Esophagus and Stomach
What is significant about the Lymphatic nodules & scattered immunocompetent cells in the lamina Propria?
Lamina propria of the small & large intestines is a relevant site of immune responses (Peyer's Patch or GALT)
What is the location, structure and function of Parietal cells?
Location: -Upper portion of the body of the gastric gland Structure: -cytoplasm displays tubulovesicles and intracellular canaliculus -after stimulation, tubulovesicles fuse with plasma membrane of intracellular canaliculus Function: -Secretes HCl and intrinsic factor in humans -acetylcholine and gastrin, produced by enteroendocrine cells stimulate HCl secretion
What is the location, structure and function of Chief cells?
Location: -predominate in the lower third of the gastric gland. -not present in cardiac glands/seldom found in the pyloric antrum Structure: Pepsinogen-containing secretory granules Function: Pepsinogen is released into the lumen of the gland and converted in the acid environment of the stomach to pepsin, a proteolytic enzyme capable of digesting most proteins.
What is the location, structure and function of Gastroendocrine cells?
Location: pyloric antrum Structure: The population of gastroenteroendocrine cells is so large that the gastrointestinal segment is regarded as the largest endocrine organ in the body. Function: gastroenteroendocrine cells produces peptide hormones which regulates the alimentary tube
What is the location, structure and function of Mucous cells?
Location: (1) the surface mucous cells lining the pit (2) the mucous neck cells located at the opening of the gastric gland into the pit Structure: Apical granules containing mucins Function: Forms a protective mucus blanket which traps bicarbonate ions and neutralizes the microenvironment adjacent to the apical region of the surface mucous cells to an alkaline pH.
What are the esophageal sphincters?
Lower esophageal sphincter (LES): -anterior to the gastroesophageal junction -helps prevent reflux and regurgiation of stomach contents Upper esophageal sphincter (UES): -near the cricopharyngeus muscle -prevents gastric reflux
Describe the source and function of Motilin
Motilin is released cyclically (every 90 minutes) during fasting from the upper small intestine and stimulates gastrointestinal motility. A neural control mechanism regulates the release of motilin.
Describe epithelium of esophagus
nonkeratinized stratified squamous epithelium. This layer is nonabsorptive and friction-resistant.
What does the gastric juice consist of?
(1) an alkaline mucosal gel protective component, produced by surface mucous cells and mucous neck cells (2) HCl and pepsin, two parietal-chief cell-derived potentially aggressive components
What are the four concentric layers of esophagus, stomach, small intestine, and large intestine? List from lumen outwards
(1) mucosa (2) submucosa (3) muscularis externa (4) adventitia (esophagus, most of duodenum)/Serosa (Rest of GI tract)
What are the general function of Peptide hormones?
(1) regulation of water, electrolyte metabolism, and enzyme secretion; (2) regulation of gastrointestinal motility and mucosal growth (3) stimulation of the release of other peptide hormones
Which disease is characterized by a change in epithelium to columnar (like stomach), chronic esophagitis/ulceration, dysphagia, fibrosis a/o esophageal strictures?
GERD (Gastroesophageal reflux disease)
Describe the source and function of Gastrin.
Gastrin is produced by G cells located in the pyloric antrum. The main function of gastrin is to stimulate the production of hydrochloric acid by parietal cells. Gastrin can also activate CCK to stimulate gallbladder contraction.
Describe the source and function of Ghrelin
Ghrelin is produced in the stomach (fundus). Ghrelin binds to its receptor present in growth hormone-secreting cells of the anterior hypophysis. Ghrelin stimulates the secretion of growth hormone. Ghrelin plasma levels increase during fasting triggering hunger by acting on hypothalamic feeding centers.
Describe the source and function of Glucose dependent insulinotropic peptide (GIP)
Glucose-dependent insulinotropic peptide (GIP) is produced in the duodenum. GIP stimulates insulin release (insulinotropic effect) when glucose is detected in the small intestine.
Name concentric layer: -Binds to the body wall
Adventitia
Name concentric layer: -Outside the Peritoneal Cavity
Adventitia
The Stomach is usually divided into which 4 regions?
cardia, fundus, body & pylorus/antrum
Both Secretin and acetylcholine do what?
-stimulate chief cells to secrete pepsinogen -inhibits gastrin release to reduce HCl secretion in the stomach.
What are the two layers of smooth muscle of the muscularis externa?
-Circular Layer - inner layer is arranged around the tube lumen -Longitudinal layer- fibers of the outer layer are disposed along the tube.
Describe the Intrinsic/Enteric innervation of the gastrointestinal system
-Submucosal plexus (Meissner) -Myenteric (Auerbach): between inner & outer layers of muscularis externa -> 1. Peristaltic contractions to move food bolus 2. Secretory activity of mucosal/submucosal glands
What are the difference in muscularis externa between different segments of the esophagus?
-Upper 1/3 - skeletal muscle -Middle 1/3 - transition, primarily smooth muscle -Lower 1/3 - smooth muscle
Compare the differences between the lamina propria of upper and lower esophagus
-Upper esophagus: thin elastic fibers -Lower esophagus contains smooth muscle fibers
What are the results of contraction of the different smooth muscles of the muscularis externa?
-circular layer: reduces the lumen -longitudinal layer: shortens the tube.
What are the function of the Muscularis mucosae?
-local movement of the mucosa -Increases contact area with food -Propel and mix food in GI tract
What are the 3 components of the mucosa. List from lumen outwards
1. a lining epithelium with mucosal & submucosal= glands& ducts 2. an underlying lamina propria consisting of a vascularized loose connective tissue 3. a thin layer of smooth muscle, the muscularis mucosae.
