Stomach and Spleen

• With regards to the visceral organs, learning about:

  • size, shape, and position is important to recognise any pathological sizes, shapes, and abnormal positions.
  • relationships in order to understand how enlargement of those relationship will impact the organ.
  • parts of the organ to precisely pinpoint locations and localise treatments.
  • functions
  • Blood vessels, innervations, and lymphatic drainage. The latter two are important when considering the spread of infection and cancer.
  • clinical symptoms of the diseased organ.
• The stomach is the most dilated part of the alimentary canal, and is located between the oesophagus and the small intestine. In the supine position, the stomach is located in the upper left quadrant of the abdomen, within the epigastric, left hypochondriac, and umbilical regions.
• The stomach is an intra-peritoneal organ, meaning it's mobile and its position isn't fixed. However, the top and bottom of the stomach are firmly anchored; the oesophagus is anchored to the diaphragm above, and the pyloric end is anchored to the duodenum.
• The end of the stomach is the pyloric region and it lies in the transpyloric plane.
• For the mobile portion of the stomach, its position is determined by the tone of the muscular wall:

  Too much tone = hypertonia (stomach is shorter and flatter).

  Too little tone = hypotonia (stomach sags into the abdominal cavity).

  Complete loss of tone = atonia (stomach sags into the pelvic cavity).

  Position of the stomach also depends upon the state of filling due to the ingestions of food and fluids.

  Stomach shape is also dictated by body shape.
• Functions of the stomach include:

  • temporary storage of chyme
  • breakdown of food via churning and breaking down proteins using pepsin. Hydrochloric acid provides the optimal environment for pepsin and it also destroys bacteria.
  • releasing secretions (gastrin and intrinsic factor) to aid in breakdown of food.
  • absorption.
• The stomach is a J-shape, and this shape was created due to the expansion of the stomach towards the left during development. The oesophagus and duodenum - the two areas to which the stomach is connected to - are fixed, with the duodenum further towards the right compared to the oesophagus. The stomach hangs between the oesophagus and duodenum on the left side.
• The stomach as 5 regions:

  • cardiac region - opening of the oesophagus into the stomach
  • fundus - where gas bubbles are trapped in the stomach
  • body - both the body and the fundus contain glands to aid digestion.
  • pyloric region - contains the pyloric antrum, a canal, and a pyloric sphincter.
• Angles of the stomach are:

  • cardial notch - angle between the cardia and fundus
  • incisura angularis - angle between the pyloric antrum and the lesser curvature of the stomach.
• The cardial region/cardia is ill-defined, as there is no external landmark that indicates where it begins. However, on the inside, the gastro-oesophageal junction gives a clear indication in the form of a sharp transition from the stratified squamous epithelium of the oesophagus to the simple columnar epithelium of the stomach.

  The main function of the cardia is to increase mucus secretion to reduce the effect of acid reflux into the oesophagus.
• The fundus rises to the 5th intercostal space and is directly underneath the left lobe of the diaphragm. The fundus normally filled with air, so it can be seen clearly on an abdominal X-ray as a big black spot.
• The body of the stomach is a storage site for ingested food. This food is broken down by HCl and pepsinogen released from the stomach wall.
• The pyloric antrum is the 1st part of the pyloric region. The second part is the pylorus. There is often a groove between the pylorus and the antrum.

  The antrum has a high proportion of gastrin-secreting cells. Gastrin increases the motility of the intestines. There is also a lot of mixing and grinding of chyme in the pyloric antrum, and there are peristaltic waves pushing the chyme towards the pylorus.
• The pylorus contains a sphincter to control what leaves the antrum. The sphincter is large, forced by a ring of smooth muscle. The gap between the sphincter muscle is known as the pyloric canal. When this sphincter contracts, it closes the pyloric canal and prevents the entry of chyme into the duodenum.
• The greater and lesser omenta are attached to the greater and lesser curvatures of the stomach respectively. The lesser omentum is also attached to the liver.
• The entirety of the gut wall has a general organisation of 4 layers (the stomach has its own specialisations):

  • the mucosa
  • the submucosa
  • the muscularis externa
  • the adventitia/serosa
• The mucosa is the 1st layer from the lumen outwards and consists of gut epithelium, the lamina propria (loose connective tissue immediately beneath the epithelium), and the muscularis mucosa (a thin sheath of smooth muscle whose contractions serve to propel food through the digestive tract).
• There are several ducts that traverse the mucosa to get to the lumen: ducts from the liver and pancreas, and ducts of the mucosal and submucosal glands that also secrete mucus.

  The lamina propria also contains gut-associated lymphoid tissue (GALT), which are nodules of lymphatic tissue being lymphocytes and other macrophages. These protect the GI tract wall from bacteria and other pathogens that may've been ingested with the food.
• The submucosa is the 2nd layer from the lumen outwards, and is a layer of loose connective tissue that carries many blood vessels, lymphatics, and nerves.

  The nerves form an intrinsic plexus on this layer called the submucosal plexus. These nerves control the secretion of glands within the mucosa and submucosa, and they control the contractions of the muscularis mucosa. The nerves of the submucosal plexus have their own autonomy, but can be influenced by parasympathetic nerves of the vagus or pelvic splanchnic nerves. The submucosal plexus is part of the enteric nervous system.
• The muscularis externa consists of 2 layers: an inner circular layer, and an outer longitudinal layer. This layer generates peristaltic contractions that propel food down the tract, as well as movements that churn the chyme of the stomach, and expel faeces from the bowel.

