Anatomy Lecture Exam 2

• Individual body cells


  Specialized - each type performs specific functions that maintain homeostasis
• Tissues


  Groups of cells similar in structure that perform common or related function
• Histology


  Study of tissues
• Four basic tissue types

  • Epithelial
  • Connective
  • Muscle
  • Nervous tissue
• Epithelial tissue (epithelium)


  A sheet of cells that covers body surfaces or cavities
• Two main forms of epithelial tissue

  • Covering and lining epithelia
  • Glandular epithelia
• Covering and lining epithelia


  • On external and internal surfaces (example: skin)
• Glandular epithelia


  • Secretory tissue in glands (example: salivary glands)
• Main functions of epithelial tissue

  • Protection
  • Absorption
  • Filtration
  • Excretion
  • Secretion
  • Sensory reception
• Five distinguishing characteristics of epithelial tissue

  • Polarity
  • Specialized contacts
  • Supported by connective tissues
  • Avascular, but innervated
  • Regeneration
• Polarity


  Cells have polarity (top and bottom)
• Apical surface


  Upper free side, is exposed to surface or cavity
• Basal surface


  Lower attached side, faces inwards toward body
• Specialized contacts


  Epithelial tissues need to fit closely together, many form continuous sheets, specialized contact points bind adjacent epithelial cells together
• Supported by connective tissues


  All epithelial sheets are supported by connective tissue
• Basement membrane


  Made up of basal and reticular lamina, reinforces epithelial sheet, resists stretching and tearing, defines epithelial boundary
• Avascular, but innervated


  No blood vessels are found in epithelial tissue, must be nourished by diffusion from underlying connective tissues, but are supplied by nerve fibers
• Regeneration


  Epithelial cells have high regenerative capacities, stimulated by loss of apical-basal polarity and broken lateral contacts, some cells are exposed to friction or hostile substances resulting in damage that must be replaced, requires adequate nutrients and cell division
• Simple epithelia


  Involved in absorption, secretion, or filtration processes
• Simple squamous epithelium


  Cells are flattened laterally, and cytoplasm is sparse, function where rapid diffusion is priority, example: kidney, lungs
• Endothelium


  Lining of lymphatic vessels, blood vessels, and heart
• Simple cuboidal epithelium


  Single layer of cells, involved in secretion and absorption, forms walls of smallest ducts of glands and many kidney tubules
• Simple columnar epithelium


  Single layer of tall, closely packed cells, some cells have microvilli, some have cilia, some layers contain mucus-secreting goblet cells, involved in absorption and secretion of mucus, enzymes, and other substances, found in digestive tract, gallbladder, ducts of some glands, bronchi, and uterine tubes
• Pseudostratified columnar epithelium


  Cells vary in height and appear to be multi-layered and stratified, but tissue is in fact single-layered simple epithelium, many cells are ciliated, involved in secretion, particularly of mucus, and also in movement of mucus via ciliary sweeping action, located mostly in upper respiratory tract, ducts of large glands, and tubules in testes
• Stratified epithelial tissues


  Involve two or more layers of cells, new cells regenerate from below, basal cells divide and migrate toward surface, more durable than simple epithelia because protection is the major role
• Stratified squamous epithelium


  Most widespread of stratified epithelia, free surface is squamous, with deeper cuboidal or columnar layers, located in areas of high wear and tear (example: skin), keratinized cells found in skin, nonkeratinized cells are found in moist linings
• Stratified cuboidal epithelium


  Quite rare, found in some sweat and mammary glands, typically only two cell layers thick
• Stratified columnar epithelium


  Also very limited distribution in body, small amounts found in pharynx, in male urethra, and lining some glandular ducts, usually occurs at transition areas between two other types of epithelia, only apical layer is columnar
• Transitional epithelium


  Forms lining of hollow urinary organs, found in bladder, ureters, and urethra, basal layer cells are cuboidal or columnar, ability of cells to change shape when stretched allows for increased flow of urine and, in the case of bladder, more storage space
• Gland


  One or more cells that makes and secretes an aqueous fluid called a secretion
• Glands classified by


  • Site of product release: Endocrine (internally secreting, example: hormones), Exocrine (externally secreting, example: sweat)
  • Relative number of cells forming the gland: Unicellular (example: goblet cells), Multicellular (example: salivary)
• Endocrine glands


  Ductless glands, secretions are not released into a duct, are released into surrounding interstitial fluid, which is picked up by circulatory system, secrete hormones, messenger chemicals that travel through lymph or blood to their specific target organs
• Exocrine glands


  Secretions are released onto body surfaces, such as skin, or into body cavities, more numerous than endocrine glands, secrete products into ducts, examples include mucous, sweat, oil, and salivary glands, can be unicellular or multicellular
• Connective tissue


  The most abundant and widely distributed of primary tissues, major functions: binding and support, protecting, insulating, storing reserve fuel, and transporting substances (blood)
• Four main classes of connective tissue

  • Connective tissue proper
  • Cartilage
  • Bone
  • Blood
• Characteristics that make connective tissues different from other primary tissues

  • All have common embryonic origin: all arise from mesenchyme tissue as their tissue of origin
  • Have varying degrees of vascularity (cartilage is avascular, bone is highly vascularized)
  • Cells are suspended/embedded in extracellular matrix (ECM) (protein-sugar mesh)
• Three main elements of connective tissue

  • Ground substance
  • Fibers
  • Cells
• Ground substance


  Unstructured gel-like material that fills space between cells, medium through which solutes diffuse between blood capillaries and cells, components include interstitial fluid, cell adhesion proteins, proteoglycans, and water
• Three types of connective tissue fibers

  • Collagen
  • Elastic fibers
  • Reticular
• Collagen


  Strongest and most abundant type, tough, provides high tensile strength