Stomach

CHAPTER 14
Stomach


Rona Altaras and Dale A. Dangleben


Test Taking Tips


Stomach questions remain high yield, and core knowledge of basic physiology and anatomy is essential. Know the stomach’s blood supply including common aberrations/variations. The acid production with function/products of different cells is a favorite of the boards.


The stomach with its variety of benign and malignant conditions is also a rich ground for clinical questions. Study the etiology plus treatment of upper gastrointestinal (UGI) bleeding, types of ulcers and gastrointestinal stromal tumor (GIST) and lymphoma. Regarding cancer, have basic knowledge of basic staging and treatment modalities.


ANATOMY


Where does the lesser curvature abruptly angle to the right and the body of the stomach ends and the antrum begins?


Angularis incisura


Term for where the fundus forms with the left margin of the esophagus:


Angle of His


What is the arterial blood supply to the stomach?


4 main arteries: left gastric and right gastric arteries along lesser curvature and left and right gastroepiploic arteries along greater curvature; blood is also supplied to the proximal stomach by the inferior phrenic arteries and short gastric arteries


Approximate percentage that an aberrant left hepatic artery originates from the left gastric artery?


15% to 20%


What is the largest artery to the stomach?


Left gastric artery


In general, what is the maximal number of arteries that can be ligated, provided that the arcades along the greater and lesser curvatures are intact, that will still supply enough blood flow for the stomach to survive?


3 of 4 arteries can be ligated


Describe the venous drainage of the stomach:


Left gastric (coronary) and right gastric veins usually drain into the portal vein; left gastroepiploic vein drains into the splenic vein; right gastroepiploic vein drains into the superior mesenteric vein


Image


FIGURE 14-1. Arterial blood supply to the stomach. a., artery; v., vein. (This article was published in Mercer DW, Liu TH, Castaneda A. Anatomy and physiology of the stomach. In: Zuidema GD, Yeo CJ, et al, eds. Shackelford’s Surgery of the Alimentary Tract. 5th ed. Vol II. Philadelphia: Saunders; 2002:3, Copyright © Elsevier 2002.)


What happens to the left vagus and right vagus at the gastroesophageal (GE) junction?


Left vagus becomes anterior and the right vagus becomes posterior (LARP mnemonic)


Where does the stomach receive its extrinsic parasympathetic and sympathetic innervation?


Parasympathetic via the vagus and sympathetic via the celiac plexus


Where does the sympathetic nerve supply to the stomach originate from?


From T5 to T10 (travels in splanchnic nerve to celiac ganglion)


Which vagus gives off a hepatic branch to the liver and continues along the lesser curvature as the anterior nerve of Latarjet?


The left vagus


Which nerve gives off a branch to the celiac plexus and continues posteriorly along the lesser curvature?


The right vagus


Which nerve is the first branch of the right or posterior vagus nerve and can lead to recurrent ulcers if left undivided?


The criminal nerve of Grassi


Image


FIGURE 14-2. Vagotomy (nerves to be preserved are in black). (A) Truncal vagotomy. (B) Selective vagotomy. (C) Parietal cell or proximal gastric vagotomy. (Modified from Skandalakis LJ, Gray SW, Skandalakis JE. The history and surgical anatomy of the vagus nerve. Surg Gynecol Obstet. 1986;162:75–85. Reprinted with permission from the Journal of the American College of Surgeons, formerly Surgery Gynecology & Obstetrics.)


Where along the vagus is a truncal vagotomy performed?


Above the celiac and hepatic branches of the vagi


Where along the vagus nerve is a selective truncal vagotomy performed?


Below the celiac and hepatic branches of the vagi


Where along the vagus nerve is a highly selective vagotomy performed?


At the crow’s feet to the proximal stomach while preserving the portion innervating the antrum and pylorus


The intrinsic or enteric nervous system of the stomach consists of which autonomic plexuses?


Auerbach and Meissner autonomic plexuses


What layer of the stomach lies between the mucosa and the muscularis propria that is the strongest layer of the gastric wall?


Submucosa


How many layers of smooth muscle make up the muscularis propria (muscularis externa) of the stomach?


3 layers of smooth muscle


Which layer of the muscularis propria (muscularis externa) is the only complete muscle layer of the stomach wall, is circular, and becomes progressively thicker and functions as a true anatomic sphincter at the pylorus?


The middle layer of smooth muscle


Gastric mucosa consists of what kind of epithelium?


Columnar glandular epithelium


PHYSIOLOGY


Where are parietal cells in the stomach mainly found? What do parietal cells secrete?


Body; secretion of intrinsic factor and acid


Where in the stomach will there be a complete absence of parietal cells?


The cardia and prepyloric antrum


Where are chief cells in the stomach mainly found? What do chief cells secrete?


