1. Kharkov National Medical University
Department of histology, cytology and embryology

2. Tissues 1. Epithelial tissue
Lecture 3
Tissues
1. Epithelial tissue

3. Definition
Tissues -- groups of cells organised to perform one or more functions.
Note!!(but do not write) Cell is the basic structural unit of the body. But in the multicellular organism there are tissues that are responsible for maintaining body functions due to collaborative efforts of their individual cells.

4. 4 basic types of tissues:
Epithelial Tissue (Epithelium).
Connective tissue.
Muscular Tissue (Muscle).
Nervous tissue (Nerve).

5. Epithelial Tissue
covers body surfaces, - - lines body cavities, and
- - forms glands.
There are 2 main types of ET:
Covering and lining (covers outer body surfaces (skin) and inner body surfaces (lumen of hollow organs (intestine) and cavities (peritoneal, pericardial, pleural), blood vessels, ducts, tubules). They separate the underlying connective tissue from the external environment or environment of internal cavities
Glandular - forms glands

6. Main function :
Epithelium creates a selective barrier between the organism and its external environment.
This barrier facilitates or inhibit the passage of specific substances.
Any substances that enter the body as a metabolites or discharges from the body as a waste products must pass through the epithelial cell, not between them.

7. Other functions protection
diffusion or absorption or excretion = exchange
transport (along free surface)
secretion
sensation.

8. Characteristics
1. There is no extracellular substance between the cells,
cells are tightly apposed in sheets and strongly attached to one other by means of special junctions.

9. Characteristics.
2. Their basal surface is attached to an underlying basement membrane – extracellular protein-polysaccharide-rich layer.
3. polarity - cells have 2 surfaces :
the apical or free side (surface) - is the side towards the lumen or outside medium
the basal side (surface) - is the side closest to the basement membrane

10. Epithelial Tissues and Their Basement Membrane

11. The Polarity of Epithelial Cells

12. Characteristics. 4. Epithelia are avascular :
epithelium does not contain blood vessels but is nourished by diffusion of substances from capillaries of underlying connective tissue.
5. It is frequently mitotically active

13. Morphological classification of Epithelial Tissues
is based on combination of the number of cell layers (first name) and the shape of surface cell (second name).
E. can be called simple or stratified on the basis of the number of cell layers which comprise it:
Epithelium may be simple, when it is one cell layer thick and stratified when it is two or more cell layer thick.

14. The second name describes the shape of the cells:
Squamous, where the width of the cell is greater than its height.
Cuboidal, where the width, depth and height are approximately the same.
Columnar, where the height appreciably exceeded the width.
!!! In case of stratified epithelia the second name describes the shape of the top layer of cells.

15. Simple Squamous Epithelium
Single layer of flat cells (very thin)
lines blood vessels (endothelium), closed body cavities (mesothelium), alveoli in the lungs
Function: controls diffusion, osmosis and filtration

16. Simple Cuboidal Epithelium
Single layer of cube-shaped cells, lines tubules and ducts

17. Simple Columnar
Lines stomach, intestine. Usuallly has microvilli = finger-like projections of the cell membrane
Function – absorption.

18. Pseudostratified Columnar
Single cell layer
All cells attach to basement membrane but not all reach free surface
Nuclei at varying depths

19. Stratified squamous Epithelium
Several cell layers thick,
Surface cells are flat
2 types:
Keratinized = surface cells are dead and filled with keratin
Example - Skin
Nonkeratinized = no keratin in moist, living cells at apical surface
Example - Cornea

20. Stratified Cuboidal Epithelium
Surface cells cuboidal
Lines sweat gland ducts

21. Stratified Columnar Epithelium
Surface cells are columnar
Lines very large ducts of gland

22. Transitional Epithelium
Multilayered
Surface cells vary in shape from round to flat if stretched
Lines hollow organs of the urinary tract that expand from within

23. !! The morphology of an epithelium often correlates with its function:
- Epithelia involved in secretion or absorption are typically simple.
-- Stratification of the epithelium usually correlates with impermeability and protection
--- The height of the cell often reflects the level of secretory or absorptive activity.

24. GLANDULAR EPITHELIA
Secretion is the main function of the glandular epithelia.
Secretion – cyclic process. 4 phases:
1. diffusion of metabolites into the cell
2. synthesis proper
3. releasing of substances from the cell
4. cell restoration

25. There are two types of glands in the body: exocrine and endocrine.
Exocrine glands secrete through ducts or directly onto the surface (skin or cavity of inner organs).
Without ducts - surface mucous cells of the stomach;
With ducts - most exocrine glands; Ex.: salivary glands.
Endocrine secrete hormones into the bloodstream.

26. Classification of glands by cell number
Unicellular gland Ex.: Goblet cell secrete mucus and lubricate small and large intestine, respiratory tract
Multicellular gland

27. 2 portions of gland: Parenchyma and Stroma
Parenchyma - the epithelial, secreting cells of the gland which perform the gland's essential function.
Stroma - supporting cellular framework of connective tissue which contains blood vessels and nerves and gives structure to the gland.

28. Classification of Exocrine Glands by type of secretion
1. Mucous - viscous, slimy mucus
Ex.: glands of esophagus, Brunner's glands of duodenum
2. Serous - watery serum
Produce wide variety of proteins (enzymes).
Ex.: exocrine pancreas, parotid salivary glands, uterine glands.

31. Classification of Exocrine Glands by type of secretion
3. Mixed (Sero-mucous)
Ex.: Submandibular and sublingual salivary glands; mixed glands of the nasal cavity, paranasal sinuses, nasopharynx, larynx, trachea and bronchi.

33. Secretion mechanism – 3 types
Merocrine (= eccrine)
Apocrine
Holocrine

34. Merocrine (eccrine)
( (note!) This is the most common type of secretion mechanism).
Secretory granules are formed in the cells and accumulated in the apex.
The granules fuse with the apical plasma membrane and are secreted into the lumen of the gland by exocytosis.

36. Apocrine (ex.: lactating mammary gland (fat droplets))
- secretion of product plus a small portion of pinched off apical cytoplasm, enclosed by a membrane derived from the plasma membrane.

38. Holocrine - ex: Sebaceous glands of the skin
the cell get filled with its secretory product while the nucleus becomes smaller.
maturing cells filled with lipid move to the center, then toward the opening of the acinus.
the cell dies and the entire cell is released and disintegrates, releasing its product.

41. Mechanisms of Glandular Secretion

42. A Structural Classification of Exocrine Glands
By branching of the duct exocrine glands may be: simple or compound
By the shape of secretory ends – tubular or alveolar (acinar)
By branching of secretory ends exocrine glands may be: branched or non-branched

43. A Structural Classification of Exocrine Glands