A&P - Intro to Integumentary System

Skin, hair, nails, sweat glands, oil glands

Integumentary system

The body’s outer covering that consists of skin, hair, nails, sweat glands, and oil glands

Integumentary system - Functions

• Barrier against infection and injury (including UV protection)

• Helps regulate body temperature (sweating and shivering)

• Receiver of pressure, pain, heat, and cold

• Maintains fluid balance (prevents cells from drying out)

• Excretes excess fluids and waste

• UV rays convert modified cholesterol into vitamin D

Epidermis - Structure

• Made of stratified squamous epithelium

• Main cell type is a keratinocyte

• Contains melanocytes

• Contains Merkel cells

• Contains Langerhans cells

• Outer layer are flattened, dead cells; Inner layer are living cells

• Keratinocytes in the stratum basale layer do mitosis, pushing other cells to the surface

• Cells die when they’re too far from blood supply (which is found in the dermis)

• As the cells move up, they become flattened and make keratin

• Takes 25-45 days for new cells to reach the top

• Contains nerve endings, but no blood vessels (epithelial tissue is avascular)

• Attached to the dermis by the basement membrane

Integumentary system - Functions

• Water resistance (keratin-filled dead cells)

• Protective layer against biological and chemical assault

• Produces pigment

• Detects/senses touch and pain

Keratinocyte

A type of cell responsible for producing keratin

The main cell type found in the epidermis

Keratin

A tough, fibrous protein that forms the structural framework of the skin and protects it from damage

Melanocyte

A cell that produces the pigment melanin, which protects from UV rays

Merkel cell

A cell that is attached to nerves to detect touch

Langerhans cell

A cell that guards against toxins, microbes, and other pathogens

If detected, they alert the immune system

Layers of the epidermis (deep to superficial)

1. Stratum basale

2. Stratum spinosum

3. Stratum granulosum

4. Stratum lucidum

5. Stratum corneum

Stratum basale

Continuously divides and pushes up towards the surface of the skin

A layer of single cells, lays on the basement membrane of the dermis

Contains melanocytes

Most deep of the epidermal layers

Stratum spinosum

This layer of cells that have been pushed out from the stratum basale

Cells are “spiny,” and the spines interlock together to form a support layer

Stratum granulosum

This layer of cells begin producing keratin and begin to die

Cells of this layer are still living, but none of the nutrients reach them

Stratum lucidum

This layer of cells are dead keratinized cells

Only found in areas where skin is thick (soles of the feet, palms of the hands), not where skin is thin (eyelids, forearm)

Stratum corneum

This layer of cells are the outermost layer of dead keratinized cells, tightly bound together

The keratin protects from fluid loss while keeping the skin elastic (much thicker on the soles of the feet and palms of the hands)

Skin color

Due to mainly the pigment melanin

Melanin

• Made by melanocytes in the stratum basale layer of the epidermis

• Contains 2 types: Eumelanin and Phomelanin

• Darker skin is due to the kind and the amount of melanin produced (everyone has relatively similar numbers of melanocytes)

• UV rays stimulate melanocytes to make more melanin (resulting in tanning)

• Protects skin from harmful UVB rays

Eumelanin

A type of melanin pigment that comes in brown and black

Phomelanin

A type of melanin pigment that comes in pink-ish red

Abinism

A genetic skin condition that causes a lack of pigment in the skin, hair, and eyes

Those with this condition have a normal number of melanocytes in the epidermis, but lacks the enzyme tyrosinase that converts the amino acid tyrosine to melanin

Vitiligo

A chronic skin condition that causes a loss of pigmentation, resulting in white patches on the skin

An autoimmune disorder that attacks melanocytes

Carotene

• Yellow-ish pigment found in certain plant products (ex. carrots)

• Accumulates in cells of stratum corneum and the subcutaneous fat (hypodermis layer)

• Often seen in heels and calluses of the feet because that’s where stratum corneum is the thickest

Jaundice

A liver condition that causes yellowing of the skin and eyes

Due to buildup of bilirubin in the blood

Hemoglobin

The red pigment of blood, which imparts reddish to pink-ish hues as blood vessels show through the skin

The less melanin, the more it shows

Cyanosis

Bluish color of the skin, usually caused by low oxygen levels on the hemoglobin of red blood cells

Dermis - Structures

Made of strong, flexible connective tissue layers (areolar and dense irregular)

