Histology

• What are the four categories of tissue in histology?

  Epithelial, connective tissue, muscular tissue, and nervous tissue
• What are the functions of epithelium?

  • Acts as a barrier for internal/external environment
  • Provides mechanical protection
  • Involved in absorption or secretion
• Into what two types can epithelium be subdivided?

  Surface epithelium and glandular epithelium
• How can specialized functions of epithelium be determined?

  • Structural modifications to the surface
  • Internal modifications
  • Types of junctions between cells
• What are the three types of junctions in epithelial cells and their functions?

  1. Occluding (tight) junctions: prevent diffusion of molecules and vary permeability
  2. Anchoring (adhering) junctions: link cells and provide mechanical strength
  3. Communicating (gap) junctions: allow movement of molecules between cells
• Where do all epithelial cells rest?

  On the basement membrane
• How can surface epithelial cells be classified?

  • Number of cell layers
  • Shape
  • Specialization
• What is the characteristic of simple squamous epithelium?

  It is suited for areas where mechanical protection is not required, such as blood vessels
• What is the function of simple cuboidal epithelium?

  It is suited to surfaces with an absorptive or secretory role
• Where is simple columnar epithelium typically found?

  In areas with an absorptive role, such as the small intestine
• What characterizes stratified squamous epithelium and where is it functionally suited?

  • Cells are stacked on top of each other on the basement membrane
  • Functionally suited for areas with varying mechanical protection needs, such as the esophagus
  • May have keratinized cells on top in areas of mechanical action, like the foot pad of a dog
• What is transitional epithelium and where is it found?

  It is functionally suited to surfaces that need to stretch, such as the urinary bladder
• What is pseudostratified ciliated columnar epithelium and its function?

  It is involved in cleansing and moistening surfaces, such as in the respiratory system
• What are the two types of glandular epithelial tissue?

  • Goblet cells
  • Secretory cells
• What are goblet cells?

  Single cells that retain connection with surface epithelial cells
• How are secretory cells classified in relation to ducts?

  If they have a duct to the surface, they are exocrine; if without a duct, they are endocrine
• How do exocrine and endocrine glands develop from epithelial cells?

  • Both proliferate on the surface of epithelial cells into the underlying connective tissue
  • Exocrine glands invaginate down into the connective tissue and specialize into secretion-producing cells
  • Endocrine glands disintegrate their connection to the surface epithelium, allowing secretion to travel to target organs
• How do exocrine glands function in secretion?

  • Cells invaginate down into the connective tissue
  • Specialize into secretion-producing cells
  • Cells closest to the surface act as ducts, allowing secretion to travel to the surface
• How do endocrine glands function in secretion?

  • Cells become secretory and invaginate down into the connective tissue
  • Surface epithelium separates from the secretory unit
  • Secretion travels to target organs
• What are the two main types of secretion produced by exocrine glands?

  • Serous secretion: dark under H&E stain
  • Mucus secretion: pale under H&E stain
• What is the primary function of connective tissue?

  To connect and support overlying epithelium
• What structures pass through connective tissue?

  Blood vessels, glandular epithelium, and nerves
• What are the four types of connective tissue?

  • Embryonic
  • General adult (subtypes: loose, dense regular, and irregular)
  • Adipose
  • Special supportive (subtypes: cartilage, bone, and blood)
• What is the role of general adult connective tissue?

  • Supports and connects different tissues
• What are the functions of adipose connective tissue?

  • Provides protection
  • Offers insulation
  • Serves as energy reserves
• What components make up connective tissue?

  Cell type, fiber, extracellular matrix, and ground substance
• What are resident cells in connective tissue?

  • Always present in connective tissue
  • Include mesenchymal cells, macrophages, adipocytes, and fibroblasts
• What are transient cell populations in connective tissue?

  • Not always present in connective tissue
  • Include plasma cells, eosinophils, neutrophils, and lymphocytes
• What are the characteristics of loose, dense regular, and dense irregular connective tissues?

  • Loose CT: more cells than fibers, found where little support is needed
  • Dense regular CT: more fibers than cells, fibers are aligned, found in tendons
  • Dense irregular CT: more fibers than cells, fibers arranged in multiple directions
• What do adipose cells produce?

  Fat
• What are the differences between white fat and brown fat?

  • White fat: energy store
  • Brown fat: involved in heat production
• What is unique about adipocytes in connective tissue?

  • They have secretory glands embedded into them
• What is the structure of adipocytes?

  • Cytoplasm filled with a single lipid droplet
  • Nucleus pushed to the edge
• Where is muscle tissue found?

  In the wall of hollow organs, associated with the skeleton, and in the heart
• What are the three types of muscle fibers?

  • Skeletal
  • Cardiac
  • Smooth
• How can muscle tissue be classified based on control?

  It can be classified as voluntary or involuntary
• What are the characteristics of skeletal muscle tissue?

  • Transverse section shows multiple peripheral nuclei
  • Cytoplasm is full of myofibrils
  • Long unbranched fibers with limited connective tissue between fibers
• What are the characteristics of cardiac muscle tissue?

  • Transverse section shows a single central nucleus
  • Cross-section is fairly uniform in size with lots of connective tissue
  • Longitudinal section shows a central nucleus, striations, short branched fibers, and intercalated discs
• What are the characteristics of smooth muscle tissue?

  • Transverse section shows variable diameter with a couple of central nuclei
  • Longitudinal section shows central nuclei, non-striated, and short tapering fibers