Unit 4:Structure of Integument

and its Appendages

Regions of Integument (skin) Epidermis – outermost region• Keratinized stratified

squamous epithelium• Non-vascular• 4 cell types• 4 - 5 layers

4 Epidermal Cell TypesKeratinocytes – make keratin fibrous protein• Protective• Hardens and waterproofs skin.• Cells connected by desmosomes:

• prevent tearing and cell separation from mechanical stress

• Arise from hightly mitotic stratum basale

• Cells dead at free surface

4 Epidermal Cell TypesKeratinocytes – make keratin fibrous protein

Langerhans’ Cells – star shaped, epidermal dendritic phagocytic cells• activate the immune system • ingest foreign material

4 Epidermal Cell TypesKeratinocytes – make keratin fibrous protein

Langerhans’ Cells – star shaped, epidermal dendritic phagocytic cells

Merkel Cells – half-sun touch receptors• associated w/ sensory nerve

endings

4 Epidermal Cell TypesKeratinocytes – make keratin fibrous protein

Langerhans’ Cells – star shaped, epidermal dendritic phagocytic cells

Merkel Cells – half-sun touch receptors• associated w/ sensory nerve

endings

Melanocytes – makes brown pigment melanin • shields keratinocyte DNA from UV

damage

melanin

Layers of the Epidermis

Stratum basale

Stratum Spinosum

Stratum granulosum

Stratum lucidum (absent in thin skin)

Stratum corneum

Stratum Basale (Basal Layer)• AKA stratum germinativum• Deepest epidermal layer,

attached to the dermis• Single row of the youngest

keratinocytes• Rapidly mitotic, making new

cells daily • Melanocytes and Merkel cells

found here

dermis

Stratum basale

Stratum Spinosum (Prickly Layer)• Cells filled with

filaments connected to desmosomes. (gives prickly look)

• Melanin granules filling cells in response to UV or genetics

• Langerhans’ cells found here

dermis

Stratum basale

Stratum Spinosum

Stratum Granulosum (Granular) • 3-5 cell layers• Keratinocytes change,

flatten, lose nuclei• Keratin granules

accumulate in the cells of this layer

• Lamellated granules release extracellular glycolipids in intercellular space that waterproof skin

• Too far from nutrient rich dermal blood, cells begin to die

dermis

Stratum basale

Stratum Spinosum

Stratum granulosum

Stratum Lucidum (Clear Layer)

• Transparent band of flat, dead keratinocytes

• Only in thick skin– Sole of feet, palms, calluses

• Reduces friction between the granulosum (inferior) and the corneum (superior)

dermis

Stratum basale

Stratum Spinosum

Stratum granulosum

Stratum lucidum would be here, if present

Stratum Corneum (Horny Layer)

• 20-30 layers of DEAD keratinized cells; ¾ of epidermal thickness

• Functions include:– Waterproofing (due to

glycolipids)– Protection from:

• Abrasion• Penetration• biological, chemical,

and physical assaultsdermis

Stratum basale

Stratum corneum

Stratum granulosum

Stratum lucidum would be here, if present

Stratum Spinosum

Stratum Corneum (Horny Layer)

dermis

Stratum Basale

Stratum Corneum

Stratum Granulosum

Stratum Lucidum

Stratum Spinosum

CanLittle

Girls

Smell

Bad?

http://www.lab.anhb.uwa.edu.au/mb140/corepages/integumentary/integum.htm#labepidermis

Let’s take a break from lecture to draw the difference between thick and thin skin.• Use appropriate drawing and

coloring methods.• Horizontal labeling with leader

lines

Regions of Integument (skin) Epidermis – outermost region• Keratinized stratified

squamous epithelium• Non-vascular• 4 cell types• 4 - 5 layers

Dermis – middle region• Vascularized• 80%

dense irregular connective tissue

• 20% areolar connective tissue

Overview of the Dermis

• Cell types: fibroblasts, phagocytes, mast cells and white blood cells

• 2 layers – papillary (upper) and– reticular (lower)

• Rich with nerves, blood and lymph vessels

• Most hair follicles, oil and sweat glands derived here

Papillary Layer of Dermis

• Areolar connective tissue with collagen and elastic fibers• Superior surface with dermal papillae: peg-like projections (reason for fingerprints)

• Dermal papillae with:• capillary loops (thin blood vessels)

• Meissner’s corpuscles (touch),

• and free nerve endings (pain)

Papillary Layer of Dermis

• Krause’s end bulb: (cold)

• Ruffini end organs: (heat and sustained pressure)

In Reticular Layer:

Pacinian corpuscle: (touch, deep vibrations, transient pressure)

Reticular Layer of the Dermis

• 80% of the thickness of the dermis (dense –irregular CT)

• Collagen fibers:– add strength and resiliency– Binds water, keeping skin hydrated

• Elastin fibers:– stretch-recoil properties

• Rich in blood vessels:– dilate or constrict in response to emotions or

temperature changes

Name the epidermal and dermal layers (review)

5. Stratum Corneum (Epidermis)

4. Stratum Lucidum (Epidermis)

3. Stratum Granulosum (Epidermis)

2. Stratum Spinosum (Epidermis)

1. Stratum Basale (Epidermis)

6. Papillary Layer (Dermis)

7. Reticular Layer (Dermis)

Regions of Integument (skin) Epidermis – outermost region• Keratinized stratified

squamous epithelium• Non-vascular• 4 cell types• 4 - 5 layers

Hypodermis (superficial fascia)• deepest region• Mostly adipose (fat storage),

some areolar• Vascularized

Dermis – middle region• Vascularized• 80%

dense irregular connective tissue

• 20% areolar connective tissue

Hypodermis(superficial or subcutaneous fascia)• Composed mostly of adipose and some

areolar connective tissue • Adipose cells swell and thicken with fatty

droplets during weight gain• Connects skin to underlying muscle• Absorbs shock• Insulates

