Unit 1- Epithelium

1. What is epithelium?

A tissue made of tightly packed cells that covers body surfaces, lines organs, and forms glands.

2. Is epithelium vascular?

No. Epithelium has no blood vessels (avascular).

3. Why is epithelium avascular?

To prevent infections from entering the bloodstream directly.

4. What happens when epithelium is lost (ulcer)?

The protective barrier is gone, exposing underlying tissue.

5. Where does epithelium come from (embryonic origin)?

All three layers:

• Ectoderm (epidermis)

• Endoderm (digestive, respiratory, glands)

• Mesoderm (endothelium, mesothelium)

6. What are key characteristics of epithelium?

• Tightly packed cells

• Avascular

• Lies on a basement membrane

• Shows polarity

• Self-renewing

• Forms a selective barrier

7. What is cell polarity?

Cells have different sides:

• Apical (top)

• Lateral

• Basal (attached to basement membrane)

8. What is the basement membrane?

A non-cellular layer that anchors epithelium and separates it from connective tissue.

9. Why is polarity important clinically?

Loss of polarity is a sign of cancer.

10. What are cell junctions?

Special structures that connect epithelial cells together.

11. What are tight junctions (occluding junctions)?

Seal cells together to prevent substances passing between them.

12. Function of tight junctions?

Force substances to pass through cells, not between them.

13. What are adherens junctions (zonula adherens)?

Strong cell-to-cell anchors connected to actin filaments.

14. What are desmosomes?

Spot-like anchors that connect cells via keratin filaments.

15. What disease is linked to desmosomes?

Pemphigus → loss of cell adhesion in skin.

16. What are hemidesmosomes?

Anchor epithelial cells to the basement membrane.

17. What are gap junctions?

Channels that allow small molecules to pass between cells for communication.

18. How is epithelium classified?

By:

• Number of layers

• Shape of cells

19. What is simple epithelium?

One layer of cells.

20. What is stratified epithelium?

Multiple layers of cells.

21. What is simple squamous epithelium?

One layer of flat cells; allows diffusion and fluid movement.

22. Where is simple squamous epithelium found?

Blood vessels (endothelium) and body cavities (mesothelium).

23. What is simple cuboidal epithelium?

One layer of cube-shaped cells; secretion and absorption.

24. Example of simple cuboidal epithelium?

Glands (e.g. mammary gland).

25. What is simple columnar epithelium?

One layer of tall cells; absorption and secretion.

26. What is pseudostratified epithelium?

Looks layered but is actually one layer; all cells touch the basement membrane.

27. Why does pseudostratified epithelium look stratified?

Nuclei are at different heights.

28. What is transitional epithelium (urothelium)?

Special epithelium that stretches.

29. Where is transitional epithelium found?

Only in the urinary tract (bladder, urethra).

30. Why is transitional epithelium important?

Allows bladder expansion without leaking toxic urine into blood.