Epithelium 4

Question 1

Intercellular junctions types:

Answer 1

1. Tight or occluding junctions
2. Anchoring junctions
3. Gap junctions
4. Desmosores (macula adherens)

Question 2

Tight a occluding junctions structure
(Like a glue )

Answer 2

Adjacent cell membranes appear used together due to tight interactions between the transmembrane proteins
* cluadin and occluding

Question 3

Function at occluding junctions

Answer 3

1. Molecules only go through the cells when crossing the epithelium ( transcellular pathway rather than the para cellular pathway)
2. Prevents passive flow of materials between the cells
3. Maintain 2 distinct membrane domains topical and basolateral )

Question 4

Site of occluding junctions,

Answer 4

Present at the apical end of cells
Encircling the cells ( zonulae occludes )

Question 5

Anchoring junctions: zonulae adherent
( touching finger tips )
Structure

Answer 5

• Cell adhesions are mediated by cadherins transmembrane proteins
• identical cadherins bind to each other from adjacent cells
  *At the cytoplasmic ends cadherins bind to catching that link to actin
• a small electron dense plaque appears at the intercellular component. (Where fingers touch)

Question 6

Function of anchoring junctions

Answer 6

1.tight and adherent junctions hold cells together
2. Stabilize, and strengthen the occluding bands

Question 7

.desmosome structure

Answer 7

Disc shaped structures that consists of a cytoplasmic adhesions plaques formed of proteins and placed on the cytosolic race of the 2 cell membranes
The 2 plaques are connected by transmembrane linker proteins which extend into the intercellular space terming an interlacing network which binds to the cells and appears as a dense line in the intercellular space

Question 8

Gap junction structure
Pores/tunnel between cells

Answer 8

They consist of aggregated transmembrane protein complexes that form from circular patches in the plasma membrane
Form hexameric complexes called connexons
Each connexon has a central hydrophilic pore

Question 9

Function of gap junctions

Answer 9

• Permit intercellular exchange of small molecules
  *Provides synchronous contractions in cardiac muscle cells

Question 10

Strongest junction?

Answer 10

Desmosomes due to intermediate filaments

Question 11

Interdigitations: function, and site

Answer 11

• Site: kidney tubules
• function: provide a wide surface fer intercellular passage of material

Question 12

Intercellular canaliculi: function and site
(secretary material mom adjacent cells is accumulated in channels)

Answer 12

• Function: carry the secretions to ducts
  *Site: liver cells

Question 13

Modification of the PM at the apical parts

Answer 13

1. Cilia
2. Stereocillia
3. Microvilli
4. Cuticle
5. Caveoles

Question 14

Microvili structure

Answer 14

Projected in the lumen
Smaller than cilia.
Has a thick glycocalyx ( cell coat ) that contains enzymes
Contain bundled actin microfilaments

Question 15

Microvili function and site

Answer 15

Function:Increase apical surface area for better absorption
Site: intestines

Question 16

Cilia structure

Answer 16

*Highly motile apical structures
*Contain internal arrays of microtubles
*each microtubule has a core structure of 2 central microtubules surrounded by 9 peripheral microtubules (axoneme)
*the peripheral ones are attached to the centrals by radial spokes (dynein)
*the basal body anchors the axoneme
*the basal body has triplets of microtubules and protofilaments anchoring the structure

Question 17

Function of cilia

Answer 17

For transportation due to rapid beating patterns that move fluid in one direction along the epithelium
Primary cilium (does NOT move) enriched with receptors to detect stimuli

Question 18

Site of cilia

Answer 18

Respiratory tract

Question 19

Cuticle structure

Answer 19

Rich in proteins on the outer lamina of the plasma membrane

Question 20

Function of cuticle

Answer 20

On the epical surface for protection

Question 21

Site of cuticle

Answer 21

Ureter
Urinary bladder

Question 22

Claveolae structure

Answer 22

The secretory surface of cells have invaginations (caves) which result from exocytosis and pinocytosis

Question 23

Sites of caveolae

Answer 23

Endothelial lining of blood capillaries

Question 24

Modification of the PM at the cell base types

Answer 24

1.basal infolding
2.hemidesmosomes

Question 25

Function of basal infolding

Answer 25

Increase the surface of the membrane for effective basal flow of materials

Question 26

Site of basal infolding

Answer 26

Kidney tubules

Question 27

Hemidesmosomes (half)

Answer 27

Site: basal membrane of protective cells
Function: hold cells to underlying tissues