March 11th 2025

Histological Examination

• Procedure: When tissue may be infected or cancerous, a small sample is scraped off and sent for histological examination.

• The examination allows pathologists to differentiate between healthy and non-healthy (cancerous) cells.

• Tissue Preservation and Staining:

  • Tissue is preserved and stained to enhance visibility of details since cells in the body are typically colorless.

  • Staining helps in distinguishing histological features better.

Cancer Diagnosis

• If the examined tissue is found to be noncancerous, the patient is clear. If cancerous, further evaluation is done to determine the stage of cancer.

• Cancer stages indicate how far cancerous cells have spread from the primary tumor location.

Importance of Staining and Sectioning

• Sectioning: Provides a thinner slice of tissue for detailed observation.

• Staining: Enhances visibility, allowing for better differentiation of cell types, especially between hydrophobic (poorly stained) and hydrophilic (well-stained) cells.

Cell Junctions

• Cells are connected by structures termed cell junctions, which facilitate communication and material movement between cells.

• Types of junctions include:

  • Tight Junctions: Fluid seals that prevent passage between cells, ensuring some materials only move in designated directions.

  • Gap Junctions: Channels that allow ions and small molecules to freely move between adjacent cells, crucial for function in cardiac and smooth muscle tissues.

  • Desmosomes: Act like glue, anchoring adjacent cells together, providing stability during mechanical stress.

  • Hemidesmosomes: Attach cells to the basement membrane, anchoring cells from one side only.

Epithelial Tissue Overview

• Function: Epithelial tissue forms boundaries between different environments within the body, lining organs and cavities (internal and external).

• Characteristics:

  • Cells are tightly packed with minimal extracellular matrix.

  • Two surfaces:

    • Apical Surface: Faces the exterior or cavity; superficial.

    • Basal Surface: Anchored to the basement membrane, facing deeper tissues.

  • Epithelial tissues are avascular and rely on diffusion for nutrient supply from connected tissues.

  • High turnover rate due to constant exposure to stress and abrasion.

Functions of Epithelial Cells

• Barrier Creation: Protects underlying structures by separating different environments.

• Secretion: Produces mucous and other substances.

• Absorption: Engages in absorbing necessary substances while excreting waste.

• Sensory Reception: Involved in sensing external stimuli.

Basement Membrane Structure

• Composed of:

  • Basal Lamina: Contains epithelial cells and collagen fibers for support.

  • Reticular Lamina: Contains reticular fibers, acting as a scaffold over connective tissue.

• Nutrients diffuse from the connective tissue through the membrane into epithelial cells.

• Impact of Thickness: A thicker basement membrane impedes nutrient diffusion, leading to potential complications (e.g., in diabetes).

Types of Epithelia

• Simple Epithelia: One layer, primarily for absorption and filtration.

  • Simple Squamous: Flat cells for quick exchange of materials (e.g., lungs, blood vessels).

  • Simple Cuboidal: Cube-shaped cells mainly for filtration (e.g., kidney tubules).

  • Simple Columnar: Taller cells; secreting enzymes and mucus, often having microvilli for increased absorption surface area.

• Stratified Epithelia: Multiple layers, primarily for protection.

  • Stratified Squamous: Flat cells; protects, keratinized to prevent water loss (e.g., skin).

  • Stratified Cuboidal: Rare, mainly for protection (e.g., salivary glands).

  • Stratified Columnar: Rare, for protection and secretion (found in some glands).

• Pseudostratified Columnar: Appears stratified but is a single layer; often found in the respiratory tract and has cilia.

• Transitional Epithelial: Multiple shapes allowing for stretching (e.g., bladder).

Clinical Relevance

• Pap Smear: A procedure to collect cells from the cervix for examination to detect potential malignancies (e.g., cervical cancer).

• Understanding epithelial tissue’s structure and function is vital for diagnosing diseases and conditions affecting various body systems.