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Epithelium

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Slide 1: Small intestine, x-sect. Mesothelium covering the outside surface is simple squamous epithelium. The epithelium covering the inside surface (and glands) is simple columnar.  

Slide 2: Mesothelium (on rat bladder with underlying connective tissue and smooth muscle). Note also the endothelium of the prominent venule in the field. (1μm Epon section, toluidine blue).  

Slide 3: This is a section through an aortic valve. The simple squamous epithelium layers on both surfaces are endothelium. Note that the nuclei of these cells are not always in the plane of section so that it appears that it is discontinuous. The intervening tissue is connective tissue.  

Slide 4: Endothelium is a simple squamous epithelium which lines blood vessels. In this slide the large triangular lumen belongs to a vein (filled with clumped red blood cells) and the small oval lumen belongs to an arteriole. Note the way in which the nuclei of the endothelial cells protrude into its lumen. The large spaces at the bottom of the slide, delineated by thin pink strips of tissue, are fat cells.  

Slide 5: This section is from the cortex of the kidney and shows a single kidney glomerulus in the upper center of the slide surrounded by tubules cut in various planes. The outer layer of the glomerulus, called the parietal layer, is simple squamous epithelium. This can be contrasted with the epithelium lining the kidney tubules in this section which is simple cuboidal epithelium. A higher magnification of a glomerulus is shown on the next slide.  

Slide 6: In this slide one can see quite clearly the simple squamous parietal layer of the glomerulus. This is a plastic embedded 0.5micron section stained with toluidine blue.  

Slide 7: Lung parenchyma, alveoli. Note that in paraffin sections such as this the epithelium is impossible to see - it is too attenuated.  

Slide 8: In this higher magnification of lung alveoli, dilated capillaries can be identified by their red cell content. This epithelium lining the alveoli is very thin and difficult to see with certainty (see slide 10).  

Slide 9: Lung, alveoli at higher magnification. Capillaries are collapsed and, again, epithelia and endothelia are difficult to distinguish.  

Slide 10: In this electron micrograph of an inter-alveolar septum one can see the alveolar epithelium of 2 adjacent alveoli (3 arrows in one of them) and the intervening capillary (single arrow in the narrow lumen and a double arrow indicating the attenuated endothelium) containing an erythrocyte (rbc). CT designates the connective tissue of the alveolar wall.  

Slide 11: This section of a thyroid gland shows a field of thyroid follicles lined by simple cuboidal epithelium. The material in the center of each follicle is stored secretory product. The space between the secretory product and the apical cell surface is an artifact.  

Slide 12: Thyroid gland of dog with "C" cells. Note that the epithelium is not simple squamous in regions where there are C cells: these are within the basement membrane but do not reach the lumen (C stands for “calcitonin” which is the hormone that they produce or “clear” which what their cytoplasm is). PAS-H stain.  

Slide 13: The large lumen or passage through the middle of this slide is a lung bronchiole lined by low columnar epithelium (truthfully, a bit too tall to be simple cuboidal). Lung alveoli can be seen adjacent to bronchiole at top and bottom of slide.  

Slide 14: This low power micrograph of pig liver shows epithelial cells arranged in irregular plates. A liver lobule roughly pentagonal in shape in the center is comprised of a central vein (a round empty spot in the center) with plates of cuboidal cells radiating out from the central vein.  

Slide 15: Liver hepatic cells (hepatocytes), human. Note that there are flattened endothelial cells visible in the field as well.  

Slide 16: This plastic embedded section of rat liver has been stained with methylene blue-Azure H. The largest cells are the hepatocytes and the cytoplasmic granules represent cell organelles. The flattened nuclei of one sinusoidal cell in the center is visible. The red cells in the sinusoids have been stained blue.  

Slide 17: This slide shows kidney tubule profiles again lined with cells that could be classified as either cuboidal or low columnar epithelium.  

Slide 18: Once again in the kidney! This time a longitudinally sectioned collecting tubule (very lightly stained compared to the surrounding proximal and distal tubules) is seen which is lined by simple columnar epithelium in contrast to other tubules in this slide which are lined by cuboidal epithelium.  

Slide 19: Here in the intestine one sees a simple columnar epithelium covering the surface of the villi. This epithelium has two cell types: absorptive and goblet (the ones with white spaces).  

Slide 20: This is a higher power view of a similar area as the last slide but stained with PAS-H. Note the PAS+ staining of the basal lamina, mucous secretory product in goblet cells and the glycocalyx. The small round dark staining cells which appear scattered within the epithelium are lymphocytes.  

Slide 21: Oviduct. The inner surface of the oviduct is lined by two cell types - ciliated and secretory. They compromise a simple columnar epithelium.  

Slide 22: Apocrine sweat glands and ducts. The epithelium lining the lumen of these ducts and glands vary from almost squamous to columnar.  

Slide 23: Trachea. This plastic embedded section shows the cilia on epithelial cells at free surface. The dark line beneath their surfaces represents basal bodies of the cilia. As usual, the tissue underlying the epithelium is connective tissue with hyaline cartilage beneath that (on the bottom of the slide).  

Slide 24: Ductus deferens. Note the numerous basal cells indicative of pseudostratified epithelium. There is some adherent secretory material which is sticking to the free surface.  

