Overview
This lecture introduces the four major types of tissues in the human body, with an in-depth focus on epithelial tissue, its characteristics, classifications, and functions.
Types of Human Tissue
- The four main tissue types are epithelial, connective, nervous, and muscle tissue.
- Tissues are groups of similar cells performing a common or related function.
Epithelial Tissue Overview
- Epithelial tissue covers body surfaces, lines cavities, and forms glands.
- It acts as a boundary, with all substances entering or exiting the body passing through epithelium.
- There are two main types: covering/lining epithelium and glandular epithelium.
Structure and Features of Epithelial Tissue
- Epithelial cells have an apical (exposed) surface and a basal (attached) surface, showing polarity.
- The apical surface can have microvilli (increase surface area) or cilia (move substances).
- The basal surface attaches to the basal lamina, part of the basement membrane.
- Basement membrane consists of basal lamina and reticular lamina, providing support.
- Epithelial cells are tightly joined by desmosomes (adhesion), tight junctions (blockage), and gap junctions (communication).
- Epithelial tissue is avascular (no blood vessels) but innervated (has nerves).
- Cells regenerate rapidly due to friction and potential injury.
- 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).
- Classified by cell shape: squamous (flat), cuboidal (cube-shaped), columnar (tall).
- Simple epithelia are involved in absorption, secretion, and filtration.
- Stratified epithelia provide protection, with stratified squamous being most common.
- Pseudostratified epithelium appears layered but is not.
- Transitional epithelium stretches to accommodate fluctuating volumes (e.g., urinary system).
Glandular Epithelium
- Glands are collections of cells that secrete substances.
- Exocrine glands secrete through ducts onto epithelial surfaces.
- Endocrine glands secrete directly into the bloodstream.
Key Terms & Definitions
- Tissue — A group of similar cells performing a specific function.
- Epithelial tissue — Tissue that covers surfaces and lines cavities.
- Apical surface — The exposed surface of an epithelial cell.
- Basal surface — The attached surface of an epithelial cell.
- Basement membrane — Layer supporting epithelial tissue, made of basal and reticular lamina.
- Avascular — Lacking blood vessels.
- Innervated — Supplied with nerves.
- Simple epithelium — One layer of epithelial cells.
- Stratified epithelium — Multiple layers of epithelial cells.
- Squamous, cuboidal, columnar — Flat, cube-shaped, and tall cell shapes, respectively.
- Desmosome — Cell junction providing strong adhesion.
- Tight junction — Junction blocking fluid flow between cells.
- Gap junction — Junction allowing communication between cells.
Action Items / Next Steps
- Review the classification of epithelial tissues by shape and number of layers.
- Prepare for upcoming discussion on connective tissue.
- Note to study glandular functions and differences between exocrine and endocrine glands.