47. epithelial tissue def and characteristics

Question 1

What are epithelial tissues composed of

Answer 1

closely aggregated polyhedral cells with small amount of ECM

they form cellular sheets that line cavities of organs ( epithelium)and cover the body surface (epidermis)

Question 2

Functions of epithelia

Answer 2

COVERING- lining and protecting surfaces eg epidermis

ABSORBTION- eg intestinal lining

SECRETORY- eg parenchymal cells of the glands

Question 3

Some common features of epithelia

Answer 3

• rest on basement membrane
• morphological and functional cell polarity- basal and free apical poles (organelles and proteins distributed unevenly)
• Avascular
• high regeneratory capacity
• limited intercellular space

Question 4

What is the basement membrane

Answer 4

thin extracellular sheet of macromolecules which is semipermeable
basal surface of epithelia lies on basement membrane

Question 5

What are the components of the basement membrane

Answer 5

basal lamina(nearest to epithelial)- Type IV collagen, glycoporteins like laminin or nidogen, heparane sulfate proteoglycans like perlecans

anchoring fibrils - type vII collagen

reticular lamina - type III collagen

Question 6

Function of basement membrane

Answer 6

elastic support

semiconductive filter

Question 7

What are the types of intercellular adhesion and junctions

Answer 7

tight/occluding junctiion: impermeable and forms seal
between adjacent cells.
Most apical
claudin and occludin transmembrane
protein

Adhering junction: sites of strong cell adhesion
encircles epithelial cell
cadherins

Desmosomes: Type of adhering junction
does not form belt, but spot weld
bound to intermediate filaments, provides
strong attachment

Gap junctions: mediate intercellular communication
transmembrane protein connexin

hemidesmosomes: attaches to basal lamina
integrins indirectly link to intermediate f
filaments

Question 8

What are the 2 main groups epithelia can be divided into?

Answer 8

covering (lining)
secretory (glandular)

Question 9

What are some special features of the epithelium

Answer 9

microvilli- small finger like projection increase SA. Brush border 1um long contains bundled actin filaments

stereocilia- non motile and long cilia, seen on absorptive epithelia in male reproductive system

cilia- hair like appendages on apical surface of cilia abundant in cuboidal/columnar cells

goblet- produces mucous to lubricate and protect surface of organ