The Integumentary System Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

The Integumentary System

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Structure of the Skin

o Also called the cutaneous membrane or the integument

o Covers the entire surface of the body

o Largest organ in the bodyo Comprised of all 4 tissue typeso The integumentary system is

made up of the skin and several accessory organs

Structure of the Skin

o Regions of the Skin• Epidermis

Outer, thinner region Made of stratified squamous epithelium Five layers (strata)

Stratum Basale Stratum Spinosum Stratum Granulosum Stratum Lucidum Stratum Corneum

Structure of the Skin

o Stratum Basale• Just superior to dermis• Constantly dividing and new cells are

pushed to the surface• As cells move toward the surface of the

epidermis, they die and are sloughed off• Cells

Langerhans cells – macrophages Melanocytes – produce melanin

Skin color Protection from UV radiation

• Sensory nerves Free nerve endings – pain and temperature

sensations Tactile cells (Merkel cells) – touch sensations

Structure of the Skin

o Stratum Lucidum• Just deep to stratum corneum• Found only in thick skin• Provides protection from constant friction

o Stratum Corneum• Tough, uppermost layer of epidermis• Cells are keratinized (hardened)• Keratin prevents water loss and water gain• Serves as a mechanical barrier against

microbes

Structure of the Skin

• Dermis Thicker than epidermis Made of dense, irregular connective tissue Dermal papillae Collagenous fibers prevent skin from

being torn Elastic fibers stretch to allow movement

of muscles and joints Vascularization of dermis supplies oxygen

and nutrients to cells of dermis and epidermis

Numerous sensory nerve fibers

Structure of the Skin

• Hypodermis Subcutaneous layer located below the

dermis Composed of loose connective tissue Energy storage Insulation

Accessory Structures of the Skin

o Hair• On all body parts except the palms, soles,

lips, nipples, and portions of the external reproductive organs

• After puberty there is noticeable hair in the axillary and pelvic regions

• Hirsutism – characterized by excessive body and facial hair in women due to increased production of male sex hormone

• Alopecia – hair loss Androgenic alopecia – male pattern baldness Alopecia areata – sudden onset of patchy hair loss

Accessory Structures of the Skin

• Hair follicles Formed from epidermal

cells Located in dermis Cells become keratinized

as they are pushed out Hair root – portion of hair

within follicle Hair shaft – portion of hair

that continues beyond the skin

• Sebaceous (oil) glands• Arrector pili muscle –

smooth muscle attached to hair follicle

Accessory Structures of the Skin

o Nails• Formed from

specialized epithelial cells

• Nail root – base of the nail

• Nail body – visible portion of the nail

• Cuticles – fold of skin that hides the root

• Epithelial cells become keratinized as they move away from the root

Accessory Structures of the Skin

o Glands – specialized cells that produce and secrete substances into ducts• Sweat glands• Sebaceous glands

Accessory Structures of the Skin

• Sweat (sudoriferous) glands – active under stress

Apocrine glands Open into hair follicles in anal region, groin, and

armpits Begin to secrete at puberty Mammary glands are modified apocrine glands

Eccrine sweat glands Open onto surface of skin Active when body heats up; helps lower body

temperature Sweat (perspiration) is mostly water, but also

excretes wastes Ceruminous glands – modified sweat

glands that produce cerumen (earwax)

Accessory Structures of the Skin

• Sebaceous glands Most are associated with a hair follicle Secrete an oily substance called sebum

Lubricates and waterproofs hair and skin Weakens or kills bacteria on skin surface

