Lecture 2: cytoskeleton, cell junctions, basement membrane

Question 1

describe the function of epithelial tissue

Answer 1

covers body surfaces, lines hollow organs, caities, ducts, forms the glands of the body

Question 2

What are key functions of epithelium?

Answer 2

selective barriers (limit or aid transfer), secretory (onto a surface), protective (especially from abrasion)

Question 3

microfilaments description

Answer 3

bundles beneath the cell membrane and cytoplasm, confer strength , alter cell shape, link cytoplasm to membrane, holds cell together, allow for muscle contraction (ie. actin)

Question 4

intermediate filaments description

Answer 4

strength, move materials through the cytoplasm (ie. keratin)

Question 5

tight junctions function

Answer 5

• individual sealing strands, transmembrane
• the more strands the tighter the junction
• many proteins involved but key ones are occludin and claudins
• join the cytoskeleton of adjacent cells
• keep cell polarity by preventing migration of proteins between apica; and basal surfaces
• lots of tight junctions found in stomach, intestines and bladder

Question 6

adherens junction description

Answer 6

also called”belt desmosome” or “adhesion belts”. in cells where less continuous it is called adhesion plaques

• more basal located than tight junctions
• cadherins span the gap
• catenins link adherens to actin
• adherens junctions associated with actin filaments
• adherens junctions prevent cell separation from tension forces like contractions

Question 7

desmosome junctions description

Answer 7

• found on the lateral wall
• have plaque like adherens junctions
• resist shearing forces
• bind muscle cells
• cadherins span the gap but link to keratin of the cytoskeleton
• keratin spans from one desmosome to the other offering structural integrity
• most common in skin epithelium and cardiac cells

Question 8

gap junctions function

Answer 8

• direct connection between cells
• 6 connexin protein molecules form one conexon/hemicannal and two connexons make up a gap junction
• allow 1kDa molecules through

Question 9

Hemidesmosomes function

Answer 9

• connect epithelia to basement membrane
• links cellular basal intermediate filament (keratin) to basement membrane
• integrin (linker protein) binds to laminin in BM and keratin in the epithelial cells

Question 10

Composition of basement membrane

Answer 10

composed of two parts;

• basal lamina (secreted by epithelial cells) and contains collagen, laminin, other proteoglycans and glycoproteins and
• reticular lamina (produced by fibroblasts in underlying CT) and contains fibrous proteins such as fibronectin and collagen

Question 11

Functions of Basement membrane

Answer 11

• supports the overlying connective tissue
  -provides a surface along which the epithelial cells migrate during growth and wound healing
  -acts as a physical barrier (against invading pathogens)
  -participates in the filtration of substances in the kidneys
  (barrier to invasion by malignant melanoma)

Question 12

What is the ABCD of malignant melanoma?

Answer 12

A- asymmetry (one half of the mole doesn’t match the other half)
B- border irregularity (edges are ragged, notched or blurred)
C- colour (mix of brown, blue, black, white, red)
d- diameter (more than 6mm, metastasis chances increase)