Basic Sciency - Gastro 48 Stomach - Anatomy and physiology

• The posterior surface of the stomach is related to structures forming the stomach bed, all of which are separated from the stomach by the cavity of the lesser sac.
• These structures are : (1) The diaphragm; (2) the left kidney; (3) the left suprarenal gland; (4) the pancreas; (5) the transverse mesocolon; (6) the splenic flexure of the colon; and (7) the splenic artery.
• Sometimes the spleen is also included in the stomach bed, but it is separated from the stomach by the cavity of the greater sac.

• Left gastric - Celiac trunk
• Right gastric - GDA or hepatic artery
• left gastroepiploic - Splenic artery
• Right gastroepiploic - GDA
• Short gastric - from splenic artery

• Aberrant left hepatic artery from Left gastric artery 
• Aberrant right hepatic artery from SMA

• Left gastric (Coronary) and right gastric - Portal vein
• Left gastroepiploic - Splenic vein
• right gastroepiploic - SMV

The lymphatic drainage of the stomach parallels the vasculature and drains into four zones of lymph nodes.

• The superior gastric group drains lymph from the upper lesser curvature into the left gastric and paracardial nodes.
• The suprapyloric group of nodes drains the antral segment on the lesser curvature of the stomach into the right suprapancreatic nodes.
• The pancreaticolienal group of nodes drains lymph high on the greater curvature into the left gastroepiploic and splenic nodes.
• The inferior gastric  and subpyloric group of nodes drains lymph along the right gastroepiploic vascular pedicle.

All four zones of lymph nodes drain into the celiac group and into the thoracic duct.

• Although these lymph nodes drain different areas of the stomach, gastric cancers may metastasize to any of the four nodal groups, regardless of the cancer location.
• In addition, the extensive submucosal plexus of lymphatics accounts for the fact that there is frequently microscopic evidence of malignant cells several centimeters from gross disease.

Vagus - Left Anterior, Right Posterior (LARP)

Left vagus - give hepatic branch to liver, continue along the lesser curvature as the anterior nerve of Laterjet

Right vagus - Gives first branch - criminal nerve of Grassei, second branch to celiac plexus, then continue along lesser curvature

• Truncal vagotomy - above celiac and hepatic branches
• Highly selective Vagotomy - Dividing crow's feet to proximal stomach by preserving innervation to antrum and pylorus

• SMS-(Submucosal plexus: Meissner`s:controls Secretions)
• MAM- (Myenteric plexus:Auerbach`s:controls Motility)

• Epithelium
• Lamina propria
• Muscularis mucosa

(three layers of muscles in stomach - outer and inner longitudinal, middle circular)

The foregut rotates 90◦ clockwise around its longitudinal axis, causing its left side to face anteriorly and its right side to face posteriorly. Hence the left vagus nerve, initially innervating the left side of the stomach, now innervates the anterior wall; similarly, the right vagus nerve innervates the posterior wall. During this rotation the original posterior wall of the stomach grows faster than the anterior portion, forming the greater and lesser curvatures.

Development of the midgut is characterized by rapid elongation of the gut and its mesentery, resulting in formation of the primary intestinal loop. At its apex, the loop remains in open connection with the yolk sac by way of the narrow vitelline duct Coincident with growth in length, the primary intestinal loop rotates around an axis formed by the superior mesenteric artery. When viewed from the front, this rotation is counterclockwise, and it amounts to approximately 270◦ when it is complete

• Congenital anomalies associated with rotation 
• - Gastroschisis and Omphalocele 
• - Vitelline Duct Abnormalities
• - Abnormal rotation of the intestinal loop- volvulus

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There is central role of the enterochromaffin-like (ECL) cell in regulation of acid secretion by the parietal cell.

• Cephalic phase - originates with the sight, smell, thought, or taste of food, release acetylcholine
• Gastric phase - acid secretion by stimulation of G cells to release gastrin, stimulation by gastric distension.
• Intestinal phase - initiated by entry of chyme into small intestine

The gastric parietal cell is equipped with apical ion transport mechanisms that allow for the secretion of concentrated hydrochloric acid.

• Activation of basolateral secretagogue receptors mainly leads to an increase in either cAMP (histamine) or calcium (acetylcholine, gastrin), causing apical insertion and activation of the H+-K+-ATPase.
• Somatostatin reduces intracellular cAMP levels.
• (ACh, acetylcholine; APAs, acid pump antagonists; Gast, gastrin; Hist, histamine; PPIs, proton pump inhibitors; SST, somatostatin.)

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