Skin Color

Three pigments contribute to skin color1. Melanin: yellow to reddish-brown to black – only pigment made in skin by melanocytes and passed

onto keratinocytes– Freckles and pigmented moles – result from local

accumulations of melanin2. Carotene: yellow to orange pigment– Pigment incorporated into skin due to diet– Accumulates in stratum corneum and in adipose3. Hemoglobin: reddish pigment, gives pink hue to skin– Due to oxygenation of red blood cells

Skin “Appendages”

Epidermal Derivatives include:

6

hair

hair follicles

Sebaceous Oil Glands

Sudoriferous Sweat Glands

Sudoriferous Sweat Glands(2 types: Eccrine and Apocrine)

Eccrine glands • Covers entire body (3 million

p/person)– Most abundant on palms, soles

of the feet, and forehead • Coiled in dermis• Duct opens on skin’s surface (pore)• “sweat” = hypotonic blood filtrate

released by exocytosis: – 99% water, salts, antibodies,

anti-biotic proteins, and N-wastes, vitamin C

• Evaporation of sweat cools the body

Sudoriferous Sweat Glands(2 types: Eccrine and Apocrine)

Apocrine glands• Only 2000 p/person• Found in axillary and

anogenital areas with pheromone secretions

• Ducts empty into hair follicles• Odorless initially.

– Secretions contains lipids and protein that bacteria feed on.

– Decomposition of secretions by bacteria produce “body odor”

Sweat glands modified

Ceruminous glands – modified apocrine glands in external ear canal that secrete cerumen (ear wax)

Mammary glands – specialized sweat glands that secrete milk

Sebaceous “Oil” Glands

• Simple branched alveolar glands• Holocrine: glandular cells rupture to release

secretions

• Sebum Secretions:– Oils + ruptured cell fragments– moisturize hair and skin– Slows water-loss– bactericidal

• Released onto hair within follicle then flows onto skin surface.

• Acne due to blockage of hair follicle w/ infected sebum

Video SummaryYou tube: What is skin? The Layers of Human Skin

Hair (Pili)• Strands of dead, hard-keratinized cells

made by follicles– Softer keratin in epidermal cells

• Shaft projects from skin; Root embeded within dermis and hypodermis

• 3 concentric layers: - Medulla: absent in fine hair - Cortex: gives hair color - Cuticle: overlapping keratin• Split ends: cuticle worn away, exposing cortex

Structure of Hair FollicleFollicle created by

in-vagination of epidermal surface (epithelial root sheath) into dermis and hypodermis to create a “bag” or “sac” that builds hair

medulla

Basement membrane

Structure of Hair FollicleDeep end of follicle: expanded forming a hair bulb

Hair papilla created from in-folding of dermal tissue into hair bulb

Hair papilla supplies nutrients to hair (via capillaries) and signals growth

Melanocytes on superior surface of papilla pigments hair by creating melanin

Structure of Hair FollicleArrector pili muscle – attached to hair follicle and skin. When contracted, holds hair erect

• Root hair plexus wraps around each hair bulb

• Bending hair stimulates these endings, hence our hairs act as sensitive touch receptors

Hair Shape

• Internal shape of shaft and follicle determines hair shape– Round shaft: straight hair– Oval shaft: wavy hair– Flat or ribbon like shaft: kinky, curly hair** One head can have many shaft shapes resulting in interesting

hair textures.

Hair Types

• Vellus – pale, fine body hair found in children and the adult female (immature)

• Terminal – coarse, long hair of eyebrows, scalp, axillary, and pubic regions

• Hair growth influenced by:– Nutrition– Blood flow: reduced blood flow

hair lossEx. Brick layer shoulders: increased blood flow

to area because of carrying heavy objects results in hair growth

Hair Growth Cycles• Hair has a life cycle:

– Period of Active Growth (AG)

– Regressive Phase: hair bulb shrivels and matrix dies

– Resting Phase– Cycle repeats: Older

hair falls out, replaced by new hair

• Length of AG period determine length of hairEx:

Scalp: AG of 6-10 yearsBrows AG: of 3 – 4 monthsBalding or thinning hair: short AG

Hair Thinning and Baldness

• Alopecia – hair thinning in both sexes– Rate of hair shed > Rate of hair growth

• Hirsutism: excessive hair growth in women. Caused by excessive sex hormones usually from an ovarian tumor.

• True, or frank, baldness – Genetic– Sex-influenced condition

• Male pattern baldness – caused by follicular response to DHT (Dihydrotestosterone)

• Growth cycle is so short that hairs never emerge from follicles before shedding

– Sex linked trait – carried on X chromosome, inherited from mother

Hair FunctionFunctions of hair include:

– maintaining warmth– Alerting the body to insects on skin – Guarding the scalp against trauma, heat loss,

and sunlight– Eyelashes and nose hairs act as barriers

against foreign substances

Hair Distribution

• Hair is distributed over the entire skin surface except:– Palms, soles, and lips– Nipples and portions of external genitalia

Structure of a Nail

• Scale-like epidermal modification on the distal, dorsal surface of fingers and toes

• w/ hard keratin

Figure 5.6

Back to Regions of Skin

20% Areolar Connective Tissue

80% Dense Irregular Connective TissueCollagen fibers organized in irregular patterns• Strong and flexible

Back to Regions of Skin

Adipose Tissue of Hypodermis

Dense irregular connective tissue of reticular layer of dermis

Adipose tissue of hypodermis

Back to Regions of Skin

Mostly fat droplets