CH 5 Integumentary System

General Characteristics• The integumentary system includes the skin and

its accessory organs.• The skin includes the epidermis, dermis and

hypodermis (subcutaneous layer).• The skin is the largest organ of the body

– Approximately 22 ft2

– Approximately 16% of total body weight– 0.5mm-4 mm thick

• Thickest regions= hands and feet• Thinnest regions= eyelids and scrotum

Epidermis

Dermis

Subcutaneous(Hypodermis)

THE SKIN

Skin Functions• Thermoregulation: regulation of body

temperature.• Most important function• Excess heat is carried to the skin by the blood vessels.• Skin absorbs heat and transfers it to the surrounding

air.

• Protection: acts as a barrier against physical trauma, chemical and biological substances.• Works the best as a barrier when it is intact- no cuts,

scrapes, etc..• Approximately 50 layers of cells.

Skin Functions• Sense organ: provides the body with

cutaneous sensations.• Sensations of touch, vibration and pain• Collects information from the outside world and

sends it to the brain• What part of the body is the most sensitive?

• Lips• Genitals• Hands/Feet

Skin Functions• Secretion and absorption: allowing certain

materials to pass into or out of the skin.• Secretion:

• Secretes water and oils through glands.• Can remove some waste like salts, urea, carbon dioxide

and heat.

• Absorption:• Taking materials into the body through the skin.• Most absorbed- fat soluble vitamins (A, D, E, K)• Some toxins are absorbed- rubbing alcohol, acetone,

chlorine

Skin Functions• Vitamin D production: a precursor to the

vitamin D molecule can be found within the skin.• When exposed to sunlight, the precursor

becomes vitamin D because the light energy transforms its shapes.

• It takes hours of sun exposure to produce the amount of vitamin D in a glass of milk. Is it worth it?

General Characteristics and Function of the Epidermis- outer layer of skin• 40-50 layers of stratified squamous

epithelial tissue.

• Avascular

• Designed to be shed and replaced frequently

• Waterproof

• Function: Protection

Cells of the Epidermis• Keratinocytes- cells that produce keratin.

– These cells make up 90% of the epidermis

– Keratin is a tough, fibrous, water-proof protein

– Most keratinocytes are dead

– They don’t really become flattened until they reach the top layers due to pressures from above and below as the cells move up the epidermis.

– Keratinization: the process by which the cytoplasm and organelles of a keratinocyte are replaced by keratin.

• Happens as cells move up through the epidermis

• This is what eventually kills the keratinocytes

Cells of the Epidermis• Melanocytes- cells that produce melanin.

– Function to protect the skin from UV radiation– Produce melanin- a brown, black pigment

• It is produced by positive feedback. The more exposure- the more melanin produced- which means the more the skin can be exposed to the sun.

– We all have the same # of melanocytes per square inch of the skin. Our melanocytes just produce a varying amount of melanin.

• Langerhans cells- immune cells– Function to protect the body from foreign particles– These are phagocytes- engulf and destroy

Cells of the Epidermis

• Merkel cells- touch cells.– Function to gather information (touch, temperature,

vibration, and pain) and send it to the brain to be interpreted.

– Melanocytes, Langerhans cells and Merkel cells account for the remaining 10% of the epidermis.

Layers of the Epidermis- from the bottom to top

• Stratum Basale- deepest layer• Simple cuboidal layer

• Lies above the dermis and blood vessels in the dermis supply this layer with blood (by diffusion)

• Here is where cell division takes place, producing new skin cells and pushing older cells toward the surface.

• Stratum Spinosum- superficial to the stratum basale.• 8-10 layers

• Cells have small projections “spiny” that help lock the cells together like velcro.

Layers of the Epidermis- from the bottom to top

• Stratum Granulosum- superficial to the stratum spinosum.• 3-5 layers• Cells are starting to look more squamous because

of pressure from the cells above and below.• Layer where keratinization starts and cells

produce keratin in large quantities.• Can see granules of keratin in the cells.• The transition layer between living and dead cells.

Layers of the Epidermis- from the bottom to top

• Stratum Lucidum- superficial to the stratum granulosum.• 3-5 layers• Only found on the soles and palms• Shock absorbers

• Stratum Corneum- the most superficial layer of the epidermis• 25-30 layers of squamous keratinocytes• Spines start to break off which causes the cells to fall off• Waterproofs the skin• Takes 5 weeks for cells to reach this layer from the stratum basale

1.

LAYERS OF EPIDERMIS

Dermis- Inner Layer of Skin

• General Characteristics:– Thicker than the epidermis

– Composed of connective tissue

– Highly vascular

– Contains all accessory organs necessary for skin function (nerves, blood vessels, glands, hair follicles)

• That’s why burns that extend into the dermis are much more severe. They interfere with skin’s ability to function.

Dermis continued….

• Function:– Supports the epidermis by keeping the dividing

cells of the stratum basale healthy– Regulates body temperature– Provides skin with its strength and flexibility

Dermis continued….• Layers of the dermis:

– Papillary region: lies deep to the stratum basale of the epidermis

• 20% of the thickness of the dermis

• Composed of areolar connective tissue with thin collagen and fine elastic fibers

• Small capillary (tiny blood vessel) loops to supply nutrients to the epidermis

• Contains dermal papillae

Dermis continued…• Dermal papillae: small projections that

anchor the epidermis to the dermis– Prevent the epidermis from laterally sliding off

of the dermis

• Epidermal ridges: the ridges that form the fingerprints– Larger, downward projections of the epidermis

that force some of the dermal papillae sideways – Function to lock the epidermis in place

Dermal papillae and epidermal ridges

What type are you?

65% 30%

5%

• Reticular layer: lies deep to the papillary region– Includes the remaining 80% of the dermis– Composed of dense irregular tissue– Collagen fibers run in various directions

which adds strength– Functions to house the accessory organs of

the skin and provide the skin with strength and flexibility

ACT-UP• Knowing what you know

about the skin, answer the following questions:

• 1) Why would a person with tattoos not need to have them retouched every five weeks?

• 2) What would cause them to fade over time?

Accessory Structures of the Skin

• Hair- present on most surfaces of the skin– Shaft is the hair above the skin (dead

keratinocytes)– Root is the hair below the skin– Follicle- Layers that surround and protect the hair

root– Matrix- The dividing cells of the hair root that cause

hair growth – Papillae- Small projections that anchor each hair.

• Contain blood vessels that keep the matrix alive.

Accessory Structures of the Skin• Hair function:

– Insulates against heat loss– Protects from UV radiation

• Arrector pili muscle: A small muscle attached to the bulb of a hair.– Attaches to the follicle sheath– Contracts under physiological or emotional stress,

which pulls the hair shafts perpendicular to the skin surface.

Glands- Present in different concentrations in all areas of the skin

• Sebaceous glands: oil glands

– Associated with hair follicles

– Function to produce oil (sebum)

• Keeps hair soft and flexible

• Keeps skin around the hair soft and flexible

• Destroys some bacteria

• Sudoriferous glands: sweat glands– Function to release a watery secretion (sweat) to

cool the body.– Two types:

• Eccrine- Respond to elevated body temperatures• Apocrine- Respond to stress (adrenaline rush)

–These release sweat along with some proteins and fat that bacteria LOVE! As bacteria feed on this thick sweat, they produce a stinky by-product = B.O.!!

• Ceruminous glands: modified sweat glands that are only found within the external ear canal– Function to produce cerumen (wax) that

protects the eardrum by trapping substances.

– It’s important to keep this production at a low level- so water doesn’t get trapped that will support the breeding of bacteria.