The stomach is also called the gaster (Greek belly) or venter from which we have the adjective gastric applied to structures related to the organ (Fig. 19.1).
Introduction
The stomach is a muscular bag forming the widest and most distensible part of the digestive tube. It is connected above to the lower end of the oesophagus, and below to the duodenum. It acts as a reservoir of food and helps in digestion of carbohydrates, proteins and fats.
Location
The stomach lies obliquely in the upper and left part of the abdomen, occupying the epigastric, umbilical and
left hypochondriac regions. Most of it lies under cover of the left costal margin and the ribs (Figs 19.1 and 19.8).
Shape and Position
The shape of the stomach depends upon the degree of tone of its muscles and tone of muscles of the body. In normal active persons (sthenic) its shape is somewhat J-shaped (Fig. 19.2). In thin, tall persons (hyposthenic) its shape is J-shaped, while in broad, strong and very active persons its shape is horizontal. The shape of the stomach can be studied in the living by radiographic examination after giving a barium meal (see Fig. 36.3).
Size and Capacity
The stomach is a very distensible organ. It is about 25 cm long, and the mean capacity is one ounce (30 ml)
at birth, one litre (1000 ml) at puberty, and 1½ to 2 litres or more in adults.
EXTERNAL FEATURES
The stomach has two orifices or openings, two curvatures or borders, two surfaces and two parts (Fig. 19.2).
Two Orifices
The cardiac orifice is joined by the lower end of the oesophagus. It lies behind the left 7th costal cartilage 2.5 cm from its junction with the sternum, at the level of vertebra T11. There is physiological evidence of sphincteric action at this site, but a sphincter cannot be demonstrated anatomically.
The pyloric orifice opens into the duodenum. In an empty stomach and in the supine position, it lies 1.2 cm
to the right of median plane, at the level of lower border of vertebra L1 or transpyloric plane. Its position is
indicated on the surface of the stomach:
a. By a circular groove (pyloric constriction produced by the underlying pyloric sphincter or pylorus;
pylorus = gate guard) which feels like a large firm nodule (Fig. 19.2).
b. By the prepyloric vein of Mayo which lies in front of the constriction (Fig. 19.3).
Two Curvatures
The lesser curvature is concave and forms the right border of the stomach. It provides attachment to the
Clesser omentum. The most dependent part of the curvature is marked by the angular notch or incisura
angularis (Fig. 19.2a).
The greater curvature is convex and forms the left border of the stomach (Fig. 19.1). It provides attachment
to the greater omentum, the gastrosplenic ligament and the gastrophrenic ligament. At its upper end the greater curvature presents the cardiac notch which separates it from the oesophagus. It is 5 times longer than lesser curvature.
Two Surfaces
The anterior or anterosuperior surface faces forwards and upwards. The posterior orposteroinferior surface faces backwards and downwards.
Two Parts
The stomach is divided into two parts-cardiac and pyloric. By a line drawn downwards and to the left from the cardiac end to the angular notch (lowest point of lesser curvature). The line is extended further to the greater curvature. The larger cardiac part is further subdivided into fundus and body) The smaller pyloric part is subdivided into pyloric antrum and pyloric canal (Fig. 19.2a).
Cardiac Part
1 The fundus of the stomach is the upper convex dome- shaped part situated above a horizontal line drawn
at the level of the cardiac orifice (Fig. 19.2a). It is commonly distended with gas which is seen clearly in radiographic examination under the left dome of the diaphragm (see Fig. 20.14).
2 The body of the stomach lies between the fundus and the pyloric antrum. It can be distended enormously along the greater curvature. The gastric glands distributed in the fundus and body of stomach, contain all three types of secretory cells, namely:
a. The mucous cells.
b. The chief, peptic or zymogenic cells which secrete
the digestive enzymes.
c. The parietal or oxyntic cells which secrete HC1.
Pyloric Part
1 The pyloric antrum is separated from the pyloric canal by an inconstant sulcus, sulcus intermedius present
on the greater curvature. It is about 7.5 cm long. The pyloric glands are richest in mucous cells.
2 The pyloric canal is about 2.5 cm long. It is narrow and tubular. At its right end, it terminates at the
Pylorus.
