Classifying Epithelial Cells

Basement Membrane

• Anchors epithelial cells to underlying connective tissue.
• Acts as a mechanical barrier and plays a role in angiogenesis.
• Composed of basal lamina and reticular lamina.
• Basal lamina (40-120 nm thick) provides strong support and is formed by proteins like laminin, Type IV collagen, entactin, and perlecan.
• Reticular lamina is mainly made of Type III collagen and further anchors epithelial tissues.

Simple Columnar Ciliated Epithelium

• A type of epithelium characterized by a single layer of tall, column-like cells with cilia.
• Cilia assist in movement, especially in respiratory pathways.
• Shape of nuclei is crucial for identifying this epithelium type.

Simple Squamous Epithelium

• Composed of a single layer of thin, wide cells.
• Functions include absorption and facilitating the movement of substances due to its thin structure.

Transitional Epithelium

• Features a distensible barrier primarily found in the bladder, renal calyces, ureters, and urethra.
• Allows for the expansion and contraction of the urinary system as it fills and empties.

Epithelial Surface Specializations

• Apical domain of epithelial cells can exhibit various structural modifications for specialized functions.
• Stereocilia: Long, immotile microvilli aiding absorption in the male reproductive system and serving as sensory receptors in the inner ear.

Keratinized Surface of Skin

• Covered by keratinized squamous epithelium providing an inert protective layer.
• Keratin and phospholipids minimize water loss and prevent evaporation.

Signaling Mechanisms

• Paracrine Signaling: Involves the release of substances that affect nearby cells through diffusion, not entering the bloodstream.
• Endothelial cells release factors affecting vascular smooth muscle contraction or relaxation.
• Autocrine Signaling: Cells secrete substances that act on themselves, often related to immune responses via interleukin signaling.

Classification of Exocrine Glands

• Divided into unicellular and multicellular glands based on structure.
• Unicellular Exocrine Glands: Composed of individual cells like goblet cells found in intestines and respiratory tracts.
• Multicellular Exocrine Glands: Comprise multiple cells with varying complexity and can be subclassified based on cell arrangement and duct branching.

Mechanisms of Secretion

• Three mechanisms of secretion for multicellular glands include:
  • Merochrine Secretion: Secretory products are delivered to the apical surface, important for functions such as mucus movement in respiratory tracts.### Magnification and Resolution
• Magnification: Refers to the enlargement of a specimen observed through a microscope.
• Resolution: The ability to distinguish closely spaced structures as distinct entities.

Stains in Histology

• Stains enhance the visibility of histological structures, providing contrast, color, and revealing chemical information.

Hematoxylin and Eosin (H&E)

• H&E staining: Most common for routine histology and pathology sections.
• Hematoxylin: Basic dye, positively charged, stains negatively charged structures (nucleus, rough ER) purple to blue.
• Eosin: Acidic dye, negatively charged, stains eosinophilic structures (collagen, mitochondria) pink.

Light Microscope

• Compound bright-field microscope: Utilizes two glass lenses to form the final image.
• Enables viewing of stained tissues for cellular components.

Epithelial Tissue Staining Properties

• Basophilia: Structures stained by hematoxylin due to their negative charge.
• Eosinophilia: Refers to structures that stain with eosin; indicative of acidic components.

Metal Stains

• Metal staining used for electron microscopy often involves lead and uranium.
• Heavy metals block electron passage, producing dark and light areas in images.

Osmium Tetroxide

• Serves as both stain and fixative for lipids, producing a brown color upon reaction.
• Preserves lipid structures effectively.

Toluidine Blue

• Basic dye, reacts with negatively charged tissue components.
• Commonly used for quick staining of frozen or resin-embedded sections.

Periodic Acid-Schiff (PAS)

• Histochemical stain that localizes specific chemical groups, producing a magenta color.
• Effective for visualizing carbohydrates like glycogen.

Cresyl Violet-Luxol Fast Blue

• Commonly used for nervous tissue staining.
• Binds to myelin sheath, producing a turquoise color; identifies basophilic structures.

Masson’s Trichrome

• Combines three dyes to reveal collagen presence; collagen stains green, cytoplasm varies from red to purple.
• Efficient for differentiating tissue components.

Elastin Stain (Verhoeff’s-Van Gieson)

• Specifically stains elastin in elastic fibers, resulting in a black or brown coloration.
• Highlights the structural properties and distribution of elastic fibers.

Silver Staining

• Involves the precipitation of reduced silver onto tissue elements.
• Effectively visualizes neuronal structures and reticular fibers crucial for connective tissue.

Summary of Key Structures

• Cytoplasmic structures can be identified by their staining properties (basophilic vs. eosinophilic).
• Identification and differentiation of cellular components enhance histological understanding and applications.