Apical And Basolateral Specializations Of Cells Flashcards
Epithelial tissues are divided into
Lining epithelia and glandular (or secreting epithelia)
Lining epithelia short description
Cells are tightly apposed forming sheets
Glandular or secreting epithelia short description
Cells are tightly apposed together and they form aggregates with different morphology
Characteristics of epithelial cells
- Cells adhere to one another by junctions
- Exhibit polarity, with an apical, basal and lateral domain
- The apical domain is a free surface (not in contact with other cells on this surface)
Cell polarity: regions with biochemical, functional and morphological features:
- morphological-functional polarity
- cytoskeleton key role
- specializations om the plasma membrane of the lateral, basal and apical domains
Morphological-functional polarity meaning + example
Apical region is different from the basal side both at the morphological and biochemical level.
E.g. columnar epithelium of intestine and secreting cells.
Apical specializations
Microvilli, cilia and stereocilia
Microvilli: 1-2 micrometers in length
Cilia: 5-10 micrometers in length
Microvilli in the intestine
Microvilli togetherness with glycocalix (glycoproteins and glycosaminoglycans) form the striated border of the columnar epithelium.
What are microvilli made of?
Actin filaments
What are cilia made of and where are they found?
Contain microtubules. A central couple of microtubules with 9 couples of microtubules at the periphery (atonement). Are enveloped by the plasma membrane. They are inserted into the cell membrane in the basal body, which is formed by 9 triplets of microtubules.
Cilia can remove things we don’t need or help move things along to their final destination. E.g. in the airways with a cleaning function and in the Fallopian tube, transporting the fertilized egg to the uterus.
Apical specializations: stereocilia: how are they formed and where are they found?
Made of actin filaments, very long and branched. Similar to long microvilli. Projections of the apical surface.
Found in the epididymis where they secrete factors needed for spermatozoa maturation.
Lateral specializations types
Cell junctions:
- occluding junctions
- anchoring junctions
- communicating junctions
Occluding junctions and their general function
Tight junctions (also called zonulae occludens) Barrier function, prevent diffusion of water and substances and prevent movement of apical proteins to the lateral domains.
Anchoring junctions and their general function
Adherens junctions (also called zonulae adherens) Desmosomes (also called maculae adherens) Provide mechanical stability linking adjacent cells
Communicating junctions and their general function
Gap junctions
Allow direct communication between adjacent cells
How are occluding/tight junctions formed?
Most apical junction
Point to point fusion of adjacent cells mediated by trans-membrane proteins
This causes the localized sealing of the plasma membrane
Tight junctions look like a series of loops between two adjacent cells due to the point to point adhesion of the external sheets of the two plasma membranes
Type of proteins present in the tight junctions and how they work
Claudin, occludin
Able to bind to cytoplasmic proteins and the cytoskeleton (on the other side of the plasma membrane)
JAM (junction adhesion molecule)
Glycoproteins displaying a long extracellular domain.
Anchoring junctions: adherens junction function and how they are formed
Provide mechanical stability and attach the cells to each other
Contain proteins called cadherins, which are important for pathology
Belt like appearance
Anchoring junctions: desmosomes function and how they are formed
Important to keep epidermal layers attached together
Especially well developed junctions in lining epithelia that’s exposed to much abrasion, like stratified squamous epithelium of the tongue, oral mucosa and skin
Anchored to intermediate keratin filaments
Communicating junctions: gap junctions function and how it is formed
Provide direct communication between adjacent cells
Belt like appearance
Very important protein called beta-catenin
Usually at the base of the lateral domain
Formed by micro channels
Crucial for the survival of bone cells, for example, as they allow diffusion of nutrients and other molecules to the osteocytes
Basal specialization: basement membrane brief description and where it is found
Involves extracellular matrix between the cells of a tissue and the underlying connective tissue which cells are bound to
Found in the lining epithelia, glandular epithelia, endothelium, smooth and skeletal muscle cells, adipocytes and Schwann cells
Functions of the basement membrane
Links cells to underlying connective tissue
Regulate cell polarity and metabolism
Regulate epithelial repair and regeneration processes
Acts as a selective barrier. This selective barrier is critical to the metastatic potential of epithelial cancer cells (carcinomas)
The basement membrane is composed of 2 components
Basal laminators and reticular lamina (lamina reticularis)
The basal lamina
Part of the epithelial cell