RELATIONS OF STOMACH
Peritoneal Relations
The stomach is lined by peritoneum on both its surfaces. At the lesser curvature, the layers of peritoneum lining the anterior and posterior surfaces meet and become continuous with the lesser omentum (see Fig. 18.8a).
Along the greater part of the greater curvature, the two layers meet to form the greater omentum.
Near the fundus, the two layers meet to form the gastrosplenic ligament.
Near the cardiac end, the peritoneum on the posterior surface is reflected on to the diaphragm as the
gastrophrenic ligament (see Fig. 18.8a). Cranial to this ligament a small part of the posterior surface of the
stomach is in direct contact with the diaphragm (left crus). This is the bare area of the stomach. The greater lesser curvatures along the peritoneal reflections are also bare.
Visceral Relations
The anterior surface of the stomach is related to the liver, the diaphragm, transverse colon and the anterior
abdominal wall. The areas of the stomach related to these structures are shown in Fig. 19.8. The diaphragm
separates the stomach from the left pleura, the pericardium, and the sixth to ninth ribs. The costal cartilages are separated from the stomach by the transversus abdominis. Gastric nerves and vessels
ramify deep to the peritoneum.
The space between left costal margin and lower edge of left lung on stomach is known as Traube’s space. Normally, on percussion, there is resonant note over this space; but in splenomegaly or pleural effusion, a
dull note is felt at this site.
The posterior surface of the stomach is related structures forming the stomach bed, all of which an
separated from the stomach by the cavity of the lesser sac. These structures are:wol orii od svode
- Diaphragm
- Left kidney
- Left suprarenal gland
- Pancreas (Fig. 19.9)
- Transverse mesocolon
- Splenic flexure of the colon
- Splenic artery (Fig. 19.9). Sometimes the spleen is also included in the stomach bed, but it is separated from the stomach by the cavity of the greater sac (and not of the lesser sac). Gastric nerves and vessels ramify deep to the peritoneum (Figs 19.10 and 19.12).
BLOOD SUPPLY
The stomach is supplied along:
- The lesser curvature by: The left gastric artery, a branch of the coeliac trunk and the right gastric artery, a branch of the proper hepatic artery.
- Along the greater curvature, it is supplied by the right gastroepiploic artery, a branch of the gastroduodenal and the left gastroepiploic artery, a branch of the splenic.
- Fundus is supplied by 5 to7 short gastric arteries, which are also branches of the splenic artery (Fig. 19.10).
The veins of the stomach drain into the portal, superior mesenteric and splenic veins.
Right and left gastric veins drain in the portal vein.
Right gastroepiploic ends in superior mesenteric vein; while left gastroepiploic and short gastric veins terminate in splenic vein (Fig. 19.3).
LYMPHATIC DRAINAGE
The stomach can be divided into four lymphatic territories as shown in Fig. 19.11. The drainage of these
areas is as followws.
Area (a) of Fig. 19.11, i.e. upper part of left 1/3rd drains into the pancreaticosplenic nodes lying along the
Splenic artery, i.e. on the back of the stomach. Lymph vessels from these nodes travel along the splernic artery to reach the coeliac nodes.
Area (b), i.e. right 2/3rd drains into the left gastric nodes lying along the artery of the same name. These
nodes also drain the abdominal part of the oesophagus. Lymph from these nodes drains into the coeliac nodes.
Area (c), i.e. lower part of left 1/3rd drains into the right gastroepiploic nodes that lie along the artery of
the same name. Lymph vessels arising in these nodes drain into the subpyloric nodes which lie in the angle
between the first and second parts of the duodenum.
From here the lymph is drained further into the hepatic nodes that lie along the hepatic artery; and finally into the coeliac nodes.
Lymph from area (d), i.e. pyloric part drains in different directions into the pyloric, hepatic, and left
gastric nodes, and passes from all these nodes to the coeliac nodes.
Note that lymph from all areas of the stomach ultimately reaches the coeliac nodes. From here it passes
through the intestinl lymph trunk to reach the cisterna chyli.
