PSIO 202 Required Handout
Department of Physiology
Histology Slides Digestive System
*Students are required to know all the bold terms included in this handout
Slide 1: Esophagus (longitudinal section)
• Stratified squamous epithelium forms the most superficial layer of the organ.
• In the esophagus, there is relatively little lamina propria, and it is very difficult to distinguish the
connective tissue of the lamina propria from that of the submucosa. This is true of this particular
slide. Within the connective tissue that underlies the epithelium, you can see small sections of
muscle tissue which represent the muscularis mucosae. The submucosa of the esophagus also
contains mucus secreting glands, which although not depicted in this slide, are present along most of
the length of the esophagus.
• The third and outermost layer shown in the slide is the inner circular layer of the muscularis
externa. Since this is a longitudinal section of the esophagus, the orientation of the circular layer
looks different compared to a cross section through the alimentary canal.
Slide 2: Esophagus (longitudinal section)
• Stratified squamous epithelium forms the most superficial layer of the organ (stained pink).
• The lamina propria and submucosa lies just deep to the epithelium (stained blue). Recall that it is
difficult to distinguish the lamina propria from the submucosa in the esophagus. Small sections of
muscle tissue within the connective tissue represent the muscularis mucosae (stained pink).
• The third layer in the slide (stained pink) is the inner circular layer of the muscularis externa.
Slide 3: Stomach (longitudinal section)
• This slide depicts three general layers of the stomach wall. The innermost layer, the mucosa, is
stained dark pink and appears highly cellular. Deep to this layer is the loosely arranged connective
tissue of the submucosa, followed by two portions of the muscularis externa (inner circular and
• Notice the arrangement of the mucosal epithelium. At higher magnification you will be able to
discern gastric pits and glands. This is one of the key features that distinguishes the stomach from
the rest of the GI tract.
Slide 4: Stomach (higher magnification—depicts gastric pits)
• The mucosal epithelium of the stomach is organized into gastric pits and glands. Notice the simple
columnar epithelium and how it is invaginated at regular intervals. The invaginations are the
gastric pits. The simple columnar cells lining the gastric pits secrete mucus into the stomach lumen.
• At the base of the gastric pits are many cells that collectively form gastric glands. The gastric pits
act as ducts for the materials that are secreted by these cells.
• Notice the lamina propria that extends between the epithelium.
Slide 5: Stomach (better view of gastric pits)
• This slide illustrates the gastric pits, lined by simple columnar epithelium, the lamina propria
extending between the epithelium, and the gastric glands that lie below the pits. If you look closely
you should also be able to see very thin sections of muscle tissue extending between the
epithelium—this represents the muscularis mucosae.
• Notice the cells that make up the gastric glands. In this slide the majority of cells are large and stain
light-pink. These are the parietal cells that secrete H+ and Cl- into the gastric pits and stomach
PSIO 202 Required Handout
Department of Physiology
Slide 6: Stomach (depicts the base of the gastric glands)
• At the base of the gastric glands the majority of cells are chief cells. These cells are smaller than
parietal cells and stain blue to purple in color. They secrete pepsinogen, a precursor enzyme of
Slide 7: Small intestine (cross section)
• This slide depicts three general layers of the small intestine. The mucosa is stained bright blue, the
submucosa is light gray in color and contains clusters of glands, and the outer muscularis externa
layers (inner circular and outer longitudinal) are blue-gray in color.
• Notice that the mucosal epithelium has both extensions and invaginations. The extensions are called
villi, and they are lined by simple columnar epithelium with goblet cells interspersed. Note that in
this slide mucin, a component of mucus, stains red. The invaginations of the epithelium are called
intestinal glands or crypts of Lieberkuhn. The simple columnar cells of the crypts participate
mainly in absorption, although some secrete mucus or other chemicals that aid digestion (hormones,
lyzozyme). Although it is difficult to see in this section, the lamina propria and muscularis mucosae
typically extend between the villi in the small intestine.
Slide 8: Small intestine (depicts villi and a plica circularis)
• Notice how the tissue in the slide appears folded. The gross anatomy of the small intestinal mucosa
forms folds called the plicae circularis. Histologically, the epithelium of the mucosa then forms
invaginations and extensions (the crypts and villi).
• Notice that the lamina propria is easier to see in this slide, extending up between the villi. Also
note the muscularis mucosa that lies at the base of the mucosa and also extends up in small portions
between the villi (the muscle tissue is stained bright blue).
• Deep to the muscularis mucosae you can see the submucosa.
Slide 9: Villus of the small intestine
• This slide shows a villus at a higher magnification. Notice the simple columnar epithelium lining
the villus, and the lamina propria extending within the interior of the villus. Within the lamina
propria notice the capillary containing red blood cells.
