Body Membranes

Overview and Functions

Body membranes are essential structures that cover body surfaces, line body cavities, and form protective sheets around organs. Their primary functions include:

• Protection: Prevent drying out and mechanical damage.

• Compartmentalization: Line body cavities and separate organs.

Classification of Body Membranes

• Epithelial Membranes: Composed of epithelial tissue and underlying connective tissue. Types include:

  • Cutaneous Membrane: The skin; dry, superficial, and composed of keratinized stratified squamous epithelium. Provides a thick layer of protection.

  • Mucous Membranes: Line body cavities open to the exterior (e.g., digestive, respiratory, urinary tracts). Surface epithelium varies by site (stratified squamous in mouth/esophagus, simple columnar in digestive tract). Underlying layer is loose connective tissue (lamina propria).

  • Serous Membranes: Line body cavities closed to the exterior (e.g., thoracic, abdominal cavities). Composed of simple squamous epithelium and areolar connective tissue. Secrete serous fluid for lubrication. Layers include parietal (lines cavity wall) and visceral (covers organ).

• Connective Tissue Membranes: Include synovial membranes, which provide fibrous capsules around joints and secrete synovial fluid for lubrication.

Integumentary System

Structure and Functions

The integumentary system consists of the skin (cutaneous membrane) and its derivatives, including sweat glands, oil glands, hair, and nails. Its main functions are:

• Protection: Against mechanical, chemical, bacterial, and UV damage.

• Thermoregulation: Regulates body temperature via sweat and blood flow.

• Excretion: Removes urea and uric acid.

• Sensation: Detects environmental stimuli through nerve endings.

Layers of the Skin

• Epidermis: Superficial layer, composed of keratinized stratified squamous epithelium. Contains keratinocytes and melanocytes.

• Dermis: Deep layer, primarily dense connective tissue. Highly vascularized and provides nutrients to the epidermis.

• Hypodermis (Subcutaneous Tissue): Not technically part of the skin; anchors skin to underlying organs and acts as insulation and shock absorber.

Layers of the Epidermis (Deep to Superficial)

Stratum Basale (Stratum Germinativum)

• Deepest layer; single row of germinating skin cells.

• Cells actively divide and receive nutrients from the dermis.

Stratum Spinosum (Spiny Layer)

• Where keratinization begins.

• Contains layers of cells with pre-keratin filaments.

Stratum Granulosum (Granular Layer)

• Cells begin to die; abundant granules present.

• Granules help waterproof the skin.

Stratum Lucidum (Clear Layer)

• Only in thick skin (palms, soles).

• Thin, translucent band of dead keratinocytes.

Stratum Corneum

• Outermost layer; 20-30 layers of dead, flattened keratinocytes.

• Provides waterproof barrier and is constantly shed and replaced.

Specialized Epidermal Cells

• Melanocytes: Produce melanin pigment, which protects against UV damage. Color ranges from yellow to brown to black.

• Merkel Cells: Associated with touch receptors.

• Epidermal Dendritic Cells: Part of the immune system; monitor for pathogens and trigger immune responses.

Dermis

Layers of the Dermis

• Papillary Layer: Upper dermal region; contains dermal papillae that form fingerprints and house touch receptors.

• Reticular Layer: Deepest skin layer; contains blood vessels, sweat and oil glands, and deep pressure receptors.

Overall Dermis Structure

• Collagen fibers provide toughness.

• Elastic fibers provide elasticity.

• Blood vessels regulate temperature.

Normal Skin Color Determinants

• Melanin: Yellow, brown, or black pigment.

• Carotene: Orange-yellow pigment from vegetables.

• Hemoglobin: Red coloring from blood cells and capillaries.

Alterations in Skin Color

• Erythema: Redness due to embarrassment, inflammation, hypertension, fever, or allergy.

• Pallor: Blanching due to emotional stress, anemia, low blood pressure.

• Jaundice: Yellowing due to liver disorder.

• Bruises: Black/blue marks due to mechanical trauma.

Skin Appendages

Cutaneous Glands

• Sebaceous (Oil) Glands: Produce sebum; lubricates skin and hair, inhibits bacteria.

• Sudoriferous (Sweat) Glands: Produce sweat for temperature regulation. Two types:

  • Eccrine: Most common; clear, mostly water and salt; ducts open on skin surface.

  • Apocrine: Found in axillary/genital areas; secretion contains fatty acids and proteins; ducts empty into hair follicles.

Hair

• Produced by hair follicles; consists of hard keratinized epithelial cells.

• Color determined by melanocytes in the hair bulb.

• Structure includes central medulla, cortex, and cuticle.

Hair Follicles

• Dermal and epidermal sheath surround the hair root.

• Arrector pili muscle causes hair to stand upright when cold or frightened.

Nails

• Scale-like modifications of the epidermis; heavily keratinized.

• Structure includes free edge, body, root, and cuticle.

Skin Homeostatic Imbalances

Burns

• First Degree: Only epidermis is damaged; skin is red and swollen.

• Second Degree: Epidermis and upper dermis are damaged; skin is red with blisters.

• Third Degree: Entire skin layer destroyed; burned area is painless, regeneration not possible; skin appears gray-white or black.

• Critical burns: Over 25% of body has second degree burns, over 10% has third degree burns, or third degree burns on face.

Infections

• Athlete's foot: Fungal infection.

• Boils and carbuncles: Bacterial infection.

• Cold sores: Viral infection.

Allergies and Other Disorders

• Contact dermatitis: Itching, redness, swelling due to exposure.

• Impetigo: Bacterial infection, common in children.

• Psoriasis: Autoimmune disorder; triggered by stress, infection, trauma.

Skin Cancer

Types of Skin Cancer

• Basal Cell Carcinoma: Least malignant, most common, arises from stratum basale, easy to remove.

• Squamous Cell Carcinoma: Arises from stratum spinosum, metastasizes to lymph nodes if not removed, believed to be sun-induced.

• Malignant Melanoma: Most deadly, cancer of melanocytes, metastasizes quickly, often found on hands or feet.

ABCD Rule for Melanoma Detection

• A: Asymmetry – Two sides of pigmented mole do not match.

• B: Border Irregularity – Borders are not smooth.

• C: Color – Different colors in pigmented area.

• D: Diameter – Spot is larger than 6 mm.

• E: Elevation – Sometimes present.

Additional info: The notes have been expanded to include definitions, examples, and academic context for each topic. Tables have been recreated for membrane types and burn severity. All key terms are bolded, and scientific names are italicized where relevant.