Overview
This lecture introduces the four main tissue types in the human body, with a focus on the structure, features, and classification of epithelial tissue.
Types of Human Tissue
- Tissues are groups of similar cells performing a common function.
- The four main tissue types are epithelial, connective, nervous, and muscle tissue.
Epithelial Tissue: Functions and Features
- Epithelial tissue covers body surfaces and lines cavities, forming boundaries.
- All substances entering/exiting the body pass through epithelium.
- There are two types: covering/lining epithelium and glandular epithelium.
- Epithelial cells have polarity: an apical (exposed) surface and a basal (attached) surface.
- The apical surface may have microvilli (increase surface area) or cilia (move substances).
- The basal surface is attached to the basal lamina, which, along with the reticular lamina, forms the basement membrane.
- Epithelial cells are closely packed in sheets, held by desmosomes, tight junctions, and gap junctions.
- They are avascular (no blood vessels) but innervated (supplied by nerves).
- Epithelial cells regenerate quickly due to their exposed position.
- Functions include protection, absorption, filtration, excretion, secretion, and sensory reception.
Classification of Epithelial Tissue
- Classified by number of layers: simple (one layer) or stratified (multiple layers).
- Cell shape types: squamous (flat), cuboidal (boxy), and columnar (tall).
- Simple squamous epithelium allows for rapid diffusion (e.g., endothelium, mesothelium).
- Simple cuboidal and columnar epithelia specialize in absorption and secretion.
- Pseudostratified columnar epithelium appears layered due to staggered nuclei, but is a single layer.
- Stratified squamous epithelium provides protection (outer skin); surface cells are flat, deeper cells may be cuboidal/columnar.
- Stratified cuboidal and columnar are rare, found mainly in some glands.
- Transitional epithelium stretches to accommodate fluctuating volumes (urinary system).
Glandular Epithelium
- Makes up glands that secrete specific substances, often hormones.
- Exocrine glands secrete via ducts onto surfaces; endocrine glands secrete directly into blood.
Key Terms & Definitions
- Tissue — Group of similar cells with a common function.
- Epithelial tissue — Tissue that covers surfaces or lines cavities.
- Apical surface — The exposed surface of an epithelial cell.
- Basal surface — The attached side of an epithelial cell.
- Basal lamina — Glycoprotein and collagen layer supporting epithelium.
- Desmosome — Filament connection between adjacent cells.
- Tight junction — Seal that blocks fluid between cells.
- Gap junction — Pore that connects cells for communication.
- Avascular — Lacking blood vessels.
- Innervated — Supplied by nerves.
- Simple epithelium — Single cell layer.
- Stratified epithelium — Multiple cell layers.
- Squamous/cuboidal/columnar — Cell shapes: flat, boxy, tall.
- Glandular epithelium — Tissue forming glands for secretion.
Action Items / Next Steps
- Review the classification of epithelial tissues by layers and cell shapes.
- Prepare to study connective tissue in the next session.