Skin Structure

Layers of the Epidermis

Stratum Basale/Basal Layer

• All about that “Base”• Deepest epidermal layer• Attached to the Dermis beneath it along a

wavy texture• Looks like corrugated cardboard• Mostly single row of cells• Continually renewing cell population• Mitotic nuclei

Stratum Basale/Basal Layer

Also called Stratum Germinativum

Stratum Spinosum

• “Prickly” layer• Several cell layers thick• Contain weblike system of intermediate

filaments• Keratinocytes appear spiny in shape• Langerhans’ cell are most abundant in this

layer

Stratum Spinosum

Stratum Spinosum

Stratum Granulosum• Granular Layer• Thin – 3 to 5 cell layers thick• Keratinocyte appearance changes

drastically• They flatten• Nuclei and organelles begin to disintegrate• Accumulate granules

• Keratohyaline: helps form keratin in the upper layers

• Lamellated: contain a waterproofing glycolipid that is spewed into the extracellular space• Slows water loss across the epidermis

Stratum Granulosum

• Plasma membrane thickens• Cytosol proteins bind to inner membrane• Lipids released by lamellated granules coat

the external surface• Process of toughening up• Above the stratum granulosum, the

epidermal cells are too far from the dermal capillaries, so they die

Stratum Granulosum

Stratum Granulosum

Stratum Lucidum

• Appears as thin, translucent band• A few rows of dead, flat keratinocytes with

indistinct boundaries• Visible only in thick skin

Stratum Lucidum

Stratum Lucidum

Stratum Corneum

• “Horny” layer• Outermost layer of epidermis• 20-30 cell layers thick• Accounts for up to ¾ of the epidermal

thickness• Durable “overcoat” for the body• Protects deeper cells from the hostile

external environment

Stratum Corneum

Stratum Corneum

• Cornu = horn• Dandruff, flakes the slough off dry skin• Average person sheds 40lb of skin flakes in

a lifetime• When you look at someone’s skin, you are

looking at dead cells.

Skin Structure

Dermis

Dermis

• Strong, flexible connective tissue• Fibroblasts, macrophages, mast cells and

white blood cells• Heavily embedded with fibers• Binds the body together like a stocking• Your “hide”

Dermis

• Nerve fibers• Blood vessels• Lymphatic vessels• Hair follicles • Oil and sweat glands• 2 layers

• Papillary & reticular

Papillary

• Areolar connective tissue• Heavily invested with blood vessels• Dermal papillae

Dermal Papillae• Contain capillary loops• Free nerve endings (pain receptors)• Meisners corpuscles (touch receptors)• Dermal ridges

• Cause the epidermis to form epidermal ridges• Friction• Epidermal ridge patterns (fingerprints)

• Sweat pores open along their crests

Reticular Layer

• 80% of thickness• Dense irregular connective tissue• Cutaneous plexus

• Network of blood vessels that nourishes dermal layer

• Between reticular layer and hypodermis

Reticular Layer

• Extracellular Matrix• Thick bundles of interlacing collagen fibers that

run in various planes• Most run parallel to the skin surface• Tension/cleavage lines• Surgery and healing

Reticular Layer

• Collagen fibers• Strength and resiliency prevents most jabs and

scrapes from penetrating the dermis• Collagen binds water, keeping skin hydrated

Reticular Layer

• Flexure lines• Dermal folds that occur at or near joints where

the dermis is tightly secured to deeper structures• Ex. Palms of hands

Homeostatic Imbalance

• Extreme stretching of the skin can tear the dermis. What is this called?

• Short-term but acute trauma can cause a separation of the dermal and epidermal layers by a fluid filled pocket. What is this called?

Skin Color

Skin Color

• 3 pigments contribute to skin color• Melanin• Carotene• Hemoglobin

Melanin• Only melanin is made in the skin• Polymer that ranges in color from yellow to

reddish-brown to black• Its synthesis depends on an enzyme in

melanocytes , tyrosinase• All humans have the same number of

melanocytes• Differences in skin color reflect the kind

and amount of melanin made and retained

Melanin

• Freckles and pigmented moles are local accumulations of melanin

• Melanocytes are stimulated by exposure to sunlight

• Melanin buildup is designed to help protect the DNA of viable skin cells from UV radiation and dissipating the energy as heat

Melanin

• Initial signal for speeding up melanin synthesis appears to be a faster rate of repair of photodamaged DNA

• This causes a physiological response.• What is this response called?

Carotene

• Yellow to orange pigment found in certain plant products

• Tends to accumulate in the stratum corneum and fatty tissue of the hypodermis

• Most obvious where the stratum corneum is the thickest (skin of the heels)

Hemoglobin

• Pinkish hue of fair skin• Reflecting the crimson color of oxygenated

hemoglobin in the red blood cells circulating through the dermal capillaries

• Because Caucasion skin contains only small amounts of melanin, the epidermis is nearly transparent and allows hemoglobin’s color to show through

Hemoglobin

Skin Appendages

Nails, sweat glands, sebaceous glands, hair follicles, hair

Sudoiferous Glands

• Also called sweat glands• Include eccrine & apocrine glands• Distributed over practically entire surface of

body• Up to 3million per person

Eccrine

• Also called merocrine glands• Most numerous• Abundant on palms, soles of feet, and

forehead• Simple, coiled, tubular• True “sweat”: 99% water, salts, vitamin C,

antibodies, and microbe-killing peptide• Sweat normally has a pH of 4-6

Eccrine

• Heat induced sweating begins on the forehead and then spreads out

• Emotional, or “cold sweat” begins on the palms, soles, and armpits

Apocrine

• Confined to axillary and anogenital areas• Larger than eccrine glands• Ducts empty into hair follicles• Secrete True sweat plus fatty substances

and proteins• Odorless, but when bacteria decomposes its

organic compounds, causes body odor• Begin functioning at puberty

Ceruminous

• Modified apocrine glands• Found in external ear canal• Secrete sticky bitter substance: earwax

Mammary

• Secrete milk

Sebaceous (oil) glands

• Are branched alveolar glands found all over the body except on the palms and soles

• Small on the body trunk and limbs, but large on the face neck, and upper chest

• Secrete oily substance: sebum• Sebum is secreted into the hair follicle or

occasionally to a pore on the skin surface

Sebaceous

• Sebum softens and lubricates the hair and skin, prevents hair from becoming brittle, and slows water loss from the skin

• Has bactericidal action also

Homeostatic Imbalance• When a sebaceous gland is blocked by

accumulated sebum and dead skin cells: whitehead• When a whitehead oxidizes and dries it becomes a

blackhead• Acne is an active inflammations of the sebaceous

glands, usually caused by bacteria• Cradle crap: in infants caused by overactive

sebaceous glands• Begins as pink lesions that gradually become

yellow to brown and slough off oily scales