L3 - Epithelium Flashcards
What is the principal function of epithelium
A barrier/boundary membrane
Explain the nature of epithelium
Compactly arranged cells
As sheets are tailored to fit shape of cavity
Rest on non-cellular basement membrane
Often have different types of junctions between them:
Adhering junctions are strong bonds and keep sheets intact
Occluding junctions seal of intercellular space
Gap junctions are used for communication
How do areas exposed to wear and tear manage their epithelial layers?
Often these areas will have a thicker layer of epithelium (stratified), to ensure maintenance of integrity. Basal cells may be capable of division, although cell replacement is a feature of all epithelium
What are the names of the three main epithelial shapes? Be able to describe the shape
Squamous - flat nuclei, thin cells
Cuboidal - square ish with round nuclei
Columnar - more oblong that cuboidal with extended nuclei. Goblet cells are modified columnar cells
How are epithelial layers named?
By the cells closest to the membrane/furtherest from the underlying connective tissue
What are columnar cells often used for?
Absorption, and movement of mucus. They may feature microvilli, which are important for absorption, or Cillia, which are able to ‘beat’ mucus along the surface of a cell. Cillia may be seen especially in layers featuring goblet cells
How do glands develop from epithelial layers?
Epithelial specialisation
The epi cells grow out and undergo canalisation - formation of a hollow tube
Part of the tube specialises, becoming secretory, and secretions are carried to the surface by a duct
Glands can branch and spread into connective tissue. Branched glands are called compound glands
Parts of a gland that are separated by connective tissue are called lobes/lobules
Why does epithelium need to be supported by connective tissue?
Epi are compact sheets of AVASCULAR cells. They need nutritional support from connective tissue, which carries blood vessels and nerves for the epi. In addition, if epi are breached, the underlying connective tissue will release Mast cells (defence reaction)
