Chapter 04 - Tissues

• Tissue


  A group of cells with similar structure and function, plus the extracellular substance surrounding them
• Histology


  The study of tissues
• Types of tissues in the human body

  • Epithelial
  • Connective
  • Muscle
  • Nervous
• Epithelial tissue


  • Covers and protects surfaces, both outside and inside the body
  • Includes exocrine and endocrine glands
• Characteristics of epithelial tissue

  • Mostly composed of cells
  • Covers body surfaces
  • Distinct cell surfaces
  • Cell and matrix connections
  • Nonvascular
  • Capable of regeneration
• Functions of epithelial tissues

  • Protects underlying structures
  • Acts as a barrier
  • Permits passage of substances
  • Secretes substances
  • Absorption of substances
• Classification of epithelia based on cell layers

  • Simple
  • Stratified
  • Pseudostratified
• Classification of epithelia based on cell shape

  • Squamous
  • Cuboidal
  • Columnar
  • Transitional
• Simple epithelium


  A single layer of cells, with each cell extending from the basement membrane to the free surface
• Stratified epithelium


  More than one layer of cells, but only the basal layer attaches the deepest layer to the basement membrane
• Pseudostratified columnar epithelium


  A special type of simple epithelium that appears to be falsely stratified
• Types of epithelial cells based on shape

  • Squamous
  • Cuboidal
  • Columnar
• Simple squamous epithelium


  • A single layer of thin, flat cells
  • Some substances easily pass through this thin layer of cells, but other substances do not
• Functions of simple squamous epithelium

  • Lungs - allows for gas exchange
  • Kidneys - helps filter wastes from the blood while keeping blood cells inside the blood vessels
• Simple cuboidal epithelium


  • A single layer of cube-like cells that carry out active transport, facilitated diffusion, or secretion
  • Have a greater secretory capacity than simple squamous epithelial cells
• Simple columnar epithelium


  • A single layer of tall, thin cells
  • The large size of these cells enables them to perform complex functions, such as secretion
• Functions of simple columnar epithelium

  • Small intestine - produces and secretes mucus and digestive enzymes
• Pseudostratified columnar epithelium


  • Secretes mucus, which covers its free surface
  • Cilia in the airways move the mucus and accumulated debris toward the throat, where it is swallowed
• Types of stratified squamous epithelium

  • Keratinized
  • Nonkeratinized
• Keratinized stratified squamous epithelium

  • The outer layer of the skin
  • The keratin reduces the loss of water from the body
• Nonkeratinized stratified squamous epithelium

  • Provides protection against abrasion and acts as a mechanical barrier
  • Water can move across it more readily than across the skin (keratinized stratified squamous)
• Stratified cuboidal epithelium


  • Consists of more than one layer of cuboidal epithelial cells
  • Functions in absorption, secretion, and protection
• Stratified columnar epithelium


  • Consists of more than one layer of epithelial cells; the surface cells are columnar but the deeper cells are irregular or cuboidal in shape
  • Carries out secretion, protection, and some absorption
• Transitional epithelium


  • A special type of stratified epithelium that can be greatly stretched
  • The shape of the cells change as the epithelium is stretched
  • Lines cavities that can expand greatly, such as the urinary bladder
  • Protects underlying structures from the caustic effects of urine
• Characteristics of the free surface of epithelia

  • Smooth
  • Lined with microvilli
  • Lined with cilia
• Cell connections in epithelia

  • Desmosomes - mechanical links that bind cells together
  • Hemidesmosomes - anchor cells to the basement membrane
  • Tight junctions - prevent the passage of materials between epithelial cells
  • Gap junctions - allow small molecules and ions to pass from one epithelial cell to an adjacent one
• Glands


  Secretory organs that secrete substances onto a surface, into a cavity, or into the bloodstream
• Types of glands


  • Exocrine - with ducts
  • Endocrine - ductless
• Types of exocrine glands based on structure

  • Simple - single, non-branched duct
  • Compound - multiple, branched ducts
• Shapes of exocrine gland secretory regions

  • Tubular
  • Acinar or alveolar
  • Tubuloacinar or tubuloalveolar
• Types of exocrine secretion

  • Merocrine - release of secretory products by exocytosis
  • Apocrine - release of secretory products as pinched-off fragments of the gland cells
  • Holocrine - shedding of entire cells
• Connective tissue


  • Diverse primary tissue type that makes up part of every organ in the body
  • Consists of cells separated from each other by abundant extracellular matrix
• Functions of connective tissue

  • Enclose and separate other tissues
  • Connecting tissues to one another
  • Supporting and moving parts of the body
  • Storing compounds
  • Cushioning and insulating
  • Transporting
  • Protecting
• Connective tissue cells


  • Osteoblasts - form bone
  • Osteocytes - maintain bone
  • Osteoclasts - break down bone
  • Fibroblasts - form fibrous connective tissue
  • Fibrocytes - maintain fibrous connective tissue
  • Chondroblasts - form cartilage
  • Chondrocytes - maintain cartilage
  • Macrophages - ingest foreign substances
  • Mast cells - release chemicals that promote inflammation
• Extracellular matrix of connective tissue

  • Has three major components: protein fibers, ground substance, and fluid
  • The structure of the matrix is responsible for the functional characteristics of connective tissues
• Types of matrix protein fibers

  • Collagen - very flexible but resist stretching
  • Reticular - very fine, short collagen fibers that branch to form a supporting network
  • Elastic - have the ability to return to their original shape after being stretched or compressed
• Ground substance


  • Consists of non-fibrous molecules and is shapeless
  • Consists of proteoglycans, which are large molecules that consist of a protein core attached to many long polysaccharides
• Ground substance


  Non-fibrous protein and other molecules
• Matrix


  • Responsible for the functional characteristics of connective tissues - enables bones and cartilage to bear weight
• Protein fibers in connective tissues

  • Collagen
  • Reticular
  • Elastic