Contains nerves, blood vessels, lymph vessels, hair follicles, sweat glands, and muscles (attached to hair follicles)

Dermis - Functions

• Gives skin its elasticity and strength from collagen and elastin fibers

• Contains sweat glands (3000/in²) that regulate body temperature and release various wastes from the bloodstream

• Mammary glands and ear wax glands are modified sweat glands

• Contains many sebaceous (oil) glands (2 per hair) that release sebum, keeping the epidermis and hair flexible and waterproof

• Contains many sensory cells

Hypodermis/subcutaneous

• The base of blood vessels, nerves, and some hair follicles extend into this layer

• Primarily made of adipose tissue, and functions in insulation and protection

• Bottommost layer of skin, located under the dermis

Types of burns

• First-degree

• Second-degree

• Third-degree

First-degree burn

• Inflamed, red skin

• Surface of the epidermis is shed

Second-degree burn

• Burns the epidermis and part of the dermis

• Blisters form as fluid builds beneath the epidermis

• Can take weeks to months to heal, and will often scar

Third-degree burn

• Epidermis and dermis is destroyed

• Catastrophic loss of fluids (dehydration)

• Highly susceptible to infection

Types of skin cancer

• Basal cell carcinoma

• Squamous cell carcinoma

• Malignant melanoma

Basal cell carcinoma

A type of skin cancer

Metastasizes (spreads to other sites of the body) slowly

Most common, but 99% fully cured

Squamous cell carcinoma

A type of skin cancer

Induced by the sun

From cells immediately superficial to stratum basale

Malignant melanoma

A type of skin cancer

Cancer of the melanocytes, often begins with mole-like growths

Rare (1% of skin cancer) and most deadly (~9,000 deaths/year)

Hair - Structure

• Made of dead epidermal cells

• Growth is determined by hormones and genetics

• You are born with as many hair follicles as you will ever have

Hair - Functions

• Covers almost every exposed surface

• Used for warmth and protection (from the sun or dirt)

Hair - Color and texture

Color depends on the kind of melanin (red, brown-black) and the amount of melanin

Texture is related to difference in shape of hair: Straight = round, wavy = oval, tightly curly = flat

Hair shaft - Structures

• Hair follicle → Made of epidermal stem cells, have a club-shaped structure, and the end has blood vessel to supply nutrients to the hair to feed and grow (called papilla)

• Hair root → Part of the hair below the surface of the skin

• Hair shaft → Part of the hair that can be seen above the scape

New skin in burn patients comes from hair follicles

Types of sweat glands

Merocrine and apocrine

Merocrine glands

• Found all over the body (especially the forehead, back, palms, and soles)

• Formed before birth

• Function in evaporative cooling (thermoregulation)

• Sweat is mostly water, and small amounts of salt and wastes (urea and uric acid)

• Comes out of pores

Lacrimal glands

Glands that produce the watery, aqueous layer of tears to lubricate, clean, and protect the eye

Located in the upper outer corner of each eye

Eccrine glands

Glands that secrete clear, odorless sweat that helps regulate body temperature through evaporative cooling

Widely distributed throughout the body (especially the forehead, armpits, palms, and soles)

Apocrine glands

Glands that secrete a thick, milky fluid that contains lipids and proteins into hair follicles; The secretions are metabolized by bacteria and create odor

Regulated by hormones and become active in puberty

Located in the armpits, groin, and around the nipples

Ceruminous glands

Modified sweat glands that produce ear wax (cerumen) by mixing their secretions with sebum from nearby sebaceous glands

Located in the outer third of the external ear canal

Sebaceous (oil) glands

Glands that secrete sebum (mainly lipids) from the stimulation of testosterone (which is why it increases during puberty), lubricating and waterproofing skin and hair

Stratified cuboidal epithelium (holocrine glands)

Nails - Structure

Scale-like modifications of the epidermis that are made of keratin

Nails - Functions

• Protects the ends of fingers

• Fingernails grow 1mm/week, while toenails are slow

Effects of aging

• Hair → Thin and gray: Melanocytes die and mitosis slows down

• Oil glands → Skin and hair become drier: Sebaceous glands atrophy (shrink)

• Skin layers → 

  • Mitosis slows, collagen lost from dermis = Skin becomes thin and translucent

  • Loose and sagging as elastic fibers are lost in dermis (UV rays damage elastin)

  • Fewer blood vessels/walls thinner = More bruising and slower healing

  • Age spots: Accumulation of pigment cells