Epithelium

Why this matters

Almost everything a dentist cuts, retracts, injects through, seals against or watches for cancer is epithelium. The seal around every tooth in your patient's mouth is a non-keratinised stratified squamous epithelium that thins to one to three cell layers at its apical end. The lining an implant surgeon elevates off a sinus floor is a different type entirely, and its cilia are the reason a perforation matters. The word 'dysplasia' on a report is a statement about epithelial polarity failing.

The big picture

One tissue type, three questions. How many cell layers, what shape are the cells at the free surface, and what is on that surface. Everything else in this lesson - keratinisation, polarity, the basement membrane beneath it, the rate it renews, and the glands that grew down out of it - is that same sheet solving a local problem.

The 15 cards in this lesson

1. 01An epithelium is a polarised avascular sheet on a basement membrane, and you can only see part of that
2. 02Simple epithelium is one layer, and its shape is a judgement about the neighbours
3. 03A stratified epithelium is named for its surface cell, never for its basal cell
4. 04Pseudostratified: the criterion is true, tiny, and invisible on your slide
5. 05Apex, sides and base are three different membranes doing three different jobs
6. 06Clinical alert — in the lesson
7. 07The basement membrane is a chain of links, and each link is a disease
8. 08The junctional epithelium makes a basement membrane on both of its faces
9. 09Keratinisation is a differentiation programme read from the basement membrane upwards
10. 10Ortho-, para- and non-keratinised are called by nuclei, not by how pink the top is
11. 11Two answers to what makes gingiva keratinise, and both have evidence
12. 12Renewal rate is a property of the individual epithelium, not of epithelium as a category
13. 13A gland is surface epithelium that grew downwards and either kept its connection or lost it
14. 14Classify a gland twice: by what it secretes and by how the cell survives releasing it
15. 15Four ways to lose a slide viva, and what to do instead

You have got it when

You can: (1) classify an epithelium by layers, surface cell shape and free-surface specialisation, and say which of those a routine section can settle; (2) call ortho-, para- or non-keratinised from nuclei, not colour; (3) say what loss of polarity means on a biopsy report; (4) trace the attachment chain from basal keratin to lamina propria and name the two oral blistering split levels; (5) classify a gland on all…