Slide 25: Epididymis. The basal cells are not as numerous here as they are in the ductus deferens. The luminal surface is covered with stereocilia (long microvilli, not cilia). The small darkly staining nuclei in the lumen belong to spermatozoa.  

Slide 26: Nasal surface of palate. Goblet cells are numerous and the epithelium can appear stratified. Loose connective tissue and mucous glands are seen underneath.  

Slide 27: Olfactory mucosa. This is probably the most difficult type of pseudostratified epithelium to identify. Its characteristic feature is the uniform absence of nuclei near the free surface.  

Slide 28: Bronchiole. The section is cut in such a way that the epithelium appears stratified in several areas. This is why when you look at your own slides you must look carefully at the tissue. In the connective tissue under the bronchiolar epithelium, are ducts of glands lined by simple cuboidal epithelium.  

Slide 29: Tongue. This stratified squamous epithelium is classified as non-keratinized because the squamous cells at the free surface have recognizable nuclei.  

Slide 30: Lip. This is also non-keratinized  

Slide 31: Thick Skin. This stratified squamous epithelium is classified as keratinized because the squamous cells at the free surface have no nuclei.  

Slide 32: Skin. In this higher power micrograph the elongated duct of a sweat gland is seen extending from the base of the epithelium and is lined by stratified cuboidal epithelium.  

Slide 33: Skin. Keratinized. Very thick skin (The spiral course of exit of a sweat gland duct is seen in the center of the field).  

Slide 34: Sweat gland ducts. For location in connective tissue under epidermis of skin, see #31. Stratified cuboidal epithelium is rare in the body and this is a classic example.  

Slide 35: Ovary. This is an unusual epithelium surrounding the cavity of maturing ovarian follicle.  

Slide 36: Urethra, penile. The epithelium is often difficult to classify with certainty.  

Slide 37: Gland (submandibular) with mucous and serous alveoli, ducts (simple columnar epithelium) (human, phosphotungstic acid hematoxylin [PTA-H]).  

Slide 38: Ureter. This section shows transitional epithelium in a relaxed state. Note the two prominent characteristics.

  1. binucleate surface cells and
  2. dome shaped appearance of cells at the surface.
 

Slide 39: Relaxed state transitional epithelium. Note binucleate, domed surface cells. High mag.  

Slide 40: Ureter. Plastic embedded section. Surface cells flattened over epithelial fold. Binucleate cells are also quite evident.  

Slide 41: Testis. Seminiferous tubules. This is a cytogenic epithelium. It produces sperm as its epithelial product but it is difficult to classify morphologically.  

Slide 42: Small intestine. Plastic embedded section. Within the epithelium of this section note the presence of several goblet cells. The mucus droplets of these cells can be seen outlined in the bulbous part of the cell. Note the endothelium of the capillary in the underlying connective tissue. The microvillous border of epithelium is well delineated.  

Slide 43: Serous gland. This section is from the lacrimal gland. The lumina of the secretory portions are very small and sometimes indiscernable. Note the duct shown near center with a nicely delineated lumen (cuboidal epithelium).  

Slide 44: Mostly serous, but with mucous secretory elements also. Submandibular gland. Higher magnification of serous acini showing zymogen granules. Plastic embedding.  

Slide 45: Mixed serous and mucous glands. The mucus-secreting cells can be seen in outline only because most mucous has been extracted during specimen preparation. Serous demilunes cap some of the mucous acini. No clear ducts in the field.  

Slide 46: Adrenal. The cells of the adrenal cortex have no free surface but are considered to be epithelial because of their close apposition to one another. A thin basal lamina separates them from the adjacent connective tissue cells and endothelium. A more proper term for such cells might be epitheloid.  

Slide 47: Brushed border microvilli in columnar intestinal epithelium. Note the goblet cell that is preparing for mucus secretion. (Plastic embedded, toluidine blue, acid fuchsin stain)  

Slide 48: Microvilli of intestinal epithelial cells, EM. Note filaments of core inserting into terminal web (can you describe the filaments - actin based? myosin?).  

Slide 49: Bronchial epithelium (human). This is pseudostratified ciliated columnar epithelium with goblet cells.  

Slide 50: Cilia of the bronchial epithelium (human) in x.s. and l.s. with basal bodies, rootlets and intercellular junction (TJ) regions. Also seen are microvilli x.s. & l.s. TEM  

Slide 51: Basal infoldings of proximal convoluted tubule cells in the kidney, EM. Mitochondria are aligned with the infoldings. Basal lamina is distinct.  

Slide 52: Endothelium and adjacent proximal convoluted tubule(PCT) epithelial basal region guinea pig, kidney. There are 2 basal laminas present; one of the epithelium and one of the endothelium: the endothelium is uppermost.  

Slide 53: Lateral interdigitations seen in cross section of intestinal epithelium, EM.  

Slide 54: Microvilli on intestinal epithelial cells (lumen to the upper left hand side). Note the junctional complexes between the cells (yes, you did see this slide in the Cell Biology course). TEM.  

Slide 55: Gap junction between adrenocortical cells shown in a freeze fracture preparation, EM.  

Slide 56: TEM of desmosome (between 2 cells of human bronchial epithelium)  

Slide 57: The stria vascularis is an unusual vascularised epithelium found in the lateral wall of the scala media in the cochlea. You will cover this is detail in the "Ear" section of the course. (Image: from uiuc.edu)


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