Exam 2 Epithelial Tissues

Characteristics of ALL Tissues

• Cells: Different types of tissues contain different types of cells and various relationships between these cells.

  • Can examine cell shapes, prominent organelles, and protein products.

• Extracellular Material:

  • Fluid: Interstitial fluid specifically found in tissue spaces.

  • Matrix (Extracellular Matrix - ECM):

  • Composition: Contains fibrous proteins and other organic molecules.

  • Ground Substance: Water, polysaccharides, and fibrous proteins such as collagen.

    • Purpose of ECM:

    • Holds cells together.

    • Influences the activity of cells.

Types of Tissues

• Epithelial Tissue:

  • Covers internal and external body surfaces.

  • Uses of Epithelial Tissue:

  • Covers body surfaces, including:

    • Outside of the body.

    • Inside surface (lining) of organs, such as digestive and respiratory tracts.

    • Linings of body cavities and blood vessels.

    • Glands (subtype of epithelial).

  • Development: Derived developmentally from body surfaces,

  • Releases proteins or solutions into blood, cavities, or body surfaces.

• Basic Functions of Epithelial Tissue:

  • Protection

  • Absorption

  • Filtration

  • Excretion

  • Secretion

  • Sensory reception

• Special Characteristics of Epithelial Tissue:

  • Tightly packed cells arranged in continuous sheets.

  • Polarity: Cells have distinct "sides."

  • Apical Surface:

    • "Luminal" if facing a lumen.

    • Free side that is not in contact with other cells.

  • Basolateral Surface (Basal):

    • Attached to other cells via cell junctions.

    • Attached to the connective tissue below by a basement membrane.

  • Support:

  • Supported by connective tissue beneath.

  • Vascularity: Avascular but innervated (no blood flow but possesses nerve endings).

  • Blood vessels do not penetrate epithelial membranes.

  • Gases and nutrients must diffuse across the epithelial tissue.

  • In multilayered epithelial tissue, behavior can be modified by the nervous system.

  • High proliferative/regenerative capacity (turnover) due to a high-stress environment (wear and tear).

  • Epithelial tissue is susceptible to collateral damage from chemotherapy.

Criteria for Classification of Epithelial Tissue

• Number of Cell Layers:

  • Simple: Single layer of cells.

  • Stratified: Multiple layers of cells.

  • Pseudostratified: Appears to have multiple layers due to varying cell heights but is a single layer.

• Cell Shape:

  • Squamous: Flat cells.

  • Cuboidal: Cube-shaped cells.

  • Columnar: Long, column-like cells.

Types of Epithelial Tissues

• Simple Squamous Epithelium:

  • Function: Facilitates rapid diffusion.

  • Locations:

  • Lung alveoli.

  • Endothelium of blood vessels (lines blood and lymph vessels).

  • Mesothelium of cavity lining membranes.

• Simple Cuboidal Epithelium:

  • Function: Secretion and absorption.

  • Locations:

  • Glands (both endocrine and exocrine).

  • Kidney tubules.

• Simple Columnar Epithelium:

  • Function: Secretion and absorption.

  • Locations:

  • Lining of the stomach and intestine.

  • Glands.

• Pseudostratified (Ciliated) Columnar Epithelium:

  • Function: Traps and removes particles utilizing cilia (sweeping action).

  • Location:

  • Lining of the respiratory tract, generally associated with goblet cells that secrete mucus.

• Stratified Squamous Epithelium:

  • Characteristics: Composed of multiple layers of cells.

  • Types:

  • Moist: Living cells on the apical surface.

  • Keratinized: Comprising dead cells on the apical surface.

  • Function: Protects against mechanical damage and infection.

  • Locations:

  • Moist areas: lining of mouth, throat, larynx, and esophagus.

  • Urogenital openings: anus and urethra, lining of the vagina.

  • Keratinized: epidermis (skin).

• Stratified Cuboidal Epithelium:

  • Function: Acts as a barrier.

  • Location:

  • Ducts of sweat glands and mammary glands.

• Stratified Columnar Epithelium:

  • Function: Acts as a barrier.

  • Location:

  • Pharynx, though rare.

• Transitional Epithelium:

  • Characteristics: Composed of cells that can change shape (long and short, mixed).

  • Function: Allows stretching.

  • Locations:

  • Urinary bladder and ureters.

• Glandular Epithelium:

  • General Features:

  • Manufactures or secretes chemicals.

  • Can be unicellular or multicellular.

  • Endocrine Glands:

  • Release chemicals (hormones) into the blood for long-distance communication in the body.

  • Ductless; chemicals move into the bloodstream and travel throughout the body through exocytosis.

  • Exocrine Glands:

  • Release chemical solutions onto body surfaces.

  • Multicellular exocrine glands release solutions into ducts.

  • Unicellular exocrine glands: such as goblet cells.

• Classification by Shape:

  • Squamous: Flat cells.

  • Cuboidal: Round cells.

  • Columnar: Tall rectangular cells.

  • Stratified Types:

  • Stratified Squamous.

  • Stratified Cuboidal.

  • Stratified Columnar.

  • Pseudostratified and transitional types are also noteworthy.