Epithelial Tissue

Overview

Epithelial tissue is one of the four major tissue types in the human body, serving essential roles in protection, absorption, secretion, and filtration. Understanding its structure and function is fundamental in anatomy and physiology.

• Functions: Protection, absorption, secretion, filtration.

• Locations: Covers body surfaces, lines cavities, forms glands.

• Other Major Tissues: Connective, muscle, nervous.

Epithelial Characteristics

Key Features

• Polarity: Has an apical (free) surface and a basal (attached) surface.

• Specialized Contacts: Cells joined by tight junctions and desmosomes for structural integrity.

• Supported by Basement Membrane: Epithelial tissue rests on a basement membrane composed of epithelial and connective tissue fibers.

• Avascular but Innervated: Contains no blood vessels but is supplied by nerve fibers.

• High Regeneration Capacity: Rapidly replaces lost or damaged cells.

Classification of Epithelia

Layering and Shape

• Layers:

  • Simple: Single cell layer.

  • Stratified: Multiple cell layers (2 or more).

• Cell Shapes:

  • Squamous: Flat, scale-like.

  • Cuboidal: Cube-shaped.

  • Columnar: Tall, column-like.

• Naming: Based on apical (top) cell layer.

Examples of Epithelial Types

• Simple Squamous: Diffusion/filtration (lungs, capillaries).

• Simple Cuboidal: Absorption/secretion (kidneys, glands).

• Simple Columnar: Absorption/secretion (digestive tract).

• Pseudostratified Columnar: Secretion, movement (respiratory tract).

• Stratified Squamous: Protection (skin, mouth, esophagus).

• Transitional: Stretch (bladder).

Glandular Epithelium

Types and Secretion Mechanisms

• Endocrine Glands: Secrete hormones directly into blood or lymph.

• Exocrine Glands: Secrete products onto body surfaces or into body cavities (e.g., sweat, saliva, mucus).

• Unicellular Glands: Single cells (e.g., goblet cells).

• Multicellular Glands: Composed of many cells; classified by duct structure and secretory units.

• Secretion Types:

  • Merocrine: Secrete by exocytosis (e.g., sweat glands).

  • Holocrine: Entire cell ruptures to release secretion (e.g., sebaceous glands).

  • Apocrine: Apex of cell pinches off (controversial in humans).

Skin Cancer & Burns

Skin Cancer

• Basal Cell Carcinoma: Most common, least malignant, slow-growing.

• Squamous Cell Carcinoma: Readily spreads, can be cured if detected early.

• Melanoma: Most dangerous, spreads rapidly; early detection is critical for survival.

Burns

• 1st Degree: Affects only the epidermis; redness and pain (e.g., mild sunburn).

• 2nd Degree: Involves epidermis and part of dermis; blisters form.

• 3rd Degree: Full thickness burn; destroys entire skin layer, may damage nerves (no pain in burned area).

• 4th Degree: Extends into muscle and bone; often requires amputation.

Table: Comparison of Burn Degrees

Additional info:

• Early detection of melanoma is crucial due to its aggressive nature.

• Burn severity is classified by depth and extent of tissue damage.