GI/Alimentary Canal Histology Flashcards
esophagus
-muscular tube
-connecting the pharynx and stomach
-function: moves food from pharynx to stomach by peristalsis
layers of the esophagus
from lumen down:
-adventitia- serosa is absent in the cervical and mediastinal esophagus —> loose and weak connective tissue
-muscularis propria- two layers of an inner circular muscular layer and an outer longitudinal muscle layer
-submucosa- loose connective tissue and the thick submucosa layer is the strongest layer of the esophagus
-mucosa- innermost layer of the esophagus —> thick, nonkeratinized (soft), stratified squamous epithelium that is a continuation of the oropharyngeeal mucosa
what do the salivary enzymes do?
-convert food into a mass called foot bolus
-once the food bolus reaches the pharynx —> swallowing starts and relaxation of the upper esophageal sphincter ensues to allow passage of food bolus into the esophagus —> bolus then travels down the esophageal body aided by peristaltic contractions of the esophageal mucles —> when it finally reaches the distal end of the esophageal body, it triggers relaxation of the lower esophageal sphincter and permits entry of the food bolus into the stomach
lower esophageal sphincter
-not an anatomical sphincter —> no well defined thickening or muscle that controls it
-considered a physiological or functional sphincter
-when it is not functioning properly, it can cause gastric acid reflux from the stomach into the LES and this can cause heart burn
esophagus mucosa
-3 layers: epithelium, lamina propria, muscularis mucosa
-lower esophageal sphincter is not an anatomical sphincter
esophagus submucosa
-contains fibroblasts, elastin fibers (allow esophagus to expand when food passes through), sparse ganglia (meissner plexus), lymphatic channels, blood vessels, and submucosal glands
-submucosal glands are comprised of mucinous cells surrounding a central lumen that produces acid mucin —> found only in the esophagus and duodenum (helps lubricate the surface of the esophagus)
muscularis propria
-composed of striated skeletal muscle and smooth muscle
-skeletal muscle in the proximal esophagus (voluntary control)
-smooth muscle in the distal esophagus
-inner layers orient circumferentially whereas the outer layers orient longitudinally to allow for segmental contraction and peristalsis
-myenteric plexuses (nerves and ganglia) found between inner and outer layers —> produce rhythmic contraction to result in parastaltic movement of the esophagus
adventitia
-outermost layer
-loose irregulat connective tissue
-function: connect esophagus to external structures (retroperitoneal organs)
-serosa is the last 1-2 cm of the esophagus and within the abdominal cavity below the diaphragm —> composed of simple squamous epithelium or mesothelium and it is continuous with the abdominal mesenteris
pits and glands of the stomach
-cardiac, fundic, and pyloric regions of the stomach contain different arrangements of gastric pits/glands
-smooth lining of the gut is columnar epithelial cells (mucuous cells) and the lining is punctured by gastric pits with tubular glands emptying into pits
-gastric fluid or digestive enzymes/HCl are produced within these glands depending on the region
-gastric pits are mucuous cells that are uniform throughout
-gastric glands are secretory/endocrine cells
cardiac region
-narrow circular region at gastrointestinal junction
-contains short pits with mucosal-secreting cardiac glands
-pits are coiled tubular glands producing thick mucous cells that are simple columnar
-mucous made of alkaline to protect adjacent esophageal mucosa from stomach acid secretions
-thin layer of mucosa and reduced number of gastric pits/glands
fundic region
-projects into dome-like structure above esophagus forming largest and central region of the stomach
-contains gastric pits/glands that produce gastric digestive enzymes/HCl to digest foods
-thicker layer of gastric pits and glands have smaller lumens
pyloric region
-funnel-shape opening up into the pyloric sphincter
-contains long pits and mucous-secreting glands
-deeper pits and shorter glands that produce gastrin hormone
parietal cells
-facilitate digestions through secretions
-secrete gastric acid or HCl, which will activate gastric enzymes and kill bacteria
-intrinsic factor is required for B12 absorption —> important for a variety of cellular processes
-“fried egg” appearance with a central nucleus and eosinophilic cytoplasm
chief cells
-work in conjunction with parietal cells to induce digestive activity
-produce a protein called pepsinogen –> at a normal pH, it is completely inactive but upon HCl secretion, it increases acidity and is activated into pepsin, proteolytic enzyme within the stomach liquid —> processes digested proteins since the pepsin can break down the proteins into polypeptides
