Epithelium

Surface Epithelium

Simple squamous epithelium:

Uterine tube
Simple squamous epithelium can be studied by looking at cells which line blood and lymph vessels. These flattened cells are called endothelial cells. The nuclei are frequently found protruding into the lumen of the vessel. Observe the numerous large blood vessels present in the periphery of this section. Simple squamous epithelium is also the outer covering of the uterine tube which is termed the mesothelium.

Kidney
Simple squamous epithelium is readily seen in the in the cortex of the kidney, lining the urinary space as Bowman’s capsule. Simple squamous epithelium is also observed lining the vasa recta vessels of the kidney. Note how the nuclei protrude into the lumen.

Simple cuboidal epithelium:

Kidney
Simple cuboidal epithelium is prominent in the cortex and medulla of the kidney. Proximal convoluted tubules, distal convoluted tubules, and collecting ducts are examples of simple cuboidal epithelium.

Thyroid gland
The follicular epithelium of the thyroid gland is an example of simple cuboidal epithelium which lines the active colloid-filled follicles. Simple squamous epithelium also line inactive thyroid follicles.

Simple columnar epithelium:

Duodenum
Locate a large fingerlike projection at the surface of the organ (this is an intestinal villus). Observe that the projection has an internal component and a surface. The surface of each villus is covered with simple columnar epithelium. The free surface of these cells has very tiny projections called microvilli, which are specialized for absorption (absorptive cells). Numerous pale-staining mucus-secreting cells, known as goblet cells because of their shape, are dispersed between the absorptive cells.

Jejunum (small intestine)
Locate the fingerlike projections at the surface of the organ (intestinal villus). Observe that each villus is covered with simple columnar epithelium. The free surfaces of these cells are covered with numerous very small finger-like projections called microvilli, which are specialized for absorption. They appear as a densely-stained apical border (often referred to as a “brush border”). Numerous pale-staining mucus-secreting goblet cells are dispersed between the absorptive cells.

Stomach
Another example of simple columnar epithelium is the surface absorptive cells of the stomach.

Pseudostratified columnar epithelium:

Trachea
Note the ciliated, pseudostratified columnar epithelium lining the tracheal lumen. This epithelium is commonly referred to as "respiratory epithelium". Compare cilia with the microvilli in the previous slide (small intestine). Note that the cilia are much longer.

Epididymis, efferent ducts
Distinguish between the epididymis and the efferent ducts in this slide by the appearance of the lumen in each organ. The epididymis has a smooth, even epithelium lining its lumen; while the efferent ducts are more scalloped in appearance. Both are examples of pseudostratified columnar epithelium. Especially note the stereocilia (long microvilli) of the epididymis.

Stratified squamous epithelium (keratinized and non-keratinized):

Esophagus
Stratified squamous nonkeratinized epithelium lines the lumen of the esophagus. This type of epithelium is found in mucous membranes. Note that the surface layer of cells (apical) that contact the lumen are squamous (flattened), whereas the deeper layers (basal) of cells are not squamous in shape.

Skin, sole of foot
Observe the thick cornified layer of stratified squamous keratinized epithelium of the skin. Note the changes in cellular morphology and intercellular spaces as you scan from the basal cells to the squamous (flat) living surface cells, and then to the lifeless keratinized cells on the surface. This specimen is typical of thick skin due to the relative thickness of the keratinized layer.

Skin, scalp
This specimen is another of example of stratified squamous keratinized epithelium. It is typical of thin skin due to the relative thinness of the keratinized layer compared to thick skin. Note the difference in the thickness of the stratum corneum, which is the keratinized layer, compared to the previous specimen.

Thick skin
This specimen is another example of stratified squamous keratinized epithelium.

Stratified cuboidal and stratified columnar epithelium:

Submaxillary Gland
Stratified columnar epithelium is often found at the junction between simple columnar epithelium and stratified squamous epithelium. The ducts of the salivary glands fit into this category and are shown in this slide. Also observe some stratified cuboidal epithelium lining the larger ducts found in this section (typically lying within connective tissue septa).

Skin, sole of foot
Stratified cuboidal epithelium is found in the ducts of sweat glands. Look for these sweat glands well beneath the surfacing epithelium.

Skin, scalp
Again, search for the stratified cuboidal epithelium in the ducts of sweat glands.

Transitional epithelium:

Ureter
Note the presence of characteristic surface dome cells in the transitional epithelium.

Urinary bladder
Find the transitional epithelium that lines the urinary bladder.

Ureter
In this specimen, the ureter is preserved in various degrees of distention for better observation of the features of transitional epithelium. Compare the distended epithelium to the relaxed epithelium. Note that the surface dome cells are readily identified in the relaxed epithelium, but not in the distended epithelium.

Basement membrane:

Trachea
The basement membrane is clearly seen underlining the "respiratory epithelium". This is refractile and pink, and much thicker in the trachea than in most other organs.

Cell junctions:

Skin, scalp
Examine the stratified squamous epithelium of the epidermis of the skin. Examine the epidermis and try to resolve the cell borders, which stain lighter. These lighter-stained thin areas between the cells are artifacts of fixation, in which the cells have retracted away from each other, but which nevertheless remain attached together via desmosomes (macula adherens).

Glandular epithelium

Serous glands:

Pancreas
Note the arrangement of the glandular epithelium forming rounded masses of epithelial cells termed acini. The centrally located lumen of each is continuous with the duct system of the gland. Individual cells are pyramidal shaped. The nuclei are round and found basally while the eosinophilic secretory granules are located apically. The basal region of each acinar cell is basophilic due to the abundance of ribosomes in the rough endoplasmic reticulum.

Parotid gland
The parotid gland is a pure serous gland and thus made up of all serous acini. Note the duct system of the gland.

Mixed (mucous and serous) glands:

Submaxillary gland
Also organized as acini, the submaxillary gland secretes both serous and mucous products. Serous cells are more numerous in the submaxillary (also called submandibular) gland. Mucous-secreting cells have flat nuclei located basally. The apical region typically appears empty due to the extraction of mucous in routine tissue preparation. Serous cells are often found capping mucous acini. These are called serous demilunes and are easily distinguished by the intense eosinophilic staining of the storage granules.

Submaxillary gland
This specimen shows a less typical picture of serous cells and mucous cells in a preparation that has been stained with PAS to stain the glycoprotein red in mucous cells. Serous demilunes are readily observed in this preparation.

Sublingual gland
Mucous cells (stained with PAS) predominate in the sublingual gland. Observe the small serous component of this gland present as serous demilunes.

Trachea
The glands in the lamina propria of the trachea illustrate another example of mucous cells and serous demilunes.

Unicellular glands:

Duodenum
Observe goblet cells in the simple columnar epithelium of the duodenum.