Experiments on the observation of the microstructure of the digestive system
Experiments on the observation of the microstructure of the digestive system
1. Observe the structure of the taste buds.
2. Comparative observation of the structural features of plasma alveoli, mucus alveoli and mixed alveoli.
3. Observe sections of the esophagus, stomach, and small intestine to understand the layering and general organization of the walls of the alimentary canal. Compare observations of the structural features of the mucosa of the esophagus, stomach, small intestine and colon in relation to the functional focus.
4. Understand the general organization of the pancreas and distinguish the structure of exocrine vesicles and endocrine islets.
5. Understand the structure of hepatic lobules and hepatic ducts in relation to the function of the liver and the characteristics of blood circulation.
Operation method
Experiments on the observation of the microstructure of the digestive system
Materials and Instruments
Stomach, Small Intestine, Liver Lobule Tissue Model Move I. Taste buds For more product details, please visit Aladdin Scientific website.
Tongue contour papilla section Leafy papilla section Submandibular gland section Esophagus section Gastric body section Duodenum or jejunum section Colon section Small intestine section Pancreas section Liver vascular injection section Liver vivo stained section Liver section Ciliac duct section Fundic glands Small intestinal epithelium section Electron microscopy images of hepatocytes
Observations were made with slices (H-E stained) of the contour papillae of the human tongue or the lobulated papillae of the rabbit tongue.
1. Low magnification observation: Find the protruding part of the mucous membrane that is the papilla of the tongue, see its epithelium for the complex flat epithelium, the epithelium has a lot of light coloring of the oval taste buds. The taste buds at the lobular papillae of the rabbit tongue are more numerous, so they are easy to find.
2. High magnification observation The taste buds are ovoid, and their length and diameter are equal to the thickness of the epithelium where they are located. There were three kinds of cells in the taste buds: type I cells were pike-shaped, few in number. The nucleus was narrow and long, and the coloring was darker; type II cells were pike-shaped or columnar, more in number, the nucleus was large and round, and the coloring was lighter; type I and II cells had taste hairs at the tip, which were vaguely visible. The basal cells are cone-shaped and located at the base of the taste buds. If the section is cut through the middle of the taste bud, the taste hole at the tip of the taste bud can also be seen.
Second, the plasma, mucus and mixed vesicles of the salivary glands
Observe the submandibular gland of a dog in section (H-E stain). Only the structural features of the 3 types of vesicles are required to be observed.
(i) Low magnification observation
The glandular tissue was seen to be separated by connective tissue into many lobules, within which many alveoli and a few ducts were visible.
(B) High magnification observation
Look for 3 types of glandular follicles under high magnification.
1. plasma follicles The shape of the follicles is nearly round and the lumen is very small. The cytosol is conical and the cytoplasm is darker colored, purplish red. The nucleus is rounded and located at the base of the cell.
Mucous follicles The shape of the follicles is long oval, which is more human than the plasma follicles. Cytoplasm coloring light, light blue-violet cytoplasm nucleus flat and round, located at the base of the cell, close to the cell membrane.
3. Mixed vesicles At the end of the mucous vesicles are attached to several plasma vesicles arranged in a semilunar shape.
Esophagus
When observing the muscularis propria in sections of the esophagus, stomach, small intestine, and colon, it is important to note whether this section is cut longitudinally or transversely, because, the muscularis propria seen in different sections has different orientations of muscle fiber arrangement.
Human esophagus section (H-E stain) viewed with low magnification. The wall of the tube can be divided sequentially from the lumen of the esophagus outward into four layers: mucosa, submucosa, muscularis propria, and tunica albuginea. Yellow
1. The mucosa can be divided into two layers: the epithelium is complex flat epithelium; the lamina propria is connective tissue; the muscular layer of the mucosa is longitudinal smooth muscle, which is thicker.
