Histo FWA

Tissues and Histology

  • Definition of Tissues: A tissue is a collection of similar cells and extracellular matrix that together carry out a specific function.

  • Extracellular Matrix (ECM): A three-dimensional network of extracellular macromolecules (collagen, enzymes, glycoproteins) that provide structural and biochemical support to surrounding cells.

  • Histology: The study of tissues of the body and their arrangement into organs.

Types of Tissues in the Human Body

  • Four basic types:

    • Epithelium: Lines and covers surfaces.

    • Connective Tissue: Protects, supports, and binds together (blood, bone, cartilage, lymphatic tissue).

    • Muscular Tissue: Produces movement.

    • Nervous Tissue: Reacts to stimuli and conducts impulses.

Functions of Epithelium

  • Primary Functions:

    • Protection

    • Absorption

    • Excretion

    • Secretion

    • Filtration

    • Sensory reception

Classification of Epithelium

  • Based on Cell Shape:

    • Squamous: Flat, thin scale-like cells.

    • Cuboidal: Cube-shaped cells with equal height and width.

    • Columnar: Tall, rectangular cells, usually taller than wide.

  • Based on Arrangement:

    • Simple: Single layer of cells.

    • Stratified: Two or more layers of cells.

    • Pseudostratified: Appears to have multiple layers due to variance in cell height.

    • Transitional: Cells that can slide over one another to allow stretching.

Specific Types of Epithelium

  • Simple Squamous Epithelium:

    • Location: Alveoli of lungs, lining of heart and blood vessels.

    • Function: Allows diffusion and filtration; secretes lubricating substances.

  • Simple Cuboidal Epithelium:

    • Location: Covering of ovaries, thyroid.

    • Function: Secretion and absorption.

  • Simple Columnar Epithelium:

    • Location: Digestive tract (non-ciliated), bronchi, uterine tubes (ciliated).

    • Function: Protection, absorption, and secretion of mucus and enzymes.

  • Pseudostratified Columnar Epithelium:

    • Location: Lined trachea and nasal cavity.

    • Function: Protection, secretion, ciliated tissue moves mucus.

  • Stratified Epithelium:

    • Stratified Squamous: Protects against abrasion.

    • Stratified Cuboidal: Protects glands like sweat and salivary.

    • Stratified Columnar: Rare, found in the male urethra.

  • Transitional Epithelium:

    • Location: Bladder, urethra, ureters.

    • Function: Protects, allows for distension.

Special Features of Epithelium

  • Cilia: Hair-like appendages for movement.

  • Goblet Cells: Produce mucus for lubrication and protection.

  • Villi and Microvilli: Increase the surface area for absorption.

Functions of Epithelial Tissue

  • Acts as a barrier between different environments.

  • Functions include protection from physical damage, absorption in the digestive tract, secretion of hormones and enzymes, sensory reception, and filtration.

Characteristics of Epithelial Layers

  • Composed of closely packed cells with minimal extracellular material.

  • Avascular but innervated, receiving nourishment via diffusion from underlying connective tissue.

  • Orientation with one free surface and an attached basal surface to the basement membrane.

Microscopy

How a Microscope Works

  • Angle of Light: Changes image size based on the angle of light entering the eye.

  • Refraction: Light is bent by glass, producing a magnified image.

  • Light Properties: Wavelength, frequency, and amplitude are important for resolution.

  • Components of a Microscope: Mechanical stage, lighting system, focusing system, eyepieces, objectives.

Types of Lenses

  • Neofluar Lens: Transmits ultraviolet light for fluorescence microscopy.

  • Apochromatic Lens: Corrected for chromatic aberration.

  • Plan Lens: Provides a flat field of view.

Types of Microscopy Used

  • Light Microscopy: Traditional microscopy that uses visible light to view specimens.

  • Electron Microscopy: Uses electron beams for high-resolution imaging.

    • Transmission Electron Microscope (TEM): Requires thin specimen sections, provides high detail.

    • Scanning Electron Microscope (SEM): Provides 3D images by scanning the surface of specimens.

Cell Pathology

Definitions

  • Health: Complete physical, mental, and social well-being.

  • Disease: Harmful deviations from normal structure/function, may arise from multiple factors.

Mechanisms of Disease

  • Injury: Can be reversible (mild stress) or irreversible (severe stress).

  • Cell Injury Types: Hypoxia, toxins, microbes, inflammation, genetic disorders.

Cell Death

  • Apoptosis: Programmed cell death, controlled process.

  • Necrosis: Caused by injury, leads to inflammatory response.

Wound Healing and Repair

Phases of Healing

  1. Hemostasis: Clot formation and platelet aggregation.

  2. Inflammation: Immune response and debris cleanup.

  3. Proliferation: Granulation tissue formation and re-epithelization.

  4. Remodeling: Replacement with mature scar tissue.

Factors Affecting Healing

  • Local Factors: Infection, blood supply, foreign bodies.

  • Systemic Factors: Anemia, nutrition, genetic disorders.

Fixation and Processing of Tissues

Fixation

  • Purpose: Preserve tissues in a lifelike condition, prevent decay.

  • Common Fixatives: Formaldehyde, glutaraldehyde, mercurials.

Processing Steps

  1. Dehydration: Remove water using alcohols.

  2. Clearing: Replace dehydrating agent with a miscible solution (xylene or similar).

  3. Impregnation: Embed tissue in paraffin for sectioning.

Staining Histology

Staining Techniques

  • Hematoxylin and Eosin (H&E): Most common staining method, contrasts nuclei and cytoplasm.

  • Histochemical Stains: Identify specific chemical compositions within cells.

  • Immunohistochemistry: Detects specific proteins or antigens in tissues using antibodies.

Principles of Staining

  • Affinities: Dyes bind based on ionic charges (basic dyes stain acidic elements like DNA).

  • Mordants: Enhance the interaction between dye and tissue, crucial for effective staining.

Conclusion

  • Understanding histology and the techniques used for tissue examination is crucial for diagnosing diseases and understanding cell function.