Characteristics of the epithelial cells:They are tightly packed together with very little intercellularmatrix. (Intercellular junctions: t ight j unct ions, zonulaeadherent 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 andlining of surfaces (cove r in g e pit h e lia ), absorpt ion ofsubtances (a bsor pt ive e pit h e liu m ), secret ion ofsubstances (gla n du la r e pit h e liu m ), sensation (sensoryepithelium/neuroepithelium).The epithelial cells rest on a basem ent m em brane (laminalucida + lamina densa + lamina fibroreticularis), and areconnected to this membrane by hemi- desmosomes.The apical surface of the epithelial cells may be equippedwith structures that greatly increase t he surface area(microvilli, stereocilia), and structures which areresponsible for motility (kinocilia, flagellum).
The simple squamous epithelium consists of a single row offlattened cells. In cross section the cytoplasm of these cellsis extremely attenuated, so that it is hardly visible. The partof the cell containing the nucleus is enlarged, the nucleusstands out in relief.Location: squamous alveolar cells in the lung (type Ipneumocytes), 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 theheart and blood vessels2. Mesothelium: epithelium of serous membranes liningcertain 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.Mesothelcells 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 possessspherical nuclei .Location: Follicles of the thyroid gland Distal and proximal renal tubules Epithelium germinativum covering the ovary Amniotic epitheliumThe cuboidal cells may have resorbing function,presenting m icr o villi attached to their apical surface(e.g. proximal renal tubules).
Simple cuboidal epithelium: 68. Thyroid gland (HE) 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 areCell nuclei Follicles 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 orprismatic shape and oval nuclei.Location: In the digestive tract from the cardia to the anal canal. Striated ducts of the salivary glands Epithelium of the uterusCells that have resorbing function present brush borderformed by microvilli that are disposed on the apical surface.Location of the simple columnar epithelium with brushborder: Small and large intestineLocation 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 atdifferent levels so that it gives the illusion of stratification.Every cell is lying on the basal membrane, that s why this isa type of simple epithelium. Cells that reach the surfaceusually present cilia.Location of the pseudostratified epithelium with stereocilia: Ductus epididymidis Ductus deferensLocation of the pseudostratified epithelium with kinocilia: Respiratory tract to bronchioles Auditory tube, lining of the tympanic cavity Inner surface of the lacrimal sac
The inner surface of the The trachea is covered by epithelial pseudostratified lining of epithelium with kinocilia. the trachea Goblet cells appear among the ciliated columnar cells; their secretion product is not stainable with H.E., but exhibits positive PAS reaction.Unstainedgoblet cells
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. Simple columnar epithelium (gallbladder)2. Simple cuboidal epithelium (medulla of kidney)3. Pseudostratified ciliated epithelium (respiratory tract)4. Simple columnar epithelium (small intestine)5. Simple ciliated columnar epithelium (oviduct)6. Simple cuboidal epithelium (medulla of kidney)7. Pseudostratified ciliated epithelium (respiratory tract)8. Simple columnar epithelium (uterus)9. Pseudostratified ciliated epithelium (tail of the epididymis)10. Mesothelium11. Pseudostratified ciliated epithelium (tail of the epididymis)