2. Submucosa The submucosa is lightly stained and is loose connective tissue, and the esophageal glands can be seen as mucous glands and mixed glands. In
The muscular layer of the esophagus is thick and is roughly divided into two layers: the inner circular muscle and the outer longitudinal muscle. Observe and determine in the section you are looking at, which muscle fiber is the esophageal myenteric layer?
4. epithelium The epithelium of the esophagus is a fibrous membrane, a layer of loose connective tissue.
Sections of blood vessels and nerves can be seen in the connective tissue in each of the above locations.
IV. Stomach
Sections (H-E stained) of the body of the stomach of a cat or dog were taken and combined with a model of gastric organization focusing on the structure of the fundic glands.
(I) Low magnification observation
Distinguish the four layers of mucosa, submucosa, muscularis propria and epithelium. The mucosal surface of the stomach was characterized by papillary mucosal elevations as mucosal wrinkles, which were composed of mucosa and submucosa.
The surface of the mucosa is a single layer of columnar epithelium, and the epithelium is concave to form a short and broad gastric notch. The apical cytoplasm of the epithelial cells contained mucogenic granules, which were dissolved in H-E stained sections, resulting in a vacuolated apical surface.
The lamina propria was a loose connective tissue with a large number of fundic glands, which were tightly arranged, so that there was little interglandular connective tissue in the lamina propria. The fundic glands were single tubular glands or branched tubular glands, which opened into the gastric notch. On section, the fundic glands were cut into longitudinal, transverse and oblique sections.
The muscular layer of the mucosa is thin and is smooth muscle of the internal circular and external longitudinal muscles.
2. The submucosa is loose connective tissue, rich in blood vessels and nerves.
3. The muscular layer is very thick, composed of smooth muscle, divided into three layers: internal oblique muscle, middle circular muscle and external longitudinal muscle. The boundaries of the first two layers are not easy to distinguish.
4. The outer membrane is the plasma membrane, that is, in the thin layer of loose connective tissue is also covered with a single layer of flat epithelium (mesothelium).
(ii) High magnification observation
Observe the several types of cells that make up the alveoli of the fundic glands. Only the following three types of cells can be distinguished in H-E stained sections:
1. Mural cells Very large, nearly round. The nucleus is large, round and centrally located. The cytoplasm is strongly eosinophilic and stained dark red by eosin.
2. Principal cells are located between the wall cells, the most numerous on several days, and are columnar in shape. The nucleus is rounded and located at the base of the cell. Cytoplasm is basophilic, stained blue, cell boundaries are not clear.
3. Cervical mucus cells are few in number, located in the neck of the gland, mostly cuneate, with rounded nuclei, located at the base of the cell, and light cytoplasmic coloration.
(iii) Demonstrate the electron microscopic structure of wall cells and main cells.
Observe with the transmission electron microscope picture of the gastric fundus gland. The cytoplasm of the mural cells has tortuous branches of intracellular secretory tubules, the walls of which are connected to the cell membrane on the top surface of the cell, with microvilli, mitochondria are abundant, and other organelles are not developed. The perinuclear area of the principal cell had a large number of rough endoplasmic reticulum with well-developed Golgi complexes, and the cytoplasmic tip had many round zymogen granules.
Five small intestines
(A) Observations on human duodenum or jejunum sections (H-E staining) and models of small intestinal organization and structure
Focus on the structure of small intestinal villi and small intestinal glands.
1. Naked eye observation There are several large protrusions protruding into the lumen of the mucosal surface, which are mucosal folds. What structures does it consist of?
2. Low magnification observation First roughly observe the layering of the small intestine wall, and then carefully observe layer by layer.
(1) Mucosa in the whole intestinal mucosal surface (including the surface of the mucosal folds) is covered with many irregular small finger-like protrusions, that is, for the small intestinal villi. On section, the small intestinal villi are often cut into longitudinal, transverse and oblique sections. The surface of small intestinal villi is a single layer of columnar epithelium, and the deeper surface of the epithelium is the loose connective tissue of the lamina propria.
