Chapter 5

Unit II: OrganizationIntegumentary System

Part I

• Body’s largest organ (15% of body wt, 2m2 surface area)• Made of two layers:

• Epidermis• Dermis

• Accessory Organs• Hair• Nails• Cutaneous Glands

• Hypodermis• Below the dermis• Not part of the skin

Integumentary System

Epidermis

Epidermal ridge

Dermis

Dermal papilla

Thick skin

LM x 225

LM x 225

Thin skin

Integumentary System• Thick skin – covers the palms, soles, fingers and toes

- ~0.5mm- stratum corneum is very thick (5 layers)- no sebaceous glands or hair follicles

• Thin skin – covers the rest of the body- ~0.1mm- thin stratum corneum (4 layers)- hair follicles and glands

• Protection of underlying tissues - bears most physical injuries.

• Barrier against pathogens - Few microbes can penetrate intact skin.

• Acid Mantle - slight acidity of pH 4-6 on the surface

• Water proofing

• Barrier to ultraviolet light (UV radiation)

• Vitamin D synthesis Calcitriol – needed for bone health

• Cutaneous absorption & excretion – O2, CO2, fat soluble vitamins

• Sensory - touch, texture, pressure, vibration, and tissue injury

• Thermoregulation - thermoreceptors

• Communication

Functions of your Skin

Composed of five types of cells:• Stem cells – undifferentiated cells

• Keratinocytes – majority of epidermis cells, durability and flexibility

• Melanocytes – synthesize pigment (melanin) shields from UV

• Tactile (Merkel) – receptors for touch

• Dendritic (Langerhans) – stand guard against foreign invaders, phagocytic

Structure of the SkinEpidermis

Layers of the Epidermis

• Simple cuboidal epithelial cells

• 4 types of cells: keratinocytes, Melanocytes, Merkel cells, stem cells

• Stem cells constantly undergoing mitotic cell division

Layers of the EpidermisStratum basale

• 8-10 layers of Keratinocytes

• Deepest cells undergo mitosis.

• Keratin filaments cause the cells to flatten near the surface.

• Desmosomes – attach the cells, give spiny appearance

• Langerhans cells – arise in bone marrow

Layers of the EpidermisStratum spinosum

• 3-5 layers of keratinocytes

• Lamellated granules secrete glycolipids

– waterproof barrier

– forms a barrier between surface cellsand deeper layers of the epidermis

– cuts off surface strata from nutrient supply

• Keratohyalin granules – cross links keratin filaments

Layers of the EpidermisStratum granulosum

• Translucent zone found only in thick skin

• Keratinocytes filled with keratohyalin and eleidin

• Cells have no nuclei or other organelles

• Undergoing dehydration

Layers of the EpidermisStratum lucidum

• Consists of up to 30 layers of dead, dead, keratinized cells

• outermost layer where surface cells flake off.

Layers of the EpidermisStratum corneum

1. Produced by stem cells in stratum basale

2. New cells push others toward surface - keratin filaments

3. Cells grow flat and fill with keratohyalin

4. Organelles disintegrate as they pass the water barrier

5. Cells die and fill with keratin fibers

6. Exfoliate

Life History of Keratinocytes

Layers of the Dermis

Layers of the Dermis

• 0.2mm – 4mm thick

• Fibrous Connective tissue composed of:

– fibroblasts

– collagen, elastic fibers: strength and flexibilty

– Accessory structures embedded here

• Layers

– papillary layer – surface layer, thin zone of areolar

Dermal papillae - extensions of the dermis into the epidermis

increase surface area for attachment, create finger prints

– reticular layer – thick layer of dense irregular

• Other names: Subcutaneous tissue/ superficial fascia

• Mostly adipose• Functions:

1.

2. • Hypodermic injections (subQ)

– highly vascular – Limits tissue damage

Hypodermis

• Composed of hard keratin

• Hair found almost everywhere

– 2.5 million/75% on general body not head

– Not found on thick skin, nipples, lips

– differences between sexes or individuals

• Texture and color

• 3 different body hair types:

– lanugo -- fine, unpigmented fetal hair

– vellus -- fine, unpigmented hair of children and women

– terminal hair -- coarse, long, pigmented hair

Skin OrgansHair

Cuticle

Cortex

Medulla

Hair matrix

Hair papilla

• Hair – keratinized cells• Follicle – oblique tube• Three zones:

– bulb = hair originates– vascular tissue (papilla) in bulb

provides nutrients– root = within follicle– shaft = above skin

• Three layers in cross section:– Medulla (core): soft keratin– Cortex: thick, hard keratin– cuticle (surface):

thin, hard keratin

Structure of Hair and Follicle

Arrector pili muscle

• Straight hair = round

• Wavy = oval

• Tight curls = flat

• Hair color = ratio of

two types of

melanin found in

the cortex

Texture and Color of Hair

Hair Growth Cycle

Epidermis

Dermis

Hair matrix

Sebaceousgland

Old club hair

PiloerectorNew hair

Bulge

Club hair(detachedfrom matrix)Club

Dermal papilla

Degenerationof lower follicle

Hair bulb

2 3Anagen (early) (Growing phase, 6–8 years)Stem cells multiply and follicle grows deeper into dermis; hair matrix cells multiply and keratinize, causing hair to grow upward; old club hair may persist temporarily alongside newly growing hair.

Anagen (mature) Catagen(Degenerative phase, 2–3 weeks)Hair growth ceases; hair bulbkeratinizes and forms club hair;lower follicle degenerates.

Telogen(Resting phase, 1–3 months)Dermal papilla has ascendedto level of bulge; club hair fallsout, usually in telogen ornext anagen.

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90% of scalp follicles Detached from Hair falls outGrows down from epidermis nutrients

• Alopecia - General term for all hair loss

• Pattern baldness

– sex-influenced trait

– males: XdefectY (can’t cover up)

– females: XdefectX (no baldness)

– expressed only with high testosterone levels

– follicles are sensitive to androgens causes them to shrink when exposed shorten their lifespan and prevents them from producing hair normally

• Hirsutism - excessive hair growth

– hormone imbalance (ovary or adrenal cortex tumor)

Hair Loss and Growth

• Body hair - (too thin to provide warmth) - alert us to parasites crawling on skin

• Scalp hair - heat retention and sunburn cover

• Beard, pubic and axillary hair - sexual maturity and help distribute sexual scents similar to pheromones

• Guard hairs - prevent foreign objects from getting in– nostrils, ear canals or eyes

• Expression of emotions with eyebrows

Functions of Hair

Skin OrgansFingernail Structure

• Derivative of stratum corneum that grows downward

– densely packed cells filled with hard keratin

• New cells added by mitosis in the nail matrix

• Flat nails allow for fleshy, sensitive fingertips

• protect fingertip and surrounding soft tissue from injury

• enhances precise delicate movements;

• enhances sensitivity (counterforce)

• tool

• Medical diagnosis

• Ex.) iron deficiency = concave nails

• Length and growth rate related to the length of the terminal phalanges

Nails