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Histology - GI Tract 1

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aupatel87's version from 2011-01-21 04:46

Section

Question Answer
What layers comprise the mucosa in the GI tract?Epithelium, Lamina propria, and Muscularis Mucosae
What 4 major layers compose the GI tract?Mucosa, Submucosa, Muscularis Externa, and Serosa (Adventitia if retroperitoneal segment)
What type of cells line the inside of the esophagus?Stratified squamous (protects esophagus from food bolus)
What type of cells line the inside of the stomach?Simple columnar without goblet cells
What type of cells line the inside of the small intestine?Simple columnar + Goblet cells
What type of cells line the inside of the large intestine?Simple columnar + Goblet cells
What type of cells line the inside of the rectum?Simple columnar + Goblet cells
What type of cells line the inside of the anal canal?Four types in order: 1. Simple Columnar 2. Simple Cuboidal --(Anal valve)-- 3. Stratified non-keratinized squmaous 4. Stratified keratinized squamous
What is the difference between villi and microvilli?Villi are projections of the mucosa and are lined by epithelial cells while microvilli line epithelial cells
What are submucosal projections/folds in the small intestine called?Plica Circularis
What is the glycocalyx?Special proteoglycans that protrude out of columnar cells in the intestine that have certain enzymes present in them that digest proteins and carbohydrates --> ex/Disaccharidases and Dipeptidases
What are the various types of secretions of the GI tract?Enzymes, mucous, hormones, antibodies (IgA --> Produced by plasma cells in the lamina propria)
Where are the secreted IgA antibodies in the GI tract made?In plasma cells in the lamina propria
What are Brunner's Glands?They produce alkaline secretions to neutralize acidic chyme
What is the relationship between the Muscularis Mucosae and peristalsis?None, this layer of muscles is not involved in peristalsis; it is responsible for mixing and propelling food
What are the various components of the lamina propria?Blood vessels/lymphatics (absorption), lymphoid tissue (immunity), glands (secretion), and sometimes smooth muscle
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Question Answer
How does the lamina propria differ along the GI Tract?At the lower end of the esophagus, it contains cardiac glands; in the stomach it contains lots of gastric glands (HCl + IF by parietal cells + Enzymes like pepsin by chief cells); in the small and large intestines there are lymphoid nodules, glands of lieberkuhn but small intestine has villi while large intestine does not. Also crypts of lieberkuhn in the large intestine do not have paneth cells while those in the small intestine do; In the anus, there are sebacious/circumanal glands, hair follicles, veins, and also lymphoid tissue
What is a lacteal?It is a blind lymphatic collecting projection from the lamina propria into villa
How does lymphoid tissues change along the GI tract?Lymphoid nodules within the lamina propria become larger and larger along the GI tract --> Very large nodules are called Peyer's patches and are located primarily in the ileum of the small intestine
What are M-cells?Stands for "Microfold cells" that are present on Peyer's patches and are responsible for transporting antigens from the lumen into the lamina propria where lymphoid tissue is present
What is the difference between M-cells and paneth cells?M-cells are located over lymphoid tissue and are responsible for transporting antigens while paneth cells are located in Crypts/Glands of Lieberkuhn and secrete lysozyme that can digest bacterial cell walls
What components of the lamina propria are present throughout the GI tract?Blood vessels/lymphatics, Lymphoid tissue (NOTE: Specialized in Ileum --> Peyer's patches with M-cells)
Where are Crypts of Lieberkuhn located?They project into the lamina propria along the small and large intestine, difference is that paneth cells that secrete lysozyme are only present in the small intestine
What are the functions of intestinal crypts (of Lieberkuhn)?They secrete various enzymes (including lysozyme by paneth cells in small intestine), and are also responsible for generation of new epithelium
What is the function of the submucosa?Contains many large blood vessels/lymphatics, nerve plexi, and occasional glands (located only at two places: in esophagus, called submucosal esophogeal glands proper and in duodenum called glands of Brunner that release alkaline secretions)
What are the two nerve plexi located in the GI tract?Submucosal/Meissner's Plexus in the submucosa and Myenteric/Aurbach Plexus located between the two muscular layers of the muscularis externa
What are the components of Meissner's and Myenteric Plexi?1) Afferent: Sympathetic and Parasympathetic Sensory nerves 2) Efferent: Post-ganglionic Sympathetic and End of Preganglionic parasympathetic fibers + cell bodies of Post-ganglionic parasympathetic fibers
What is the main function of Meissner's Plexus?Regulation of secretory glands
What is the main function of Myenteric Plexus?Control of peristalsis
What is the dividing segment between cranial and sacral parasympathetic outflow innervation of the GI tract?Cranial sympathetic flow via the Vagus nerve innervates the GI tract up to and including the transverse colon; Sacral parasympathetic outflow begins with the descending colon and continues to the anal canal
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Question Answer
