial (“sunny”) side of their
nuclei that shields their DNA from damaging effects of UV radiation in sunlight
*Find large amounts of melanin in areas such as freckles, moles, and areolae.
*Three Forms of Pigment Melanin
1. EUMELANIN: Granules which tend to be round and smooth and produce black and
brown skin pigmentation
2. PHAEOMELANIN: Granules which are more irregular in shape; more prominent in
lighter skins, particularly in association with red hair and freckles.
3. NEUROMELANIN: Dark pigment of deep brain nuclei (Substantia nigra in the
brain)
-ALBINISM: A recessive genetic trait that causes a deficiency or absence of melanin
DERMIS: “Hide”
-Consists of two regions of dense fibrous conn. Tiss.
1.
PAPPILARY LAYER: Upper dermal region
Uneven and has finger-like projections called DERMAL PAPILLAE: these
indent the above epidermis; many contain capillary loops that provide
nutrients to epidermis;
-Other DP house pain receptors and touch receptors called MEISSNER’S
CORPUSCLES
Papillary patterns are genetically determined – think fingerprints
2.
RETICULAR LAYER: Deepest skin layer
-Contains blood vessels, sweat and oil glands, and deep pressure receptors
called PACINIAN CORPUSCLES – Think Phagocytes : Eat and prevent
bacteria
-Collagen and elastic fibers are also present
Collagen: toughness of dermis; keep dermis hydrated by attracting H20
Elastic: Give elasticity to skin
-Dermis is also abundantly supplied with blood vessels: play role in regulating body
temp.
-Restriction of normal blood supply could lead to cell death and possibly DECUBITIS
ULCERS: “Bedsores”