- Skeletal system
- Blood vessels
- Respiratory system
- Digestive system
- Endocrine glands
- Nervous system
- Lymphatic system
- Female reproductive system
The stomach (Latin: gaster s. ventriculus s. stomachus) is a muscular, extended, and most dilated part of the gastrointestinal tract located inferior to the left dome of the diaphragm, providing chemical and mechanical food procession, absorption, and secretion of various substances. The stomach is located in the abdominal cavity between the esophagus and duodenum, and it has the shape of the letter "J."
The stomach is located in the upper region of the abdomen, left from the midline. Around three-fours of the stomach is located in the left hypochondriac region. The remaining one-third can be found in the epigastric region.
The stomach is an intraperitoneal organ, and the peritoneum connects it with other organs.
The stomach has two orifices.
- Above the stomach is the esophagus. Between it and the stomach is the first opening called the cardiac opening or orifice. It is situated at the level of the eleventh thoracic vertebra body (Th11).
- The second opening connects the stomach with the duodenum. It is called the pyloric opening or orifice, and it can be found at the first lumbar vertebra level (L1).
The stomach has two borders.
- The first one is shorter, concave, and located more on the right side. It is called the lesser curvature. Between the body and pyloric parts in the lesser curvature is the angular incisure, also known as the angular notch. It is the most inferior part of the lesser curvature.
- The other border locate more on the left side. It is longer, convex, and is called the greater curvature. Between the final part of the esophagus and the start point of the greater curvature (in the fundus part) is the cardiac incisure or notch.
The stomach has two surfaces between both curvatures. Anterior between the lesser and greater curvature is the anterior surface, but posterior- the posterior one.
The stomach has four parts- the fundus, body, pylorus, and cardia.
- Cardiac part, also the cardia, is small and only a few centimeters wide. It is around the cardiac opening at the eleventh thoracic vertebra (Th11) level. It is the first part of the stomach receiving the food bolus.
- The fundus is located above and left to the cardiac opening. It is the most upper part and is rounded and dome-shaped.
- The body is the most significant part, and it is inferior to the fundus; between the fundus, cardiac part, and pylorus.
- Pylorus is the most distal part, and it is the continuation of the body part connecting the stomach with the duodenum. It divides into two smaller areas. The first one is wider, and it is called the pyloric antrum. The second part is narrower, and it is called the pyloric canal. The pyloric canal ends with the pyloric orifice and sphincter.
Each of both openings of the stomach contains one sphincter providing the food bolus and chyme movement further to the following parts of the digestive system and at the same time blocking its backflow.
Inferior esophageal sphincter
It is also known as the lower sphincter of the esophagus. It locates between the stomach and esophagus left to the midline at the eleventh thoracic vertebra level (Th11). The lower sphincter is more physiological. It is made of the longitudinal and circular smooth muscle fibers, the right crura of diaphragmatic muscle, and the fibers from the phrenoesophageal ligament. The junction place is called the gastroesophageal junction. The gastric mucosa changes the esophageal mucosa at the site where the sphincter is.
The pyloric sphincter is located between the pylorus and duodenum. The sphincter controls the chyme passage to the duodenum. The pyloric sphincter is an anatomical sphincter, and it is made of the fibers of the circular muscle layer providing the constriction.
Anatomic relations of the stomach
The stomach has connections with various organs.
Superior, it connects with the esophagus and the left dome of the diaphragm. The most distal part connects with the duodenum.
Inferior locate the transverse mesocolon.
The greater omentum also combines with the greater curvature as it goes down from it. The lesser curvature connects with the lesser omentum going to the liver.
The anterior surface connects with the left lobe of the liver, diaphragm, and the anterior abdominal wall's inner surface.
- The surface connecting with the liver is called the liver area. It locates along the superior part of the lesser curvature from the esophageal opening to the pyloric one.
- Fundus part and a small area of the body part along the greater curvature covers the left dome of the diaphragm. It is called the diaphragmatic area.
- The body part in the greater curvature area connects with the abdominal wall.
At the lower part of the surface along the major curvature lies the transverse colon, and this area is known as the colic area.
The body part connects with the spleen, and it is known as the splenic area. The body part also connects with the left kidney and adrenal gland, and the connection areas are known as the renal and suprarenal areas.
The pancreatic area is at the body and pyloric parts of the stomach.
The diaphragmatic area is the place where connects the lumbar portion of the diaphragm with the cardiac, body, and fundus parts. The splenic artery crosses the posterior surface.
Ligaments are made of the serosa layer going to the nearest organs. Ligaments participate in stomach fixation.
- Hepatogastric ligament connects the liver with the stomach, and it goes from the porta hepatis to lesser curvature.