What is the difference in function between the circular and longitudinal muscular layers?Circular layer is responsible mainly for mixing and sphincter control while the longitudinal layer is mainly responsible for peristalsis
What is the distribution of muscle in the muscularis externa along the esophogus?Upper 1/3 is primarily skeletal muscle, middle 1/3 is a mix of skeletal and smooth, and lower 1/3 is primarily smooth muscle
What are the layers of the muscularis externa in the stomach?Longitudinal, circular and innermost oblique (everywhere else there are only two layers --> This layer helps in "twisting")
What is the upper esophageal sphincter?Fibers of crico
What are tinea coli?Strips of longitudinally arranged smooth muscle in the large intestine (3 strips, not continuous)
The serosal layer of the GI tract is lined by what type of cells?Mesothelial cells
What are the anatomic regions of the stomach vs the histological regions?Anatomic regions include cardia, fundus, body, and pyloric regions while Histological regions include cardia, fundus, and pylorus/antrum
What is the antrum?It is another name for the pyloric part of the stomach (histological layer)
What is a foveola?It is another name for a gastric pit (or superficial zone); a pit is a single layer of mucous secreting cells that is pretty much constant throughout the gastric mucosa and has many glands that open up to it
What are oxynitic cells?This is another name for parietal cells, which secrete HCl and IF into the lumen and HCO3 into the blood (which ends up in mucin via fenestrated capillaries); activated by binding of gastrin and ACh; potentiated by Histamine binding to H2 receptors
What are the various epithelial cell types lining gastric glands?
How do surface mucus cells differ from mucus neck cells?Differ in shape and mucin
In gastric glands, where are regenerative cells located?Primarily in the neck region
What are the major differences between parietal and chief cells of the stomach?Parietal cells are eosinophilic (pink), located in the upper portion of glands with centrally located nuclei, produce HCl/HCO3 & IF and are stimulated by ACh, gastrin, and Histamine; Chief cells are basophilic (blue), located in the lower portion of glands with basal nuclei, produce pepsinogen & Lipase, and are stimualted by ACh alone
What is the function of Mucin?It forms a protective insoluble layer on the cell surface that traps ions (HCO3-, K+, Na+, Cl-) to neutralize the acidic environment
What type of capillaries surround gastric glands and why?Fenestrated capillaries allow HCO3- to be taken up into the mucous layer (This HCO3 comes from parietal cells)
Where are neuroendocrine cells located in the stomach?At the base of gastric glands
What are the carious types of neuroendocrine cells of the stomach, their location, and their function?1. G cells located in the pyloric region secrete gastrin, which has two functions: stimulates parietal cell secretion of acid and stimulates growth of various epithelial cells; 2. D cells located in the pyloric region produce somatostatin, which inhibits secretory activity of the other neuroendocrine glands; 3. A cells located throughout the stomach produce glucagons that regulate hepatic glycogenolysis; 4. ECL Cells (Enterochromaffin-like) produce and secrete Histamine (stimulates acid secretion) and Chromogranin A (inhibits neuroendocrine function or surrounding cells)
What is the most abundant type of gastric neuroendocrine cell?ECL Cells (Enterochromaffin-like)
Why is it significant that G cells and ECL cells are not stimulated by ACh but rather the neurotransmitter gastrin-releasing peptide?When atropine is administered (an anticholinergic), it will not block the vagal stiimulation of G cells or ECL cells. This will allow for the continued secretion of gastrin and histamine.
What is the Zollinger-Ellison Syndrome?It is a triad of gastric acid hypersecretion, sever peptic ulceration, and gastrinoma (of duodenum or non Beta-islet cell tumor of pancreas). The tumor leads to hypersecretion of gastrin, which is trophic for parietal cells. This leads to hypersecretion of acid, and thus sever ulceration. 20% of cases are associated with MEN-1 --> Autosomal Dominant transmission
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Question Answer
What cells secrete gastrin?G cells --> Neuroendocrine cells located at the base of gastric glands primarily in the pyloric region
What cells secrets somatostatin?D cells --> Neuroendocrine cells located at the base of gastric glands primarily in the pyloric region
What cells secrete mucin?Surface epithelium and Mucus Neck Cells in gastric glands
What cells secrete Pepsinogen?Chief cells located at the lower portion of gastric glands (Basophilic with basal nuclei)
What cells secrete intrinsic factor?Parietal cells located at the upper portion of the gastric glands
What is the significance of the Portal-Caval anastamoses in the submucosa of the esophagus?In liver disease, blood can back up into the portal system and cause dilation/varicies in this system --> This can lead to bleeding, Hematemasis/Hemoptysis
How do aspirin or other NSAID's increase risk for peptic ulcers?Mucin production is dependent on prostaglandins, which are inhibited by NSAIDs. Thus Mucin production is decreased leaving the stomach lining susceptible to damage by the surrounding acidic environment
What are the two functions of Muscularis Mucosae? What is this controlled by?1. Controls the infolding of mucosa in the lumen to regulate surface area; 2. Controls length of villi in intestines to help drain/milk the lacteals; This muscle is controlled by the Submucosal Plexus/Meissner's plexus
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