epithelium 2

• lateral membrane specialisations: tight junctions, communicating junctions, adhering junctions
• adhering junctions stick epithelial cells together or to basal lamina
• communicating junctions

  allow cytoplasms of adjacent cells to be connected
• tight junction functions

  prevent substances moving between cells, forcing them to use transcellular pathway, and keeps apical membrane proteins in the apical region
• tight junctions are known as zonula occludens
• tight junctions from blood brain barrier
• adhering junctions: zonula adherens, spot desmosome, hemidesmosome
• zonula adherens (belt desmosome) is the most apical and found under zonla occludens
• ZA action

  form a band around top of cell, adhering it to neighbour cells. they are leaky but strong
• ZA have adhesion plaques where actin anchor
• macula adherens is known as desmosome
• desmosomes are only found in isolated spots and have intermediate filaments anchoring into plaques, making them electron dense
• the more friction, the greater the number of desmosomes
• epidermis has many desmosomes
• gap junction action

  allow communication between cytoplasms of adjacent cells
• connexon channel action

  in gap junctions, allow H2o, ions, nutrient and waste movement
• hemidesmosomes are found on the on the basal cell surface of the epitheliam cell, adhering it to the basal lamina
• hemidesmosomes have intermediate filaments that anchor the cell to the basement membrane
• basement membrane is a product of epithelial cells and connective tissue
• can see the basement membrane with a PAS stain
• cilia move substances along apical surfaces
• microvilli are immotile and increase the surface area for absorption
• stereocilia are immotile and increase surface area
• microvilli have a core of actin microfilaments
• every epithelial surface has microvilli but extent is determined by functional needs
• stereocilia regions

  epididymis and ear
• cilia placement

  respiratory and reproductive lining
• cilia move in sequence and work together to move material on the surface, due to dynein attached to microtubules
• cilia stain acidophilic
• retain connection: exocrine glands secrete substances onto the surface of epithelium via a duct
• endocrine glands: loose connection with epithelium, secretes hormones into blood vessels of connective tissue
• unicellular gland: goblet cell
• goblet cell location

  digestive and respiratory systems
• goblet cell action

  secrete mucus to protect lining from enzymes, acids and invaders
• serous secretion

  watery and protein rich (usually enzymes)
• serous secretion example

  salivary glands and pancreas
• serous glands have a basally located nuclei with close rER, base is stained H and top is stained E
• mucous secretion

  glycoprotein rich (mucus)
• mucous secretion example

  sublingual salivary gland, goblet cell
• mucous cells stain poorly and have a pale cytoplasm