  The muscular contractions of this layer are controlled by the myenteric plexus of nerves. The myenteric plexus is another part of the enteric nervous system, and can also be influenced by parasympathetic innervation of the vagus and splanchnic nerves.
• The final/outermost layer of the general gut wall organisation is the adventitia for retroperitoneal organs, and the serosa for intraperitoneal organs. This final layer carries blood vessels and extrinsic nerves.
• The enteric nervous system provides direct control over gut secretions via the submucosal plexus, and gut motility via the myenteric plexus. Nerve cells within the myenteric plexus can also influence the submucosal plexus and vice versa. There are sensory nerves within this plexus that can respond to local factors within the gut wall and gut lumen.
• The enteric nervous system has reflex pathways that respond to sensory stimuli. However, the brain and spine can also influence the enteric nervous system when needed: parasympathetic signals stimulates these plexuses, while sympathetic signals inhibit them.
• The stomach wall is specialised. The mucosa contains gastric glands, and the muscularis externa contains 3 layers instead of two, the additional layer being an innermost layer of oblique smooth muscle. The circular layer is also increased significantly at the pyloric sphincter to control the release of gastric content into the duodenum.
• The lower oesophageal sphincter isn't an anatomical sphincter, but a functional one. This is due to the distinct muscle around the lower end of the oesophagus. The control of reflux of gastric secretions into the oesophagus is largely controlled by the muscular fibres of the diaphragm, particularly from the right crux which loops around the oesophagus. Another important factor in preventing acid reflux is the angulation that the oesophagus makes with the cardia. These provide a functioning flap-valve that prevents reflux into the oesophagus.
• The mucous membrane is arranged in large, longitudinal folds called rugae. Rugae produce a characteristic appearance on contract X-rays of the stomach. Rugae allow the stomach to expand after consumption of food and fluids, and allow the stomach to adapt to movements of the stomach wall caused by contractions of the muscularis mucosa and peristalsis in the muscularis externa.
• The relations of the stomach are:

  • the left lobe of the liver that passes anteriorly, crossing the cardial region and the fundus.
  • the left dome of the diaphragm immediately above.
  • the spleen posteriorly to the left.
  • the pancreas, which is very close posteriorly to the pyloric region and body.
  • the left kidney and supra-renal gland behind the stomach (and pancreas).
  • the duodenojejunal flexure proximal to the pyloric antrum.
  • the coeliac trunk close to the incisura angularis, splenic artery behind the stomach, and hepatic portal vein behind the pyloric region.
• The coeliac trunk supplies the foregut, and so, supplies the upper abdominal organs. It arises from the anterior aspect of the abdominal aorta, just after the aorta appears through the aortic opening of the diaphragm at the level of T12.
• The coeliac trunk divides into 3 branches:

  • the common hepatic artery, heading towards the liver on the right. This artery will become the proper hepatic artery before dividing into the right and left hepatic arteries.
  • the splenic artery heading behind the stomach to the spleen.
  • the left gastric artery, which supplies the stomach in a small vessels, so the stomach has to get an arterial blood supply from the common hepatic and splenic branches as well.
• The common hepatic artery travels to the right and divides into the proper hepatic artery and the gastroduodenal artery. The former heads upwards to the liver, and the latter travels downwards behind the duodenum. In this location the gastroduodenal artery is at risk of lesion following ulceration of the duodenum.
• The proper hepatic artery divides into right and left hepatic branches. The main trunk of the proper hepatic artery usually gives off the right gastric artery, which supplies the right side of the lesser curvature of the stomach. The origin of the right gastric artery is highly variable.
• The gastroduodenal artery divides into the right gastroepiploic and the superior pancreaticoduodenal arteries. The former supplies the right side of the greater curvature of the stomach. The latter partly supplies the duodenum and pancreas.
• The left gastric artery (coming directly from the coeliac trunk) ascends to the oesophagus and then supplies the lesser curvature of the stomach, anastomosing with the right gastric artery. It also gives oesophageal branches.
• The splenic artery follows a course along the upper border of the pancreas, which it supplies, and then reaches the spleen via the lienorenal ligament. It gives off pancreatic branches and the short gastric artery, and the left gastroepiploic artery, which reach the stomach via the gastrosplenic ligament.
• Arterial blood supply to the stomach comes from:

  • the left gastroepiploic artery - stems from the splenic artery and supplied the left side of the greater curvature of the stomach
  • the right gastroepiploic artery - stems from the gastroduodenal artery and supplies the right side of the greater curvature of the stomach
  • the left gastric artery - stems from the coeliac trunk and supplies the left side of the lesser curvature of the stomach
  • the right gastric artery - stems from proper hepatic artery and supplies the right side of the lesser curvature of the stomach.
  • the posterior gastric artery.
• The venous drainage of the oesophagus is mostly into the azygos vein, which is a vein of the thorax terminating in the superior vena cava.
• The venous drainage of the stomach and spleen is via gastric, gastroepiploic and splenic veins. These all drain into the hepatic portal vein, which then reaches the liver.
• There is a rich anastomosis around the lower part of the oesophagus, and hence the oesophagus is partly connected with the portal venous system. Should venous drainage of the hepatic portal vein be obstructed, then the blood of the portal system may attempt to return to the heart via the azygos system instead at the oesophagus. Oesophageal veins may then enlarge and become varicosed. These can rupture and cause the patient to vomit blood.
• Gastric lymphatics are continuous at the pylorus with the duodenal lymphatics, and the oesophageal lymphatics at the cardia.
• Lymph channels largely follow the blood vessels and there are 4 main groups:

  • Left Gastric nodes
  • Pancreaticolienal nodes
  • Right Gastro-omental nodes
  • Right Gastric and Pyloric nodes

  All the nodes eventually drain into the coeliac nodes (pre-aortic nodes), and from there to the paraortic nodes, then to the cysterna chyli, and then to the thoracic duct