Skin and Body Membranes

Skin and Body Membranes
Introduction to the Integument

  • What: The integument includes body membranes, skin, hair, fingernails, and sweat and oil glands.

  • Why: The skin provides the first barrier, maintaining water retention and preventing harmful bacteria from entering.

  • How: Skin comprises multiple layers that protect the body, regulate temperature, and excrete waste through sweat.

Body Membranes

  • Body membranes cover surfaces, line body cavities, and form protective sheets around organs.

  • Classified into two major groups:

      1. Epithelial membranes (cutaneous, mucous, serous)

      2. Connective tissue membranes (synovial membranes)

4.1 Classification of Body Membranes
Learning Objectives

  • List general functions and locations of membrane types: cutaneous, mucous, serous, synovial.

  • Compare structures of major membrane types.

Epithelial Membranes

  1. Epithelial membranes (also termed covering and lining membranes): includes the cutaneous membrane (skin), mucous membranes, and serous membranes.

      - Contain an epithelial layer and an underlying layer of connective tissue, making them simple organs.

Cutaneous Membrane

  • Composed of:

      - Epidermis: Stratified squamous epithelium.

      - Dermis: Dense irregular connective tissue.

  • Characteristics: Exposed to air and classified as a dry membrane.

  • Function: Protects underlying tissues and prevents water loss.

Mucous Membranes

  • Composed of epithelium (varies with location) resting on loose (areolar) connective tissue (lamina propria).

  • Lines body cavities open to exterior (respiratory, digestive, urinary, reproductive).

  • Function: Adapted for absorption or secretion with moisture from secretions (like mucus).

Serous Membranes

  • Composed of simple squamous epithelium on a thin layer of areolar connective tissue.

  • Lines compartments in the ventral body cavity closed to exterior, occurring in pairs:

      - Parietal layer: Lines cavity walls.

      - Visceral layer: Covers organ surfaces.

  • Function: Provides lubrication to reduce friction between organs.

Synovial Membranes

  • Composed purely of loose areolar connective tissue, no epithelial cells.

     - Function: Line fibrous capsules around joints and small connective tissue sacs (bursae, tendon sheaths).

4.2 The Integumentary System (Skin)
Learning Objectives

  • List functions of the integumentary system and how they are accomplished.

  • Recognize skin structures on models/diagrams: epidermis, dermis (papillary/reticular layers), hair/fair follicle, sebaceous gland, sweat gland.

  • Name layers of epidermis and describe characteristics.

  • Explain what factors determine skin color and the function of melanin.

  • Describe the functions of sebaceous glands, sweat glands, hair, and nails.

  • Compare and contrast each of the four classification levels of burns.

  • Explain the importance of the "rules of nines."

  • Describe skin cancers: basal cell carcinoma, squamous cell carcinoma, and malignant melanoma.

  • Identify infectious and allergic conditions: cold sores, impetigo, psoriasis, contact dermatitis, athlete’s foot, and boils and carbuncles.

Functions of the Integumentary System

  • Also called the integument, meaning "covering."

  • Performs various functions, primarily protective:

      - Insulates and cushions organs.

      - Protects against mechanical (bumps/cuts), chemical (acids/bases), thermal (heat/cold), UV radiation, and microbes.

      - Prevents water loss from surface due to hardened upper layer.

      - Vital for body temperature regulation (via capillary networks and sweat glands).

      - Acts as a mini-excretory system (excreting urea, salts, water via sweat).

      - Synthesize vitamin D (modified cholesterol converts to vitamin D upon sunlight exposure).

      - Produces acidic secretions (acid mantle) for bacterial invasion prevention.

Structure of the Skin

  • Epidermis: Made of stratified squamous epithelium; avascular (no direct blood supply).

  • Dermis: Mostly dense irregular connective tissue, strong and stretchy.

  • Subcutaneous tissue (hypodermis): Adipose tissue, not part of skin but anchors it to underlying organs, providing shock absorption and insulation.

Epidermal Layers

  • Composed of 5 strata:

      1. Stratum Basale: Closest to dermis, vital for cell division, contains stem cells; also called stratum germinativum.

      2. Stratum Spinosum: Cells contain pre-keratin bundles.

      3. Stratum Granulosum: Cell’s organelles deteriorating; cytoplasm full of granules.

      4. Stratum Lucidum: Clear layer found only in thick skin (palms/soles).

      5. Stratum Corneum: 20-30 layers thick, keratin-filled dead cells (cornified). Provides durable protection.

Skin Color

  • Factors contributing to skin color:

      - Melanin: Type and amount influence color (ranges from yellow to black); produced by melanocytes.

      - Carotene: Yellow-orange pigment in stratum corneum.

      - Hemoglobin: Oxygen-rich in blood; visible through skin layers.

Skin Appendages

  • Includes cutaneous glands (sebaceous and sweat), hair, and nails.

  • Sebaceous Glands: Produce sebum for skin and hair lubrication, active during adolescence.

  • Sweat Glands: Two types:

      - Eccrine: Most common, regulates temperature, produces water and salts.

      - Apocrine: Located in axillary/genital areas with fatty acids and proteins, involved in stress response.

Homeostatic Imbalances of Skin

  • Common skin disorders:
      - Infections: Athlete's foot (fungal), boils, cold sores (viral), impetigo (bacterial).

      - Psoriasis: Autoimmune disease resulting in rapid skin cell production.

      - Burn Types:

      - First Degree: Only epidermis affected (redness).

      - Second Degree: Epidermis and part of dermis (blistering).

      - Third Degree: Destroys both layers, affecting deeper tissues, often feels pain due to nerve endings.

      - Skin Cancer Types: Basal cell carcinoma, squamous cell carcinoma, malignant melanoma.

Rules of Nines

  • The "rules of nines" is a method used to assess the percentage of burned body surface area: each major region of the body accounts for approximately 9% or a multiple thereof. This is key for guiding treatment decisions.