Ch.4- The Tissue Level of Organization

• Tissue


  a collection of specialized cells and cell products that perform a specific function; Tissues in combination form organs, such as the heart or liver
• Histology


  study of tissues
• Four types of tissue

  epithelial, connective, muscle, nervous
• epithelial tissue


  covers exposed surfaces; lines internal passageways; forms glands
• connective tissue

  Fills internal spaces;

  Supports other tissues;

  Transports materials;

  Stores energy
• muscle tissue


  Specialized for contraction;

  Skeletal muscle, heart muscle, and walls of hollow organs
• nervous tissue


  carries electrical signals from one part of the body to another
• epithelial tissue


  includes epithelia and glands
• epithelia(singular)


  Layers of cells covering internal or external surfaces
• Glands


  structures that produce fluid secretions
• functions of epithelial tissue


  provide physical protection; control permeability; provide sensation;produce specialized secretions
• characteristics of epithelia


  Polarity (apical and basal surfaces)

  Cellularity (cell junctions)

  Attachment (basement membrane)

  Avascularity (avascular)

  Regeneration
• Specialization of epithelial cells


  Move fluids over the epithelium (protection)

  Move fluids through the epithelium (permeability)

  Produce secretions (protection and messengers)
• Polarity


  apical surface

  -microvilli increase absorption or secretion

  - cilia on a ciliated epithelium move fluids

  Basolateral surface
• Integrity of epithelia is maintained by

  1. Intercellular connections

  2. Attachment to the basement membrane

  3. Epithelial maintenance and repair
• intercellular connections

  support and communication
• cell adhesion molecules (CAMs)


  transmembrane proteins
• what act as intercellular cement?

  Proteoglycans
• cell junctions


  form bonds with other cells or extracellular material

  1.) Gap junctions

  2.)Tight junctions

  3.)Desosomes
• gap junctions


  -Allow rapid communication

  -Cells held together by interlocking transmembrane proteins

  - Allow small molecules and ions to pass
• Desosomes


  CAMs and proteoglycans link opposing plasma membranes
• spot desmosomes


  tie cells together; allow bend and twist
• Hemidesmosomes


  attach cells to the basement membrane
• tight junctions


  Between two plasma membranes; Adhesion belts attaches to terminal web; Prevent passage of water and solutes; Keep enzymes,acids, and wastes in the lumen of the digestive tract; Attachment to the basement membrane
• basal lamina


  closest to the epithelium
• reticular lamina


  deeper portion of the basement membrane, provides strength
• Epithelial Maintenance and Repair


  Epithelial cells are replaced by continual division of stem cells; located near basement membrane
• based on shape


  Squamous epithelia — thin and flat

  Cuboidal epithelia — square shaped

  Columnar epithelia — tall, slender rectangles
• Based on layers


  Simple epithelium — single layer of cells

  Stratified epithelium — several layers of cells
• Squamous epithelia


  -simple squamous epithelia

  a.) Absorption and diffusion

  -Stratified squamous epithelia

  a.) Protect against mechanical stresses
• Cuboidal epithelia


  -Simple cuboidal epithelia

  a.) Secretion and absorption

  b.) Glands and portions of kidney tubules

  - Stratified cuboidal epithelia

  a.) Relatively rare

  b.) Ducts of sweat glands and mammary glands
• Transitional epithelia


  Tolerate repeated cycles of stretching without damage;

  Appearance changes as stretching occurs;

  Found in urinary bladder
• Columnar epithelia


  -Simple columnar epithelia

  a.) Absorption and secretion

  b.) Found in stomach, small intestine, large intestine
• Pseudostratified columnar epithelia


  Typically have cilia;

  Found in nasal cavity, trachea, bronchi
• Stratified columnar epithelia


  Relatively rare;

  Provide protection in pharynx, anus, urethra
• Glandular epithelia


  Glands are collections of epithelial cells that produce secretions
• endocrine glands


  release hormones into the bloodstream
• exocrine glands


  produce exocrine secretions; discharge secretions through ducts onto epithelial surfaces
• Methods of secretion


  merocrine, apocrine, holocrine
• merocrine secretion


  Released by secretory vesicles (exocytosis)

  Example: merocrine sweat glands