Overview
This lecture covers the structure and functions of epithelial tissue, including its types, classifications, and roles in organization and protection within the body.
Role and Function of Epithelial Tissue
- Epithelial tissue creates boundaries and organizes the body's complex systems.
- It lines and covers the body's surfaces, as well as internal cavities and organs.
- Epithelial tissue protects from injury, infection, and maintains internal order.
Types of Epithelial Tissue
- Proper epithelium covers and lines inner and outer body areas.
- Glandular epithelium forms glands and secretes substances like hormones.
Structural Features
- Epithelial tissues are avascular (no direct blood supply) and rely on connective tissues for nutrients.
- All epithelial cells are polar, having an apical (outer/exposed) and basal (attached) side.
- The basal side attaches to the basement membrane, anchoring the tissue.
Classification by Shape and Layers
- Three cell shapes: squamous (flat), cuboidal (cube-shaped), and columnar (tall/column-like).
- Three layering types: simple (one layer), stratified (multiple layers), and pseudostratified (appears multi-layered but isn't).
- Tissue is named by layering first, then shape (e.g., simple squamous, stratified cuboidal).
Structure-Function Relationships
- Thin, flat squamous cells allow easy absorption and are found in lungs and blood vessels.
- Cuboidal and columnar cells are larger, for secretion and absorption, found in glands and intestinal lining.
- Stratified squamous tissues are protective and found in areas with high cell loss, like skin and mouth.
Glandular Epithelial Function
- Glandular epithelium forms two main gland types: endocrine (secretes hormones into blood) and exocrine (secretes into ducts).
- Endocrine glands distribute hormones like thyroxin.
- Exocrine glands produce sweat, saliva, mucus, stomach acid, and milk.
Key Terms & Definitions
- Epithelial tissue â tissue that lines, covers, and organizes body surfaces and cavities.
- Avascular â lacking blood vessels.
- Polar cells â cells with distinct top (apical) and bottom (basal) surfaces.
- Basement membrane â collagen-rich layer anchoring epithelial tissue.
- Simple epithelium â single cell layer.
- Stratified epithelium â multiple cell layers.
- Pseudostratified epithelium â single cell layer with nuclei at different levels.
- Squamous/cuboidal/columnar â flat/cube-shaped/tall cell types.
- Endocrine gland â gland releasing hormones into blood.
- Exocrine gland â gland releasing secretions into ducts.
Action Items / Next Steps
- Review the classification of epithelial tissue types by shape and layering.
- Study examples of where each type of epithelial tissue is found in the body.
- Prepare to identify epithelial tissues under a microscope in lab sessions.