Digestive System: Large Intestine, Liver, and Pancreas
6 topics with concise breakdowns: definitions, key facts, and class questions.
In this section, we analyze the terminal parts of the digestive tube and the largest digestive glands. You will study the microscopic structure of the large intestine and rectum, vermiform appendix, liver, gallbladder with biliary tract, and pancreas.
Special attention is paid here to the relationship between structure and function. We will examine how the abundance of goblet cells in the crypts of the large intestine helps form fecal masses, why the vermiform appendix is called the "intestinal tonsil", and how the unique blood circulation system in hepatic lobules is organized.
What is most frequently asked on tests and exams? Instructors love questions about the classical hepatic lobule (and its differences from the portal lobule and hepatic acinus). You will also be required to have a clear understanding of the difference between the exocrine and endocrine parts of the pancreas and the ability to distinguish at a glance an appendix section from a colon section based on the abundance of lymphoid nodules. Pay attention to these markers when working with microslides!
Haustra arise due to differences in the lengths of the wall layers: the longitudinal muscular bands (teniae) are shorter than the other tunics, causing the intestine to gather into folds and form transverse sacculations.
How to distinguish the vermiform appendix from the colon on a histological specimen?
In the appendix, the outer muscular layer is continuous (teniae are absent), there are fewer goblet cells in the epithelium, and giant accumulations of lymphoid tissue are located in the mucosa and submucosa, disrupting the muscularis mucosae.
What is the difference between permanent and inconstant folds of the rectum?
Permanent transverse folds are formed by three layers (mucosa, submucosa, and circular muscle) and do not disappear. Inconstant longitudinal folds are formed only by the mucous membrane and are easily smoothed out when the organ fills.
Is the liver considered an endocrine organ?
No. Despite the fact that the liver actively synthesizes proteins, glucose, and lipids, secreting them directly into blood plasma, it does not produce true regulatory hormones.
How does the gallbladder wall differ from the intestinal wall?
The main histological difference is that the submucosa is completely absent in the gallbladder wall. Because of this, the mucosa transitions directly into the muscle layer.
Why does an exocrine acinus look two-toned?
This is due to the polarity of acinar cells. The basal part is rich in granular ER (stained basophilically dark), while the apical part contains zymogen granules (stained oxyphilically light).
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