-secrete lipase which breaks down fats
-secrete leptin which controls signals for food intake and energy expenditure
-eccentric nuclei with more blue/purple cytoplasm
enteroendocrine cells (G cells)
-provide important role in controlling digestion
-works with nervous system to initiate digestive actions
-secretes gastrin, which induces HCl production in parietal cells
-located near the base of glands in the stomach
-inconspicuous appearance with H&E, commonly IDed with immunohistochemistry
three parts to the small intestine
- duodenum
- jenjunum
- illeum
function of the small intestine: absorb nutrients
duodenum
-adjusts pH, tonicity
-distinguishing features are flatter villi, brunner’s glands in the submucosa
jejunum
-digests and absorbs
-distinguishing feature is the paneth cells, which are secretory glands between villi and within crypts of lieberkuhn
illeum
-absorbs bile salts
-distinguishing feature of shorter villi and peyer’s patch in the submucosa
features of the large intestine/colon
-cecum —> ascending colon —> transverse colon —> descending colon —> sigmoid colon
-involved in fluid absorption
large intestine
-increased goblet cells to produce mucus for easy passage
-crypts instead of villi
-made up of the mucosa, submucosa and muscularis propria
structural unit of the intestines
-villi are lined by simple columnar epithelium
-evaginations of mucosa in finger-like projections
-function to increase surface area for absorption and allow for secretion of substances by specialized cell types
layers of the GI tract
-mucosa is the innermost layer with direct contact with food
-submucosa is made up of connective tissue with blood vessels, nerves, and lymphatics
-muscularis has smooth muscle with the inner being circular and the outer longitudinal
-serosa is the outermost layer with smooth muscle
intestines- peristalsis
-muscularis propria has longitudinal layer made up of smooth muscle and circular layer
-circular layer contracts to propel the chyme forward
-longitudinal layer contracts to shorten the small intestine
-circular layer contracts
-contraction and relaxation of the muscularis propria allows the bolus to move through the small intestine
brunner’s glands
-distinguishing feature of the duodenum
-found in the submucosa of the duodenum
-compound tubular glands that secrete alkaline mucus (rich in HCO3) to neutralize acidic chyme from the stomach
peyer’s patches
-distinguishing feature of the illeum
-large aggregations of lymphoid follicles in the lamina propria and submucosa of the illeum
-specialized epithelial cells called M cells that cover peyer’s patches and their apical microfolds uptake particles, microorganisms, and transport antigens to lymphatic tissues
paneth cells
-specialized intestinal columnar cells
-located at the basal portion of the intestinal glands (crypts)
-exocrine cells with large, eosinophilic secretory granules
-provide protective function through granule release of defensins, lactoferrin, and lysozymes
auerbach’s and meissner’s nerve plexus —> innervation of the GI tract
-enteric nervous system- autonomic neurons organized into small ganglia in the submucosa and muscularis externa of the GI tract
-meissner’s submucosal plexus controls activity of glands and smooth muscle in the mucosa
-auerbach’s myenteric plexus controls peristalsis, the activity of the muscularis externa
esophageal-gastric junction
-located in the meeting point between esophagus and the stomach (cardiac region)
-stratified squamous non-keratinized epithelium (esophageal) to mucinous simple columnar epithelium (gastric)
-lose submucosal esophageal glands and gain gastric oxyntic glands
-prevents food and stomach acid from retrograding
recto-anal junction
-bend in the GI tract where the rectum meets the anus
-combo of internal and external sphincters with the puborectalis muscle
-simple columnar (colon) to stratified squamous (skin)
-prevents passage of fecal material
pyloric region
-distal portion of the stomach that opens into the small intestine at the sphincter
-long pits and pyloric glands
-valve that allows passage of food to the small intestine
appendix
-appendage to the cecum
-similar structure to the large intestine except with smaller lumen and lower density of glands
-many lymphoid follicles in mucosa/submucosa
-no known function
duodenum
-pylorus of stomach to the duodenojejunal junction
-initial segments of the small intestine and retroperitoneal
-brunner’s glands in the submucosa with alkaline mucous and urogastrone
-absorbs iron
illeum
-distally to the jejunum and connected to the cecum —> distal segment of the small intestine
-peyer’s patchs in the lamina propria
-absorbs B12 and bile salts plus produces mucin
what composes villi of the small intestine?
