Epithelial Tissue Flashcards
4 basic types of tissues
- Epithelial
- Connective
- Muscle
- Nervous
3 main locations of epithelial tissue
- Cover exterior surfaces (barrier epithelium)
- Line internal cavities (barrier epithelium)
- Form secretory portion of glands and their ducts (glandular epithelium)
Epithelial has exposed free surfaces that makes them different from other other tissue. What are the free surfaces?
- External body surface (skin)
- Luminal surface (lining of the intestine)
Cellular composition of epithelial tissue
- cells are closely aggregated
- little or no extracellular matrix.
- adhesion between cells is very strong
- Avascular, but epithelial cells are found lining the walls of blood vessels.
3 domains of epithelial cells
- Apical domain
- Lateral domain
- Basal domain
What is the apical domain and what modifications does it have?
- forms the external or luminal surface of the cell.
- modifications include: microvilli, Stereocilia, or cilia.
Microvilli: Function? Location? Size? What filaments? Other characteristics?
- increases the surface are and are found in the epithelia where absorption is important (small intestine, kidney)
- 1 x 0.01 microns
- Core of microvillus is formed by actin filaments and bound together by actin proteins (fimbrin and fascin).
- Anchored into the membrane by the lateral anchoring proteins (myosin I)
- Amorphous apex is formed by villin into which the actin filaments are anchored.
Stereocilia:
Characteristics?
Function?
- modified microvilli, not related to cilia
- long, sometimes branching projections with the core formed by actin filaments.
- when found in epididymis they play an important role in the absorption of fluid
- in the inner ear cochlea they are sensory receptors
Cilia:
Function?
Size?
Structure?
- important to move substances (mucus) along the surface of the epithelium and are found in the area where this transport is necessary (respiratory tract, oviduct)
- 2-10 x 0.25 microns
- Core is formed by 10 microtubules that form the axoneme
- base is attached to the centriole (basal body), formed by 9 triplets of microtubules without a central pair.
What causes primary ciliary dyskinesia (immotile ciliary syndrome)?
-consequences?
-genetic defect of ciliary proteins that results in the malformation of the skeleton of cilia
-causes uncoordinated or absent ciliary beating
-Consequences:
A. Embryological pathologies (dextrocardia)
B. Impaired development of skull air sinuses
C. No mucus removal from lungs causes recurrent and severe chest infections
D. Infertility is common-flagella of spermatozoa and cilia in ovum don’t beat
What do secretory vesicles in epithelial cells do?
-involved in the production and secretion of macromolecules, such as enzymes and mucins
What is the lateral domain?
-characterized by the presence of cell junctions that allow the tissue to function as a whole.
Three major classes of cellular junctions in the epithelium?
What are terminal bars?
- Occluding junctions
- Anchoring junctions
- Communicating junctions
-Junctions often occur together and form junctional complexes. In light microscope these junctional complexes can be visualized as terminal bars.
What are occluding junctions (tight junctions) and what is there role? They are in the lateral domain.
- mostly present towards the apical portion of the cell and represented by zonula occludens.
- are belt-like junctions formed by sealing strands of transmembrane proteins that bind membranes of two adjacent cells
- found in cells with secretory role (stomach epithelia) or in cells with absorptive role (kidney tubule cells)
- zonula occludens are virtually impermeable
- main function is to prevent diffusion by blocking paracellular pathways
