INTEGUMENTARY SYSTEM

Bio 137 Anatomy & Physiology I

Organ System• Groups of closely related organs that work together to

perform similar functions

• For each organ system studied, know:• What are the organs that compose the system?

• What are the functions of the system?

Structures of the Integumentary System

•Organ:• Skin

•Accessory Structures• Hair • Sweat Glands• Sebaceous Glands• Nails

Skin• Also called the Cutaneous Membrane • The largest human organ by weight & surface area• 22 ft2

• 4.5-5kg (16% of body weight)• Thickness varies by location: eyelids vs. heels of feet

Structure of the Skin

• Composed of 2 layers1. Epidermis – epithelial tissue2. Dermis – connective tissue

• Subcutaneous (SubQ) layer below dermis• Adipose and areolar connective tissue

• We lose almost a kg of skin epithelium a year that becomes a major part of household “dust”.

Structures of the Skin

Integumentary System Functions

•Protection• Immunity•Regulation of body temperature

•Excretion•Sensory reception•Synthesis of vitamin D•Blood reservoir

The Epidermis• Types of skin:

• Thin (hairy) skin covers all body regions except the palms, palmar

surfaces of digits, and soles.

• Thick (hairless)

skin covers the

palms, palmar

surfaces of

digits, and

soles.

Epidermis• Keratinized Stratified Squamous Epithelium• Avascular• Usually very thin, 0.07mm-0.12mm• Outermost cells are keratinized and dead

• These cells are sloughed off as new cells below mature and move up

• The epidermis contains four major types of cells:• Keratinocytes• Melanocytes• Langerhans cells• Merkel cells

Cells of the Epidermis

Cells of The Epidermis

• Keratinocytes (90% of the cells)• Produce keratin - a tough fibrous protein that provides protection.

• Melanocytes • Produce the pigment melanin that protects against damage by

ultraviolet radiation.

• Langerhans cells• Macrophages that originated in the red bone marrow.

• Involved in the immune responses.

• Merkel cells (least numerous)• Function in the sensation of touch along with the other adjacent tactile

discs (receptors).

Epidermis• Keratinized stratified squamous epithelium

• 5 distinct layers of the epidermis in thick skin (4 in thin)

• Stratum corneum• Stratum lucidum• Stratum granulosum• Stratum spinosum• Stratum basale

Outermost

Deepest

Epidermal Layers• Stratum corneum – Oldest, outermost layer

• 25-50 layers of dead keratinocytes, filled with keratin• Continuously shed• Constant friction can stimulate the cell production in this layer and produces a callus

• Stratum lucidum - Only in thick skin

of soles and palms• 4-6 layers of dead keratinocytes

• Stratum granulosum - non-dividing 3rd layer• 3-5 layers of keratinocytes undergoing apoptosis (cell

death) • Barrier between metabolically active and dead cells

Epidermal Layers• Stratum spinosum

• Multilayered keratinocytes

• Stratum basale – deepest layer• Contains melanocytes and a

single row of cuboidal keratinocytes undergoing mitosis

• Skin stem cells (Youngest layer of cells) produces all other epidermal layers

The Epidermis

Five Epidermal Layers

epidermis

dermis

corneum lucidum

granulosum spinosum basale

16

Growth of the Epidermis

• Keratinization • Process where new cells in the stratum basale move up in

epidermal layers and accumulate more and more keratin protein

• Takes about 4-6 weeks

Melanin Distribution• Melanin Pigment is produced by melanocytes in the

stratum basale• Eumelanin (brown to black)

• Pheomelanin (yellow to red)

• Same # of melanocytes in individuals BUT different amounts of melanin produced by these cells

•• Melanin production affected by our DNA, sunlight,

chemicals and drugs

Skin Color is due to accumulation of melanin within melanocytes

The Epidermis• Skin Pigments• Freckles are clusters of concentrated melanin triggered

by exposure to sunlight.• Moles are benign localized overgrowth of melanocytes • Malignant melanoma is a cancer of melanocytes.

Skin Conditions• Production of epidermal cells closely balances loss

of dead cells• If skin is rubbed regularly rate of mitosis increases

• Calluses and corns

• Psoriasis - chronic skin disease• Cells divide seven times more frequently• Shed prematurely: 7-10 days• Make abnormal keratin: flaky, silvery scales at skin surface• Effective treatments: suppressing cell division

The Epidermis• Skin Pigment Disorders• Vitiligo – The partial or complete loss of melanocytes in the

skin. • Irregular white spots in skin

• Possible autoimmune disorder

• Albinism is the inherited inability to produce melanin. • Characterized by the complete or partial absence of pigment in the

skin, hair, and eyes due to a defect of an enzyme involved in the

production of melanin.

Aging• With age, there is an increased susceptibility to pathological conditions

• Decubitus ulcer

The Dermis• Connective tissue containing collagen and elastic fibers• 1mm - 2mm thick

• Contains: • Blood vessels, nerves, Hair follicles and glands are

embedded here

• Functions: Binds epidermis to underlying tissues & nourishes epidermis, great tensile strength

2 Layers of Dermis1. Papillary Layer – thin uppermost layer

• Thin collagen fibers with elastic fibers• Dermal papillae - Responsible for a person’s fingerprint• Sensory receptors for touch (Meissner’s corpuscles)

2. Reticular Layer – attached to SubQ• Thick Collagen fibers with elastic fibers• Abundant capillary networks• Hair follicles, glands, vessels & nerves here

• Tears or excessive stretching in this region cause stretch marks

The Dermis

Subcutaneous Layer• Also called the hypodermis • Contains adipose tissue, blood vessels, nerves & Pacinian Corpuscles

• Attaches skin to underlying tissue

subQ

Sensory Receptors for Touch

• Meissner’s Corpuscles• Light touch receptors• Located in dermal

papillae of papillary layer• Abundant in hairless

portions of skin• Lips, fingertips, palms, soles,

nipples, external genitalia

• Pacinian Corpuscles• Deep pressure receptors• Located deep in dermis

and/or subcutaneous layer• Found in deeper dermal

tissues of hands, feet, penis, clitoris, urethra, breasts, tendons and ligaments

The skin contains different types of sensory receptors to differentiate

between the different tactile (“touch”) sensations.