What is Barrett's esophagus? What is concerning regarding diagnosis?
A condition in which an abnormal columnar epithelium replaces the stratified squamous epithelium that normally lines the distal esophagus. Premalignant disorder may be present for up to 20 years before it is clinically recognized
At the lower end of the esophagus, ______________ drain into both the systemic venous system and the portal venous system. An increase in pressure in the ______________, caused by chronic liver disease results in dilation of the submucosal venous sinuses and the formation of _______________. Rupture of the varices can produce ________________ into the esophagus and stomach
At the lower end of the esophagus, SUBMUCOSAL VENOUS PLEXUSES drain into both the systemic venous system and the portal venous system. An increase in pressure in the PORTAL VENOUS SYSTEM, caused by chronic liver disease results in dilation of the submucosal venous sinuses and the formation of ESOPHAGEAL VARICES. Rupture of the varices can HEMORRHAGE into the esophagus and stomach
How is Autoimmune gastritis caused? What does it lead to?
Autoimmune gastritis is caused by autoantibodies to H+,K+-dependent ATPase, a parietal cell antigen, and intrinsic factor. Destruction of parietal cells causes a reduction in HCl in the gastric juice and a lack of synthesis of intrinsic factor. The resulting vitamin B12 deficiency disrupts the formation of red blood cells in the bone marrow, leading to pernicious anemia.
Describe the source and function of CCK
CCK is produced in the duodenum. CCK stimulates gallbladder contraction and relaxation of the sphincter of Oddi when protein- and fat-rich chyme enters the duodenum.
What are the differences between cardiac glands and gastric glands?
Cardiac glands: -simple tubular, coiled at the end -lined by mucus-secreting cells Gastric glands: -2 or more long and straight tubular glands -major contributors to gastric juice
Describe the muscularis externa of the stomach
Consists of three poorly defined layers of smooth muscle oriented in circular, oblique, and longitudinal directions. At the level of the distal pyloric antrum, the circular muscle layer thickens to form the annular pyloric sphincter.
Describe the cellular composition of gastric glands
Mucous Chief Parietal Gastroendocrine Stem
How does the mucosa transition at the gastroesophageal junction? What about the muscularis mucosa, submucosa and muscularis propria?
Muscosa: stratified squamous epithelium of the esophagus to simple columnar epithelium and glandular secretory mucosa. Muscularis mucosa, submucosa and muscularis propria: continuous through this junction.
Based on motility patterns, the stomach can be divided into 2 areas. What is the difference between the Orad and Caudad areas of the stomach?
Orad: consists of Fundus and a portion of the body. Along with the LES relax during swallowing (upper half) Caudad: Consists of the distal body and antrum. Involved in the regulation of gastric emptying (lower half)
Describe the Mucosa of the stomach
Reticular and collagen fibers predominate in the lamina propria, and elastic fibers are rare. The cell components of the lamina propria include fibroblasts, lymphocytes, mast cells, eosinophils, and a few plasma cells.
In stomach & small intestine, folds of the mucosa/submucosa extend into the lumen as what type of folds?
Rugae (stomach) Plicae (S.I.)
Describe the source and function of Secretin.
Secretin is released by cells in the duodenal glands of Lieberkühn when the gastric contents enter the duodenum. Secretin stimulates pancreatic and duodenal (Brunner's glands) bicarbonate and fluid release to control the gastric acid secretion (antacid effect) and regulate the pH of the duodenal contents.
Name concentric layer: -Simple Squamous Epithelium
Serosa
Name concentric layer: -Within the Peritoneal Cavity
Serosa
Name type of cells in the epithelium: Stomach, Small Intestine, Large Intestine and Rectum
Simple Columnar
Secretin together with CCK functions to do what?
Stimulates the growth of the exocrine pancreas.
Name type of cells in the epithelium: Oral Cavity, Oropharynx, Esophagus, Anal Canal
Stratified Squamous
Describe the autonomic/Extrinsic innervation of the gastrointestinal system
Sympathetic (Thoracolumbar) - decreases motility/secretions Parasympathetic (Vagus) - increases motility/secretions
The Muscularis externa of the esophagus transitions from _______________ in the upper third of the esophagus for voluntary swallowing to smooth muscle in the lower two-thirds that controls ______________
The Muscularis externa of the esophagus transitions from SKELETAL MUSCLE in the upper third of the esophagus for voluntary swallowing to smooth muscle in the lower two-thirds that controls PERISTALSIS
What part of the gastric glands is primarily affected by Helicobacter pylori and what are the resulting clinical pathologies?
The mucus blanket lining the gastric epithelium, in particular in the pyloric antrum, is the site where the flagellated bacterium Helicobacter pylori resides in spite of the hostile environment. H. pylori survives and replicates in the gastric lumen. Its presence has been associated with acid peptic ulcers and adenocarcinoma of the stomach.
The submucosa consists of a dense irregular _________________ with _________ blood vessels, lymphatics, and nerves branching into the mucosa and muscularis. Glands are present in the submucosa of the __________ and ______________.
The submucosa consists of a dense irregular CONNECTIVE TISSUE with LARGE blood vessels, lymphatics, and nerves branching into the mucosa and muscularis. Glands are present in the submucosa of the ESOPHAGUS and DUODENUM.
Describe the submucosa of the stomach
The submucosa consists of dense irregular connective tissue in which collagenous and elastic fibers are abundant. A large number of arterioles, venous plexuses, and lymphatics are present. Also present are the cell bodies and nerve fibers of the submucosal plexus of Meissner.
How does the esophagus carries food from the oropharynx to the stomach?
strong peristaltic reflex