NERVE SUPPLY
The stomach is supplied by sympathetic and parasympathetic nerves. The sympathetic nerves are
derived from thoracic six to ten segments of the spinal cord, via the greater splanchnic nerves, coeliac and
hepatic plexuses. They travel along the arteries supplying the stomach. These nerves are:
- Vasomotor.
- Motor to the pyloric sphincter, but inhibitory to the rest of the gastric musculature.
- The chief pathway for pain sensations from the stomach.
The parasympathetic nerves (Figs 19.12a and b) are derived from the vagi, through the oesophageal plexus and gastric nerves. The anterior gastric nerve (made up of one or two trunks) contains mainly the left vagal fibres, and the posterior gastric nerve (again made up of one to two trunks) contains mainly the right vagal fibres.
The anterior gastric nerve divides into:
- A number of gastric branches for the anterior surface of the fundus and body of the stomach.
- Two pyloric branches, one for the pyloric ant and another for the pylorus.
The posterior gastric nerve divides into:
- Smaller, gastric branches for the posterior surface of the fundus, the body and the pyloric antrum.
- Larger, coeliac branches for the coeliac plexus. Parasympathetic nerves are motor and secreto- motor to the stomach. Their stimulation causes increased motility of the stomach and secretion of gastric juice rich in pepsin and HCL. These are inhibitory to the pyloric sphincter.
INTERIOR OF STOMACH
DISSECTION
Open the stomach along the greater curvature and examine the mucous membrane with a hand lens.
Then strip the mucous membrane from one part and expose the internal muscle coat. Dissect the muscle coat, e.g. outer longitudinal, middle circular and inner oblique muscle fibres. Feel thickened pyloric sphincter.
Incise the beginning of duodenum and examine the duodenal and pylorio aspects of the pyloric sphincter (refer to BDO App).
Features
The stomach has to be opened to see its internal structure.
1. The mucosa of an empty stomach is thrown into folds termed as gastric rugae. The rugae are longitudinal
along the lesser curvature and may be irregular elsewhere. The rugae are flattened in a distended stomach. On the mucosal surface there are numerous small depressions that can be seen with a hand lens. These are the gastric pits. The gastric glands open into these pits.
The part of the lumen of the stomach that lies along the lesser curvature, and has longitudinal rugae, is called the gastric canal or magenstrasse. This canal allows rapid passage of swallowed liquids along the
lesser curvature directly to the lower part before it spreads to the other part of stomach (Fig. 19.13).
Thus lesser curvature bears maximum insult of the swallowed liquids, which makes it vulnerable to peptic ulcer. So, beware of your drinks.
2. Submucous coat is made of connective tissue, arterioles and nerve plexus.
3. Muscle coat is arranged as under:
- Longitudinal fibres are most superficial, mainly along the curvatures.
- Inner circular fibres encircle the body and are thickened at pylorus to form pyloric sphincter (Fig. 19.14).
- The deepest layer consists of oblique fibres which loop over the cardiac notch. Some fibres spread
in the fundus and body of stomach. Rest form a well-developed ridge on each side of the lesser curvature. These fibres on contraction form “gastric canal” for the passage of fluids.
4. Serous coat consists of the peritoneal covering.
Functions of Stomach
- The stomach acts primarily as a reservoir of food. It also acts as a mixer of food.
- By its peristaltic movements, it softens and mixes the food with the gastric juice.
- The gastric glands produce the gastric juice which Contains enzymes that play an important role in digestion of food.
- The gastric glands also produce hydrochloric acid which destroys many organisms present in food and drink.
- The lining cells of the stomach produce abundant mucus which protects the gastric mucosa against the corrosive action of hydrochloric acid.
- Some substances like alcohol, water, salt and a few drugs are absorbed in the stomach.
- Stomach produces the “intrinsic factor” of Castle which helps in the absorption of vitamin B2
CLINICAL ANATOMY
- Gastric pain is felt in the epigastrium because the stomach is supplied from segments T6 to T9 of
the spinal cord, which also supply the upper part of the abdominawall. Pain is produced either by
spasm of muscle,or by over-distension. Ulcer pain is attributed to local spasm due to irritation (see Fig. 18.35). - Peptic ulcer can occur in the sites of pepsin and hydrochloric acid, namely the stomach, first part of duodenum, lower end of oesophagus and Meckel’s diverticulum. It is common in blood group ‘0.
