Gastrointestinal Histology Lab

1. GastrointestinalHistology Lab The Final Histo PowerPoint http://www.compumedsystems.com/htmls/gi_home.html

2. This laboratory is concerned with the identification of the histological features of the Gastrointestinal system.Be able to distinguish each of the organs of this system and recognize their salient features as described in the text associated with each of the images.

3. Lip. This is a section from the inner portion of a lip. Notice that it is lined by a non-keratinized stratified squamous epithelium. Deep to the epithelium is a fibroelastic connective tissue containing mucous-secreting labial glands (red arrows). The core of the lip contains skeletal muscle (oris orbicularis – not shown). L=Lumen.

4. Filiform Papillae. The tongue consists of a mass of skeletal muscle covered by a mucous membrane. The mucous membrane is smooth on the ventral surface, but irregular on the dorsum due to the presence of numerous papillae. Several filiform papillae (red arrows) are illustrated in this micrograph. These papillae are partially keratinized and serve to roughen the surface of the tongue to aid in licking. In some species such as cats, the filiformes have a higher degree of keratinization which yields a very “raspy’ surface. Skeletal muscle is located in the area below the red line.

5. Circumvallate Papilla. The tongue contains 7-12 circumvallate papillae in the area of the sulcus terminalis. This is a low magnification section of tongue illustrating one of these papillae (red arrow). Taste buds are present on the lateral surfaces of the papilla (area encircled in green). A “trough” surrounds each of these papillae. Emptying into these troughs are the serous secretions of the glands of Von Ebner (yellow arrows).

6. Circumvallate Papilla. This is a higher magnification of the previous image illustrating the serous units of Von Ebner’s glands (yellow arrow) and its duct (red arrow) emptying into the trough surrounding a circumvallate papilla of the tongue. Note the lighter staining structures (taste buds) on the sides of the papilla (encircled in green).

7. Taste Buds. This is a high magnification of the side of a circumvallate papilla illustrating several taste buds (yellow arrows). The three cells types associated with this structure include sensory cells, supporting or sustentacular cells, and basal cells. The darker-staining sensory cells (white arrows) can be easily distinguished from the sustentacular.

8. Parotid Gland. The major salivary glands include parotid, submandibular, and sublingual. The is a low magnification image of a section of parotid gland. The secretory units of this gland are entirely serous (yellow arrows). Numerous intralobular (striated) ducts are present (orange arrows). Duct cells tend to stain a light pink. Several fat cells are scattered throughout the gland (red arrows).

9. Parotid Gland. This is a “thin” section (1.5µm) of a parotid gland illustrating two intercalated ducts (red arrows). These are the first ducts off of the secretory units and generally have a smaller cross-sectional diameter than the secretory units.

10. Submandibular Gland. The submandibular gland contains about 80% serous cells and 5% mucous cells. In this image, examples of serous cells are indicated by yellow arrows. Mucous cells (black arrows) exhibit very little staining. Intralobular ducts are indicated by he orange arrows and stain light pink.

11. Sublingual Gland. The sublingual gland is primarily mucous-secreting contains about 30% serous cells and 60% mucous cells. In this image, examples of mucous cells are indicated by black arrows. Numerous serous demilunes (green arrows) capping the mucous units are present. The tip of the orange arrow is in the lumen of an interlobular duct.

12. Sublingual Gland. The sublingual gland is primarily mucous-secreting contains about 30% serous cells and 60% mucous cells. In this image, examples of mucous cells are indicated by black arrows. The serous cells are indicated by the red arrows. Numerous intralobular ducts are present (green arrows). The blue arrow is pointing to an interlobular duct. Note that this type of duct has a noticeable amount of connective tissue associated in contrast to the intralobular ducts.

13. Sublingual Gland. This is a high magnification of a sublingual gland illustrating the associated cell types. Examples of mucous cells are indicated by black arrows. Numerous serous demilunes (yellow arrows) capping the mucous units are present.

14. Dental Lamina. The first sign of tooth development is the formation of a dental lamina along the position of the future dental arch. Following the initiation process, there is increased mitotic activity of the epithelial cells in this area and then a downward growth of these cells as the mitotic activity continues (black arrow). This forms a continuous ridge, called the dental lamina, along the future dental arch. Associated with the dental lamina formation is an increase in the density of mesenchymal cells in this area (red arrow).

