upper GI histology Flashcards
Be able to identify the 4 layers of the gastrointestinal tract and describe why variations in those layers are important along the length of the tract.
Mucosa
-Comprised of the epithelium and underlying vascularized –connective tissue called the lamina propria, scattered with lymphocytes, plasma cells, and macrophages.
The layer underlying the lamina propria is the muscularis mucosae.
Submucosa
Denser layer of connective tissue containing larger blood vessels, nerve plexuses, glands, and lymphatic nodules.
Lymphoid cells scattered throughout.
Muscularis externa
Inner circular and outer longitudinal muscle and nerve plexus layers.
Serosa (aka adventitia – above the diaphragm in the esophagus)
Thin layer of connective tissue and outer covering of squamous epithelial cells
Describe how the major components of our food sources (proteins, nucleic acids, complex carbohydrates and lipids) are digested and absorbed. What components and conditions need to be secreted and met in order to do this?
Proteins – amino acids. Carbohydrates – monosaccharides. Fats – monoglycerides and fatty acids. ➔Requires digestive enzymes. Vitamins and ions, water.
What mechanisms are in place to avoid digesting ourselves?
Surface mucous cells in the stomach contain vesicles full of mucin and bicarb that create a protective layer.
Their short microvilli are covered by cell surface glycoproteins, the glycocalyx.
Digestive enzymes of the pancreas are synthesized as zymogens and converted to active enzymes in the intestine so they don’t digest self along the way.
Identify the fundamental aspects of mucosal structures/functions that prevent bacterial infection along the gastrointestinal tract? Describe the organization and role(s) of mucosal associated lymphoid tissue in the G.I. tract.
Lymphoid tissue is present in the GI tract as both individual cells and as Peyer’s Patches in the mucosa of the intestine.
M cells take up antigens and present them to lymphocytes and macrophages. Plasma cells of the nodules release IgA that are transcytosed to luminal surface as antibacterial agents.
Mucous interfered with bacterial adherence and colonization.
Describe the roles of smooth muscle and the enteric nervous system in gut motility, and the advantage of extrinsic control as well.
Enable churning and peristalsis movements.
Regulation and coordination of digestion via autonomic nerves (enteric nerves) and hormones.
Sympathetic and parasympathetic tone directed by the CNS coordinate peristalsis and effects on blood vessels and glands.
Endocrine cells affect many functions.
Delineate the requirements for pH control in different regions of the gut. Why in general do we have a much lower pH in the stomach?
Important for digestion as enzymes that breakdown food in absorbable monomers are effective at low pH.
Inhospitable environment for pathogens.
- Describe some of the effects of key endocrine cells in the G.I. tract and understand their more general roles in regulation of GI coordination.
Located in stomach, intestine, and pancreas.
K, L, I, G, enterochromaffin, N, S cells secrete somatostatin, motilin, gastrin, cholecystokinin, neurotensin, etc.
- Identify the normal histology of the esophagus and be able to differentiate it from other regions of the GI tract.
No digestive function. Specialized for passage of food.
Upper portion contains skeletal muscle under voluntary control, and midway, a mix of skeletal and smooth muscle is present. Lower third is only smooth muscle.
Mucous glands exist in the mucosa and submucosa to help moisten food (but that mostly happens in the mouth with saliva).
Esophogeal-gastric junction made up of incomplete sphincter whose muscular contraction generally prevents reflux (not a true valve).
The esophagus lacks a thick mucous covering so ulceration can occur with chronic GERD.
- Describe the layers of the stomach, identify unique features of the cells in these layers and be able to differentiate them from other regions of the GI tract.
Three regions: the cardia (secretes mucous), fundus (secretes acid, digestive enzymes, and mucous), and pyloris (secretes mucous and gastrin).
Stomach wall has extensive rugae (folds) that disappear with distension.
**The muscularis externa has extra oblique layer.
The epithelium is unique in that contains deep folds called gastric pits that secrete mucous. They become tubular gastric glands continuing deep into the mucosa.
Stem cells in upper neck region renew every 3-5 days.
Surface mucous cells contain vesicles full of mucin and bicarb that create a protective layer. Their short microvilli are covered by cell surface glycoproteins, the glycocalyx.
Chief cells secrete pepsinogen, which gets converted to pepsin at low pH. Extensive RER.