Body; pepsinogen (converted to pepsin by gastric acid)


Where are G cells in the stomach mainly found? What do G cells secrete?


Antrum; gastrin


Where are D cells in the stomach mainly found? What do D cells secrete?


Body and antrum; somatostatin


Where are gastric mucosal interneurons mainly found? What peptide is released by gastric mucosal interneurons?


Body and antrum; gastrin-releasing peptide


Where are endocrine cells in the stomach mainly found? What hormone do endocrine cells in the stomach release?


Body; ghrelin


Process by which the proximal portion of the stomach relaxes in anticipation of food intake:


Receptive relaxation and gastric accommodation


Name ulcerogenic (excess acid secretion) causes of hypergastrinemia:


Antral G-cell hyperplasia or hyperfunction, gastric outlet obstruction, retained excluded antrum, short-gut syndrome, Zolinger-Ellison syndrome


Name nonulcerogenic (normal or low acid secretion) causes of hypergastrinemia:


Acid-reducing procedure (vagotomy), antisecretory agents (proton pump inhibitors [PPIs]), atrophic gastritis, chronic renal failure, Helicobacter pylori infection, pernicious anemia


What are the 3 local stimuli that regulate gastric acid secretion by the parietal cell?


Acetylcholine, gastrin, and histamine


The basal level of acid secretion accounts for roughly what percentage of maximal acid output?


~10%


What is the approximate rate of hydrochloric acid production during basal acid secretion?


1 to 5 mmol/h


What are the 3 phases of acid secretory response to a meal?


Cephalic, gastric, and intestinal


Histamine utilizes which second messenger to stimulate acid secretion by parietal cells?


Intracellular cyclic AMP


Acetylcholine and gastrin utilize which second messenger to stimulate acid secretion by parietal cells?


Calcium (phospholipase C converts membrane-bound phospholipids into inositol triphosphate (IP3), which mobilizes calcium from intracellular stores)


Mechanism by which PPIs inhibit acid secretion?


A covalent disulfate bond forms between the drug and the cysteine residues on the subunit of the H/K-ATPase leading to irreversible inhibition of the proton pump


Why do PPIs have a longer duration of action than their plasma half-life?


The drug is covalently bonded to the H/K-ATPase leading to irreversible inhibition, so new proton pumps need to be synthesized before the recovery of acid secretion occurs


What converts pepsinogen into pepsin?


Gastric acid


How is the maximal acid output (MAO) determined after gastric analysis?


By averaging the output of the last two 15-minute periods after secretogogue administration


What is the usual range for MAO?


10 to 15 mEq/h


How is the peak acid output obtained after gastric analysis?


It is the highest rate of secretion obtained during a 15-minute period following secretogogue administration


Gastric motility begins with the depolarization of which cells?


Gastric pacemaker cells of Cajal located in the midbody of the stomach along the greater curvature


How many phases are in the myoelectric migrating complex (MMC)?


4 phases


How long does each cycle of the MMC last?


90 to 120 minutes


What happens in phase I of the MMC?


Also known as the quiescent phase; slow waves are present without action potentials; increase in gastric tone but no gastric contraction


What happens in phase II of the MMC?


Motor spikes are associated with slow waves and occasional gastric contractions; gallbladder contraction


What happens in phase III of the MMC?


Motor spike activity is associated with each slow wave; forceful gastric contractions happen every 15 to 20 seconds; the stomach is cleared of large indigestible food substances


What happens in phase IV of the MMC?


A brief recovery period before the next MMC cycle


List protective factors to gastric barrier function:


Blood flow, bicarbonate secretion, cell renewal, endogenous prostaglandins, growth factors, mucus production


List damaging factors to gastric barrier function:


Duodenal reflux of bile, ethanol ingestion, H pylori, hydrochloric acid secretion, hypoxia, ischemia, nonsteroidal anti-inflammatory drugs (NSAIDs), pepsins, smoking


BENIGN CONDITIONS


Approximate percentage of gastric ulcers associated with H pylori:


75%


Approximate percentage of duodenal ulcers associated with H pylori:


90%


Most common cause of peptic ulcer disease:


H pylori infection


What is the second most common cause of peptic ulcer disease?


NSAID ingestion


Where do gastric ulcers usually occur?


On the lesser curve near the incisura (~60%; type I)


What is a type I gastric ulcer?


Gastric ulcer occurring on the lesser curvature near the incisura


What is a type II gastric ulcer?


Gastric ulcer located in the body of the stomach in combination with a duodenal ulcer


What is a type III gastric ulcer?


Prepyloric gastric ulcer


What is a type IV gastric ulcer?


Gastric ulcer that occurs high on the lesser curve near the GE junction

Aug 13, 2019 | Posted by in ABDOMINAL MEDICINE | Comments Off on Stomach
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