Chapter 4 (notes)

• Tissue


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


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

  • Epithelial
  • Connective
  • Muscle
  • Nervous
• 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
• Simple epithelium


  Consists of a single layer of cells, with each extending from the basement to the free surface
• Pseudostratified columnar epithelium


  A special type of simple epithelium that appears to be falsely stratified, consisting of one layer of cells with all attached to the basement membrane, due to variations in the shape of the cells
• Types of epithelial cells based on idealized shapes

  • Squamous
  • Cuboidal
  • Columnar
• 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
• 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
• Stratified squamous epithelium


  • Forms a thick epithelium because it consists of several layers of cells
  • The deepest cells are cuboidal or columnar and are capable of dividing and producing new cells, but the naming is based on the shape of the surface cells
  • There are two types: keratinized and nonkeratinized
• Keratinized stratified squamous epithelium

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

  • The stratified squamous epithelium of the mouth is a moist nonkeratinized stratified squamous epithelium
  • This nonkeratinized stratified squamous epithelium provides protection against abrasion and acts as a mechanical barrier
  • Water, however, 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
  • This epithelial type is relatively rare and is found in sweat gland ducts, ovarian follicular cells, and the salivary glands
  • Its function is 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
  • Like stratified cuboidal epithelium, stratified columnar epithelium is relatively rare, found in the mammary gland ducts, the larynx, and a portion of the male urethra
  • This epithelium 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
  • Also protects underlying structure, like the urinary bladder, from the caustic effects of urine
• Free cell surfaces


  Most epithelia have a free surface that is not in contact with other cells and faces away from underlying tissues<|>The characteristics of the free surface reflect its functions<|>The free surface can be smooth or lined with microvilli or cilia<|>Cilia move materials over the top of the cell<|>Microvilli increase surface area
• Columnar cells


  • Deeper
  • Irregular or cuboidal in shape
• Stratified columnar epithelium


  • Relatively rare, found in the mammary gland ducts, the larynx, and a portion of the male urethra
• Transitional epithelium


  A special type of stratified epithelium that can be greatly stretched
• Transitional epithelium


  • The shape of the cells change as the epithelium is stretched
  • Lines cavities that can expand greatly, such as the urinary bladder
  • Protects underlying structure, like the urinary bladder, from the caustic effects of urine
• Free cell surfaces


  • Most epithelia have a free surface that is not in contact with other cells and faces away from underlying tissues
  • The characteristics of the free surface reflect its functions
  • The free surface can be smooth or lined with microvilli or cilia
  • Cilia move materials over the top of the cell
  • Microvilli increase surface area
• Cell connections


  • Cells have several structures that hold one cell to one another or to the basement membrane
  • These structures do three things: mechanically bind the cells together, help form a permeability barrier, and provide a mechanism for intercellular communication
  • Desmosomes are mechanical links that bind cells together
  • Hemidesmosomes are half desmosomes that anchor cells to the basement membrane
  • Tight junctions prevent the passage of materials between epithelial cells because they completely surround each cell, similar to the way a belt surrounds the waist. Tight junctions are found in the lining of the intestines
  • Materials that pass through the epithelial layer must pass through the cells, so those cells regulate what materials can cross
  • Gap junctions are small channels that allow small molecules and ions to pass from one epithelial cell to an adjacent one
  • Most epithelial cells are connected to one another by gap junctions, and researchers believe that molecules or ions moving through the gap junctions act as communication signals to coordinate the activities of the cells
• Exocrine gland structures


  Exocrine glands can be classified according to how products leave the cell<|>Merocrine secretion involves the release of secretory products by exocytosis<|>Apocrine secretion involves the release of secretory products as pinched-off fragments of the gland cells<|>Holocrine secretion involves the shedding of the entire cells
• Connective tissue


  • A diverse primary tissue type that makes up part of every organ in the body
  • Connective tissue differs from the other three tissue types in that it consists of cells separated from each other by abundant extracellular matrix
  • Connective tissue is diverse in both structure and function
  • Connective tissue is comprised of cells, protein fibers, and 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
• Extracellular matrix


  The extracellular matrix of connective tissue has three major components: protein fibers, ground substance, and fluid<|>Ground substance consists of non-fibrous protein and other molecules<|>The structure of the matrix is responsible for the functional characteristics of connective tissues- for example, they enable bones and cartilage to bear weight
• Matrix protein fibers


  • Three types of protein fibers - collagen, reticular, and elastic - help form most connective tissues
  • Collagen fibers, which resemble microscopic ropes, are very flexible but resist stretching
  • Reticular fibers are very fine, short collagen fibers that branch to form a supporting network
  • Elastic fibers have the ability to return to their original shape after being stretched or compressed, giving tissue an elastic quality
• Matrix ground substance consists of non-fibrous protein and other molecules
• Blǂ of movinDž abouǓ anǁ ingestinDž foreigǏ suǞtanceǒ, includinDž microorganismǒ

  In the connective tissue
• Components of the extracellular matrix of connective tissue

  • Protein fibers
  • Ground substance
  • Fluid
• Ground substance


  Consists of non-fibrous protein and other molecules
• Structure of the matrix

  Responsible for the functional characteristics of connective tissues - for example, they enable bones and cartilage to bear weight
• Types of protein fibers

  • Collagen
  • Reticular
  • Elastic
• Reticular fibers


  • Very fine, short collagen fibers that branch to form a supporting network
• Elastic fibers


  • Have the ability to return to their original shape after being stretched or compressed, giving tissue an elastic quality
• Proteoglycans


  Trap large quantities of water between the polysaccharides, which allows them to return to their original shape when compressed or deformed
• Types of connective tissue

  • Embryonic
  • Adult
• Loose connective tissue


  Consists of relatively few protein fibers that form a lacy network, with numerous spaces filled with ground substance and fluid
• Subdivisions of loose connective tissue

  • Areolar
  • Adipose
  • Reticular