• Light touch, pressure, vibration, itch and tickle

Figure 12.01

Accessory Structures of the Skin

Hair• Hair is present on most skin surfaces except the palms,

anterior surfaces of fingers, and the soles of the feet.• It is composed of dead, keratinized epidermal cells.• Genetics determines thickness and distribution.• Functions in touch sensations,

protects the body against

the harmful effects of the

sun and against heat loss.

Hair • Hair develops from epithelial cells at the base of a hair

follicle deep in the dermis• Hair shaft – superficial portion above skin surface• Hair follicle – below the level of the skin• Hair root – penetrates deep in dermis • Color is due to melanin production from stratum basale

Nails

• Nails are composed of hard, keratinized epidermal cells located over the dorsal surfaces of the ends of fingers and toes.

• Nail structures include:• Free edge

• Transparent nail body (plate)

with a whitish lunula at its base

• Nail root embedded in a fold of skin

• Functions:• Manipulation• Protection

Nails

• Recall from Chapter 4 that glands are epithelial cells that secrete a substance.

• Sebaceous (oil) glands are connected to hair follicles.• They secrete an oily substance called

sebum which does 2 important things:

• Prevents dehydration of hair

and skin

• Inhibits growth of certain bacteria

Skin Glands

Eccrine Sweat Glands

• Most numerous• Secrete a water solution (600ml/day) that cools the body

• Secretion is water, salts and wastes (urea/uric acid); no odor

• Respond to elevated temperature & emotional stress

• Function throughout life• Common and widely distributed throughout skin

• Forehead• Neck• Back

Apocrine Sweat Glands• Secretion empties into a hair follicle• Located mainly in the SubQ layer

• Not involved in thermoregulation• Function from puberty on• Secretion is water, salts, wastes and cellular debris that is

metabolized by bacteria = ODOR

• Most abundant Locations:• Axillary region (Armpit)• Groin

Skin Glands

• Ceruminous glands are modified sweat glands located in the ear canal.• Along with nearby sebaceous glands, they are involved in producing a waxy secretion called cerumen (earwax) which provides a sticky barrier that prevents entry of foreign bodies into the ear canal.

Integumentary System Functions

•Protection•Regulation of body temperature•Excretion•Sensory reception• Immunity•Synthesis of vitamin D•Blood reservoir

Integumentary System Functions •Protection

•Moisture loss• Injury•Microorganisms•Chemicals

•The skin is the 1st line of defense in the immune system!!!

Regulation of Body Temperature• Involves sweat glands• Shivering

• This is the diagram we covered on the very first day of class!

Sensory Reception• Meissner’s Corpuscles

• Light Touch receptors• Located in dermal papillae

• Pacinian Corpuscles• Deep Pressure receptors• Located deep in dermis or subcutaneous layer

Integumentary System Functions • Immunity

• Langerhan Cells• Specialized immune cells that reside in the epidermis• Interact with T cells in immune responses

• Acidic pH of perspiration retards microbe growth

Integumentary System Functions • Synthesis of Vitamin D:

• Requires sunlight• Needed for bone development, growth and remodeling• Promotes absorption of calcium and phosphorous from

the small intenstine

• Cholesterol → Provitamin D → Vitamin D

Sunlight

(In skin)

Integumentary System Functions

•Blood reservoir:• 10% of our blood vessels are located in dermis

Wound Healing• Two kinds of wound-healing processes can occur, depending on the depth of the injury.

• Epidermal wound healing occurs following superficial wounds that affect only the epidermis.

• Deep wound healing occurs when an injury extends to the dermis and subcutaneous layer.• Loss of some function and development of scar tissue usually

occurs.

Wound Healing

Wound Healing• Inflammation is a normal response to injury, especially if deep• Blood vessels dilate and become leaky• Skin becomes reddened, swollen, warm• This provides tissues with more nutrients and oxygen which aids in healing

• Also allows for WBC to enter tissue and prevent infection

• Macrophages remove foreign material and begin tissue repair

Wound Healing

Burns

• A burn is tissue damage caused by excessive

heat, electricity, radioactivity, or corrosive

chemicals that denature (break down) the proteins

in the skin cells.

• Burns destroy some of the skin's important contributions

to homeostasis—protection against microbial invasion

and desiccation, and thermoregulation.

• Burns are graded according to their severity.

Burns• A first-degree burn involves only the epidermis

• It is characterized by mild pain and erythema (redness) but no blisters and skin functions remain intact.

• Mild sunburn, redness but no blisters• Heals in a few days to 2 weeks

Burns• A second-degree burn destroys the epidermis and part of the dermis - some skin functions are lost.• Redness, blister formation, edema, and pain result.• Heals in 3-4 weeks

Burns• A third-degree burn is a full-thickness burn (destroys the epidermis, dermis, and subcutaneous layer).• Most skin functions are lost, and the region is numb

because sensory nerve endings have been destroyed.• May be treated by skin grafting

Rule of Nines