Abdomen

Stomach

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Overview


The stomach is an important part of the GI tract, involved in food storage and breakdown before passing into the small bowel. It is also involved in neutralising any pathogens ingested. Its cell structure is unique to the GI tract and its innervation and blood supply are clinically relevant in numerous clinical disorders.


Gross Anatomy


The stomach is a foregut structure. At around 4 weeks, the foregut tube dilates to form the stomach. It rotates clockwise in a longitudinal plane 90 degrees, and due to the faster growth of the dorsal wall in comparison to the ventral wall, the greater and lesser curvatures are formed.

 

Surface Anatomy

 

Relations

Structure

Anterior

 liver

Posterior

 left crus of diaphragm, left kidney and adrenal, transverse colon, spleen

Medially

D1 (of duodenum)

Superiorly

Diaphragm

Inferiorly

Small bowel, D-J flexure

 

 

The stomach is split into sections, the cardia, fundus, body, antrum and pylorus. There is also an area called the incisura angularis which marks the junction between the body and the antrum. The medial and lateral borders of the stomach are called the lesser and greater curvatures of the stomach, respectively.

 

 

There are 4 layers to the stomach wall, the outer serosa, muscularis externa, submucosa and innermost mucosa. The mucosa is arranged into folds called rugae, which increase the surface area within the stomach.

 

There are 2 sphincters related to the stomach, the lower oesophageal sphincter, and the pyloric sphincter. The LOS is located at the level of T11, just below the oesophageal hiatus (T10). It is a functional sphincter; that is to say it is not a true sphincter under involuntary/voluntary control. It enters the stomach at an angle, so food is unable to enter when the stomach is full.

 

The pyloric sphincter allows for the controlled exit of chime from the stomach into D1 it is a true sphincter made up of smooth muscle. It is under contraction, but when the pressure within the stomach is higher than the resting pressure of the pylorus, chyme is expelled into the duodenum

 

The blood supply to the stomach arises from the coeliac axis. The lesser curve of the stomach is supplied by the right (branch of common hepatic artery) and the left (coeliac branch) gastric arteries. The greater curvature is supplied by the right and left gastro-epiploic arteries (branches of the gastroduodenal and splenic arteries, respectively).

 

The stomach relies upon autonomic control from the vagus nerve (parasympathetic) and coeliac plexus (sympathetic). Parasympthetic innervation stimulates and sympathetic inhibits stomach motility and secretion of gastric fluid.

 

There are distinct cell types that comprise the wall of the stomach. Their function is outlined in the quick-look box below.


Clinical Anatomy


Peptic ulcer disease

Chronic exposure of the gastric mucosa to the low pH of gastric acid can cause erosions and lead to gastric ulcers. These can be asymptomatic or cause symptoms such as indigestion, reflux, regurgitation and retrosternal chest pain. They are most commonly found along the lesser curve. Risk factors include  H pylori, smoking, age, burns, stress, NSAIDs/steroids. They are often diagnosed at endoscopy.  Treatment: CLO test for H pylori is taken during OGD- if positive, H pylori eradication (triple therapy), PPI.

 

Gastric adenocarcinoma

 

Risk factors: H pylori, smoking, atrophic gastritis. Common in East Asia especially Japan. Diagnosed via OGD most commonly THINK BIOPSIES! (can also do EUS).

Treatment is staging dependent. Partial/total gastrectomy. Palliative chemotherapy/stenting

 

Pyloric stenosis:  most commonly seen in infants. Projectil vomiting, failure to thrive. Treated surgically with myotomy

 

Hiatus hernia

A portion of the stomach extends into the chest via the oesophageal hiatus. They are usually classified as either rolling of sliding hiatus hernias. Rolling/ hernias are where the LOS stays in position but part of the stomach rolls up next to it, herniating through thte oesophageal hiatus. Sliding hernias are where the LOS slides up through thte hiatus. These are often more symptomatic as the right crus of the diaphragm no longer exerts extrinisic pressure on the LOS to help it act as a functional sphincter.

Treatment: Conservative: lifestyle modifications (stop smoking, avoid alcohol, eat small regular meals, no late night meals, avoid spicy foods); Medical: PPI/H2 receptor antagonists; Surgical- for refractory symptoms: Nissen’s fundoplication.

 


Quick Anatomy


Key Facts

Arterial supply

Lesser curvature: right & left gastric arteries

Greater curvature: right and left gastroepiploic arteries

Nerve supply

Sympathetic:

Parasympthetic

Development

Foregut structure, develops in week 4

 

Cell type

Function

Chief cells

Secrete pepsinogen

Parietal cells

Secrete intrinsic factor and hydrochloric acid

Enterochromaffin cells

Secrete hormones: gastrin, histamine, CCK and somatostatin

Goblet cells

Secrete mucus

Aide-Memoire

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Summary


The stomach is an organ lying between the levels of T7 and L3 (dependent on the supine or erect position). It is a commonly tested area, as it can incorporate anatomy, histology and pathology quite nicely into a single station. Be sure to learn the blood supply and be able to point to the relevant sections in a cadaveric specimen. The cells that make up the stomach are important in regulating acid and hormone production, and the key clinical disorders are straight forward but easy marks to overlook. 


References


S Jacob. Atlas of Human Anatomy Second Edition. Elsevier 2005

Gould D. Clinical Anatomy Flash Cards, Lippincott Wilkinson & Williams

Oxford Handbook of Clinical Medicine. 9th Edition. Oxford University Press. Jan 2014