Many intestinal glands were seen within the lamina propria of the mucosa. The intestinal glands were single straight tubular glands, often cut into longitudinal, transverse and oblique sections. The intestinal glands open doors between the villi of the small intestine and can be found in sections. The alveoli consist of a single layer of columnar epithelium with an intervening lumen known as the glandular lumen.
Dispersed lymphoid tissue or lymphoid nodules stained blue-purple are sometimes seen in the lamina propria.
The muscular layer of the mucosa is smooth muscle, and this layer is thin and often not easily distinguishable, although it is divided into two layers, the inner circular muscle and the outer longitudinal muscle.
(2) The submucosal layer is loose connective tissue. If you observe the duodenal section, the duodenal glands can be seen in this layer, which are mucous glands. In close proximity to the muscle layer can be seen several cell groups with large and round nuclei, it is the parasympathetic postganglionic neurons in the submucosal plexus.
(3) Myofibrillar layer The smooth muscle is arranged into two layers, the inner circular muscle and the outer longitudinal muscle. In the connective tissue between the circular and longitudinal muscles, large and round nuclei can also be seen in the cell groups, which are the parasympathetic postganglionic neurons in the intermuscular plexus.
(4) outer membrane most of the duodenum for a layer of loose connective tissue of the fibrous membrane, the jejunum for the plasma membrane, that is, in the loose connective tissue is also covered with a layer of mesothelium.
3. High-power microscope observation Find a longitudinal cut relatively straight small intestine villi to observe its structure. The surface of the villi of the small intestine is a single layer of columnar epithelium, epithelial cells free surface with a striated edge. There are cup-shaped cells scattered between the columnar cells (absorptive cells). The deeper part of the epithelium is connective tissue, in which smooth muscle fibers are scattered parallel to the long axis of the small intestinal villi. In the center of the lamina propria of the small intestinal villi, a hollow tube made up of layers of endothelium, the central celiac duct, can be seen, which is mostly cut into various sections in the section. Sometimes the central celiac duct is not visible even on the whole section due to the sampling of the material used in the preparation of the section. Many capillaries can be seen in various sections around the central celiac duct.
When the intestinal gland is viewed with high magnification, it is seen to be composed of columnar cells (absorptive cells) and cup-shaped cells as well. In some H-E-stained sections it is even possible to distinguish a Paneth cell at the base of the intestinal gland. The top of this cell has granules that are stained a deep red color.
(ii) Demonstration of observation of a section of cat small intestine (silver-stained)
Use low magnification to find the intestinal gland, and then change to high magnification to observe it. A small number of black colored small intestinal endocrine cells (silversmith cells) can be seen scattered between the absorptive cells of the intestinal glands.
(iii) Demonstrate the observation of microvillus structure
Observe the microvilli structure with a transmission electron microscope picture of small intestinal epithelial cells.
VI. Colon
Observe with low magnification using human colon sections (H-E stained). Focus on its mucosal structure and compare it with the mucosa of the small intestine. The intestinal wall of the colon is also divided into four layers, and the mucosa has no intestinal villi, but many intestinal glands. The intestinal glands were single rectal glands, which were cut into various longitudinal, transverse and oblique sections on the section. Do not mistake two neighboring intestinal glands for a single intestinal villus when observing. There were many cup-shaped cells in the epithelium. If the section is cut into a lymph node, it can be seen in the lamina propria, which often extends into the submucosa.
VII. Pancreas
Human or guinea pig pancreas sections (H-E staining) are taken for observation, focusing on distinguishing the alveoli and islets and understanding the islet structure.
1. Low magnification observation: A small amount of connective tissue can be seen extending into the pancreatic parenchyma, dividing the pancreas into many lobules. Inside the lobules, there are many deeply stained plasma vesicles and a few intralobular ducts, which are the exocrine part of the pancreas. Between the follicles, there is a cluster of cells of different sizes and light coloration called islets, which are the endocrine part of the pancreas. In the connective tissue of the pancreas, sometimes the ring layer of vesicles can be cut, which is the visceral receptor.
