ANAPHY

• Epithelial tissues are found in different areas like body coverings, body linings, and glandular tissue
• Epithelium characteristics:

  • Cells fit closely together
  • Tissue layer always has one free surface
  • The lower surface is bound by a basement membrane
  • Avascular (have no blood supply)
  • Regenerate easily if well nourished
• Classifications of epithelium:

  • Number of cell layers:
  • Simple: one layer
  • Stratified: more than one layer
  • Shape of cells:
  • Squamous: flattened
  • Cuboidal: cube-shaped
  • Columnar: column-like
• Simple epithelium types:

  • Simple squamous: single layer of flat cells, lines body cavities, lungs, and capillaries
  • Simple cuboidal: single layer of cube-like cells, common in glands and their ducts, forms walls of kidney tubules, covers the ovaries
  • Simple columnar: single layer of tall cells, often includes goblet cells that produce mucus, lines the digestive tract
• Transitional epithelium:

  • Shape of cells depends on the amount of stretching
  • Lines organs of the urinary system
• Glandular epithelium:

  • Gland: one or more cells that secrete a particular product
  • Two major gland types: endocrine gland (ductless, secretes hormones) and exocrine gland (empties through ducts to the epithelial surface, includes sweat and oil glands)
• Connective tissue characteristics:

  • Variations in blood supply: some well vascularized, some avascular
  • Extracellular matrix: non-living material that surrounds living cells, includes ground substance (mostly water with adhesion proteins and polysaccharide molecules) and fibers (collagen, elastic, reticular)
• Connective tissue types:

  • Bone (osseous tissue): composed of bone cells in cavities, hard matrix of calcium salts, large numbers of collagen fibers, used to protect and support the body
  • Hyaline cartilage: most common cartilage, composed of abundant collagen fibers and a rubbery matrix, fetal skeleton is hyaline cartilage
  • Elastic cartilage: provides elasticity, example: supports the external ear
• Connective tissue types (cont.):

  • Fibrocartilage: highly compressible, example: forms cushion-like discs between vertebrae
  • Dense connective tissue: main matrix element is collagen fibers, cells are fibroblasts, examples include tendons and ligaments
• Connective tissue types (cont.):

  • Areolar connective tissue: most widely distributed, soft, pliable tissue, contains all fiber types, can soak up excess fluid
  • Adipose tissue: matrix is an areolar tissue with fat globules, functions in insulation, organ protection, and fuel storage
• Connective tissue types (cont.):

  • Reticular connective tissue: delicate network of interwoven fibers, found in lymphoid organs like lymph nodes, spleen, and bone marrow
  • Blood: blood cells surrounded by fluid matrix, functions as a transport vehicle for materials
• Muscle tissue types:

  • Skeletal muscle: voluntary control, striated, multinucleated, attaches to connective tissue
  • Cardiac muscle: involuntary, found only in the heart, striated, one nucleus per cell
• Muscle tissue types (cont.):

  • Smooth muscle: involuntary, surrounds hollow organs, no visible striations, one nucleus per cell
• Nervous tissue:

  • Composed of neurons and nerve support cells
  • Functions to send impulses to other areas of the body, with irritability and conductivity
• Tissue repair:

  • Regeneration: replacement of destroyed tissue by the same kind of cells
  • Fibrosis: repair by dense fibrous connective tissue (scar tissue)
• Events in tissue repair:

  • Capillaries become very permeable, introducing clotting proteins and walling off the injured area
  • Formation of granulation tissue and regeneration of surface epithelium
• Tissues that regenerate easily:

  • Epithelial tissue, fibrous connective tissue, and bone
• Tissues that regenerate poorly:

  • Skeletal muscle
• Tissues that are replaced largely with scar tissue:

  • Cardiac muscle, nervous tissue within the brain and spinal cord
• Developmental aspects of tissue:

  • Epithelial tissue arises from all three primary germ layers
  • Muscle and connective tissue arise from the mesoderm
  • Nervous tissue arises from the ectoderm
  • With old age, there is a decrease in mass and viability in most tissues