Slide 10: Large intestine (longitudinal section)
• This slide illustrates the mucosa and submucosa of the large intestine. Notice that the epithelium of
the large intestine has invaginations like the small intestine, but lacks villi. Like the small intestine,
the invaginations here are called crypts of Lieberkuhn, and are made up of simple columnar
epithelium with goblet cells interspersed. The number of goblet cells is greater in the large intestine
compared to the small intestine.
• Note the lamina propria between the glandular epithelium and the muscularis mucosae (stained
pink) at the base of the mucosal layer. Deep to the muscularis mucosae is the submucosa, which is
loosely arranged and stained very light pink.
Slide 11: Salivary gland
• This slide illustrates the two secretory cell types contained within salivary glands—mucus and acini
(serous) cells. The mucus cells, stained white in this slide, secrete mucus, and the acini cells, stained
purple with a grainy appearance, secrete salivary amylase, an enzyme found in saliva.
• Also note the salivary ducts in the slide, formed by simple cuboidal epithelium (stained light
pink). These ducts move the mucus and salivary amylase into the oral cavity.
PSIO 202 Required Handout
Department of Physiology
Slide 12: Pancreas
• The pancreas contains an endocrine and exocrine component. The endocrine component contains
cells that secrete hormones including insulin and glucagon. These cells appear in clusters called
pancreatic islets (islets of Langerhans), the lighter staining central region of this slide.
• The other cells in the pancreas are exocrine cells that secrete precursor enzymes into the small
intestine to aid digestion. These cells are called serous or acini cells and are stained darker in color
(dark pink or purple) than the endocrine cells described above.
Slide 13: Liver lobule
• The liver is organized into lobules which contain hepatocytes (liver cells stained pink here)
arranged around a central vein (shown here in the center of the slide). Each lobule is separated
from the next by connective tissue, shown in dark blue.
• At the corners of the lobule are portal triads, regions that contain a branch of the hepatic portal
vein, a branch of the hepatic artery, and a bile duct (you can distinguish each of these structures at
higher magnification). Venous blood from the small intestine enters the liver lobule via the hepatic
portal vein branch and then filters through sinusoids, small spaces between the hepatocytes. The
hepatocytes process this blood before it drains into the central vein to exit the liver. Similarly,
arterial blood to oxygenate the hepatocytes enters the lobule via the hepatic artery branch, and flows
through the sinusoids en route to the central vein.
• Bile formed by hepatocytes moves in the direction opposite of blood, toward the bile ducts in the
portal triads via small bile canals (not identifiable in the slide).
Slide 14: Portal triad
This slide depicts a portal triad at higher magnification. The hepatic portal vein branch has the
largest lumen, very thin walls and contains red blood cells. The hepatic artery branch has a
smaller lumen, a thick muscular wall, and also contains red blood cells. The bile duct is lined by
simple cuboidal epithelium. Notice the other vessels in the area—these are either lymphatic vessels
or smaller blood venules.
CASE STUDY INTRODUCTION
Initial Case Study Presentation and Assignment 1:
DUE Friday March 27
Robert is a single, 20-year-old, Caucasian male. He has a moderately active lifestyle. He
walks his dog every day and enjoys hiking on the weekend. He is an animal lover and has
recently transitioned from a vegetarian diet to a strict vegan diet in the last 18 months.
As a sophomore at the University of Arizona, majoring in pharmaceutical science, he
spends most of his time studying for PSIO 202 and organic chemistry. He recently began
dating his PSIO lab partner, Valentina, who is also vegan. They enjoy cooking together
and eat most of their meals at home.
On Saturday, Robert went for his usual walk, but began to feel fatigued and breathless
after just half a mile. He attributed it to having only eaten a salad that day and made a
note to eat more protein, although he dislikes most meat substitutes. After a good
night’s sleep and a large breakfast, Robert decided to go on a hike with Valentina in the
morning. He struggled for most of the hike even though it was light terrain. About
halfway through the hike he began feeling some tingling in his fingers and numbness in
his feet. He was not too concerned, because he was breaking in new hiking boots and
had been swinging his arms a lot throughout the hike. However, after tripping
repeatedly and struggling to navigate the trail, Robert decided that they should turn
That following week, Valentina noticed that her usually fun-loving, boisterous boyfriend
seemed to be growing more and more moody, depressed, and tired. These changes,
along with Robert’s occasional complaint of numbness and tingling, lead Valentina to
suggest that Robert see his PCP, so he made an appointment for the next day.
Assignment 1: Diagnostic Test Recommendation
DUE Fri March 27
Based on the information presented in the scenario above, choose 2 diagnostic tests
or scans that you would recommend be performed on Robert. Briefly describe the
tests/scans and explain what information each could give you about Robert’s
Each student needs to complete the assignment individually. The assignment needs to
be put in the corresponding dropbox under the Assignments tab in D2L by Friday
March 27 at 11:59 pm. You must cite at least 1 credible reference (not Wikipedia or
WebMD) for each test
or scan mentioned using APA. Be sure to include in-text citations (No citations = No
credit). No late assignments will be accepted.
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