Epithelial Tissue 1 Histology

Epithelial tissues I.

1. 2. 3. 4.

Simple squamous epithelium Simple cuboidal epithelium Simple columnar epithelium Pseudostratified columnar epithelium with cilia

Characteristics of the epithelial cells: They are tightly packed together with very little intercellular matrix. (Intercellular junctions: t ight j unct ions, zonulae adherent es, desm osom es, gap j unct ions). Epithelia are derived from all t hree em bryonic germ layers. The principal functions of epithelial tissues are covering and lining of surfaces (cove r in g e pit h e lia ), absorpt ion of subtances (a bsor pt ive e pit h e liu m ), secret ion of substances (gla n du la r e pit h e liu m ), sensation (sensory epithelium/neuroepithelium). The epithelial cells rest on a basem ent m em brane (lamina lucida+ lamina densa+ lamina fibroreticularis), and are connected to this membrane by hemi- desmosomes. The apical surface of the epithelial cells may be equipped with structures that greatly increase t he surface area (microvilli, stereocilia), and structures which are responsible for motility (kinocilia, flagellum).

The simple squamous epithelium consists of a single row of flattened cells. In cross section the cytoplasm of these cells is extremely attenuated, so that it is hardly visible. The part of the cell containing the nucleus is enlarged, the nucleus stands out in relief. Location: squamous alveolar cells in the lung (type I pneumocytes), parietal wall of the renal Bowman capsule, the narrow segment of renal loop of Henle. Special types of simple squamous epithelium: 1. Endothelium: epithelium lining the inner surface of the heart and blood vessels 2. Mesothelium: epithelium of serous membranes lining certain body cavities (pericardium, pleura, peritoneum).

Simple squamous epithelium 1.Mesenterium (Ag) Actually it is not a section, but a very thinly stretched membrane (mesenterium of frog or rat), and each side of this membrane presents mesothel cells arranged mosaically, side by side. Mesothel cells

The cell-boundaries are visible by silver nitrate treatment as silver granules deposit in the intercellular spaces.

It is formed by one row of cuboidal cells that possess spherical nuclei . Location: Follicles of the thyroid gland Distal and proximal renal tubules Epithelium germinativum covering the ovary Amniotic epithelium The cuboidal cells may have resorbing function, presenting m icrivilli attached to their apical surface (e.g. proximal renal tubules).

Simple cuboidal epithelium: 68. Thyroid gland (HE)

Cell nuclei

Follicles

The simple cuboidal epithelium of the follicles represent an epithelium of both covering and endocrine glandular type involved in the secretion of thyroxin. The cells are flattened in hypofunction of the gland, and they are taller in hyperfunction. The cell boundaries are hardly visible, and the cuboidal epithelium might be recognized according to the spherical shape of the nuclei.

Simple columnar epithelium: It consists of a single row of cells that have cylindrical or prismatic shape and oval nuclei. Location: In the digestive tract from the oral cavity to the anal canal. Striated ducts of the salivary glands Epithelium of the uterus Cells that have resorbing function present brush border formed by microvilli that are disposed on the apical surface. Location of the simple columnar epithelium with brush border: Small and large intestine Location of the simple ciliated columnar epithelium: Oviduct

Simple columnar epithelium: 49. Gallbladder (HE) Oval cell nuclei

The inner surface of the gallbladder is lined by simple columnar epithelium equipped with brush border. The cell boundaries are not clearly visible, but this form of epithelium may be recognized by the oval nuclei disposed in one row. The brush border exhibits positive PAS reaction.

The cells form a single row, but their nuclei are disposed at different levels so that it gives the illusion of stratification. Every cell is lying on the basal membrane, that s why this is a type of simple epithelium. Cells that reach the surface usually present cilia. Location of the pseudostratified epithelium with stereocilia: Ductus epididymidis Ductus deferens Location of the pseudostratified epithelium with kinocilia: Respiratory tract to bronchioles Auditory tube, lining of the tympanic cavity Inner surface of the lacrimal sac

The epithelial lining of the trachea

Unstained goblet cells

The inner surface of the trachea is covered by pseudostratified epithelium with kinocilia. Goblet cells appear among the ciliated columnar cells; their secretion product is not stainable with H.E., but exhibits positive PAS reaction.

I de n t ify t h e t ype of t h e e pit h e liu m in t h e follow in g se ct ion s!

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.

Simple columnar epithelium (gallbladder) Simple cuboidal epithelium (medulla of kidney) Pseudostratified ciliated epithelium (respiratory tract) Simple columnar epithelium (small intestine) Simple ciliated columnar epithelium (oviduct) Simple cuboidal epithelium (medulla of kidney) Pseudostratified ciliated epithelium (respiratory tract) Simple columnar epithelium (uterus) Pseudostratified ciliated epithelium (tail of the epididymis) Mesothelium Pseudostratified ciliated epithelium (tail of the epididymis)