Epithelia are tissues that line surfaces, cavities, and tubes throughout the body. They perform functions like protection, transport, secretion, and containment. Epithelia can be classified based on cell layers (simple vs stratified), cell shape (squamous, columnar, cuboidal), and surface features (presence of cilia or keratin). Glands are clusters of epithelial cells that secrete substances. They can be classified by cell number, presence of ducts, and secretion mode. Common simple epithelia include squamous (alveoli), cuboidal (sweat glands), and columnar (small intestine). Stratified epithelia provide more protection, like those in the skin, vagina,

1. Epithelia and glands

2. Epithelia
• A group of tissues that line surfaces,
cavities and tubes.
• Mainly derived from ectoderm but afew are
from endoderm and mesoderm.
• Functions include protection(skin, vagina,
anal canal), transport(small intestines),
secretion(glands) and containment

3. continued
• Surfaces lined by epithelia include skin.
• Cavities include:oral cavity, pleural cavity
in the lungs, peritoneal cavity in the
abdomen, pericardial cavity in the
mediastinum
• Tubes include respiratory tract, anal canal
and vaginal canal.

4. Classification of epithelia
• Three ways of classification based on
1) number of cell layers
2) shape of cells
3) presence of surface modifications

5. According to number of cell
layers
Three types
1) Simple epithelia; only one cell layer.
adapted for transport.
2) Stratified epithelia: many cell layers.
Mainly for protection.
3) Pseudostratified: false stratification: one
cell layer but nuclei are at different layers
giving it an appearance of many cell
layers.

6. According to shape of cells
Three types
• Squamous epihelia: cells flat and are
shaped like pavers. Mainly adapted for
transport by diffusion.
• Columnar epithelia: cells shaped like tall
columns. Mainly for absorption.
• Cuboidal epithelia: cells between flat and
tall. Mainly for secretions.

7. According to presence of
surface modifications
Two types of modifications: cilia and keratin
• Cilia: mainly for transport, such epithelia is
said to be ciliated. Common in fallopian
tubes, respiratory system
• Keratin: mainly for protection agaist
dessication. Common on skin.

8. Simple squamous
epithelia(alveolus)

9. Simple squamous epithelia
• One cell layer, cells flat
• Adapted for transport by diffusion.
• Located in alveolar sacs, lining of pleural
and peritoneal cavities.
• Is not protective.

10. Simple cuboidal(sweat gland)

11. Simple cuboidal epithelium
• One cell layer, cells between flat and tall
columns.
• Adapted for secretions
• Found lining endocrine glands like thyroid
gland.

12. Simple columnar (small intestines)

13. Simple columnar
• One cell layer, cells shaped like tall
columns.
• Mainly adapted for absorption
• Commonly found in small intestines.

14. Pseudo stratified
epithelium(trachea)

15. Pseudostratified ciliated
columnar epithelium
• One cell layer, cells tall columns, nuclei at
different levels giving it an appearance of
many cell layers.
• Function is clean, moisten and warm
inspired air.
• Found lining upper respiratory tract.

16. Stratified squamous(vagina)

17. Stratified squamous epithelia
• Many cell layers
• Cells shaped like pavers
• Adapted for protection against abrasion.
• Located in lower half of vaginal canal,
lower half of anal canal, oral cavity.
• Doesn't protect against dessication.

18. Stratified squamous keratinised
Many cell layers
Cells flat and shaped like pavers
Presence of keratin
Protects against dessication
Located on skin

19. Stratified cuboidal: sweat glands

20. Stratified cuboidal epithelium
Many cell layers
Cells between flat and tall coulmns
Lines ducts of sweat glands.
Protective.

21. Transitional epithelia (bladder)

22. Transitional epithelia
Cells intermediate between stratified
cuboidal and stratified squamous
Located in urinary bladder
Adapted to withstand stretch and toxicity of
Urine.

23. Glands

24. Glands
A group of tissues formed as a result
of infolding or outfolding of epithelium.
Can be classified in three ways based on
1) Number of cells
2) presence or absence of ducts
3) mode of secretions

25. According to number of cells
Unicellular glands: made up of one cell.
Examples include mucous glands (goblet
cells),sebaceous glands.
Muticellular glands:made up of many cell
layers. Examples include breast, thyroid,
pancreas

26. According to presence of ducts
Endocrine glands:have no ducts. Examples
include thyroid, pituitary, adrenal, ovary
Exocrine glands: have ducts e.g sweat
glands
Mixed glands: have both exocrine and
endocrine portions e.g pancreas.

27. According to mode of secretion
Apocrine glands: seceretory components
packed in vesicles and released by
exocytosis. Secretory components have
part of the cell membrane.examples
include breast.
Merocrine glands: secretory components
released into ducts; have no components
of cell membrane e.g sweat glands.

28. Holocrine gland; there is shedding of the
entire gland during secretion e,g
sebaceous glands.

29. • Refferences
• Functional Histology by wheaters