Body Membranes: Types and Functions

• Body membranes cover body surfaces, line cavities, and form protective sheets, classified by tissue type
• Epithelial membranes include cutaneous (skin), mucous, and serous membranes
• Connective tissue membranes include synovial membranes

Cutaneous Membrane

• This is the skin, providing dry outermost protection
• The superficial epidermis is made of keratinized stratified squamous epithelium
• The underlying dermis is dense connective tissue

Mucous Membrane

• Epithelial type varies by location (stratified squamous in mouth and esophagus, simple columnar elsewhere)
• Underlying loose connective tissue called lamina propria
• Lines all body cavities open to the body's exterior, facilitating absorption and secretion

Serous Membrane

• Features a surface layer of simple squamous epithelium with a thin areolar connective tissue layer
• Lines body cavities closed to the exterior, minimizing friction
• Exists in pairs separated by serous fluid
• The visceral layer covers the organ's outside, and the parietal layer lines the ventral body cavity wall
• Peritoneum lines the abdominal cavity, pleura lines the lungs, and pericardium lines the heart
• Edema results from fluid buildup, absorbed by areolar tissue

Synovial Membrane

• Composed of connective tissue alone, lining fibrous joint capsules and secreting lubricating fluid
• Found in movable joints
• Hyaline cartilage covers bone ends, and synovial fluid lubricates the joint

Integumentary System

• Includes skin (cutaneous membrane) and derivatives like sweat/oil glands, hair, and nails
• Key functions are to protect deeper tissues from mechanical, chemical, bacterial, thermal, and UV damage
• Also prevents desiccation and aids in body heat regulation
• Plays a role in waste excretion (urea and uric acids) and synthesizes vitamin D

Epidermis

• The outer layer, made of stratified squamous epithelium
• It is cornified/keratinized for water loss prevention and avascular
• Most cells are keratinocytes

Dermis

• Composed of dense connective tissue

Subcutaneous Tissue (Hypodermis)

• Located deep to the dermis
• Not technically part of skin, anchors skin to underlying organs and is composed of mostly adipose tissue

Layers of Epidermis

• Stratum basale (deepest): wavy border anchors it to the dermis, cells undergo mitosis
• Daughter cells are pushed superficially
• Stratum spinosum
• Stratum granulosum
• Stratum lucidum: formed from dead cells, only in thick, hairless skin (calluses)
• Stratum corneum: outermost layer, shingle-like dead cells filled with keratin (prevents water loss)

Melanin

• Pigment produced by melanocytes, mostly in the stratum basale
• Color ranges from yellow to brown to black, depending on genetics and sun exposure

Dermis

• Consists of papillary and reticular layers
• The papillary layer is the upper dermal region with dermal papillae, some containing capillary loops and others with pain/touch receptors
• The reticular layer is the deepest, containing blood vessels, sweat/oil glands, and deep pressure receptors
• Overall structure contains collagen (toughness) and elastic fibers (elasticity)

Blood Vessels

• Play a role in body temperature regulation
• Meissner corpuscles are light touch receptors, while Pacinian/lamellar corpuscles sense pressure

Normal Skin Color Determinants

• Melanin: yellow, brown, black pigment
• Carotene: orange-yellow pigment from some vegetables
• Hemoglobin: red coloring from blood cells in dermal capillaries, oxygen content determines color

Alterations in Skin Color

• Redness (erythema): indicates embarrassment, inflammation, hypertension, fever, or allergy
• Pallor (blanching): Indicates emotional stress, anemia, low blood pressure, or impaired blood flow
• Jaundice (yellow): Indicates liver disorder
• Bruises/hematomas appear
• Black: from necrosis, i.e. frost bite. Blue: from cyanosis

Skin Appendages

• Cutaneous glands are exocrine glands (ducts/tubes), including sebaceous (oil) and sweat glands
• Hair, hair follicles, and nails

Oil (Sebaceous) Glands

• Produce sebum to prevent brittle hair and kill bacteria
• Most ducts empty into hair follicles, some open directly to skin surface
• Activated at puberty

Sweat (Sudoriferous) Glands

• Widely distributed and produce sweat
• Eccrine glands open via ducts to skin surface, producing clear sweat
• Apocrine glands empty into hair follicles, begin at puberty, and release sweat with fatty acids/proteins (milky/yellowish)
• Sweat composition: mostly water, salts, vitamin C, some metabolic waste, and fatty acids/proteins (apocrine)
• Functions: dissipate excess heat, excrete wastes, acidic nature inhibits bacteria growth

Hair

• Produced by hair follicle from hard, keratinized epithelial cells; melanocytes provide pigment
• Grows from the hair bulb matrix in stratum basale
• Hair anatomy: central medulla, cortex surrounds medulla, cuticle on outside of cortex (most heavily keratinized)
• Associated structures: hair follicle, arrector pili muscle (smooth muscle, pulls hair upright when cold/frightened), and sebaceous/sudoriferous glands

Nails

• Scale-like modifications of epidermis, heavily keratinized, stratum basale extends beneath nail bed (growth), lack of pigment

Skin Homeostatic Imbalances

• Burns: tissue damage/cell death from heat, electricity, UV radiation, or chemicals resulting in dangerous dehydration, electrolyte imbalance, and circulatory sock

Rule of Nines

• Determines burn extent by dividing the body into 11 areas for quick estimation
• Head an neck are 9%, each arm is 9%, each leg is 18%. Anterior and posterior torso are 18%, perineum is 1%

Burn Degrees

• First-degree burns: only epidermis damaged, red and swollen
• Second-degree burns: epidermis and upper dermis damaged, red with blisters
• Third-degree burns: destroy entire skin, burned areas are painless due to nerve damage, appear gray-white or black

Critical Burns

• Over 25% of body has second-degree burns
• Over 10% has third-degree burns
• Third-degree burns of the face, hands, or feet
• Infection is the primary complication due to broken stratified squamous epithelium

Infections

• Athlete's foot (tinea/fungal pedis): caused by fungal infection (fungicide)
• Boils & carbuncles (pimples): caused by bacterial infection (antibiotic)
• Cold sores: caused by virus, antiviral stops replication, doesn't kill virus, leads to tiredness
• Shingles: travels in dermatomes

Infections & Allergies

• Contact dermatitis: exposures lead to allergic reaction
• Impetigo: bacterial skin infection causes red, small blisters
• Psoriasis: triggered by trauma, infection, stress, involves immune system attacking itself

Cancer

• Abnormal cell mass (-oma)
• Benign tumors expand but do not spread (encapsulated)
• Malignant tumors metastasize (move) through blood/lymph nodes

Skin Cancer

• Most common type of cancer
• Basal cell carcinoma: least malignant, most common, arises in stratum basale
• Squamous cell carcinoma: metastasizes, sun-induced, arises in stratum spinosum
• Malignant melanoma: most deadly, cancer of melanocytes, detected with ABCDE rule; Asymmetry, Border irregularity, Color (different), Diameter, Evolution