This document provides an introduction to histology. It discusses the basic structures and classifications of epithelial tissues, which are the coverings and linings of organs. The major epithelial tissue types include simple squamous, simple cuboidal, simple columnar, pseudostratified columnar, stratified squamous, and transitional epithelium. Specific examples are given of where each tissue type is found. Important cellular structures like the basement membrane, junctions, and surface features of epithelial cells are also outlined. Staining techniques used to visualize histological structures under the microscope are mentioned.

1. Introduction to
Histology:

2. The science of Pathology

3. Objectives
 Introduction
 Applicable for
 Importance
 Requirement
 Various stain

4. Where it is applied??
 Microscopic anatomy (histology)
 Gross anatomy
 Other basic science courses
• Biochemistry
• Physiology
• Microbiology
• Pathology
• Pharmacology

5. WHY ??????
 Develop mental image
 Understand normal function of cell
 Differentiate slides
 Identify organs
 Exam

6. What things Need for it???
 Microscope
 Knowledge of Stains used
 Characteristics of slide
 Imagination
 H&E pencil
 A good book

7. Many stains……
 H&E (hematoxyllin and eosin)
 PAS (periodic acid schiff)
 Acid fast, toludine blue
 Masson trichome
 Van Gieson
 Orecine
 Silver nitrate
 Elastin
 Osmic acid
 Wright and Giemsa stain
 Many other…

8. Difficult to observe:
 diameter: 5 to 50um or in nm
 Like:
 Cell membrane
 Cytoplasmic organelles
 Nucleolus
 Chromatin

9. Epithelium:
The covering and lining

10. Objectives
I. Definition of Epithelia.
II.Epitheloid tissue
III.Function of Epithelia
IV.Classification of Epithelial cells.
V.Basement membrane
VI.Epithelial intercellular junctions
VII.The apical surface of epithelial
cells.

11. EPITHELIA
group cells
cover the outer surface of the body or the
luminal surfaces of body cavities
single layered to multiple layered .

12. Epitheloid tissue
 Aggregation of cell
 No free surface
 Example
 Parenchyma of adrenal gland
 Leydig cell of testis
 Luteal cell of ovary

14. Function

15. Classification of Epithelial tissues
Stratified columnar

16. Simple Squamous Epithelium
• flattened cells
• Oval and large nucleus
• Bulging of cell surface due to large nucleus
• Eg. Lines the:
 alveoli of lungs,
 the free surfaces of peritoneum,
 pleura and
 pericardium
 blood vessels (endothelium)
 heart (endocardium) (mesothelium)

17. Simple cuboidal Epithelium
• like squares or cuboid
• Nuclei is rounded and centrally placed.
• lines the:
 follicles of thyroid gland,
 kidney tubules,
 germinal layer of ovary and
 ducts of various glands .

18. Simple Columnar Epithelium
• Height >width .
• nuclei are oval & elongated toward the basement
membrane.
• lines the
 mucous membrane of the stomach
 large intestine
 Some part of bronchioles
 Uterine tube

19. Columnar epithelium
 Striated border
 Cliated
 Non-ciliated
Cell present:
 Goblet cell: intestine

20. Columnar Epithelium Striated Border
• vertical striations on free surface.
• Brush border
• Electronic view: microvilli
• Non motile
• typically seen in small intestine.

21. Ciliated columnar
 Large bronchioles
 Uterine tube

22. Pseudo stratified Epithelium
• appears to be multi-layered but actually there is
only one layer of cells.
• Cell of different height
• position of nucleus at different levels
• bears hair like projections called cilia.
• Mostly seen in trachea and
large bronchi .

23. Pseudo Stratified Columnar Epithelium
(With Stereocilia)
• Stereocilia as seen in epididymis .
• Stereocilia are actually long microvilli and not cilia.

24. Stratified Squamous Epithelium
(Non–Keratinised )
• only the most superficial cells are flattened .
• deepest are columnar
• middle layers they are polyhedral,
• while the more superficial layers show increasing
degrees of flattening .
• no superficial keratinized zone ; flattened cells
are seen in topmost layer .
• lining some internal organs like
 Oesophagus,
 Cornea, Tongue and the vagina .

25. Stratified Squamous Epithelium
(Keratinized)
 The surface layer is made up of keratin which
appears as fibers .
 Keratinization
 typically seen in epidermis of skin.

26. Stratified cuboidal
 Excretory duct of salivary gland, pancrease
Stratified columnar
 Male urethra

28. Transitional Epithelium
• Have several layers of cells with round nuclei.
• The deepest cells are columnar or cuboidal.
• The middle layers are made up of polyhedral or pear-
shaped cells.
• Superficial layer shaped as
umbrella.
• These are mostly found in
urinary tract.

29. Specialized structure:
On the apical surface of epithelial cells
 Striated border
 Steroclia
 cilia

30. Sterocilia

32. Basement membrane

33. (15-20nm)
(3nm)
20-25nm