Overview
This lecture covers the four major tissue types in the body, with an in-depth focus on epithelial tissue, its characteristics, cell types, arrangements, and specific functions.
Four Major Tissue Types
- Epithelial tissue forms protective coverings and linings.
- Connective tissue provides support, structure, and nourishment.
- Nervous tissue is responsible for transmitting signals.
- Muscle tissue enables movement.
Epithelial Tissue Overview
- Covers internal and external body surfaces, and lines cavities.
- Forms the main component of glands.
Characteristics of Epithelial Tissue
- Highly regenerative due to a high rate of cell division (mitosis).
- Avascular (no blood vessels), but innervated (contains nerve endings).
- Cells are tightly packed and anchored to a basement membrane.
- Exhibits polarity: apical (top, exposed) and basal (bottom, attached) sides.
- Specialized cell junctions like tight junctions and desmosomes connect cells.
- Supported by underlying connective tissue for strength and nourishment.
- Selectively permeable, allowing some substances to pass and blocking others.
- May have microvilli (increase absorption) or cilia (move substances).
Epithelial Cell Types & Arrangements
- Three major cell shapes: squamous (flat), cuboidal (cube-shaped), columnar (tall).
- Two main arrangements: simple (one layer) and stratified (multiple layers).
General Functions of Epithelial Tissue
- Gas exchange (e.g., oxygen and carbon dioxide).
- Absorption of nutrients.
- Secretion of substances (e.g., sweat, mucus).
- Protection against pathogens and abrasion.
Types of Epithelial Cells (with Examples)
- Simple Squamous: single layer, thin, allows gas exchange; found in lungs and capillaries.
- Stratified Squamous: multiple layers, protects; found in skin (epidermis).
- Simple Cuboidal: single layer, secretes and absorbs; found in kidneys.
- Stratified Cuboidal: multiple layers, secretes; found in glands (rare).
- Simple Columnar: single layer, increases absorption; found in stomach and intestines.
- Pseudostratified Ciliated Columnar: appears layered but isn’t, has cilia, traps debris; found in respiratory system, trachea.
- Transitional Epithelium: changes shape to stretch; found in the bladder.
Key Terms & Definitions
- Avascular — lacking blood vessels.
- Innervated — supplied with nerve endings.
- Polarity — structural and functional difference between the top (apical) and bottom (basal) surfaces.
- Basement Membrane — thin layer connecting epithelium to connective tissue.
- Microvilli — surface projections that increase absorption.
- Cilia — hair-like structures that move substances across the cell surface.
- Desmosomes — cell junctions anchoring cells together.
Action Items / Next Steps
- Review tissue types and main characteristics of epithelial tissue.
- Memorize cell type shapes and typical locations.
- Understand the general functions and arrangements of epithelial cells.