The Seamless Gut by i i♡histo
Each region of your digestive tract is histologically different.
Specialized in its own unique way to impart a specific function. When the different regions of these tubes work together they function as a seamless system that protects, absorbs and secretes. Ensuring that we digest the products we ingest, remove the nutrients that we need and dispose of those that we don’t.
Students of histology frequently meditate on the differences between these regions in an attempt to correlate structure with function and categorize regions based on appearance.
The seamless gut tube demonstrates these differences in a single image allowing junior histologists to compare and marvel in the functional specializations of each region.
The non-keratinized stratified squamous epithelium provides protection against the abrasive forces encountered as the food bolus is transmitted toward the stomach.
Note the epithelium has a thin layer of smooth muscle underneath it called the muscularis mucosa. The presence of this tells you that you are observing esophagus and not another region of non-keratinized stratified epithelium in the body (e.g. anal canal or some regions of the oral cavity like the cheek)
The muscularis externa is composed of a unique smooth and skeletal muscle mix (in the middle 1/3rd). The upper 1/3rd it is all skeletal muscle. The lower 1/3rd it is all smooth muscle.
This is the fundus of the stomach (the cardia and pylorus have a different appearance).
The large folds of mucosa and submucosa are rugae, which allow the stomach to distend as it fills with food.
The glandular epithelium is composed of gastric pits opening into deep gastric glands. These contain numerous cells each with their own role to play in the digestion process through secretion of either hydrochloric acid (parietal cells), pepsinogen (chief cells), mucus (surface/neck mucous cells) or hormones (enteroendocrine cells).
The start of the small intestine! The mucosa becomes heavily folded to form villi, finger-like projections that increase the surface area across which absorption can occur.
Each simple columnar epithelial cell also has a highly folded apical membrane forming microvilli, which further increases the surface area for absorption.
You can always identify duodenum from other regions of small intestin because of its distinctive Brunner’s glands in the submucosa. These release a bicarbonate rich secretion into the duodenal lumen to neutralize the acidic contents released from the stomach and helping prevent duodenal ulcer. The pancreatic enzymes that are released here (trypsin and chymotrypsin) also work best at a more neutral pH…so that’s a bonus!
Villi, microvilli and plicae circulares (circular folds of the mucosa) are evident in the jejunum. It lacks any submucosal features which makes it easy to distinguish from other regions of the small intestine - duodenum and ileum.
The final section of the small intestine also contains villi and epithelial cells with microvilli.
Large lymphoid aggregates known as Peyer’s patches reside in the submucosa, breach into the lamina propria. Peyer’s patches are a distinctive feature of the ileum and you will never confuse it for other regions of the small intestine if you look out for them.
Similar to the appendix at first glance, the appendix contains lymphoid nodules. However these completely surround the organ (instead of forming patches). If you look closely you will also see that this vestigial region of gut tube has no villi or microvilli (which is a feature of the small intestine). Instead its mucosa contains deep crypts of Lieberkuhn lined by goblet cells that secret mucous, like in the colon…
Distinctive because of its large crypts of Lieberkuhn lined by goblet cells that produce large volumes of mucus. The mucus facilitates the passage of feces which become increasingly dry as more water is absorbed from them as they pass through the large intestine.
The muscularis mucosa has a distinctive arrangement in the colon also. The outer longitudinal layer of muscle no longer forms a sheet of smooth muscle around the tube, but is organized into three thin, evenly spaced bands called teniae coli.
If you are a student of histology. Look for these features and you will be able to identify any region of the digestive tract. Guaranteed.
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