TISSUES

• Histology is the study of tissues
• Intercellular Junctions

  • Tight Junctions
  • Desmosomes
  • Gap Junctions
• Tight junctions are close spaces between cells and are located among cells that form linings
• Desmosomes form spot welds between cells and are located among outer skin cells
• Gap Junctions are tubular channels between cells and are located in cardiac muscle cells
• Epithelial Tissue Characteristics

  • cover organs and the body
  • line body cavities
  • line hollow organs
  • have a free surface
  • have a basement membrane
  • are avascular
  • cells readily divide
  • cells tightly packed
  • cells often have desmosomes
  • function in protection, secretion, absorption, and excretion
  • classified according to cell shape and number of cell layers
• Epithelial tissues are widespread throughout the body and form the covering of all body surfaces.
• Single Squamous

  • epithelial tissue
  • single layer of flat cells
  • substances pass easily through
  • line air sacs
  • line blood vessels
  • line lymphatic vessels
• Simple cuboidal

  • epithelial tissue
  • single layer of cube-shaped cells
  • line kidney tubules
  • cover ovaries
  • line ducts of some glands
• Simple Columnar

  • epithelial tissue
  • single layer of elongated cells
  • nuclei usually near the basement
  • membrane at the same level
  • sometimes possess cilia and microvilli
  • often have goblet cells
  • line uterus, stomach, and intestines
• Pseudostratified columnar

  • epithelial tissue
  • single layer of elongated cells
  • nuclei at two or more levels
  • appear striated
  • often have cilia and goblet cells
  • line respiratory passageways
• Stratified Squamous

  • epithelial tissue
  • many cell layers
  • top cells are flat
  • can accumulate keratin
  • outer layer of skin
  • line oral cavity, vagina, and anal canal
• Stratified Cuboidal

  • epithelial tissue
  • 2 to 3 layers
  • cube-shaped cells
  • line ducts of mammary glands, sweat glands, salivary glands, and pancreas
• Stratified Columnar

  • top layer of elongated cells
  • cube-shaped cells in deeper layers
  • line part of male urethra and part of pharynx
• Transitional

  • epithelial tissue
  • many cell layers
  • cube-shaped and elongated cells
  • line urinary bladder, ureters, and part of urethra
• Glandular Epithelium is composed of cells that are specialized to produce and secrete substances
• There are two types of glandular epithelium: endocrine glands that are ductless, and exocrine glands that have ducts
• Unicellular exocrine gland:

  • composed of one cell
  • goblet cell
• Multicellular exocrine gland

  • composed of many cells
  • sweat glands, salivary glands
  • simple and compound (single or multiple branched ducts)
• Exocrine gland that consists of a single duct is Simple Tubular

  
• Exocrine gland which has a single duct that splits to three tube-shaped ducts is Simple Branched Tubular

  
• Exocrine gland which has a coiled tube is Simple Coiled Tubular

  
• Exocrine gland which has a single duct splitting into 3 alveoli-shaped ducts is Simple Branched Alveolar

  
• Exocrine gland which has splits two times into tube-shaped ducts is Compound Tubular

  
• Exocrine gland which splits two times into alveoli-shaped ducts is Compound Alveolar

  
• The three types of glandular secretions are:

  • Merocrine glands (fluid products)
  • Apocrine glands (cellular products)
  • Holocrine glands (secretory products)
• Connective Tissues:

  • most abundant tissue type
  • bind structures
  • provide support and protection
  • serve as frameworks
  • fill spaces
  • store fat
  • produce blood cells
  • protect against infections
  • help repair tissue damage
  • have an extracellular matrix, varying degrees of vascularity, cells that usually divide
• Fibroblasts

  • major cell connective tissue
  • fixed cell
  • most common connective tissue cell
  • large and star-shaped
  • produce fibers
• Macrophages

  • major cell connective tissue
  • wandering cell
  • phagocytic (immune cells that can kill microorganisms)
  • important in injury or infection)
• Mast Cells

  • major cell connective tissue
  • fixed cell
  • release heparin (decrease clotting)
  • release histamine (causes allergic reactions)
• Collagenous Fibers

  • fiber type connective tissue
  • thick
  • composed of collagen
  • great tensile strength
  • abundant in dense connective tissue
  • hold structures together
  • tendons and ligaments
• Elastic Fibers

  • fiber type connective tissue
  • bundles of microfibrils embedded in elastin
  • fibers branch
  • elastic
  • vocal cords and air passages
• Reticular fibers

  • fiber type connective tissue
  • very thin collagenous fibers
  • highly branched
  • form supportive networks
• Connective tissue proper

  • loose connective tissue
  • adipose tissue (body fat)
  • reticular, dense, and elastic connective tissue
• Specialized connective tissue

  • Cartilage
  • Bone
  • Blood
• Loose connective tissue

  • mainly fibroblasts
  • fluid to gel-like matrix
  • collagenous fibers
  • elastic fibers
  • bind skin to structures
  • beneath most epithelia
  • blood vessels nourish nearby epithelial cells
  • between muscles
• Adipose tissue

  • connective tissue
  • Adipocytes (energy storage)
  • cushions
  • insulates
  • store fats
  • beneath skin
  • behind eyeballs
  • around kidneys and heart
• Reticular connective tissue

  • composed of reticular fibers
  • supports internal organ walls
  • walls of liver, spleen, lymphatic organs
• Dense connective tissue

  • packed collagenous fibers
  • elastic fibers
  • few fibroblasts
  • bind body parts together
  • tendons, ligaments, dermis
  • poor blood supply
• Elastic connective tissue

  • abundant in elastic fibers
  • some collagenous fibers
  • fibroblasts
  • attachments between bones
  • walls of large arteries, airways, and heart