Parietal cells pumps out protons and secrete intrinsic factor (important for uptake of B12). Extensive mitochondria. Stimulated by gastrin and histamine.
Enteroendocrine cells -
G cells secrete gastrin.
A cells secrete glucagon.
EC cells secrete serotonin.
D cells secrete somatostatin.
Lamina propria contains scattered lymphoid cells.
- Understand the functional significance of rugae in the stomach and plicae circulares in the small intestine.
Increase digestive and absorptive surface areas?
The circular folds slow the passage of the food along the intestines, and afford an increased surface for absorption
- Be able to describe the layers of the small intestine, differences in the duodenum versus other regions, and the cell types and specific functions in these layers.
the duodenum, jejunum, ileum.
Relaxation of the pyloric sphincter leads to the passage of chyme into the duodenum. Digestion continues, but at a different pH, from enzymes released by the pancreas and within the intestinal mucosa.
Digestion and absorption required a large surface area.
Plicae circulares are covered with villi are covered with microvilli at the surface of the epithelial cells called enterocytes, covered with glycocalyx where digestive enzymes are found.
Goblet cells are scattered throughout the enterocytes and produce mucous for protection and lubrication. Abundant in the duodenum.
Glands
Crypts of Liberkuhn (tubular glands) penetrate from base of villi deep into mucosa. Epithelium of the crypts is continuous with the surface epithelium.
Stem cells abundant in lower third of the crypts.
*Paneth cells contain granules full of defensins.
Brunner’s glands (in duodenum) secrete bicarb to neutralize acid from pyloric sphincter and mucins.
Villi
Very structured.
Loose lamina propria core containing capillaries and small vessels, scattered lymphocytes, and small lymphatic vessels that join the lacteals, which will eventually drain into thoracic duct.
Lacteals pass fluid as well as chylomicrons exocytosed by enterocytes. (Enterocytes take up fatty acids and monoglycerides from the gut and resynthesize di- and tri-glycerides).
Nutrients taken up into bloodstream reach hepatic portal system.
Enterocytes of the intestine contains a glycocalyx layer where final stages of digestion can occur. (E.g. Where glucose is finally produced, so it is not available as a nutrient to luminal bacteria. An example is lactase.).
Peristalsis and segmented movement of the intestine – myenteric nerve plexus of Auerbach innervates the muscularis interna – for movement of food as well as the agitation of food.
Ganglion cell bodies are present between the two layers of muscle.
- Describe and be able to recognize cellular structures of the exocrine pancreas. Define differences you would observe between pancreatic acini and acini of salivary glands. Describe the importance of zymogens and their activation.
Gland is organized into acini (like a bunch of houses around a cul-de-sac at the end of a street)
Basal RER
Apical zymogen granules
Zymogens are activated to become trypsin, chymotrypsin, elastase, carboxypeptidase, triacylglycerol lipase.
Trypsinogen is cleaved to trypsin by a duodenal membrane-anchored enzyme called enterokinase.
Trypsin then activated the other zymogens by proteolysis.
Amylase and ribonuclease are synthesized in the active form in the pancreas.
Enzymes are synthesized as zymogens and converted to active enzymes in the intestine so they don’t digest self along the way.
Centroacinar cells represent the beginning of the duct system that secretes pancreatic juice of water and bicarb to help Brunner’s glands neutralize stomach acid.
Under control of secretin and cholycystokinin.
- Be able to identify normal histological features and differences among salivary glands.
Three main glands are the paired submandibular, the sublingual, and the paired parotid glands.
Serous secretions are watery and contain enzymes (amylase, RNAse, and DNAse) and IgA.
Mucous secretion lubricate and protect.
Acinar design.
- Identify the layers of the colon, describe the cell types and their roles in the colon, and be able to differentiate the histology of the colon as compared to other regions of the G.I. tract.
Made up of the cecum and appendix, the ascending, transverse, and descending colon, and the rectum.
Smooth. Lacks plicae and villi.
Contains numerous straight tubuluar glands or crypts (like a rack of test tubes).
Two cell types: mucous-producing and absorptive (water and salt).
Lamina propria and submucosa contains scattered and aggregates of lymphocytes.
About two-thirds of the wall of the colon is muscular – circular bands called taeniae that compress and segment fecal material. This circular layer thickens to form the internal anal sphincter, and downstream is circular striated muscle – the external anal sphincter.
parietal cells looks like
fried egg look, deep in the section
HCL and IF
