GASTROINTESTINAL SYSTEM III: LABORATORY

INTRODUCTION

The gastrointestinal (G.I.) tract is a hollow tube extending from oropharynx to anus (includes oral cavity). It is coiled and dilated in some regions in accord with function. The G.I. tract is lined with specialized epithelia which function in processes of secretion, digestion, absorption, immunocompetency, excretion and peristalsis. The G.I. tract has many glands within the wall proper and other glands which empty secretions into the G.I. tract via ducts.

DEMONSTRATION

Examine the demonstrations slides located at the front of the laboratory. Slide DEMO H-66 is of pyloric glands. Slide DEMO H-67 is of gastric glands. Identify the differences in pit depth, type of cells in the glands and straight versus coiled glands.

SLIDES 25, 26: HUMAN ESOPHAGUS, ESOPHAGEAL-CARDIAC JUNCTION:
  1. Examine slide 25. The tissue cut in cross section is the esophagus. Identify the type of epithelium which lines the luminal surface of the esophagus. Is it keratinized or non- keratinized?
  2. Note the thin and ill defined lamina propria lying just under the epithelium. Diffuse lymphocytes are evident in this region.
  3. The muscularis mucosa is discontinuous and composed of only longitudinal bundles of smooth muscle fibers. You must search carefully to find these bundles.
  4. Identify the submucosa. Observe the basophilic, mucous glands of the esophagus. These are the esophageal glands proper. The ducts of these glands are lined by simple to stratified cuboidal epithelium. Aggregations of lymphocytes, diffuse or nodular are common around ducts and glands.
  5. Find the muscularis propria (externa) of the esophagus; if it is composed solely of skeletal muscle fibers, the section is from the upper 1/3 of the esophagus. If you see a mixture of smooth and skeletal muscle, the section was taken from the middle 1/3 of the esophagus. If only smooth muscle is found in the muscularis propria, your section was taken from the lower 1/3 of the esophagus.
  6. Examine slide 26. Try to find glands in the lamina propria; these are the cardiac glands of the esophagus. They are variable and not present in every esophagus. Identify nerve bundles and elements of Auerbach's plexus located in the muscularis propria between the muscle layers. Note esophageal glands and large veins in the submucosa.
  7. Is the esophagus covered by a serosa or adventitia or both? If both, in what region is a serosa found?
SLIDE 26: HUMAN CARDIAC STOMACH:
The glands of the cardiac region of the stomach are located near the esophageal-cardiac junction.

  1. Identify the gastric pits leading into the cardiac glands. Mucous cells line the gastric pits and cardiac glands in this region. Can you see any parietal cells? Are chief cells present?
  2. Compare the depth of the gastric pits in this region with the depth of the mucosa. Note that the pits are shallow.
  3. Observe that the cardiac glands are coiled as indicated by oval or round appearance of the cut gland profiles.
SLIDES 124, 127: HUMAN AND RAT STOMACH FROM CORPUS AREA:
  1. Examine slide 124. Identify gastric pits and gastric glands. Remember that in the fundus and body the glands are called gastric glands. In these regions, the gastric pits are shallow and the gastric glands are straight.
  2. Identify the surface mucous cells lining the gastric pits and the gastric lumen. What is the function of these cells? Their secretory product is released by merocrine secretion.
  3. Distinguish between chief and parietal cells in the gastric glands. Note the size and acidophilia of the parietal cells. Why do chief cells stain basophilic and parietal cells stain acidophilic? What is the secretory product of these two cells? Gastric glands are mixed because they produce both mucous and serous products.
  4. Examine slide 127 on low power. This is a PAS stain. Note the intense pink to red staining of the surface and pit cells. These are the surface mucous cells of the stomach. At high power, the pink-red staining is concentrated in apically localized mucin granules.
SLIDE 30: HUMAN PYLORIC STOMACH:
The mucosa of the pyloric antrum has gastric pits and pyloric glands. The pits are lined by mucous cells. The glands contain mucous and enteroendocrine cells.

  1. The gastric pits of the pyloric regions are deep and the glands are coiled.