EPITHELIUM LECTURE NOTES
EPITHELIUM LECTURE NOTES
Page 1: Course Introduction
- Instructors: Dr. Diana Bochynska, DVM, dipECVP, and previous instructors: Matthew Valentine, Dr. I. Irimescu, C. Fuentealba, M. Smith, M. Zibrin, L. Bogdanovic.
Page 2: Lecture Overview
- Definitions, Origin, Functions, Relevance of Epithelium
- Characteristics of Epithelium
- Classification of Epithelia:
- A. Surface/ Lining Epithelia
- B. Glandular Epithelia
Page 3: Cell Structures and Components
- Diagrammed Structures:
- Cilia
- Microtubule
- Basal body
- Plasma membrane
- Cytosol
- Centrosome
- Apical domain (lumen)
- Extracellular material
- Exocytotic vesicle
- Endocytotic vesicle
- Secretory protein
- Golgi apparatus
- Mitochondrion
- Tight junction
- Lysosome
- Peroxisome
- Free ribosome
- Gap junction
- Cytoskeleton
- Adherens junction
- Hemi-desmosome
- Desmosome
- Basement membrane
- Nuclear envelope (Perinuclear space)
Page 4: Basic Tissue Types
- Tissue Definition: An aggregation of cells and extracellular substances.
- Basic Tissue Types:
- Epithelial tissue
- Connective tissue
- Muscular tissue
- Nervoustissue
Page 5: What is Epithelium?
- Definition: A tissue composed of closely aggregated cells with very little extracellular substance.
- Main Types of Epithelium:
- Lining (Surface) Epithelia:
- Forms sheets covering body surfaces or lining organs and cavities.
- Glandular Epithelia:
- Specialized cells that synthesize, store, and release various products.
- Special Epithelia:
- Contains sensory nerve endings, found in skin, ears, tongue, and modified neurons in the nose and eyes.
Page 6: Origin and Histogenesis of Epithelia
- Germ Layer Origins:
- Ectoderm: Epidermis of skin
- Mesoderm: Mesothelium (lining body cavities), endothelium (lining vessels and heart chambers)
- Endoderm: Epithelial lining and glands of gastrointestinal tract, respiratory system, and urinary bladder.
Page 7: Functions of Epithelial Tissues
- Protection:
- Protects against mechanical injury, harmful chemicals, microorganisms, and water loss (e.g., epidermis). - Friction Reduction:
- Smooth endothelial cells reduce friction in blood vessels and heart chambers. - Cleaning:
- Ciliated respiratory epithelium removes dust and foreign particles. - Diffusion:
- Endothelium of capillaries promotes diffusion of gases and nutrients. - Absorption:
- Epithelial cells in the intestine absorb nutrients. - Secretion:
- Specialized epithelial tissues secrete enzymes, hormones, and mucus. - Sensation:
- Contains sensory nerve endings that convey sensations from various organs.
Page 8: Relevance of Epithelial Study
- Foundational Knowledge: Understanding tissue organization and functioning is essential.
- Applications:
- Systemic histology; understanding diseases related to epithelial components (glandular diseases, skin diseases, tumors/neoplasia classifications and progression).
Page 9: Characteristics of Epithelium
- High Cellular Density: Very little intercellular substance.
- Connections to Connective Tissue: Closely associated with supporting connective tissue (CT).
- Avascular Nature: Lining epithelium has few nerve endings.
- Prominent Basement Membrane (BM): Acts as a selective barrier.
- Cell Polarity: Epithelial cells are polarized with apical, lateral, and basal surfaces.
- Cohesiveness: Epithelial cells exhibit strong adhesion to each other.
Page 10: Contrast with Connective Tissue
- Connective Tissue Characteristics:
- Lots of intercellular matrix and few cells. - Histological Stains:
- H&E stain reveals differences in cellular density.
