CHAPTER 6 The Integumentary System 6-2 Structure of the Skin

CHAPTER 6

The Integumentary System

6-2

Structure of the Skin

The Integumentary System

Overview Largest organ (15% of body weight) Composed of several tissue types (Epithelial,

Connective, Muscle, and Nervous) Maintains homeostasis Protective covering Retards water loss Regulates body temperature Houses sensory receptors Contains immune system cells Synthesizes vitamin D Excretes small amounts of wastes

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Layers of the Skin

• Epidermis• Dermis• Subcutaneous layer

Stratifiedsquamousepithelium

Dense irregularconnectivetissue

Adipose tissue

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Epidermis

Outermost layer Composed mostly of Stratified squamous

epithelia Lacks blood vessels Keratinized Thickest on palms and soles (0.8-1.4mm) Contains 4 distinct cell types and 5 distinct

layers

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Cell and Layers of the Epidermis

Cell Types of the Epidermis

1. Keratinocytes – produce keratin, a fibrous protein that give the epidermis its protective properties.

These cells are tightly connected by desmosomes. They arise from the stratum basale. They undergo continuous mitosis.

Friction may lead to a thickening of the cells known as a callus(corn).


2. Melanocytes – synthesize melanin. Located at the deepest layer of the

epidermis. The melanin is transferred to the

keratocytes. Protects against UV damage.

3. Langerhans’ cells – arise from the bone marrow.

Act as macrophages that activate the immune system.


4. Tactile or Merkel cells – present at the junction of the epidermis and dermis. Associated with sensory receptors.

Layers of the Epidermis

Thick skin (on palms, fingertips, soles) has 5 strata

Thin skin has only 4 strata. The stratum lucidum is absent and the other layers are visibly thinner.

The 5 layers are the:• stratum basale• stratum spinosum • stratum granulosum• stratum lucidum• stratum corneum

Stratum Basale

Deepest layer Attached to the

dermis. Sometimes called

the stratum germinativum because of the constant mitosis that occurs there

Made of a single row of keratinocytes

Stratum Spinosum

Several layers thick Consist mainly of

keratin-like filaments.

Resist tension Melanin granules

and dendritic (Langerhan’s) cells are abundant in this layer

Stratum Granulosum

3 to 5 layers Flat keratinocytes

Contain more keratin and lamellate granules

Stratum Lucidum

Thin layer of dead kertinocytes.

Present only in thick skin

Stratum Corneum

Up to 30 layers of dead, scaly,highly keratinized cells Cell membranes

are thick surface cells flake

off (exfoliate) “Cornified”

The Dermis

Made mostly of connective tissue Richly innervated and vascularized Contains the hair follicles, sweat glands, oil

glands, lymphatic & blood vessels, and many sensory receptors

Consist of 2 layers Papillary layer – heavily vascularized, areolar

connective tissue. Contains the dermal papillae, capillary loops, and Meissner’s corpuscles.

Reticular layer – dense irregular connective tissue

The Subcutaneous or Hypodermis

Superficial fascia – it is composes of areolar connective and adipose tissue.

Functions: Connects the dermis

to the underlying muscles

Protects the underlying structures

Stores fats and provide insulation

Skin Colors (Pigmentation)

Skin color is determined by: Hemoglobin = red pigment of red blood cells Carotene = yellow pigment

concentrates in stratum corneum and fat Melanin = yellow, brown, and black hues

pigment synthesis stimulated by UV radiation

Discolorations of the Skin

Cyanosis – skin appearance is bluish in color.

Erythema – skin appearance is reddish in color.

Pallor – paleness Jaundice - skin appearance is yellowish

in color. Albinism – a genetic lack of melanin Bruises & hematomas

Accessory Organs of the Skin Sweat glands or Sudoriferous – more than

2.5 million per person. Coiled in the dermis, a duct leads to a pore at the skin’s surface

2 types Eccrine sweat glands – most numerous sweat

glands Apocrine sweat glands – in the axillary and anal-

genital areas. Empty into the hair follicles. Contain fatty substances and proteins. May cause body odor. Begin to function at puberty. May contain pheromones. Secretion is thicker and milky.

Accessory Organs of the Skin Ceruminous glands – secrete earwax. Sebaceous glands – oil glands. Found

everywhere except the palms and soles. Secrete sebum, usually into the hair

follicles. Acts as a bactericide An accumulation of sebum causes a pimple.

Skin Appendages

Hair – covers the entire body except for the palms, soles, lips, nipples, and parts of the genitalia.

Mostly dead keratinized cells. Three (3) parts:

Hair shaft Hair follicle Hair root

Hair

Hair shaft – protrudes above the skin Hair follicle - is oblique tube within the

skin Consist of the medulla, cortex, and cuticle

Hair root – Consist of the:

hair bulb Root hair plexus Arector pili Hair papilla

Hair color

Genes that direct the type and amount of pigment produced by epidermal melanocytes determine hair color.

Bright red hair contains an iron pigment (trichosiderin) that does not occur in hair of any other color. Gray hair is the result of a mixture of pigmented and unpigmented hair.

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Hair Growth and Loss Hair cycle = 3 repeating cycles

Anagen is growth stage (90% of scalp follicles) lasts 6-8 years in young adult

Catagen is shrinking follicle (lasts 2-3 weeks) Telogen is resting stage (lasts 1-3 months)

Thinning or baldness = alopecia Pattern baldness = genetic and hormonal

sex-influenced trait(dominant in males, recessive in females); expressed only with high testosterone levels

Hirsutism = excessive hair growth hormone imbalance (ovary or adrenal cortex problem)

Alopecia

Hirsutism

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Functions of Hair

Body hair (too thin to provide warmth) alert us to parasites crawling on skin

Scalp hair heat retention and sunburn cover

Beard, pubic and axillary hair indicate sexual maturity and help distribute sexual scents

Guard hairs and eyelashes prevent foreign objects from getting into

nostrils, ear canals or eyes Expression of emotions with eyebrows

Nails Modification of the

epidermis Composed of densely

packed cells filled with hard keratin

Consist of a free edge, body, and root

Nail bed – skin where the nail plate rests

Nail matrix – growth occurs here

Nail bed Nail plateLunula

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Lunula – the whitish, half-moon region located at the base of the nail plate

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Fingernail Structure

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Skin Cancer Induced by UV rays of the sun

Basal cell carcinoma (least dangerous) arises from stratum basale and invades dermis

Squamous cell carcinoma arises from keratinocytes in stratum spinosum metastasis to the lymph nodes can be lethal

Malignant melanoma (most deadly) arises from melanocytes of a preexisting mole ABCD rule - asymmetry, border irregular, color and

diameter over 6 mm

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Burns

Can be caused by hot water, sunlight, radiation, electric shock or acids and bases

Denaturation of cell proteins Dehydration, protein loss, and infection can occur Degrees of burns

1st-degree = only the epidermis (red, painful and edema)

2nd-degree = epidermis and part of dermis (blistered) epidermis regenerates from hair follicles and sweat glands

3rd-degree = epidermis, dermis and more is destroyed often requires grafts or fibrosis and disfigurement may occur

Treatment – IV nutrition and fluid replacement, debridement and infection control

Burns

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Skin Grafts and Artificial Skin

Third-degree burns require skin grafts Graft options

autograft -- tissue from the patient isograft -- tissue from identical twin cultured keratinocyte patches

Temporary grafts (immune system) homograft (allograft) -- from unrelated person heterograft (xenograft) -- from another species amnion from afterbirth artificial skin from silicone and collagen

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CHAPTER 6 The Integumentary System 6-2 Structure of the Skin