This document discusses epithelial tissue, which lines body surfaces and cavities. It notes that epithelial tissue is classified as either unstratified or stratified, and derives from ectoderm, endoderm, or mesoderm. Stratified squamous epithelium is the most common type found in skin and oral mucosa. Epithelial tissue is avascular, relying on diffusion from connective tissue for nutrients. It has a high renewal rate through mitosis and shedding of older cells. Oral epithelium renews faster than skin. After injury, a clot forms and epithelial cells migrate under it to repair the surface.

1. ORAL HISTOLOGY (BASIC TISSUES)
EPITHELIAL TISSUE

2. BASIC TISSUES
• Cells (similar shape & function) are grouped to form tissues
*cells → tissues
• Tissues are collections of similarly specialized cells
• During prenatal period, embryonic cell layers differentiate into 4 basic histological type of tissues :
→ epithelium
→ connective tissue
→ muscle
→ nerve
• Most of body tissues can be renewed as their cells component die & removed from tissue
*tissue renewal rate (tissue turnover time) = rate at which cells are completely replaced overall in the tissue
*tissue renewal rate differs for each of the basic tissues

3. EPTHELIAL TISSUE (ET)
• lines external & internal body surfaces, including vessels & small cavities
• not only serve as protective covering or lining, but also involved in tissue
absorption, secretion, sensory & specialized functions
• can be derived from any of 3 embryonic layers → ectoderm, endoderm,
mesoderm
*those of skin & oral regions are of ectodermal origin
• consists of grouped polyhedral cells surrounded by very little or no
intercellular substance or tissue fluid
• capable of renewal
• highly regenerative
• undergo cellullar differentiation as they move to surface
• tightly joined to each other by desmosomes

4. EPTHELIAL TISSUE (ET)
• ET is avascular (no blood supply on its own)
• cells obtained oxygen & metabolites by diffusion from connective
tissue which is highly vascularized
• bw epithelium & connective tissue is a basement membrane

5. Classification of epithelial tissue
• √ 2 main types of ET :
**unstratified (or simple epithelium) --> squamous cells
(single cell layer) --> cuboidal cells
--> columnar cells
**stratified --> squamous cells
(2 or more cell layers) --> cuboidal cells
--> columnar cells
--> combination

9. • ET can also be classified as pseudostratified epithelium which falsely appears as
multiple cell layers when viewed under low-power microscope → because cells' nuclei
appear at different levels
• most of ET in body are stratified squamous epithelium (SSE), which include superficial
layers of skin & oral mucosa
*extensions of ET into connective tissue are called rete ridges (in histological section)
• SSE can be keratinized or non-keratinized :
→keratin is an opaque, waterproof substance that is impervious to bacterial invasion &
resistance to friction
→keratin is produced during cells maturation as they migrate to surface of keratinized
tissue
→keratin is soft in skin & oral cavity, but hard in nails & hair

10. Epithelial tissue renewal rate & repair
• ET renewal occurs as newly formed deepest cells migrate superficially
• in order to migrate, cells release & then regain their desmosomal cellular
junctions in the more superficial location
• ET has high renewal rate as a result of high level of mitotic activity in deepest
cells
• the older superficial ET are being shed at the same rate as deeper germinal
cells are dividing into more cells
• these high renewal rates vary for different types of ET
• oral epithelium has higher tissue renewal rate than skin epidermis
→ eg : gingival epithelium that attaches to tooth surface has higher renewal rate
(4 - 6 days) than epithelium that lines cheek (10 - 14 days)
**traumatic injury to inner cheek lasting for weeks vs qucker healing in gingival sulcus after
periodontal therapy

11. • after injury to skin & oral mucosa, a clot from blood products forms in the
area & inflammatory response is triggered by white blood cells
• if source of injury is removed, tissue repair can begin within next few days
• the ET at periphery will lose their desmosomal cellular junctions & migrate
to form new epithelial surface layer beneath the clot
• thus, clot is important in epithelium repair & must be retained in first days
of repair since it act as a guide to form a new surface
• after epithelial suface is repaired, clot is broken down by enzymes & is no
longer needed

12. Repair of skin & oral mucosa

13. TERIMA KASIH
Prepared by :
Norazreen Abdul Jalil
Pegawai Pergigian, Hospital Melaka