Overview
This lecture introduces the four basic tissue types in the human body, focusing in detail on the structure, function, and classification of epithelial tissue.
Types of Tissue in the Human Body
- Tissues are groups of similar cells that perform a common function.
- Four main tissue types: epithelial, connective, nervous, and muscle tissue.
- Cell specialization allows complexity in multicellular organisms like humans.
Epithelial Tissue: Structure and Features
- Epithelial tissue covers body surfaces, lines cavities, organs, and forms glands.
- Covering and lining epithelium acts as a barrier; glandular epithelium forms glands.
- Cells have an apical surface (exposed side) and basal surface (attached side), showing polarity.
- Apical surfaces may have microvilli (increase surface area) or cilia (move substances).
- Basal surface connects to the basal lamina; together with reticular lamina forms the basement membrane.
- Epithelial cells are tightly joined by desmosomes, tight junctions, and gap junctions.
- These tissues are avascular (no blood vessels) but innervated (have nerves).
- Epithelial cells regenerate quickly due to high exposure to friction and injury.
- Functions include protection, absorption, filtration, excretion, secretion, and sensory reception.
Classification of Epithelial Tissue
- Classified by cell layers: simple (one layer) or stratified (multiple layers).
- Classified by cell shape: squamous (flat), cuboidal (cube-shaped), columnar (tall).
- Simple squamous epithelium allows rapid diffusion (e.g., endothelium, mesothelium).
- Simple cuboidal and columnar epithelia are specialized for secretion and absorption.
- Pseudostratified columnar epithelium appears stratified due to staggered nuclei.
- Stratified squamous epithelium provides protection (e.g., skin surface).
- Stratified cuboidal and columnar epithelia are rare, found in some glands.
- Transitional epithelium stretches to accommodate changes in volume (e.g., urinary system).
Glandular Epithelium
- Glands consist of epithelial cells that secrete substances.
- Exocrine glands secrete substances via ducts; endocrine glands secrete directly into blood.
Key Terms & Definitions
- Tissue — group of similar cells performing a specific function.
- Epithelium — tissue covering surfaces or lining cavities and organs.
- Apical surface — upper, free surface exposed to body exterior or cavity.
- Basal surface — bottom surface attached to connective tissue.
- Polarity (in cells) — presence of structural and functional differences between cell surfaces.
- Microvilli — tiny membrane projections to increase surface area.
- Cilia — hairlike structures that move substances along surfaces.
- Basement membrane — structure supporting epithelial tissue, made of basal and reticular lamina.
- Avascular — lacking blood vessels.
- Innervated — supplied with nerves.
- Simple epithelium — single cell layer.
- Stratified epithelium — multiple cell layers.
- Squamous — flat cells.
- Cuboidal — cube-shaped cells.
- Columnar — tall, column-like cells.
- Gland — structure that makes and releases substances (hormones, enzymes).
Action Items / Next Steps
- Review epithelial tissue types, features, and classifications.
- Prepare to learn about connective tissue in the next lecture.