In-Depth Notes on Cells and Tissues in Medical Sciences

Introduction to Medical Sciences

  • Focus on cells and tissues.
  • Presented by Dr. Yousif Hamad.

Key Terms in Medical Histology

  • Tissue: A group of cells with similar structure and function (e.g., cartilage, bone, muscle).
  • Organ: An anatomically discrete collection of tissues that perform specific functions (e.g., liver, kidney, eyes).
  • Mesenchyme: Embryological tissue from which all supporting tissue elements are derived. Mesenchymal cells are relatively unspecialized and can differentiate into various connective tissues.
  • Stroma: The connective tissues that support organs, consisting of blood vessels, lymphatic vessels, and nerves. Parenchyma refers to the functional specialized cells, while stroma refers to the supporting tissue.

Histological Techniques

  • Haematoxylin and Eosin (H&E) Staining:
    • H&E is the most common staining technique in histology.
    • Haematoxylin: Stains acidic structures (like nuclei) bluish-purple.
    • Eosin: Stains basic structures (like cytoplasmic proteins) pink or red.

Key Features of Epithelial Tissue

  • Epithelia are tightly packed cells with minimal extracellular matrix.
  • Polarity: Presence of an apical and a basal surface.
  • Attachment: Anchored to the basement membrane.
  • Avascularity: Lack blood vessels, supported by underlying connective tissue (lamina propria).
  • Regeneration: High capacity for regeneration through cell division.
  • Intercellular Junctions: Maintain tissue integrity and allow communication.

Types of Cell-Cell Adhesion in Epithelial Tissue

  • Tight Junctions: Occluding junctions that prevent diffusion between cells.
  • Adherens Junctions: Provide strong mechanical attachment between adjacent cells.
  • Desmosomes: Provide structural integrity.
  • Gap Junctions: Allow communication between cells.
  • Hemidesmosomes: Attach epithelial cells to the basement membrane.

Disease Correlations in Epithelial Tissues

  • Bullous Pemphigoid:

    • An autoimmune blistering skin disorder.
    • Autoantibodies target hemidesmosomal proteins, causing inflammatory reactions that destroy hemidesmosomes, leading to subepidermal blisters.
    • Symptoms: tense blisters on a red base, itching.

  • Pemphigus Vulgaris:

    • An autoimmune condition with autoantibodies against desmoglein proteins in the skin.
    • Symptoms: flaccid bullae or erosions.

Types of Epithelial Tissue

Simple Epithelia (Single Layer of Cells)
  • Simple Squamous: Flat cells, allows for permeability.
  • Simple Cuboidal: Cube-shaped cells, involved in secretion and absorption.
  • Simple Columnar: Rectangular cells, may have cilia; involved in absorption and secretion.
  • Pseudostratified Columnar: Appears layered due to varying cell heights; contains cilia.
Stratified Epithelia (Multiple Cell Layers)
  • Stratified Squamous: Provides protection, keratinized form prevents water loss, non-keratinized provides flexibility.
  • Stratified Cuboidal: Rare, found in ducts, provides some absorption and secretion.
  • Stratified Columnar: Limited locations, provides protection and secretion.
  • Transitional Epithelium: Specialized for stretching; found in the urinary bladder.

Site-Specific Adaptations of Epithelial Cells

  • Skin: Keratinized stratified squamous epithelium, provides waterproof barrier.
  • GI Tract: Simple columnar epithelium with microvilli for absorption.
  • Urothelium: Transitional epithelium that allows distensibility in the bladder, forming an impermeable barrier.

Coeliac Disease

  • Characterized by the breakdown of the epithelial barrier and villous atrophy due to immune-mediated damage to intestinal mucosa.
  • Symptoms and outcomes related to gluten exposure.

Mesenchymal Tissues

  • Types:
    • Fat (Adipose Tissue): Composed of adipocytes, provides energy storage.
    • Bone: Composed of osteoblasts, osteocytes, and osteoclasts. Types include woven and lamellar.
    • Cartilage: Composed of chondrocytes, includes hyaline, fibrocartilage, and elastic types.
    • Tendons: Connect muscle to bone, consist of dense connective tissue.
    • Muscle: Includes skeletal, cardiac, and smooth muscle.

Disorders of Mesenchymal Tissue

  • Marfan Syndrome: A genetic disorder affecting connective tissue, leading to problems in skeleton and cardiovascular system.
  • Lipoma: Benign adipose tissue tumor, usually painless.
  • Angiosarcoma: Malignant tumor derived from blood vessel linings.