15. Bud Stage. Along the dental lamina at 10 sites each in the upper jaw and the lower jaw, there is increased mitotic activity leading to the formation of the enamel organ. As the name implies these cells will be involved in the formation of enamel. The enamel organ undergoes several conformational changes due to histodifferentiation. The dental lamina narrows and the enamel organ is somewhat rounded. This is referred to as the Bud Stage (black arrow). Note the increased density of mesenchymal cells (red arrow). These cells will eventually develop into structures associated with the tooth.

16. Cap Stage. The enamel organ continues to proliferate and increase in size. An increased density of mesenchymal cells occurs on the deep surface of the enamel organ. These mesenchymal cells are in the process of forming the dental papilla, which will develop into the connective tissue of the dental cavity. Some of these cells will develop into odontoblasts responsible for the formation of dentin. There is unequal growth of the enamel organ (black arrows) leading to the formation of a shallow invagination on the deep surface. This is recognized as the Cap Stage. The blue arrow indicates the dental lamina.

17. Bell Stage. With continued growth and histodifferentiation, the enamel organ assumes a “bell” shape. The mesenchymal cells on the deep surface of the enamel organ have developed into the Dental Papilla (DP), which now fills the concavity of the bell. Cells on the outer portion or periphery of the dental papilla will develop into odontoblasts responsible for the formation of dentin. The cells in the center of the enamel organ differentiate into the Stellate Reticulum (black arrow). These cells have a “stellate” appearance due to numerous cytoplasmic processes. The spaces between the cells come to contain fluid, which will help to cushion and protect the forming surface of the tooth. The outer cells differentiate into the Outer Enamel Epithelium (red arrow). The inner cells of the enamel organ (immediately surrounding the dental papilla) differentiate into the Inner Enamel Epithelium (green arrow). The cells of the inner enamel epithelium will develop into ameloblasts responsible for the formation of enamel. The thin pink line between the inner enamel epithelium and the dental papilla (orange arrow) is the basal lamina of the enamel organ. The mesenchymal cells surrounding the bell (dashed black arrow) form the Dental Sac, which will go on to form Cementum, Periodontal Ligament, and Alveolar Bone. The blue arrow indicates the dental lamina.

18. Bell Stage. With further development of the bell stage, a secondary dental lamina (red arrow) forms off of the primary dental lamina (green arrow), projecting toward the lingual side of the forming tooth. The permanent teeth develop from the tip of the secondary laminae. A very early permanent tooth in the bud stage appears to be present in this image. DP=Dental papilla.

19. Developing Tooth (Upper). This is a section of the upper portion of a tooth well along in its development. Odontoblasts (blue arrow) on outer rim of the dental pulp (former dental papilla) are in the process of depositing dentin (green arrow). During this process, they move in a direction toward the dental pulp. The ameloblasts (red arrow) are in the process of depositing enamel (black arrow). During this process, they move in a direction away from the dentin.

20. Developing Tooth (Lower). This is a section of the lower portion of the developing tooth illustrated on the previous page. The future root will develop in the area of the yellow arrow.

21. PDL. This is an image of an edge of a tooth on the left and a portion of the alveolar bone on the right (black arrows). The cementum (C) is located on the outer edge of the dentin (D). The green arrow points to the junction between the dentin and the cementum. The Periodontal Ligament (PDL) inserts into the cementum and the alveolar bone via Sharpey’s fibers (red arrows). The PDL serves to anchor the tooth in the alveolar socket.

22. Can you believe that was all Mouth? • This is WAY Too much Histology for one system. 8 hours of Histo lecture and 6 hours of lab? Are they kidding? • Anyway, it has been my pleasure bringing you these Histology Labs!

23. Esophagus. This is a low magnification of the esophagus. It is lined by a non-keratinized stratified squamous epithelium (orange arrow). Deep to the epithelium is a thin lamina propria (blue arrow). Deep to the lamina propria is the muscularis mucosae (red arrow) consisting of smooth muscle. These three layers constitute the mucosa. The submucosa (purple arrow), located deep to the mucosa, is a band of relatively dense connective tissue. The next layer, the muscularis externa, consists of muscle. The muscle is skeletal in the upper third of the esophagus (a continuation of the skeletal muscle of the oropharynx), smooth muscle in the lower third, and mixed in between. This image is from the lower third of the esophagus illustrating an inner band of circularly arranged muscle (green arrow) and an outer band of longitudinally arranged muscle (black arrow). A small lymphatic nodule is present (yellow arrow). Esophageal glands normally scattered throughout the esophagus are not present in this section.

