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”