Types of Tissues

• Extracellular Matrix (ECM)


  A complex network of molecules that provides structural and biochemical support to surrounding cells in multicellular organisms
• Extracellular Matrix (ECM)


  • Provides a scaffold for cells to adhere to and organize themselves
  • Helps maintain tissue integrity and shape
  • Contains proteins that facilitate cell adhesion and migration
  • Contains signaling molecules that regulate cellular processes
  • Can confer mechanical properties to tissues, such as stiffness and elasticity
  • Plays a crucial role in tissue development, remodeling, and repair
• ECM Composition


  • Proteins (e.g., collagen, elastin)
  • Glycoproteins (e.g., fibronectin, laminin)
  • Proteoglycans (e.g., hyaluronic acid), and other molecules
• ECM


  • Dynamically regulated by cells through processes such as synthesis, degradation, and remodeling
  • Plays a fundamental role in maintaining tissue structure and function in both health and disease
• ECM Functions


  • Helps bind tissues together structurally
  • Allows local communication among ECM and various cells—through connection via integrins in plasma membranes
• Four Types of Tissue

  • Connective tissue
  • Epithelial tissue
  • Muscle tissue
  • Nervous tissue

  
• Nervous Tissue


  • Cells: elongated cells with extremely fine processes
  • ECM: very small amount
  • Main Functions: Transmission of nerve impulses
• Epithelial Tissue


  • Cells: aggregated polyhedral cells
  • ECM: very small amount
  • Main Functions: lining of surface or body cavities, glandular secretion

  
• Muscle Tissue


  • Cells: elongated contractile cells
  • ECM: moderate amount
  • Main Functions: strong contraction, body movement
• Connective Tissue


  • Cells: several types of fixed & wandering cells
  • ECM: Abundant amount
  • Main Functions: support & protection of tissues, organs
• Basement Membrane


  Thin non-cellular region that separates the epithelium from the underlying connective tissue

  
• Basement Membrane Components


  • Type IV collagen
  • Laminin
  • Proteoglycans
• Basement Membrane Functions


  • Supports the epithelium
  • Serves as a passive molecular sieve or ultrafilter
• Epithelial Tissue Classification


  • Cell Layers: Simple (single layer), Stratified (multiple layers)
  • Cell Shape: Squamous (flattened and scale-like), Cuboidal (cube-shaped), Columnar (elongated and column-shaped)

  
• Simple Epithelium


  Consists of a single layer of cells, typically where absorption, secretion and filtration occur
• Types of Simple Epithelium

  • Simple squamous
  • Simple cuboidal
  • Simple columnar
  • Pseudostratified
• Simple Squamous Epithelium


  • Cells are flat in shape and arranged in a single layer
  • Thin enough to form a membrane that compounds can move through via passive diffusion
• Simple Cuboidal Epithelium


  • Single row of cube-shaped cells, often with microvilli
  • Absorption & secretion; produces mucus
• Simple Columnar Epithelium


  • Single row of tall, narrow cells
  • Absorption & secretion; secretion of mucus

  
• Stratified Epithelia


  • Keratinized stratified squamous
  • Non-keratinized stratified squamous
  • Stratified cuboidal
  • Transitional epithelium

  
• Keratinized Stratified Squamous Epithelium

  • Multilayered epithelium covered with layer of compact, dead squamous cells packed with protein keratin
  • Retards water loss & prevents penetration of organisms
  • Forms epidermal layer of skin

  
• Non-keratinized Stratified Squamous Epithelium

  • Multilayered epithelium that lacks surface layer of dead cells forming abrasion-resistant, moist, slippery layer

  
• Stratified Cuboidal Epithelium


  • Two or more layers of cells; surface cells square
  • Secretes sweat; ovarian hormones & produces sperm
• Transitional Epithelium


  • Multilayered epithelium with rounded surface cells that flatten when the tissue is stretched
  • Stretches to allow filling of urinary tract

  
• Types of Muscle Tissue

  • Skeletal
  • Cardiac
  • Smooth

  
• Connective Tissue


  Provides a matrix that supports and physically connects other tissues and cells together to form the organs of the body
• Connective Tissue Components


  • Extracellular protein fibers
  • Ground substance
• Ground Substance


  Complex of anionic, hydrophilic proteoglycans, glycosaminoglycans (GAGs), and multi-adhesive glycoproteins (laminin, fibronectin, and others)
• Types of Connective Tissue

  • Connective tissue proper
  • Specialized connective tissues
• Connective Tissue Proper


  • Contains varied cell populations
  • Contains various fiber types
  • A syrupy ground substance
• Connective Tissue Fibers


  • Collagen
  • Reticular
  • Elastic
• Collagen Fibers


  • Most abundant protein, major product of fibroblasts
  • Fibrillar collagens, collagen types I, II, and III
  • Network or sheet-forming collagens - type IV collagen, major structural proteins of external laminae and all epithelial basal laminae
• Reticular Fibers


  Consist mainly of collagen type III, which forms an extensive network (reticulum) of thin fibers for the support of many different cells
• Elastic Fibers


  Have rubberlike properties that allow tissue containing these fibers to be stretched or distended and return to their original shape
• Ground Substance


  • Complex mixture of glycosaminoglycans (GAGs), proteoglycans, and multi-adhesive glycoproteins
  • Fills the space between cells and fibers in connective tissue
  • Allows diffusion of small molecules
  • Acts as both a lubricant and a barrier to the penetration of invaders
• Loose Connective Tissue


  • Collagen fibers are arranged irregularly and loosely, giving the tissue its characteristic flexibility
  • Elastic fibers provide elasticity to the tissue, allowing it to stretch and recoil
  • Contains various cell types such as fibroblasts, macrophages, mast cells, and adipocytes
  • ECM provides a medium for nutrient diffusion and supports/protects the cells

  
• Functions of Loose Connective Tissue

  • Provides support and anchorage for blood vessels, nerves, and epithelial tissues
  • Serves as a site for immune cell infiltration and inflammation
  • Acts as a reservoir for water and electrolytes, contributing to tissue hydration and maintaining homeostasis
• Dense Irregular Connective Tissue

  • Bundles of collagen fibers appear randomly interwoven, with no definite orientation
• Dense Regular Connective Tissue


  • Consists mostly of type I collagen bundles and fibroblasts aligned in parallel for great resistance to prolonged or repeated stresses from the same direction
• Reticular Tissue


  • Consists of delicate networks of type III collagen (reticulin)
  • Most abundant in certain lymphoid organs where the fibers form attachment sites for lymphocytes and other immune cells