Apical And Basolateral Specializations Of Cells

Question 1

Epithelial tissues are divided into

Answer 1

Lining epithelia and glandular (or secreting epithelia)

Question 2

Lining epithelia short description

Answer 2

Cells are tightly apposed forming sheets

Question 3

Glandular or secreting epithelia short description

Answer 3

Cells are tightly apposed together and they form aggregates with different morphology

Question 4

Characteristics of epithelial cells

Answer 4

• 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)

Question 5

Cell polarity: regions with biochemical, functional and morphological features:

Answer 5

• morphological-functional polarity
• cytoskeleton key role
• specializations om the plasma membrane of the lateral, basal and apical domains

Question 6

Morphological-functional polarity meaning + example

Answer 6

Apical region is different from the basal side both at the morphological and biochemical level.
E.g. columnar epithelium of intestine and secreting cells.

Question 7

Apical specializations

Answer 7

Microvilli, cilia and stereocilia
Microvilli: 1-2 micrometers in length
Cilia: 5-10 micrometers in length

Question 8

Microvilli in the intestine

Answer 8

Microvilli togetherness with glycocalix (glycoproteins and glycosaminoglycans) form the striated border of the columnar epithelium.

Question 9

What are microvilli made of?

Answer 9

Actin filaments

Question 10

What are cilia made of and where are they found?

Answer 10

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.

Question 11

Apical specializations: stereocilia: how are they formed and where are they found?

Answer 11

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.

Question 12

Lateral specializations types

Answer 12

Cell junctions:

• occluding junctions
• anchoring junctions
• communicating junctions

Question 13

Occluding junctions and their general function

Answer 13

Tight junctions (also called zonulae occludens)
Barrier function, prevent diffusion of water and substances and prevent movement of apical proteins to the lateral domains.

Question 14

Anchoring junctions and their general function

Answer 14

Adherens junctions (also called zonulae adherens)
Desmosomes (also called maculae adherens)
Provide mechanical stability linking adjacent cells

Question 15

Communicating junctions and their general function

Answer 15

Gap junctions

Allow direct communication between adjacent cells

Question 16

How are occluding/tight junctions formed?

Answer 16

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

Question 17

Type of proteins present in the tight junctions and how they work

Answer 17

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.

Question 18

Anchoring junctions: adherens junction function and how they are formed

Answer 18

Provide mechanical stability and attach the cells to each other
Contain proteins called cadherins, which are important for pathology
Belt like appearance

Question 19

Anchoring junctions: desmosomes function and how they are formed

Answer 19

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

Question 20

Communicating junctions: gap junctions function and how it is formed

Answer 20

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

Question 21

Basal specialization: basement membrane brief description and where it is found

Answer 21

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

Question 22

Functions of the basement membrane

Answer 22

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)

Question 23

The basement membrane is composed of 2 components

Answer 23

Basal laminators and reticular lamina (lamina reticularis)

Question 24

The basal lamina

Answer 24

Part of the epithelial cell