Tissue Types and Epithelial Characteristics

Major Tissue Types

• Four major tissue types: epithelial, connective, muscle, and nervous tissues.
• Tissues consist of groups of similar cells working together for specific functions.

Epithelial Tissue Characteristics

• Two main types: glandular (specialized for secretion) and covering & lining (covers body surfaces).
• Separated from connective tissues by a basement membrane.
• Avascular (no blood supply) but innervated (supplied with nerves).
• Cells exhibit polarity, with distinct apical and basal surfaces.
• Rapid reproduction leads to quick healing.

Classification of Epithelial Tissues

• Keratinized stratified squamous epithelium has dead cells packed with keratin.
• Nonkeratinized type (alive, no keratin) lines the mouth, esophagus, ureters, bladder, and urethra.
• Pseudostratified columnar epithelium appears stratified but is a single layer; has varying cell heights and involves cilia and mucus secretion. Common in upper respiratory passages.

Basement Membrane Structure

• Thin, acellular, and part of the extracellular matrix (ECM).
• Located between epithelial tissue and underlying connective tissue.
• Composed of two layers: basal lamina (lamina lucida and lamina densa) and reticular lamina.

Connective Tissue Structure

• Extracellular matrix (ECM) consists of a gel-like material with fibers and fluid.
• Contains collagen and elastic fibers for structural support and elasticity.
• Types of connective tissue include dense regular, dense irregular, elastic, loose (areolar, adipose, reticular).

Types of Connective Tissue

• Dense Regular: Collagen fibers arranged in parallel bundles, resists tension, found in tendons and ligaments.
• Dense Irregular: Fibers arranged in various planes, resists tension from multiple directions, found in the dermis and joint capsules.
• Elastic: Rich in elastic fibers, allows recoil after stretching; found in large arteries.
• Loose Areolar: Forms lamina propria, supports mucous membranes in various tracts.
• Adipose: Provides cushioning and insulation; stores energy.
• Reticular: Forms a supportive network for blood cells in lymphoid organs.

Skeletal Cartilage Composition

• A type of dense connective tissue consisting of chondrocytes within lacunae in the extracellular matrix.
• Contains collagenous fibers and chondroitin sulfates, produced by chondroblasts.

Types of Cartilage in Skeletal System

• Elastic: Predominant elastic fibers, provides flexible support (external ear).
• Fibrocartilage: Tough and shock-absorbing, found between vertebrae.
• Hyaline: Most abundant, forms costal cartilage of ribs, supports joints, and provides padding.

Body Membranes

• Thin sheets of tissue covering and lining body structures, consist of epithelial and connective tissue layers.
• Types of membranes include:
  • Synovial: Lines joint cavities, secretes synovial fluid for lubrication.
  • Cutaneous: Skin, the thickest membrane, covers body surface.
  • Mucous: Lines open body cavities (respiratory, digestive, urinary, and reproductive), produces mucus for protection and lubrication.
  • Serous: Lines closed body cavities, consists of layers with mesothelium, secretes serous fluid to reduce organ friction, includes pericardium, pleura, and peritoneum.

Tissue Types

• Four major tissue types: Epithelial, Connective, Muscle, Nervous.
• Tissues consist of similar cells performing common functions.

Epithelial Tissue

• Types of Epithelial Tissue:

  • Glandular epithelium: Specialized for secretion, forms glands.
  • Covering & Lining epithelium: Covers body surfaces internally and externally.

• Characteristics:

  • Avascular (lack blood supply) but innervated (supplied with nerves).
  • Exhibits polarity with distinct apical and basal surfaces.
  • Rapid cell division enables quick healing.

• Classification:

  • Keratinized: Surface cells are dead and filled with keratin.
  • Nonkeratinized: Living cells that line moist areas (e.g., mouth, esophagus).
  • Pseudostratified Columnar Epithelium: Appears stratified but is a single layer with varying cell heights; often contains cilia and mucus-secreting cells.

Basement Membrane

• Thin, acellular layer separating epithelium from underlying connective tissue.
• Composed of two layers:
  • Basal Lamina: Contains lamina lucida and lamina densa.
  • Reticular Lamina: Provides structural support.

Connective Tissue

• Comprises the extracellular matrix (ECM) and cells.

• Components: Gel-like matrix consisting of water (90%) and large organic molecules (10%).

• Fibers:

  • Collagen fibers: Strongest, forming networks for support.
  • Elastic fibers: Allow tissues to recoil after stretching.

• Types of Connective Tissue:

  • Proper (loose and dense)
  • Specialized (bone, blood, cartilage).

Loose vs. Dense Connective Tissue

• Loose Connective Tissue:

  • Areolar tissue: Forms lamina propria in mucous membranes.
  • Adipose tissue: Provides insulation and energy storage.
  • Reticular tissue: Supports blood cells in lymphoid organs.

• Dense Connective Tissue:

  • Dense Regular: Parallel collagen fibers resist unidirectional tension (e.g., tendons, ligaments).
  • Dense Irregular: Collagen fibers arranged in multiple planes resist tension from various directions.
  • Elastic: Contains high proportions of elastic fibers for recoil (e.g., arterial walls).

Cartilage

• A type of dense connective tissue consisting of chondrocytes in lacunae within a firm matrix.
• Lacks blood supply and nerve fibers, making it avascular.

Types of Cartilage

• Hyaline Cartilage: Provides support with flexibility, found in the nose, and articulating surfaces of bones.
• Elastic Cartilage: Contains more elastic fibers for flexibility, found in the ear.
• Fibrocartilage: Very strong, withstands heavy pressure and tension; found in intervertebral discs.

Membranes

• Mucous Membranes (Mucosa):

  • Line cavities open to exterior (e.g., respiratory, digestive, urinary tracts).
  • Composed of epithelial tissue with goblet cells producing mucus.

• Serous Membranes (Serosa):

  • Line closed body cavities; consist of mesothelium resting on connective tissue.
  • Secretes serous fluid to reduce friction between organs.
  • Major types include pericardium, pleural, and peritoneum.