Overview
This lecture introduces histology, focusing on epithelial tissues, their classifications, characteristics, functions, and major types found in the body.
Introduction to Tissues and Histology
- Tissues are groups of similar cells specialized for specific functions.
- Histology is the study of tissues.
- Nervous tissue conducts impulses to control body activities.
Epithelial Tissue Characteristics
- Epithelial tissues cover body surfaces, line cavities/organs, and are main tissue in glands.
- Always have one exposed (apical) side and one attached (basal) side.
- Anchored to connective tissue by a basement membrane.
- Epithelial tissues lack blood vessels (avascular) and get nutrients via diffusion from underlying tissue.
- Cells reproduce rapidly and are tightly packed with little intercellular space.
- Classified by cell arrangement (simple: one layer; stratified: multiple layers) and cell shape.
Epithelial Tissue Functions (GAPS)
- Glandular: make and secrete substances.
- Absorption: through microvilli on cell surface.
- Protection: densely packed layers protect underlying tissues.
- Secretion: of fluids, enzymes, mucus, etc.
Major Types of Epithelial Tissues
Simple Columnar Epithelium
- One layer of elongated, column-shaped cells with nuclei near the base.
- Contains goblet cells (secrete mucus) and microvilli (increase absorption).
- Found lining digestive tract, gall bladder, oviducts.
- Functions in absorption, mucus secretion, and movement of materials.
Simple Cuboidal Epithelium
- Single layer of cube-shaped cells with central nuclei.
- Found in small glands, ovaries, kidney tubules, retina.
- Functions in secretion and absorption.
Pseudostratified Ciliated Columnar Epithelium
- Appears layered, but all cells touch basement membrane; nuclei at different heights.
- Cilia sweep debris; goblet cells secrete mucus.
- Found in trachea, upper respiratory tract, sperm ducts.
- Functions in secretion, absorption, and protection.
Stratified Squamous Epithelium (Keratinized)
- Multiple layers; lower cells are alive, surface cells are dead and full of keratin.
- Found in epidermis, mouth, anus, vagina.
- Protects against abrasion, dehydration, pathogens.
Transitional Epithelium
- Multiple layers of cuboidal/elongated cells; surface cells rounded.
- Found in ureters, bladder, urethra.
- Allows stretching and prevents urine leakage.
Key Terms & Definitions
- Histology — study of tissues.
- Epithelial Tissue — tissue covering surfaces and lining cavities.
- Basement Membrane — non-living layer anchoring epithelium to connective tissue.
- Avascular — lacking blood vessels.
- Simple Epithelium — one cell layer thick.
- Stratified Epithelium — multiple cell layers.
- Goblet Cell — mucus-secreting cell in columnar epithelia.
- Keratin — tough, waterproof protein in skin cells.
- Microvilli — small projections increasing cell surface area for absorption.
- Cilia — hair-like structures for moving substances over cell surface.
Action Items / Next Steps
- Review and identify tissue types in histology slides.
- Complete assigned readings on epithelial tissue types and functions.
- Prepare for lab quiz on tissue identification and key characteristics.