Integumentary System

Skin as an Organ

• Largest organ in human body• All adults have 20-25 lbs of skin• 4 Functions- Skin as radiator

Integumentary Structures• Components of the Integumentary System

Figure 5-1

Quick OverviewEpidermis• Tissue= Stratified Squamous• No blood vessels in this layer• Dead Skin CellsDermis• Tissue=Dense Irregular Collagenous Connective• Active area of skinHypodermis (not actually skin)• Tissue=Areolar & Adipose• Connects skin to body

(Epi=On, On the surface of something)(Hypo=Below, Less than)

4 Major Structures in Dermis

1. Hair Follicles-• All anchored in dermis• Aid in temp regulation by trapping air to help

insulate.• Sensitive-Can sense vibrations2. Glands• Sweat Glands-Evaporation cools you• Oil Glands-Keep dead skin cells together. Protects

from things getting in. (sebaceous gland)

4 Major Structures in Dermis

3. Blood Vessels• Bring nutrients and fluids to cells.• Bleed when you cut into dermis (not epidermis).4. Sensory Nerves• Sense Temperature• Pain• Touch (Meisners Corpuscle-Light Touch; Pacinian

Corpuscle-Deep pressure)

Hypodermis

• Link Between Body & Skin• Find adipose mixed in with areolar tissue• Most fat in your body is directly under skin.• Major blood vessels

Dermis• Boundary between dermis &

epidermis isn’t flat to prevent slipping apart.

• Dermal Papilla-Bumps in dermis

• Blisters caused by intense, prolonged friction. Epidermis separates from dermis and fluid enters.

• Any change to dermis will be seen through epidermis (scars, surface contours, etc)

• Scars are in dermis• Causes Fingerprints

Dermal Papilla

Blisters

Epidermis

• Super thin• Stratified Squamous• 5 Layers

– Stratum Corneum– Stratum Lucidum (Only Soles of Feet &

Palms)– Stratum Granulosum– Stratum Spinosum– Stratum Basale

Living Layers!

Started from the bottom now we’re here..Stratum Basale (hehehe)

• All other cells come from here

• #1 Job is Reproduction- Cells born here aren’t in full production mode yet, they don’t grow up here.

Stratum Basale (cont)

• 2 Main types of cells in Stratum Basale– mostly Keratinocytes: Make

protein- keratin to give epithelium strength. Don’t produce keratin yet in basale layer.

– Melanocytes: Make pigment melanin (colors your skin). More Melanin=darker skin.

• Albinism=Malfunctioning melanocytes

Stratum Spinosum• Cells from basale

go here.• Cells here are

growing up and producing keratin, etc. Like teenagers.

Stratum Spinosum (cont)• Melanocytes don’t

reproduce in numbers. When they do=melanoma (malignant skin cancer)

• Melanin-natural sunblock– Absorbs UV Rays, blocks

UV rays from damaging dermis.

– Tanning occurs by UV radiation stimulating excess melanin production.

Stratum Granulosum

• Old cells• Been producing

keratin for so long, we can see keratin “GRANULES”

• Not much moisture/nutrients

• Cells on the verge of death.

Stratum Corneum

• Top layer • Dead skin cells• Still tough because

of protein keratin.

Stratum Lucidum

• Palms/Soles of Feet

• Less melanocytes, decreased pigment

• Change from granulosum before corneum to thicken.

Sebaceous Glands (oil glands)• Occur over entire body - Except palms and soles• Simple alveolar glands

– Holocrine secretion – entire cell breaks up to form secretion– Secretes an oily substance called sebum– Most are associated with a hair follicle

• Functions of sebum– Softens and lubricates hair and skin– Skin waterproofing – Collects dirt

Sweat (Sudoriferous) Glands

• Two types:• Eccrine (Merocrine)

– Most abundant sweat gland– “True sweat”

• 99% water with some salts• Contains traces of

metabolic wastes ~ 2% urea

– Role in thermoregulation– Widely present in skin (up to

500/cm2)• Apocrine

– Odorous secretion – Absent before puberty– Present in axillary, areolar,

anal and genital areas

Eccrine (Merocrine) Gland

Figure 5.10b

Nails• Scalelike modification of epidermis made of hard keratin• Parts of the nail

– Free edge– Body - dense mass of keratinized cells– Root– Nail folds– Eponychium – cuticle

Bleeding occurs at the site of injury immediately after the injury, and mast cells in the region trigger an inflammatory response.

Epidermis

Dermis

After several hours, a scab has formed and cells of the stratum germinativum are migrating along the edges of the wound. Phagocytic cells are removing debris, and more of these cells are arriving with the enhanced circulationin the area. Clotting around the edgesof the affected area partially isolatesthe region.

Sweat gland

Scab

Macrophagesand

fibroblasts

Migratoryepithelialcells

Granulationtissue

Skin Injury and Repair

One week after the injury, the scab has been undermined by epidermal cells migrating over the meshwork produced by fibroblast activity. Phagocytic activity around the site has almost ended, and the fibrin clot is disintegrating.

Fibroblasts

After several weeks, the scab has been shed, and the epidermis is complete. A shallow depression marks the injury site, but fibroblasts in the dermis continue to create scar tissue that will gradually elevate the overlying epidermis.

Scartissue

Skin Injury and Repair

Skin Injury and Repair

Table 5-1

Aging of the Skin• Major Age-Related Changes

– Injury and infection increase– Immune cells decrease– Sun protection diminishes– Skin becomes dry, scaly– Hair thins, grays– Sagging, wrinkles occur– Heat loss decreases– Repair slows

Effects of UV Radiation• Beneficial effect - activates synthesis of

vitamin D3

• Harmful effects– Sun burn– Wrinkles, premature aging– Malignant melanoma– Basal cell carcinoma

Types and Growth of Hair

• Vellus hairs– Body hairs of women and children

• Terminal hairs– Hair of scalp– Axillary and pubic area (at puberty)

• Hair thinning and baldness– Due to aging– Male pattern baldness

Burns

• Classified by severity– First-degree burn – only upper epidermis is

damaged– Second-degree burn – upper part of dermis

is also damaged• Blisters appear• Skin heals with little scarring

– Third-degree burn• Consume thickness of skin• Burned area appears white, red, or blackened

Burns

First-degree(epidermis only; redness)

Second-degree(epidermis and dermis,with blistering)

Third-degree(full thickness, destroying epidermis, dermis, often part of hypodermis)

Estimating Burns Using the Rule of Nines

Figure 5.11a

Skin Cancer

• Basal cell carcinoma– Least malignant and most common

• Squamous cell carcinoma– Arises from keratinocytes of stratum

spinosum

• Melanoma– A cancer of melanocytes – The most dangerous type of skin cancer

Skin Cancer

Squamous cell carcinoma

Figure 5.12Melanoma

Squamous cell carcinoma

Basal cell carcinoma

The Skin Throughout Life

• Epidermis– Develops from embryonic ectoderm

• Dermis and hypodermis– Develop from mesoderm

• Melanocytes– Develop from neural crest cells

The Skin Throughout Life

• Fetal skin– Well formed after the fourth month– At 5-6 months

• The fetus is covered with lanugo (downy hairs)

– Fetal sebaceous glands produce vernix caseosa