Page 11: Epithelial Cell Polarity
- Surface Types:
- Apical (Free) Surface
- Lateral Surfaces
- Basal Surface
Page 12: Epithelial-Connective Tissue Interface
- Basement Membrane (BM):
- Acts as a selective barrier; small blood capillaries do not penetrate epithelium.
- Stains with PAS (Periodic acid Schiff) for carbohydrate detection.
Page 13: Cohesion in Epithelial Cells
- Intercellular Adhesion:
- Epithelial tissues subject to pressure and traction (e.g., epidermis, urinary bladder) exhibit marked adhesion, strong due to cell junctions like E-cadherins.
Page 14: Types of Intercellular Junctions
- Tight Junctions:
- Prevent molecules from passing through the intercellular space (impermeable). - Desmosomes:
- Anchoring junctions that bind adjacent cells and reduce internal tension. - Gap Junctions:
- Allow communication between cells (ions, small molecules).
Page 15: Gap Junctions Explained
- Function: Provides cytoplasmic channels connecting adjacent cells; necessary for chemical and electrical communication (e.g., in heart muscle and nervous tissue).
Page 16: Classification of Epithelia
- Two Main Types:
- A. Lining Epithelia
- Simple (one layer)
- Stratified
- B. Glandular Epithelia
- C. Specific Types:
- Pigment, sensory, etc.
Page 17: Types of Epithelia Based on Shape
- Various Types of Epithelium:
- Simple squamous
- Simple columnar
- Stratified squamous
- Transitional
- Pseudostratified columnar
Page 18: Simple Squamous Epithelium
- Structure: Flat, elongated cells with a centrally located nucleus.
- Common Locations:
- Mesothelium (lining body cavities)
- Alveolar walls in lungs
- Endothelium (capillaries)
Page 19: Vascular Endothelium Example
- Notes on Staining: H&E = Hematoxylin & Eosin - common histological staining method.
Page 20: Simple Cuboidal Epithelium
- Characteristics: Cuboidal shape, all sides equal, distinct cell limits.
- Examples:
- Lining ducts of glands, choroid plexus, thyroid follicles, lens of the eye.
Page 21: Collecting Tubule Example
- Observation: Notice the distinct cell limits and euchromatin.
Page 22: Simple Columnar Epithelium
- Structure: Tall, narrow cells; ovoid nucleus near base.
- Common Locations:
- Lining stomach, intestines, gall bladder, uterine tubes.
Page 23: Simple Columnar Epithelium in Gall Bladder
- Components Present: Basement membrane, cilia, goblet cells.
Page 24: Simple Columnar Ciliated Epithelium
- Characteristics: Diagram and staining differences highlighted.
Page 25: Pseudostratified Epithelium
- Structure: Single layer of irregularly shaped cells; all cells touch basement membrane but not all reach the luminal surface.
- Examples:
- Nasal cavity, upper respiratory tract, male reproductive structures.
Page 26: Pseudostratified Ciliated Columnar Epithelium Example
- Details on Structure: Highlight presence of goblet cells and cilia.
Page 27: Stratified Squamous Epithelium
- Configuration: Composed of multiple cell layers; superficial cells dictate type, either keratinized or non-keratinized.
Page 28: Keratinized Stratified Squamous Epithelium
- Characteristics: Surface cells lose nuclei, consist mainly of keratin.
Page 29: Esophageal Epithelium (Non-keratinized)
- Noteworthy Features: Stratification visible at high magnification.
Page 30: Keratinized Cells in Mammary Gland
- Observation: Dead keratinized cells visible in tissues of high abrasion areas.
Page 31: Transitional Epithelium (Urothelium)
- Function: Lines urinary passages, providing an osmotic barrier.
- Key Characteristics: Changes shape from cuboidal to flattened depending on bladder fullness.
Page 32: Bladder Epithelium Changes
- Relaxed vs Stretched: Observed changes in epithelium structure based on bladder volume.
Page 33: Epithelial Repair Mechanisms
- Dynamics: Epithelial cells are constantly lost and replaced; stem cells have high mitotic potential located in basal layers.