24. Esophagus. This is a low magnification of the esophagus (from the upper third). In this image, a submucosal esophageal gland is illustrated (black arrow). These glands are primarily mucous-secreting. Some serous-secreting cells are scattered within the gland. Can you identify the muscularis mucosae??

25. Stomach. This is a low magnification image of a section through the stomach illustrating its overall general structure. Some variation occurs in the cardia, fundus/body, and the pyloris. The fundus and the body are histologically identical. As can be noted in this image, the epithelial lining invaginates into the mucosa forming gastric pits or foveolae (red arrows). The pits are shallowest in the cardia and deepest in the pylorus. Several gastric glands open into the bottom of each pit. Mucous-secreting cells line the surface and the opening of the pit (yellow line to the surface). The thick mucous secreted by these cells protects the surface of stomach. The neck of the gastric gland (yellow line to red line) is lined by mucous neck cells and parietal (oxyntic) cells. A few regenerative cells are located in this region. The base of the glands contains chief (zymogenic) cells, parietal cells, and a few enteroendocrine cells. The submucosa is indicated by the black arrow; the muscularis externa is encircled in blue.

26. Stomach. This is a higher magnification of the previous image illustrating a somewhat better view of the gastric mucosa. The pits lie in the approximate area between the yellow line and the lumen (L). The red arrows point to two of the pit openings. The necks of the glands are located in the area between the yellow line and the red line; the base of the glands lie between the red and black lines. The muscularis mucosa is indicated by the blue arrow.

27. Stomach. This image is a high magnification of the base of fundic glands. The chief (zymogenic) cells (black arrows) make up the larger population of the secretory cells. Parietal cells (red arrows) are scattered among the chief cells. These latter cells are responsible for the production of hydrochloric acid and gastric intrinsic factor.

28. Duodenum. This is a section from the duodenum, the first section of the small intestine. The mucosa with its broad villi is encircled in black. Deep to the mucosa is the submucosa (blue arrow) containing Brunner’s glands (red arrow), a distinctive feature of the duodenum. Surrounding the submucosa is the muscularis externa (green arrow) consisting of inner circular and outer longitudinal layers of smooth muscle. The outer layer is the serosa consisting of the adventitia covered by mesothelium.

29. Jejunum. This is a section through the jejunum illustrating numerous villi projecting into the lumen (L). The villi consist of a core of lamina propria (blue arrow). This layer is comprised of loose connective tissue containing lots of lymphocytes and plasma cells. The orange arrow points to the lumen of a lacteal. The villi are lined by a simple columnar epithelium containing microvilli. Goblet cells are also present in the lining epithelium, but not evident at this magnification. Between the bases of the villi, the surface invaginates to form the crypts of Lieberkühn. The submucosa is indicated by the red arrow; the muscularis with its inner circular and outer longitudinal smooth muscle layers by the green arrow. The adventitia is not present on this section. The image on the right is a higher magnification of the area encircled in black. The black arrow indicates a goblet cell. Microvilli are indicated by the red arrow.

30. Lacteal. This is a high magnification of a villus of the jejunum illustrating a lacteal (yellow arrow), which is an example of lymphatic capillaries typically found in villi. Lacteals are lined by endothelium.

31. Myenteric Plexus. This is a high magnification of the muscularis externa of the small intestine. The inner circular layer of smooth muscle is indicated by the yellow line and the outer layer by the red line. Located between the two layers is the myenteric (Auerbach’s) plexus, parasympathetic ganglion (black arrows). Numerous such ganglia are present in the wall of the small intestine. The myenteric plexus control the motility of the muscularis externa and therefore peristalsis. Similar ganglia are located in the submucosa and are known as submucosal (Meissner’s) plexuses. The parasympathetic fibers of the submucosal plexus control the secretory activity of the epithelial lining cells and of the glands in the lamina propria. They also control the movement of the muscularis mucosae.The image on the right is a higher magnification of a myenteric plexus. The black arrows in the image on the right point to three perikarya, which are the cell bodies of post-ganglionic neurons.

32. Colon. This is a low magnification of a section through the colon. This organ has no villi but does contain lots of crypts of Lieberkühn. The cells of the crypts are similar to those of the small intestine except for the absence of Paneth cells. The density of goblet cells increases along the length of the colon while the absorptive cells decrease in number. The mucosa occupies the area between the black line and the lumen (top of image). The submucosa is located between the black and red lines. One of three taenia coli that are located around the colon is illustrated at the bottom of the image (TC). The image on the right is a higher magnification of the colon illustrating the numerous the crypts of Lieberkühn (black arrows). The lining cells include absorptive cells, goblet cells, some regenerative cells, and enteroendocrine cells. The latter two groups of cells are found near the base of the crypts.

