Epithelial Tissue Characteristics

• Human Histology lecture MT120225, Unit 2: Epithelial Tissue is lectured at UST General Santos, School of Health Sciences, Department of Medical Technology, Second Semester A.Y. 2024-2025.
• At the end of this unit, the student must be able to identify and describe the various epithelial tissue types.
• Course content covers: Epithelial Cells, Epithelial Domains, Covering or Lining Epithelia, Secretory Epithelia and Glands, Transport Across Epithelia, and Renewal of Epithelial Cells.

Characteristic Features of Epithelial Cells

• Epithelial cells are characterized by their shape and dimensions.
• Nuclear shape corresponds roughly to cell shape.

Epithelial Cells: Squamous

• Simple squamous epithelial cells have a height less than their width (H < W) and can be found lining the alveoli of lungs.

Epithelial Cells: Cuboidal

• Cuboidal epithelial cells have a height equal to their width (H = W).

Epithelial Cells: Columnar

• Columnar epithelial cells have a height that is greater than their width (H > W).

Characteristic Features: Polarity & Domains

• Epithelial cells exhibit distinct polarity
• They have three domains which include the apical domain, basal domain, and lateral domain.

Epithelial Domains

• Consist of the Apical Domain, Lateral Domain, and Basal Domain.

Basal Surface

• The basal surface rests on the basement membrane made up of the basal lamina (BL) and reticular lamina (RL).

Basal Lamina

• The Basal Lamina is 20-100 nm thick
• It is composed of glycoproteins, collagen, and proteoglycans.
• It is produced by epithelial cells and supports the overlying epithelium, acts as a semipermeable barrier, and provides an interaction site for many cell adhesion molecules.

Reticular Lamina

• The Reticular Lamina contains collagen III fibers
• They are produced by fibroblasts (connective tissue).

Lateral Surface

• Intercellular adhesion and other junctions exist on this surface.
• Tight/Occluding Junctions (Zonula Occludens) seal between adjacent cells and prevent passive flow of materials between cells.
• Anchoring Junctions serve as sites of strong cell adhesion.
• Gap Junctions (Nexus) are patches many connexons; they permit intercellular exchange of small molecules.

MEDICAL APPLICATION

• The enterotoxin secreted by Clostridium perfringens, which causes food poisoning, prevents maintenance of the tight juntion by inhibiting insertion of claudin molecules of intestinal cells, causing loss of tissue fluid into the intestinal lumen via paracellular pathway.

Apical Surface

• The apical surface contains microvilli, stereocilia, and cilia.

Microvilli

• Microvilli are finger-like cytoplasmic projections of epithelial tissue specialized for absorption.
• They are 1 μm long and 0.1 μm wide.
• They increase surface area by 20-30 fold
• The internal structure has a core of actin filaments and actin binding proteins.

MEDICAL APPLICATION

• Celiac disease leads to loss of microvilli brush border of the absorptive cells of the small intestine.
• It is caused by the immune reaction against wheat protein (gluten) during its digestion, which causes diffuse enteritis and malabsorption.

Stereocilia

• Stereocilia are seen on absorptive epithelial cells lining the male reproductive system and sensory cells of the inner ear.
• They have a core of actin filaments and actin binding proteins.
• Stereocilia are longer and less motile than microvilli and often have distal branching.

Cilia

• Cilia are long and larger than microvilli
• They are abundant on cuboidal or columnar cells
• They are 5-10 μm long and 0.2 μm.
• They contain microtubules internally
• Cilia exhibit beating patterns that move materials in one direction.
• The primary cilium, which is not motile, detects light, odor, motion, and the flow of liquid.

Covering or Lining Epithelia

• Tissue is a group of similarly specialized cells that work together to perform a specific function.
• Main functions include:
• Epithelial tissue has a small amount extracellular matrix and functions to line the surface/body cavities and grandular secretion.
• Connective tissue has an abundant amount of extracellular matrix and functions to support and protection tissues/organs.
• Muscle tissue has a moderate amount of extracellular matrix and functions to strong contraction body movements.
• Nervous tissue has very small amount of extracellular matrix and functions to transmission of nerve impulses.

Covering or Lining Epithelia: Epithelial Tissue Characteristics

• Epi upon + thele nipple
• Composed of closely aggregated polyhedral cells adhering strongly to one another and to ECM.
• Covers external surfaces of the body, line the internal cavities and the organs, form various organs and glands, and line their ducts.

Covering or Lining Epithelia: Characteristics of Epithelial Tissue

• Cellularity – in close contact with each other.
• Specialized contacts - have junctions for attachment and communication.
• Polarity - have apical, basal, and lateral surfaces.
• Supported by connective tissue - source of nutrients, metabolites, and oxygen.
• Avascular but innervated.
• Regeneration - high mitotic rate.

Covering or Lining Epithelia are Classified According to:

• Cell layers.
• Cell shape.

Explore epithelial cell characteristics, apical domain features, tight junction functions, and basement membrane composition. Investigate claudin disruption and fibroblast roles. Understand cell adhesion and epithelial tissue components.