2. High magnification observation The structure of the plasma alveoli is basically similar to that of the salivary glands. The difference is that the small cells can be seen in the lumen of the alveoli, which are cubic or flat, and are the vesicular cells, with rounded nuclei and lighter cytoplasmic coloring.
The islet cells are arranged in clusters and are connected to each other in a network. Capillaries are scattered between the cells. The nuclei of the islet cells were rounded, and the darker stained islets were A cells in H-E stained sections. Darker stained, flat or spindle-shaped fibroblasts are also interspersed within the islets. Special staining is required to distinguish A, B, and D cells.
Liver
(A) observation of liver section
Liver sections (H-E stained) were taken from pigs and observed in conjunction with a model of liver tissue structure
1. Observation with low magnification, many polygonal liver lobules can be seen, with connective tissue separating the lobules, and the separation of pig liver lobules is clearer than that of human liver. There is a central vein in the center of each lobule. Hepatocytes are arranged in single rows with the central vein as the center to form an uneven plate-like structure (liver plate). However, in the section, the liver plate shows cords radiating to the periphery of the lobules, which are called hepatic cords. The branches of the hepatic cords are interconnected to form a mesh. The irregular spaces between the cords are called sinusoids. It is easier to understand the above structures by looking at a model of liver tissue structure.
Between the lobules of the liver there are some nearly triangular areas of connective tissue, in which there are three kinds of accompanying ducts [interlobular bile ducts, interlobular arteries, and interlobular veins], for the portal area.
2. High magnification observation Select a clearer hepatic lobule and use high magnification to further observe the hepatic cord and hepatic sinusoidal structures.
Hepatocytes are relatively large, polygonal, with rounded nuclei located in the center of the cells, and sometimes binucleated hepatocytes can be seen. The walls of the hepatic sinusoids consisted of flattened endothelial cells with rounded nuclei protruding into the lumen. Blood cells can be seen within the hepatic sinusoids.
Three types of ducts are recognized in the hilar region based on the wall structure. The interlobular bile ducts are easily distinguished from the interlobular arteries and veins because they consist of a single layer of cuboidal or columnar epithelium with distinct nuclei and lightly stained cytoplasm. Because all three ducts may branch, sections of more than one interlobular bile duct, interlobular artery, or interlobular vein are sometimes seen within the same hilar area.
(ii) Demonstration of the observation of an injected section of the hepatic vasculature of a cat
This section is made by injecting colorants from the hepatic portal vein, so observation under low magnification can clearly show the branching anastomosis of the hepatic sinusoids into a network and the connection with the central vein of the hepatic lobules, and the interlobular vein and the sublobular vein can be seen at the same time.
(iii) Demonstration of observation of hepatic macrophages in the hepatic sinusoids of rabbits
Hepatic macrophages, also known as Kupffer's cells. Observe the liver section made by live staining method. Under high magnification, some irregularly shaped hepatic macrophages are seen to contain phagocytosed live dye particles. The color of the granules varies with the vivo dye used. The color of the granules is blue when the sections are stained with Taipan blue, and red when stained with neutral red or carmine.
(d) Demonstration of rabbit liver sections made by PAS reaction.
The hepatocytes are rich in purplish-red glycogen granules when observed under high magnification microscope.
(E) Demonstration of rabbit liver sections made by injecting silver nitrate through the bile ducts This section was made by injecting silver nitrate through the bile ducts of the liver. Under low magnification, there are many small black branches in the lobules of the liver, and the branches anastomose with each other to form a network, and these small black branches are the bile ducts. The liver cells do not show color on this section.
(F) Demonstration of the electron microscopic structure of hepatocytes.
Observe with a transmission electron microscope picture of a hepatocyte. The hepatocyte cytoplasm is well developed with various organelles and the nucleus is located in the center of the cell. Note the structure of the three neighboring surfaces of the hepatocyte.