Gastric ulcer occurs typically along the lesser curvature (Fig. 19.13). This is possibly due to the following peculiarities of lesser curvature. -
- It is homologous with the gastric trough of ruminants.
- Mucosa is not freely movable over the muscular coat.
- The epithelium is comparatively thin.
- Blood supply is less abundant and there are fewer anastomoses.
- Nerve supply is more abundant, with large ganglia.
- Because of the gastric canal, it receives most of the insult from irritating drinks.
- Being shorter in length the wave of contraction Stays longer at a particular point, viz., the standing wave of incisura.
- H. pylori infection is also an important causative factor.
Gastric ulcers are common in people who are always in “hurry”, mostly “worry” about incidents and eat “spicy curry”.
Gastric ulcer is notoriously resistant to healing and persists for years together, causing great degree of morbidity. To promote healing, the irritating effect of HCI can be minimised by antacids, partial gastrectomy or vagotomy.
Gastric carcinoma is common and occurs along the greater curvature. Orn this account, the lymphatic
drainage of stomach assumes importance. Metastasis can occur through the thoracic duct to the left supraclavicular lymph node (Troisier’s sign). These lymph nodes are called as “signal nodes”. It is common in blood group ‘A.
Pyloric obstruction can be congenital or acquired. It causes visible peristalsis in the epigastrium and vomiting after meals (thin and long).
Hyposthenic stomach is (long and narrow) more prone for gastric ulcer, while hyperstheric stomach is prone for duodenal ulcer (short and broad).
HISTOLOGY OF STOMACH
At the cardiac end of stomach, the stratified epithelium of oesophagus abruptly changes to simple columnar
epithelium of stomach.
Cardiac End
Mucous membrane: The epithelium is simple columnar with small tubular glands. Lower half of the gland is
secretory and upper half is the conducting part. Muscularis mucosae consists of smooth muscle fibres.
Submucosa: It consists of loose connective tissue with Meissner’s (German histologist 1829-1909) plexus. Muscularis externa: It is made of outer longitudinal and inner circular layer including the myenteric plexus
of nerves or Auerbach’s plexus (German anatomist 1828-97).
Serosa: It is lined by single layer of squamous cells.
Fundus and Body of Stomach
Mucous membrane: It contains tall simple tubular gastric glands. Upper one-third is conducting, while lower
two-thirds is secretory. The various cell types seen in the gland are chief or zymogenic, oxyntic or parietal
and mucous neck cells (Fig. 19.15).
Muscularis mucosae and submucosa are same.
Muscularis externa: It contains an additional innermost oblique coat of muscle fibres.
Serosa is same as of cardiac end.
Pyloric Part
Mucous membrane: There are pyloric glands which consist of basal one-third as mucus secretory
component and upper two-thirds as conducting part. Muscularis mucosae is made of two layers of fibres. Submucosa is samne as in the cardiac end.
Muscularis externa comprises thick layer of circular fibres forming the pyloric sphincter. Serosa is same as of cardiac end.
DEVELOPMENT
Oesophagus
The posterior part of foregut forms the oesophagus.ls is very small in the beginning, but it lengthens due to
descent of lungs and heart. The muscle of upper one-third is striated, middle one-third, mixed, and lower
one-third smooth. Nerve supply to upper two-thirds is from vagus and to lower one-third is from autonomic plexus. Epithelium of oesophagus is endodermal and rest of the layers are from splanchnic mesoderm.
Stomach
The caudal part of foregut shows a fusiform dilatation with anterior and posterior borders and left and right surfaces. This is the stomach. It rotates 90° clockwise, so that left surface faces anteriorly. Even the original posterior border of stomach grows faster, forming the greater curvature.
The stomach also rotates along anteroposterior axis, so that distal or pyloric part moves to right and
proximal or cardiac part moves to left side.
The 90° rotation of stomach along the vertical axis pulls the dorsal mesogastrium to the left side creating the lessor sac or omental bursa.
Spleen appears as mesodermal condensation in the left leaf of dorsal mesogastrium.
