Histology

• Histology


  The microscopic study and classification of animal cells and tissues
• Histology links cell structure to function
• Animal bodies have a hierarchical organization

  • Cells
  • Tissues
  • Organs
  • Organ systems
• Emergent properties arise at each level (new properties that arise when components interact)
• Tissues


  Collections of cells that carry out a specific function
• Organs


  Collection of tissues working together for a specific function
• Most organs made of multiple tissue types
• Organ system


  Group of organs that have related functions
• 4 major types of tissues

  • EPITHELIAL
  • CONNECTIVE
  • MUSCLE
  • NERVOUS
• EPITHELIAL tissue


  • Cheek cells
  • Frog kidney tubule (nephron)
  • Frog intestinal lining
• NERVOUS tissue


  • SKIN (multiple tissues)
  • Human skin
  • Frog skin
• Epithelial Tissue


  • Lines all spaces inside and outside the body
  • Forms outer layer of skin and lines hollow structures (e.g. respiratory tract, digestive tract, blood vessels)
• Functions of Epithelial Tissue

  • Regulates movement of substances in and out of the body
  • Protection - e.g. skin surface keeps water in and pathogens out
  • Secreting substances - e.g. digestive enzymes, mucus
  • Absorbing substances - e.g. nutrients
• Structure of Epithelial Tissue

  • Cells closely-packed in a continuous sheet
  • Cells attached to the basement membrane - an extracellular matrix secreted by the cells
  • Apical vs. basal surfaces
• Epithelial tissue classified by number of cell layers

  • Simple - one layer
  • Stratified - multiple layers
• Epithelial tissue classified by cell shape

  • Squamous - flat
  • Cuboidal - height = width
  • Columnar - tall and narrow
• Nucleus shape reflects cell shape!
• Cell shape may change from basal to apical surface


  • When more than 1 layer, shape determined by cells at apical surface
  • Apical Surface = squamous
  • Basal Surface = cuboidal
• Frog kidney nephron (tubule)

  • Kidneys filter blood and remove nitrogenous waste
  • Make urine
  • Nephrons - functional unit of kidney; microscopic looped tubes
• Frog kidney nephron (tubule) composition

  Composed of simple cuboidal epithelial tissue rolled into tubes
• Frog intestinal lining


  • Intestine for nutrient absorption
  • Epithelial layer made of simple columnar cells
  • Secretes mucus
• Cross-section of Frog Intestine
• Functions of Connective Tissue

  Connection, support, protection, storage and insulation
• Connective tissue often found under epithelial tissue
• Structure of Connective Tissue

  • Cells widely-spaced in an extracellular matrix (ECM)
  • Matrix contains protein fibers (structure and flexibility)
  • Can be liquid (e.g. blood plasma), semisolid (e.g. cartilage), or solid (e.g. bone)
• Cartilage


  • Chondrocytes = cartilage cells ("chondro" means cartilage)
  • Lacunae - spaces in matrix that house chondrocytes
  • Matrix - made of protein fibers and a polysaccharide that gives rubbery texture (chondroitin sulfate)
• Compact Bone


  • Osteocytes = bone cells ("osteo" means bone)
  • Matrix - made of protein fibers and salts (e.g. calcium phosphate makes it hard)
  • Blood vessels and nerves travel through hollow channels due to hard matrix
• Osteon


  • The functional unit of bone contains:
  • Haversian/Central canal with blood vessels and nerves
  • Lamellae - concentric layers of bone matrix, contain bone cells
• Osteocytes


  • Bone cells
  • Lacunae - spaces that house osteocytes
  • Canaliculi - channels in matrix that extend from each lacuna
• Connective tissue: Compact Bone
• Blood


  • Erythrocytes = red blood cells (RBCs) - contain hemoglobin protein that carries O2
  • Leukocytes = white blood cell (WBCs) - immunity
  • Platelets are cell fragments that promote clotting
  • Matrix - plasma (mostly H2O)
• Connective tissue: human blood
• Muscle Tissue


  • Consists of electrically excitable fibers that contract to generate force and movement
  • Made of overlapping and interacting actin and myosin protein filaments
• 3 types of Muscle Tissue

  • Smooth
  • Skeletal
  • Cardiac
• Smooth Muscle


  Mostly found in walls of hollow structures, contract to move substances (e.g. blood vessels, digestive tract)
• Skeletal Muscle


  Attached to and moves skeleton
• Cardiac Muscle


  In heart, contracts to pump blood
• Arrangement of Muscle Tissue

  • Smooth muscle - Not striated, actin and myosin filaments arranged irregularly
  • Skeletal and Cardiac muscle - Striated, actin and myosin filaments arranged in regularly repeating pattern
• Smooth Muscle


  Involuntary movement (not consciously controlled)
• Skeletal Muscle


  • Fibers - cells that are made of multiple, fused cells
  • Skeletal muscle movement is voluntary (consciously controlled)