33. Colon. The image on the left is a low magnification image of the colon. The mucosa contains lots of crypts of Lieberkuehn (red arrow). Just deep to the mucosa is the submucosa (black arrow). The muscularis mucosa ( green arrows) contains an inner circular and outer longitudinal layer of smooth muscle. An adventitia is indicated by the blue arrow. The image on the right is an enlarged magnification of the mucosa illustrating the crypts of Lieberkuehn (black arrows). The crypts are lined by goblet and absorptive cells.

34. Liver. This is a low magnification image of a section through the liver. Several lobules (L) are outlined by their surrounding interlobular connective tissue (black arrows). The lobules are roughly hexagonal in shape. Portal “triads” (portal systems) are located at the corners of the lobules (black rings). Blood from branches of portal veins and hepatic artery located in the triads enters sinusoids and passes to the central veins located at the center of the lobules (red arrows).

35. Liver. This is a high magnification image of a section through a portal triad (portal system) which is outlined in yellow. The triads contain a hepatic portal vein (black arrow), hepatic arteriole (red arrow), bile duct (green arrow), and lymphatic vessels (blue arrow).

36. Liver. In this image, a branch (yellow arrow) of a very large portal vein (PV) is shown to be emptying into sinusoids (black arrows). Also illustrated are two bile ducts (green arrows) and an arteriole (branch of hepatic artery red arrow).

37. Liver. In this image, several sinusoids (blue arrows) are illustrated to be emptying into a central vein located in the center of a lobule. All the white spaces present in this image are of sinusoids.

38. Liver. In this image, several sinusoids (white spaces) are illustrated. One such sinusoid (blue arrow) is seen emptying into a central vein (red arrow).

39. Liver. This is a high magnification image of several hepatocytes. When bile is secreted by the hepatocytes, it first enters the bile canaliculi (red arrows). The bile then empties into the canals of Herring and then the bile ducts of the portal triads.

40. Gall Bladder. The functions of the gall bladder include the storage and concentration of bile. This image is of a section through the gall bladder showing the highly folded and complex mucosa (red arrows). The mucosa is lined by a simple columnar epithelium containing lots of microvilli. Bands of smooth muscle (Blue arrows) found in the wall. When the muscle contracts the contents of the bladder are expressed into the cystic duct. What is the stimulus for the smooth muscle contraction? The outer part of the wall is covered with serosa (adventitia plus mesothelium).

41. Gall Bladder. These images are higher magnifications of the gall bladder illustrating the lamina propria of the mucosa (red arrows) and the lining of simple columnar epithelium (green arrows). The blue arrows are pointing to the smooth muscle.

42. Pancreas. The pancreas is a mixed gland in that it has both endocrine and exocrine components. The endocrine portion consists of small clusters of cells that form what is referred to as Islets of Langerhans. These cells synthesize various hormones as insulin, glucagons, somatostatin, etc. The rest of the pancreas synthesize and secrete a variety of digestive enzymes. Some cells, the centroacinar cells, secrete bicarbonates. In this image, the islets of Langerhans is indicated by the green arrows. Most of the cells (eliminating the islet cells) are serous-secreting cells of the exocrine part of the pancreas (red arrows). Several intralobular ducts are present (blue arrows).

43. Pancreas. This section of pancreas is a thin section (1.5µm). Two islets are illustrated (green arrows). Serous-secreting cells are indicated by the red arrows. It is difficult to visualize the centroacinar cells at this magnification.

44. Pancreas. This is a higher magnification of the pancreas with a lone islet in the center of the image. The black arrows are pointing to centroacinar cells, which are responsible for the secretion of bicarbonates. What is the stimulation for their secretion of the bicarbonates??

45. What tissue is this Lip ? Labial Glands ?

46. Mucosa ? What tissue is this Colon (more goblet cells, less absorptive cells) ? Submucosa ? Taenia coli ?

47. Circumvallate Papilla ? ? Tasty Stuff! Yum!! ? Taste buds Von Ebner gland ?

48. ? ? Von Ebner Gland and Duct Taste Bud

49. Sinusoids ? Bile duct Arteriole Portal vein ? ? ?

50. Sensory Cells (dark staining) ? Taste Buds ?