CHPT 7

Skin and Membranes

Chapter Overview

• Focus: Skin structure, function, and body membranes.

• Learning objectives include classification and description of body membranes, skin structure, and accessory organs of the skin.

Classification of Body Membranes

Types of Body Membranes

Epithelial Membranes

• Composed of epithelial tissue and an underlying layer of connective tissue.

• Types include:

  • Mucous Membranes: Line body surfaces that open to the exterior, produce mucus to maintain moisture.

  • Cutaneous Membrane (Skin): Covers the body’s surface.

  • Serous Membranes: Simple squamous epithelium on connective tissue, lining body cavities (parietal and visceral layers).

Serous Membranes Examples

• Pleura: Line thoracic cavity and cover lungs.

• Peritoneum: Line abdominal cavity and cover its organs.

Connective Tissue Membranes

• Composed solely of connective tissues.

• Example: Synovial membranes in joint cavities produce synovial fluid, lubricating joints.

Skin Structure

Overview

• Skin consists of two primary layers: Epidermis and Dermis.

Epidermis

• Thinnest layer, composed of stratified squamous epithelium.

• Stratum Germinativum: Deepest layer with cells that continuously reproduce.

  • Contains melanocytes that produce melanin (skin pigment).

• Stratum Corneum: Outermost layer filled with keratin; provides waterproofing and protection.

Dermis

• Thicker, deeper layer predominantly made of connective tissue.

• Contains:

  • Dermal Papillae: Projections that improve nutrient exchange and grip.

  • Various structures including nerve endings, blood vessels, hair follicles, and glands (sweat and sebaceous).

• Changes with age: Decrease in elastic fibers leads to wrinkles.

• Birthmarks: Resulting from malformation of dermal blood vessels.

Skin Appendages

Hair

• Growth occurs from the hair follicle, with visible hair (shaft) above skin.

• Alopecia: Hair loss condition.

• Arrector Pili Muscle: Causes hair to stand up (goosebumps).

Nails

• Composed of hard keratin.

• Structure includes nail body, root (hidden by cuticle), and lunula (crescent at base).

• Changes in nail color or texture can indicate health issues.

Functions of the Skin

Primary Functions

1. Protection: First defense against pathogens, UV rays, chemicals, cuts.

2. Temperature Regulation: Regulates sweat secretion and blood flow.

3. Sensation: Detects touch, pressure, pain, and temperature changes.

4. Excretion: Removes waste products via sweat.

5. Synthesis of Vitamin D: Converts sunlight into usable vitamin D.

Skin Disorders

Common Categories

• Lesions: Variations from normal skin structures that can be elevated (e.g., papules, vesicles) or flat (e.g., macules).

• Inflammatory Conditions: Include psoriasis and eczema, which often present with rashes.

• Skin Infections: Examples include impetigo (bacterial) and tinea (fungal).

• Skin Cancer Types:

  • Squamous Cell Carcinoma: Often presents as raised tumors.

  • Basal Cell Carcinoma: Presents as papules; rarely metastasizes.

  • Melanoma: Most serious skin cancer, affects melanocytes.

Burns Classification

1. First-Degree Burns: Affect only the epidermis (surface).

2. Second-Degree Burns: Affect epidermis and part of dermis.

3. Third-Degree Burns: Extend through dermis, destroying all layers; may damage muscle/bone.

Conclusion

• Understanding skin and membranes is crucial for recognizing their functions, structure, and related disorders.

• Knowledge of classifications and disorders aids in effective diagnosis and treatment.