- Gastrophrenic ligament goes from the cardiac notch of the greater curvature to the diaphragm's inferior surface, connecting the stomach with the diaphragm.
- Gastrosplenic ligament connects the stomach with the spleen, going from greater curvature to splenic hilum.
- Gastrocolic ligament goes from the greater curvature to the anterior surface of the transverse colon connecting the colon with the stomach. This ligament is a component of the greater omentum.
The wall of the stomach has four parts:
- muscular layer,
Histologically, the stomach is divided into only three parts, as the body and fundus parts have the same appearance.
The mucosa, together with the submucosa, forms the inner layer of the wall of the stomach. The mucosa is covered by simple columnar epithelium. The most thinner part of the mucosa is the cardiac part. Mucosa contains lymphoid tissue aggregates.
Lamina propria and muscular mucosa
Underneath the epithelium locate lamina propria containing the connective tissue, blood, and lymphatic vessels and muscular mucosa containing smooth muscle layers.
The muscle layer is located between the mucosa and submucosa parts. The inner part contains circular, but the outer- longitudinal fibers.
The mucosa is around 2-3 centimeters (0.8-1.2 inches) thick, and it is formed in various directions going plicas or folds or rugae. In constant overeating, the folds can stay distended even when the stomach is empty.
Along the lesser curvature, plicas go in the longitudinal direction, forming the food passway to the stomach's most lower place. The passageway is called the gastric canal.
From the cardiac opening, plicas go in the radial direction. In the body and fundus parts, plicas go in various directions.
Next to the pyloric orifice, mucosa forms a circular place. It works as a sphincter and, together with the pyloric sphincter muscle, closes the opening.
The epithelium contains many surface mucous cells producing viscous mucus covering the epithelium. Because of the appearance, the mucus is called cloudy or visible mucus. Mucus is very thick and insoluble in water. Mucous cells also produce bicarbonates.
The mucus protects the stomach from hydrochloric acid destructive effects; also, mucus decreases the chance of abrasion and injury from food particles during digestion, protecting against chemical and mechanical protection.
The surface epithelium contains many small gastric pits or holes and invaginations connected with gastric glands and ensures secretion.
The pyloric part has the deepest pits expanding into two-thirds of the epithelium.
The mucosa contains gastric glands producing mucus, stomach juice, and various endocrine substances and hormones.
The stomach contains glands in every anatomical part, and there are three main groups of glands depending on the location- the gastric glands proper, cardiac, and pyloric glands.
The first ones are also known as the principal glands, and they can be found in the body and fundus parts, while the other two types contain the location in their names. Pyloric glands locate only in the pyloric antrum part.
Mainly the principal glands produce the acid, but the cardiac and pyloric glands the hormones. During the outer secretion, the stomach made substances are released to its cavity, while the enteroendocrine secretion release the substances in the bloodstream.
The stomach juice contains hydrochloric acid, electrolytes, and organic substances. Principal glands per day produce approximately 2-3 liters (68-101 ounces) of gastric juice with an acid pH, usually around two, but it can vary between 1.5-3.5.
All glands are simple tubular, long branched glands with folded end parts. One gastric pit contains many excretory ducts. For example, the gastric gland proper can have 3 to 7 excretory ducts in one hole.
Gland cell types
The site where the glands and the base of the pit connects is the isthmus. The isthmus part contains stem cells replacing damaged and injured cells.
Below the isthmus are a longer and narrower neck part containing mucous neck cells and parietal cells. The neck part is changed by the broader and shorter base part containing parietal cells and chief cells. Parietal cells produce gastric acid.
The gastric glands contain many parietal and chief cells. In contrast, the cardiac and pyloric glands have a significant amount of mucous cells but decreased amount of parietal and chief cells.
All glands contain endocrine cells such as D and G cells producing gastrin and somatostatin, but the pyloric part's glands contain even more significant amounts.
The submucosa is a relatively thick part and contains a significant amount of loose connective tissue. Because of the tissue, the stomach can quickly expand when it is full.
The submucosa contains many lymphatic and blood vessels. It has many nerve fibers, and the Meissner's plexus or submucosal nerve plexus is located in the submucosa. The nerve plexus contains fibers providing the innervation for smooth muscles in muscular mucosa, blood vessels, and glands.
The muscular layer is the middle part, and it contains smooth muscle fibers.
It has three smaller layers- the inner, middle, and outer. Muscle fiber movements participate in the mechanical food procession by moving, mixing, and crushing the food bolus.
- The inner layer contains the oblique muscle fibers. They go from the left side of the cardiac opening downwards in the anterior and posterior wall, but fibers don't reach the greater curvature.
