M3

• Tissue


  A group of cells with similar structure and function, along with extracellular substances located between cells
• Histology


  The microscopic study of tissue structure
• Four Basic Types of Tissues

  • Epithelium
  • Connective
  • Muscle
  • Nervous
• Epithelial Tissue


  • Mostly composed of cells with very little extracellular matrix between them
  • Covers body surfaces that include the exterior surface, lining of digestive, urinary, reproductive, & respiratory tracts, heart & blood vessels, and linings of body cavities
  • Distinct cell surfaces: Free/Apical, Lateral, Basal
  • Cell and matrix connections
  • Nonvascular
  • Capable of regeneration
• Major Functions of Epithelia

  • Protecting underlying structures
  • Acting as a barrier
  • Permitting the passage of substances
  • Secreting substances
  • Absorbing substances
• Classification of Epithelium based on Number of Cell Layers and Shape of Cells

  • Simple - Squamous, Cuboidal, Columnar
  • Stratified - Nonkeratinized, Keratinized - Squamous, Cuboidal, Columnar
  • Pseudostratified - Columnar
  • Transitional - Roughly cuboidal to columnar when not stretched, squamous-like when stretched

  
• Simple Epithelium


  Involved with diffusion, secretion, or absorption
• Stratified Epithelium


  Serves a protective role
• Squamous cells function in diffusion or filtration
• Cuboidal or columnar cells, which contain more organelles, secrete or absorb
• Structural Specializations of Epithelial Cells

  • Microvilli - increase cell's surface area
  • Cilia - move materials across cell's surface
  • Goblet Cells - produce mucus

  
• Cell Connections in Epithelial Tissue

  • Tight Junctions - bind adjacent cells together
  • Desmosomes - mechanical links that bind cells
  • Hemidesmosomes - bind cells to basement membrane
  • Gap Junctions - allow molecules to pass between cells & allow cells to communicate
• Glands


  Structures that secrete substances onto a surface, into a cavity, or into blood; primarily composed of epithelium, with a supporting network of connective tissue
• Types of Glands

  • Exocrine - with ducts
  • Endocrine - no ducts, secrete directly into bloodstream
• Classification of Exocrine GlandsAccording to Structure of Ducts - Simple, Compound

  • According to Type of Secretion - Merocrine, Apocrine, Holocrine

  
• Connective Tissue


  Distinguished by its extracellular matrix which results from the activity of specialized connective tissue cells

  
• Major Components of Extracellular Matrix

  • Protein Fibers - Collagen, Reticular, Elastic
  • Ground Substance - Hyaluronic Acid, Proteoglycan Aggregates, Adhesive Molecules
  • Fluid
• Functions of Connective Tissue


  • Enclosing & separating other tissues
  • Connecting tissues to one another
  • Supporting & moving parts of body
  • Storing compound
  • Cushioning & insulating
  • Transporting
  • Protecting

  
• Classification of Connective Tissues


  • Areolar
  • Adipose
  • Reticular
  • Regular Collagenous

  
• Adipose tissue


  • Little extracellular matrix
  • Adipocytes are full of lipid
  • Packing material
  • Thermal insulator
  • Energy storage
  • Protect organs against injury from being jarred

  
• Reticular tissue


  • Fine network of reticular fibers irregularly arranged
  • Provides a superstructure for lymphatic & hematopoietic tissues

  
• Classification of Connective Tissues

  • Connective Tissue Proper
  • Supporting Connective Tissue
  • Fluid Connective Tissue

  
• Loose Connective Tissue


  Relatively few protein fibers that form a lacy network, with numerous spaces filled with ground substance & fluid
• Regular Collagenous


  • Collagen fibers running in same direction
  • Withstand great pulling forces exerted in direction of fiber orientation due to great tensile strength & stretch resistance

  
• Irregular Collagenous


  • Collagen fibers run in several directions

  
• Regular Elastic


  • Matrix composed of collagen fibers & elastin fibers running the same direction
  • Capable of stretching and recoiling like a rubber band with strength in direction of fiber orientation

  
• Irregular Elastic


  • Matrix composed of collagen fibers & elastin fibers oriented in many different directions
  • Capable of stretching and recoiling in many different directions

  
• Hyaline cartilage


  • Collagen fibers are small & evenly dispersed making it transparent
  • Allows growth, provides rigidity with some flexibility, forms strong, smooth, yet somewhat flexible articulating surfaces, forms the embryonic skeleton

  
• Fibrocartilage


  • Fibers are more numerous than in others; arranged in thick bundles
  • Somewhat flexible & capable of withstanding considerable pressure; connects structures subjected to great pressure
• Elastic cartilage


  • Similar to hyaline, but matrix contains elastic fibers
  • Provides rigidity with even more flexibility; recoil after being stretched
• Simple Squamous


  1 layer of flat, tile-like cells, often hexagonal cells
• Stratified Cuboidal - many layers, cube-shaped; relatively rare absorption, secretion, & protection sweat glands, ovarian follicular cells, salivary glands.

  Stratified Columnar - many layers, but only the surface cells are columnar; deeper layers are irregular or cuboidal in shape; relatively rare secretion, protection, & some absorption mammary gland ducts, larynx, portion of male urethra

  Transitional - special type that changes shape -stretched: squamous - not stretched: cuboidal hold fluids &protects against the caustic effects of urine urinary bladder, ureters, superior urethra.
• Merocrine Secretion


  Most common; involves the release of secretory products by exocytosis ex: water-producing sweat glands, pancreas
• Apocrine Secretion


  Release of secretory products as pinched-off fragments of gland cells ex: milk producing mammary glands (combination with merocrine)
• Holocrine Secretion


  Involves the shedding of entire cells ex: sebaceous glands of skin
• Areolar


  • Fine network of fibers (mostly collagen with a few elastic fibers) with spaces in between; loose packing, support, &nourishment packing between glands, muscles, &nerves; attaches the skin to underlying tissues
• Adipose


  • Little extracellular matrix; adipocytes are full of lipid packing material, thermal insulator, energy storage, &protect organs against injury from being jarred subcutaneous areas, mesenteries, renal pelvis, around kidney, surface of colon, mammary glands
• Reticular


  • Fine network of reticular fibers irregularly arranged provides a superstructure for lymphatic & hematopoietic tissues within lymph nodes, spleen, bonemarrow
• Regular Collagenous Collagen


  • Fibers running in same direction with stand great pulling forces exerted in direction of fiber orientation due to great tensil estrength & stretch resistance tendons, ligaments
• Irregular Collagenous Collagen


  • Fibers run in several directions dermis of skin, organ capsules, outer layer of blood vessels