Skin
Skin – a membrane(epithelial tissue(stratified squamous and areolar and dense irregular
CT)
Epidermis: thin superficial layer of stratified squamous epithelium
Dermis: papillary region – areolar tissue
Reticular layer - dense irregular CT, high amount of collagen
Lines of cleavage in our skin indicate the predominant
direction of collagen fibers (see palms of hand and fingers for lines of cleavage)
Hypodermis: aka superficial fascia or subcutaneous layer –
Connects skin to underlying muscle
FCN: vitamin D synthesis – integral to Ca+2 absorption
Excretion of wastes
Perception of stimuli
Maintain body temperature
Protection: immunity
Dehydration
UV radiation
4 Types of cells
1. Keratinocytes – produce keratin, the thick, waxy protein that is responsible
For maintaining the waterproof, protective barrier
2. Melanocytes – produce melanin – protein responsible for skin color and UV
Protection : Vitiligo: absence of melanocytes appears in “white”
patches in skin: Freckles: patches in skin with concentrated number of
melanocytes
3. Langerhan cells – confer immunity
4. Granstein cells – confer immunity
Epidermis – dynamic, always renewing itself, waterproof, basal layer is living and
mitotic cells, older cells die as they move away from basal layer, cytoplasm of old, dead
cells completely filled with keratin
Epidermal layers:
From deep to superficial
1. Stratum basale aka s. germinativum: columnar, mitotic cells(stem cells)
a. Epidermal ridges = fingerprints, to increase friction, increase grip,
epidermis interlocks with the dermal papillae
2. S. spinosum: multiple layer cuboidal cells
a. Molecular bridges(desmosomes) begin to break apart, make cells appear
prickly
b. Nuclei darkened, dying = pyknosis
3. S. granulosum: grainy layer, cytoplasm appears grainy due to increase amount of
keratin
4. S. lucidum: only present in palm of hand and soles of feet
a. “ghost cells”
b. More keratin in cytoplasm
5. S. corneum: 20-50 layers of dead, keratinized, flat cells(squamous)
a. Constantly sloughing off(appears like little horns on surface of
skin(microscopic)
b. Dead cells still bound tog by desmosomes – skin shed in sheets
c. Wrinkly skin: water softens keratin, increases skins permeability to water,
osmosis in skin cells, water moves out
d. Blister: damage to superficial epidermal layers, interstitial fluid
lymph)accumulates in pockets
FYI: EGF= epidermal growth factor, produced by salivary glands and glands in
duodenum(Small intestine) Used to make epidermal sheets for burn victims
DERMIS
Ct beneath epidermis
Matrix = collagen in LARGE amounts
Has the consistency of a firm, wet sponge
VERY VASCULAR – to exchange nutrients and waste of dermis cells AND
Cells of S. basale(germinativum)
PAPILLARY REGION: superficial layer, loose areolar tissue, attaches to dermis via
PAPILLAE
Papillae: finger like projections that extend up into epidermis, like Velcro
These papillae form CONTOURS in skin’s surface = FRICTION
RIDGES = FINGER PRINTS – genetically determined pattern in palms, soles, fingers,
toes, to assist in “grasping”, and to increase friction
RETICULAR REGION:
Deep to papillary region, much thicker, dense irregular CT, collagen, reticulin and
elastin fibers
Roots of hair, sebaceous glands(oil), sweat glands, receptors, blood vessels, and toe, and
finger nails all epidermal derivatives set into the dermis(reticular region)
Aging : changes in production and quality of protein fibers – wrinkles, saggy skin
Retinin A – increases blood flow to stimulate dermal repair, wrinkle formation decreases,
and existing wrinkles diminish
SKIN COLOR
Melanocytes – between cells of s. basale, all humans have same # of melanocytes,
amount of melanin produced is determined genetically
Melanin – protein pigment
Greater amount of melanin production = darker skin
UV radiation: increases melanin production to absorb harmful UV rays, protecting other
skin cells, results in “tan”
Carotene – orange/yellow pigment, skin protein, most apparent in fair skin individuals,
accumulates in fatty tissue of dermis