epithelium

• epithelial tissue has virtually no extracellular material between cells
• cell junctions adhere cells to each other and to the extracellular matrix
• the basal lamina combines with the reticular lamina to form the basement membrane
• the epithelial cells sit on top of the basal lamina, seperating them from the connective tissue
• the reticular lamina is formed by the connective tissue
• the connective tissue provides structural and metabolic support to the epithelium
• every epithelium lacks blood vessels, making it avascular
• epithelial tissue contains stem cells that undergo mitosis, so it can regenerate
• apical specialisations: microvilli, cilia, stereocilia
• lateral specialisations: cell junctions
• basal specialisations: cell junctions and basal lamina
• simple squamous provides a barrier of least resistance to diffusion and is frictionless
• simple squamous lines surfaces for passive diffusion such as alveoli, glomerulus, and capillaries
• simple cuboidal lines surfaces of ducts and tubules, such as the kidney tubules
• simple cuboidal provides a simple conduit for movement, as well as secretion and absorption
• simple columnar provides a simple lining for absorption (with microvilli) or movement along surface (with cilia)
• simple columnar lines most of the gastrointestinal tract (with microvilli) and female reproductive tracts (with cilia)
• stratified squamous provides a solid barrier to abrasion in dry (keratinised) or moist (non keratinised) environment
• non keratinised is found in oral cavity, vagina, and anal canal
• keratinised is found on epidermis of skin
• stratified cuboidal/columnar is for transport of substances and is not involved in secretion or absorption
• stratified cuboidal is found in duct of salivary gland, pancreas, or liver
• pseudostratified columnar can transport material along it in the respiratory tract (with goblet cells), or is used for absorption in male reproductive tract (with stereocilia)
• transitional is water tight and can expand and stretch, it is found exclusively in the urinary system
• epithelium relies upon underlying LCT for metabolic support as doesnt have blood vessels