Page 34: Glandular Epithelia Classification
- Criteria for Classification:
- Number of cells (unicellular/multicellular)
- Shape of ducts and secretory units (adenomeres)
- Type of product
- Mode of secretion
Page 35: Unicellular Glands
- Locations: Found in intestinal lining and respiratory tracts; example includes goblet cells.
Page 36: Mucinogen Granule Staining
- Characteristics: Blue staining of mucinogen granules with Alcian blue in goblet cells.
Page 37: Exocrine vs Endocrine Glands
- Secretion Location Difference:
- Exocrine (body surface/internal cavities) versus Endocrine (into bloodstream). - Example Glands:
- Exocrine: Gastric, salivary, pancreas
- Endocrine: Adrenal, pituitary, thyroid
Page 38: Secretory Units of Exocrine Glands
- Adenomeres: Secretory end-pieces that manufacture products, conveyed through ducts to respective locations.
- Types of Ducts:
- Simple: single opening
- Compound: multiple branches
Page 39: Adenomere Shapes
- Classification:
- Tubular: Straight or coiled (e.g., sweat glands)
- Acinar: Pie-shaped (e.g., pancreas)
- Alveolar: Larger luminal space (e.g., mammary gland)
Page 40: General Classification of Glands
- Structural Types:
- Secretory portions can be simple tubular, branched tubular, coiled tubular, or acinar.
Page 41: Simple Tubular Glands
- Examples: Overview of simple tubular glands in small intestine and histological representation.
Page 42: Tubular Adenomeres and Histology
- Observations: Emphasis on staining patterns of mucous and goblet cells.
Page 43: Simple Coiled Tubular Gland Example
- Diagrams and Staining: Visual representation and mentions of different tissue cuts.
Page 44: Comparing Acinar and Alveolar Shapes
- Distinctions Made:
- Acinar vs. Alveolar shapes with regard to their luminal sizes.
Page 45: Myoepithelial Cells
- Definition: Contractile cells associated with glands, mentioned in context of salivary, mammary, and sweat glands.
Page 46: Gland Structure Overview
- Components: Parenchyma (secretory units & ducts) vs. stroma (connective tissue).
Page 47: Ducts and Lobules Structure
- Divisions: Lobes and lobules structure in compound glands; include explanations on functions of various ducts.
Page 48: Mammary Gland Anatomy
- Diagrammed Structures: Cross-section references to milk drainage structures and their anatomical features.
Page 49: Classification Based on Secretion Product
- Serous: Watery, enzyme-containing (e.g., sweat).
- Mucous: Viscous secretions (e.g., tracheal mucus).
- Mixed: Both mucus and serous (e.g., saliva).
- Sebaceous: Oily secretions (e.g., sebum).
Page 50: Serous Gland Cell Characteristics
- Details on cell structure and cytoplasm appearance in serous glands with histological observations.
Page 51: Mucous Gland Observations
- Characteristics: Cytoplasm looks frothy with a basal nucleus.
Page 52: Mixed Glands Overview
- Structure: Mucous and serous cells sharing duct systems and how they are arranged.
Page 53: Sebaceous Gland Characteristics
- Histological Appearance: Centrally located nuclei and pale, foamy cytoplasm due to lipid processing.
Page 54: Secretion Modes Classification
- Three Types of Secretion Methods:
1. Merocrine: Secretion without loss of cytoplasm.
2. Holocrine: Cell disintegration contributes to secretion.
3. Apocrine: Partial loss of cytoplasm during secretion process.
Page 55: Merocrine Secretion Process
- Overview: Examples including sweat glands, mechanisms discussed with microscopic examination.
Page 56: Apocrine Secretion Characteristics
- Detailed Mechanism: Describes how cells release products with partial cytoplasmic loss, with examples.
Page 57: Holocrine Secretion Mechanics
- Explanation: Process of cell disintegration in sebaceous glands as the mode of secretion.