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
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