Lecture X

• Epithelial tissues line body structures
• Epithelial tissues named by the amount of layers and the shape
• Internal only is the endothelia
• General characteristics of the epithelia:

  • avascular
  • attachment
  • cellularity
  • regeneration
  • sensation
  • polarity
• Avascular: nutrients diffuse in from other tissues
• Attachment: always attached to underlying basement membrane
• Cellularity: most of mass is cells, very little is extracellular material
• Regeneration: rapid mitosis
• Sensation: some neuroepithelia exist and allow for communication with neurons
• Polarity: not based on ions, unequal distribution of proteins and organelles
• Basal surface is attached to the basement membrane
• Basal surface is connected to basolateral surfaces
• Apical surface is also known as the free edge
• Apical surface faces either the external or internal space
• Apical surface often has cilia or microvilli
• Cilia sweeps substances to be disposed of, such as in the nose
• Cilia in the respiratory system
• Microvilli in digestive system
• Basal lamina from plasma membrane
• Reticular lamina from connective tissue
• Cells are attached via CAMS and to the basement membrane
• Two types of layers: simple and stratified
• Simple is a single layer of cells
• Simple. Every cell is attached to the basement membrane
• Simple. Lines internal structures
• Simple. Secretion and absorption (functions)
• Pseudostratified are a single layer which looks like many
• Pseudostratified. Protect, secrete, absorb (functions)
• Stratified is many layers stacked onto each other
• Stratified. Layers help protect the body, often associated with external surfaces
• Stratified. Some secretion and absorption is slower when compared the simple layers
• Three types of shapes: squamous, cuboidal, and columnar
• Squamous is flat cells, also the most common
• Simple squamous epithelia line internal structures
• Simple squamous epithelia have smooth surfaces
• Simple squamous epithelia are for rapid absorption, secretion, and diffusion
• Stratified squamous epithelia have multiple layers of cells which create the strong, thin layer of an organ
• Cuboidal is semi-thick cells for relatively rapid secretion, absorption, and diffusion
• Cuboidal is more selective than squamous
• Simple cuboidal epithelia line internal ducts, some endocrine glands