capillaries and lacteals
barrett’s esophagus
-condition involving damage to the inner lining of the esophagus
-does not cause symptoms
-associated with GERD, where the stomach contents, especially the acid, reflux into the esophagus leading to heartburn, indigestion, and nocturnal regurgitation
-diagnosis is through an upper endoscopy and biopsy —> BE has salmon pink color compared to normal white color
BE pathophysiology
-acid escapes from stomach to the lower part of the esophagus
-acid damages normal inner lining of the esophagus
-squamous cells are replaced by columnar goblet cells (intestinal cells) —> intestinal metaplasia
-goblet cells are more resistant to stomach acid
BE histology
-esophageal stratified squamous epithelium is replaced by intestinal columnar epithelium with goblet cells
BE vs chronic bronchitis
-BE: intestinal metaplasia with stratified squamous epithelium —> columnar intestinal metaplasia
-CB: squamous metaplasia with pseudostratified columnar epithelium —> squamous metaplasia
lacteals
-exclusively present in the small intestine
-located centrally in the villi within the lamina propria
-play a role in absorbing dietary fats and fat soluble vitamins
-once in the lacteals, fats —> lymphatic system —> bloodstream
-they also a play a role in the gut immune response by facilitating the transport of antigen and antigen presenting cells
primary intestinal lymphangiectasia (PIL)
-waldmann disease
-rare congenital disorder with no known cause
-mainly characterized by edema —> enlarged lacteals leading to disrupted absorption and leaking of lymph fluid back into the intestine
symptoms of intestinal lymphangiectasia
-nutrient deficiencies
-protein loss (albumin) so decreased oncotic pressure
-edema (primarily in limbs)
-abdominal discomfort with swelling of the pericardium and fluid in the chest
secondary intestinal lymphangiectasia
-due to underlying conditions that block of damage lymphatic vesels in the intestines
-cancers or tumors, inflammatory diseases like crohn’s, and trauma or lymphatic infections like whipple’s disease or TB
treatments of lymphangiectasia
-strict long term low fat diet
-diuretics
-albumin infusion leading to increase of oncotic pressure
-removal of diseased portion of intestine if localized
-secondary intestinal lymphangiectasia will be treated by addressing the primary cause of lymphatic obstruction
colon
-absorbs water and electrolytes
-produces mucus lubricating intestinal surface
-divided into four layers: mucosa, submucosa, muscularis propria, and serosa
hirschsprung
-motor disorder of the colon with missing nerve cells causing problems passing stool
-congenital defect
-mostly occurs with newborn infants who have not had a bowel movement in the first 48 hours after birth
-diagnosed via rectal biopsy
hirschsprung pathophysiology
-aganglionosis- absence of enteric ganglion cells in the submucosal and/or myenteric nerve plexus of colon
-motor disorder caused by failure of neural crest cells to migrate during intestinal development of fetal life
-aganglionic segment of the colon fails to relax causing a functional obstruction
-intestinal contents build up behind the obstruction/blockage
hirschsprung histology
-aganglionic segment with absence of submucosal and myenteric ganglion cells
-submucosal and myenteric nerve enlargement
colonic adenocarcinoma
-cancer of the epithelial cells from colonic mucosa
-third most commonly diagnosed and cause of cancer-related death in the US
-most common cancer of the GI tract
-risks include age, family history, genetic predisposition, illnesses like IBD, alcohol, smoking, obesity
symptoms of colonic adenocarcinoma
-rectal bleeding
-abdominal pain
-anemia
-diagnosed with colonoscopy, barium enema, and CT colonoscopy
pathophysiology of colonic adenocarcinoma
-accumulation of multiple genetic mutations over time
-three major pathways: ICN (APC (tumor suppression) mutations), microsatellite instability (DNA mismatch repair (MMR) mutations like MLH1, MSH2), and CpG island hypermethylation (CIMP) (BRAF (oncogene) mutations and leads to serrated polyps)
-mutations are largely acquired sporadically but ~3-5% have well defined inherited mutations with lynch syndrome (germline mutations in the MMR genes) and familial adenomatous poylposis (FAP) with germline mutations of the APC genes
colon cancer histology
-healthy colon mucosa: formation of glands with a regular pattern
-in adenocarcinoma, fewer glands and irregular pattern and structure
-colonic adenocarcinoma is typically graded by level of glandular formation —> well differentiated (>95% of tumor gland-forming), moderately differentiated (>50%), and poorly differentiated (<50%)
colonic adenocarcinoma treatments
-surgery
-chemotherapy
-immunotherapy, which is really good for microsatellite instability
