Lecture 7 - Integrating cells into tissues, organs & systems

Question 1

What 4 main things holds cells together?

Answer 1

1) Cell-cell adhesion molecules
2) Extracellular matrix proteins (fibers)
3) Internal-external scaffolding
4) Close proximity (pressure effects)

Question 2

What are 4 epithelial cell adherence systems found in the lateral surface and 4 found on the basal surface?

Answer 2

Lateral:

• Tight junctions
• Adherens junctions
• Desmosomes
• Gap junctions

Basal:

• Hemi-desmosomes
• Focal adhesions
• Integrins
• Proteoglycans

Question 3

Where are tight junctions found and what are their major 2 roles.

Answer 3

• Top of the lateral border nearest to the lumen/apical surface.
  1) Prevent movement of large molecules into the lumen
  2) Transiently open and allow for passage of small molecules between cells (paracellular transport)

Question 4

Where are adhesion junctions found and what is their role?

Answer 4

• Lateral surface of endothelial and epithelial cells, 1/3 distance down from luminal surface.
• Functions as tissue stabilising factor and additional transport barrier

Question 5

Where are desmosomes found and what are their roles?

Answer 5

• Found in tissues that experience intense mechanical stress, e.g..: bladder tissue. 1/2 of the way down from the luminal surface on lateral border.
• Provide strength and prevent tissue destruction

Question 6

Where are gap junctions found and what is their role?

Answer 6

• In smooth and cardiac muscle at the bottom of the lateral border
• Allow free movement of small molecules to rapidly communicate changes in intracellular molecular composition.

Question 7

Where are hemi-desmosomes found and what are their role?

Answer 7

• Found on the basal surface of epithelial cells only

- Anchors epithelial cells to basal lamina and prevents loss to external surface?

Question 8

Where are focal adhesions and integrins found and what are their roles

Answer 8

• Basal surface and anchor actin filaments in a cell to the basal lamina
• Basal surface and are central to cohesive forces keeping cells together by binding to EC as an alpha-beta dimer.

Question 9

What do mucosal membranes line?
What are the components in their secretions (mucus)?
What are the functions of mucosal membranes?

Answer 9

• Lines moist hollow internal organs of the body (tracts)
• mucins (attract water), electrolytes, lysozymes, and immunoglobulins
• Trap dirt and pathogens from entering the body, prevent bodily tissues from becoming dehydrated, lubricate surfaces.

Question 10

Name & describe the structure of the 5 layers of the GIT from in to out.

Answer 10

1) Mucosa - epithelial cell lining, secretes mucous
2) Muscularis mucosae - smooth muscle layer
3) Submucosa - connective tissue containing arteries & veins
4) Muscularis externae - Smooth muscle layer with fibres going in 2 directions (inner circular and outer longitudinal)
5) Serosa - connective tissue that secretes fluid to lubricate outside of GIT

Question 11

What are the 3 major functions of the GIT mucosa and how does the structure of the GIT enable these?

Answer 11

1) Absorb substances from lumen
2) Prevent ingress of pathogen
3) Move contents and expel waste material out of anus

• Epithelial cell specialisations, e.g.: folding of mucosa, microvilli and peristaltic contraction aid process 1 + 2
• Lamina propria contains lymphatic tissue to aid process 2
• Muscularis mucosae folding mucosa increases SA for process 1 &2.

Question 12

What is the epithelial layer of the respiratory tract covered in? How does this aid in its function?

Answer 12

• Cilia, helps to waft down and move debris, bacteria and dust) towards the back of the throat