Integumentary System

Skin and Body Membranes

Body Membranes

Function of body membranes
Cover body surfaces
Line body cavities
Form protective sheets around organs
Classified according to tissue types

Classification of Body Membranes
Epithelial membranes
Cutaneous membranes
Mucous membranes
Serous membranes
Connective tissue membranes
Synovial membranes

Cutaneous Membrane
Cutaneous membrane = skin
Dry membrane
Outermost protective boundary
Superficial epidermis is composed of keratinized stratified squamous epithelium
Underlying dermis is mostly dense connective tissue

Mucous Membranes
Surface epithelium type depends on site
Stratified squamous epithelium (mouth, esophagus)
Simple columnar epithelium (rest of digestive tract)
Underlying loose connective tissue (lamina propria)
Lines all body cavities that open to the exterior body surface
Often adapted for absorption or secretion

Serous Membranes
Surface is a layer of simple squamous epithelium
Underlying layer is a thin layer of areolar connective tissue
Lines open body cavities that are closed to the exterior of the body
Serous membranes occur in pairs separated by serous fluid
Visceral layer covers the outside of the organ
Parietal layer lines a portion of the wall of ventral body cavity

Specific serous membranes
Abdominal cavity
Around the lungs
Around the heart

Connective Tissue Membrane
Synovial membrane
Connective tissue only
Lines fibrous capsules surrounding joints
Secretes a lubricating fluid

Integumentary System
Skin (cutaneous membrane)
Skin derivatives
Sweat glands
Oil glands

Skin Structure
Epidermis—outer layer
Stratified squamous epithelium
Cornified or keratinized (hardened by keratin) to prevent water loss
Most cells are keratinocytes

Dense connective tissue

Subcutaneous tissue (hypodermis) is deep to dermis
Not technically part of the skin
Anchors skin to underlying organs
Composed mostly of adipose tissue

Layers of the Epidermis
Stratum basale (stratum germinativum)
Deepest layer of epidermis
Lies next to dermis 
Wavy borderline with the dermis anchors the two together
Cells undergoing mitosis
Daughter cells are pushed upward to become the more superficial layers

Stratum spinosum

Stratum granulosum

Stratum lucidum
Formed from dead cells of the deeper strata
Occurs only in thick, hairless skin of the palms of hands and soles of feet

Stratum corneum
Outermost layer of epidermis
Shingle-like dead cells are filled with keratin (protective protein prevents water loss from skin)

Summary of layers from deepest to most superficial
Stratum basale
Stratum spinosum
Stratum granulosum
Stratum lucidum (thick, hairless skin only)
Stratum corneum

Pigment (melanin) produced by melanocytes
Melanocytes are mostly in the stratum basale
Color is yellow to brown to black
Amount of melanin produced depends upon genetics and exposure to sunlight

Two layers
Papillary layer (upper dermal region)
Projections called dermal papillae 
Some contain capillary loops
Others house pain receptors and touch receptors
Reticular layer (deepest skin layer)
Blood vessels
Sweat and oil glands
Deep pressure receptors

Overall dermis structure
Collagen and elastic fibers located throughout the dermis
Collagen fibers give skin its toughness
Elastic fibers give skin elasticity
Blood vessels play a role in body temperature regulation

Normal Skin Color Determinants
Yellow, brown, or black pigments
Orange-yellow pigment from some vegetables
Red coloring from blood cells in dermal capillaries
Oxygen content determines the extent of red coloring

Alterations in Skin Color
Redness (erythema)—due to embarrassment, inflammation, hypertension, fever, or allergy
Pallor (blanching)—due to emotional stress such as fear, anemia, low blood pressure, impaired blood flow to an area
Jaundice (yellowing)—liver disorder

Skin Appendages
Cutaneous glands are all exocrine glands
Sebaceous glands
Sweat glands
Hair follicles

Appendages of the Skin
Oil (sebaceous) glands
Produce oil (sebum)
Lubricant for skin
Prevents brittle hair
Kills bacteria
Most have ducts that empty into hair follicles; others open directly onto skin surface
Glands are activated at puberty

Sweat (sudoriferous) glands
Produce sweat 
Widely distributed in skin

Two types of sudoriferous glands
Open via duct to pore on skin surface
Produce sweat (clear)

Ducts empty into hair follicles
Begin to function at puberty
Release sweat that also contains fatty acids and proteins (milky/yellowish color)

Sweat and Its Function
Mostly water
Salts and vitamin C
Some metabolic waste
Fatty acids and proteins (apocrine only)
Helps dissipate excess heat
Excretes waste products
Acidic nature inhibits bacteria growth
Odor is from associated bacteria

Produced by hair follicle
Consists of hard keratinized epithelial cells
Melanocytes provide pigment for hair color
Hair grows in the matrix of the hair bulb in stratum basale

Hair anatomy
Central medulla
Cortex surrounds medulla
Cuticle on outside of cortex
Most heavily keratinized

Associated hair structures 
Hair follicle
Dermal and epidermal sheath surround hair root
Arrector pili muscle 
Smooth muscle
Pulls hairs upright when cold or frightened
Sebaceous gland
Sudoriferous gland

Scale-like modifications of the epidermis
Heavily keratinized
Stratum basale extends beneath the nail bed
Responsible for growth
Lack of pigment makes them colorless

Nail structures
Free edge
Body is the visible attached portion
Root of nail embedded in skin
Cuticle is the proximal nail fold that projects onto the nail body

Skin Homeostatic Imbalances
Tissue damage and cell death caused by heat, electricity, UV radiation, or chemicals
Associated dangers
Electrolyte imbalance
Circulatory shock

Rule of Nines
Way to determine the extent of burns
Body is divided into 11 areas for quick estimation
Each area represents about 9 percent of total body surface area

Severity of Burns

First-degree burns
Only epidermis is damaged
Skin is red and swollen

Second-degree burns
Epidermis and upper dermis are damaged
Skin is red with blisters

Third-degree burns
Destroys entire skin layer; burned area is painless
Burn is gray-white or black

Critical Burns
Burns are considered critical if
Over 25 percent of body has second-degree burns
Over 10 percent of the body has third-degree burns
There are third-degree burns of the face, hands, or feet

Skin Homeostatic Imbalances
Athlete’s foot (tinea pedis)
Caused by fungal infection
Boils and carbuncles
Caused by bacterial infection
Cold sores
Caused by virus

Infections and allergies
Contact dermatitis
Exposures cause allergic reaction
Caused by bacterial infection
Cause is unknown
Triggered by trauma, infection, stress

Skin Cancer
Cancer—abnormal cell mass

Classified two ways
Does not spread (encapsulated)

Metastasized (moves) to other parts of the body
Skin cancer is the most common type of cancer

Skin Cancer Types
Basal cell carcinoma
Least malignant
Most common type
Arises from stratum basale

Squamous cell carcinoma
Metastasizes to lymph nodes if not removed
Early removal allows a good chance of cure
Believed to be sun-induced
Arises from stratum spinosum 

Malignant melanoma
Most deadly of skin cancers
Cancer of melanocytes
Metastasizes rapidly to lymph and blood vessels
Detection uses ABCD rule

A = Asymmetry
Two sides of pigmented mole do not match
B = Border irregularity
Borders of mole are not smooth
C = Color
Different colors in pigmented area
D = Diameter
Spot is larger then 6 mm in diameter