If sebum collects, whiteheads or blackheads form

Acne vulgaris – inflammation of the sebaceous glands

Disorders of the Skin

o Athlete’s foot – fungal infection often involving skin of the toes and soles

o Impetigo – bacterial infection common in young children

o Psoriasis – chronic condition where skin develops pink or reddish patches

o Eczema – inflammation of the skino Dandruff – caused by a dry scalp

producing flaking and itchingo Urticaria (hives) – allergic reaction

causing reddish, elevated, and often itchy patches

Disorders of the Skin

o Skin Cancer• Begins with mutation of the skin cell

DNA• Nonmelanoma cancers – less likely to

metastasize Basal cell carcinoma Squamous cell carcinoma

• Melanoma cancers

Disorders of the Skin

• Basal cell carcinoma Most common type of skin

cancer Ultraviolet (UV) radiation

causes epidermal basal cells to form a tumor

Signs are varied Open sore that will not

heal Recurring reddish patch Smooth, circular growth

with a raised edge Shiny bump Pale mark

95% of patients are easily cured by removal

Disorders of the Skin

• Squamous cell carcinoma Five times less common

than basal cell carcinoma More likely to spread than

basal cell carcinoma About 1% of cases result in

death Triggered by excessive UV

exposure Signs are the same as

those for basal cell carcinoma, but may also resemble a wart or scaly growth that bleeds and scabs

Disorders of the Skin

• Melanoma More likely to be malignant Starts in the melanocytes Has the appearance of an

unusual mole Warning signs

Asymmetry Irregular borders Uneven color Diameter greater than

6mm Most common in fair-

skinned persons

Disorders of the Skin

o Wound Healing• Causes an inflammatory response• Steps in wound healing

A blood clot forms White blood cells and fibroblasts move to

the injured area Fibroblasts pull the margins of the wound

together and promote tissue regeneration The basal layer of the epidermis produces

new cells Proliferating fibroblasts form a scar

Disorders of the Skin

Disorders of the Skin

o Burns• Usually caused by heat• Burn severity affected by:

Extent of the burned area “Rule of nines” is a technique used to estimate

the extent of a burn Lund-Browder chart is used for children

Disorders of the Skin

Depth of the burn First degree burn

­ Only epidermis affected­ Redness and pain­ No blisters or swelling occurs

Second degree burn­ Extends through entire epidermis and part of the

dermis­ Redness, pain, and blistering

Third degree burn­ Destroys entire thickness of the skin­ Surface of wound is leathery and may be brown,

tan, black, white, or red­ Patient feels no pain

Fourth degree burn – involve tissues down to the bone

Disorders of the Skin

• Burns are considered a critical injury if: Second-degree burns cover 25% or more of the

patient’s body Third-degree burns cover 10% or more of the

patient’s body Any portion of the body has a fourth-degree burn Third-degree burns occur on the face, hands, or

feet• Major concerns associated with severe

burns: Fluid loss Heat loss Bacterial infection

Effects of Aging

o Rate of cell mitosis decreaseso Dermis becomes thinner and the dermal

papillae flatteno Adipose tissue in the hypodermis decreaseso Collagen decreaseso Elastic fibers in upper layer of dermis are lost

and those in the lower layer become thicker, less elastic, and disorganized

o Wrinkles form because of:• Loose epidermis• Fewer fibers• Less padding in hypodermis

Effects of Aging

o Limited homeostatic adjustment to heat because of:

• Less vasculature (fewer blood vessels)• Fewer sweat glands

o Number of hair follicles decreaseso Reduced number of sebaceous

glandso Number of melanocytes decrease

Homeostasis

o Functions of the Skin• Protection

Safeguards from physical trauma Protection from UV radiation Help prevent bacterial invasion

Sebum is acidic, which retards growth of bacteria

Langerhans cells phagocytize pathogens and alert the immune system to the presence of pathogens

Homeostasis

• Regulation of water loss Keratinized cells prevent water from

entering the body Water is excreted through perspiration

• Vitamin D production Useful to digestive and skeletal systems Small amounts of UV radiation are needed Vitamin D leaves the skin and enters the

liver and kidneys

Homeostasis

• Gathers sensory information Sensory receptors in the epidermis and

dermis are specialized for touch, pressure, pain, hot, and cold

Receptors supply the central nervous system with information about the external environment

Homeostasis

• Helps regulate body temperature If body temperature rises, blood vessels in

the skin dilate and sweat glands become active

If the outer temperature is cool, blood vessels constrict

Arrector pili muscles contract, but insulating effect is absent in humans

Hyperthermia - body temperature above normal

Hypothermia – body temperature below normal