- The middle layer is the circular layer containing circular fibers. Next to the pyloric opening, fibers become thicker and create the pyloric sphincter muscle regulating and providing the stomach's output into the duodenum and prevent backflow. It can be up to one centimeter (0.4 inches) thick.
- The outer layer contains longitudinal fibers, and it is called the longitudinal layer. The fibers are primarily located along the greater and lesser curvature. The anterior and posterior walls have only a small number of longitudinal fibers.
The muscular layer contains many nerve cells forming nerve plexus located between the longitudinal and circular layers. The myenteric plexuses are also known as Auerbach's plexus. Opposite to Meisner's plexus containing only parasympathetic fibers, Auerbach's plexus also contains sympathetic fibers.
The serosa is the outer part of the wall. It covers the stomach from all sides, except the greater and lesser curvature.
The serosa is a continuation of the visceral peritoneum, and it forms the ligaments to the nearest organs and fixes the stomach in its place. It is covered by the mesothelium, also known as the simple squamous epithelium. Underneath it, locate the connective tissues.
The stomach provides the initial digestion of nutrients, and the food is prepared for the later stages of the digestive process, which takes place in the small intestine. It takes about 2-5 hours to empty the stomach depending on various factors such as food type, amount, and existing disorders.
There are several primary functions of the stomach.
- It temporarily stores the food and works as a tank or reservoir for two or more hours as its volume is 1,5-2 liters (51-68 ounces) and can go up to 4 liters (135 ounces).
- Its a place where the chyme, a milky-looking thick and viscous mixture, is formed as the stomach provides the mechanical food procession and motor function by crushing, grinding, and mixing the food with the gastric juice and the help of peristalsis. The stomach combines and breaks down the food bolus in even smaller particles.
- The stomach provides the mechanical food procession and the chemical one. It breaks down the nutrient chemical bonds under the hydrochloric acid's influence and produced ferments such as pepsinogen. Pepsinogen into active pepsin converts the gastric acid. Pepsin breaks down the proteins.
- The stomach provides the intrinsic factor secretion needed to absorb vitamin B12 later in the small intestines.
- The chyme dosing and its controlled release take place in the stomach as small doses are transferred to the duodenum by every muscle contraction.
- The stomach provides the secretion of various substances, hormones, and hydrochloric acid, breaking down the food and providing the protection and inducing the chemical digestion, motor function, specific substance secretion, and functions of other organs.
- It has a protective function as glands produce the mucus covering the epithelium and protecting it from hydrochloric acid.
- Hydrochloric acid not only provides digestion but also protection from various antigens. The higher is the concentration of hydrochloric acid, the fewer microbes stomach contains. Vibrio cholera can get killed after 10 to 15 minutes spent in the acid.
- The stomach provides the water, particular medication (aspirin, water-soluble vitamins), caffeine and ethanol absorption.
- The stomach induces and provides the vomiting mechanism in case of food poisoning or antigenes.
Arterial blood supply
The arterial blood supply for the stomach provides the left and right gastric arteries, going along the lesser curvature. The first artery is a branch of the celiac trunk, while the second one is a branch of the common hepatic artery arising from the celiac trunk.
The right and left gastroomental arteries have an anastomose along the greater curvature. Mentioned arteries also provide the arterial blood supply. The left one is a branch of the splenic artery, while the right is a terminal branch of the gastroduodenal artery.
All mentioned arteries are branches of the celiac trunk, a branch from the abdominal aorta, which means that it supplies the organ.
The splenic artery branches- the short gastric arteries supply the fundus part of the stomach.
The venous drainage is provided by the left and right gastric veins draining to the hepatic portal veins.
Short gastric and left gastroomental veins drain into splenic veins. The splenic vein carries the blood to the hepatic portal veins.
And finally, the blood is also drained to the superior mesenteric vein via the right gastroomental veins.
The superior mesenteric veins carry the blood to hepatic portal veins, meaning the stomach indirectly drains the liver's portal veins.
The lymphatic drainage provides the gastric and gastroomental lymph nodes located at the lesser and greater curvatures. The lymph vessels travel together with arteries to the mentioned lymph nodes.
Also, lymphatic drainage is provided by the celiac lymph nodes as the pyloric part drains indirectly via the superior and inferior pyloric lymph nodes to the celiac ones.
The autonomic nervous system innervates the stomach via the parasympathetic and sympathetic nerve fibers.
Primary, the anterior and posterior vagal trunks provide the parasympathetic motor and sensory innervation of the stomach. Both are branches of the vagus nerve (CN X). The parasympathetic nervous system induces the secretion and the pyloric sphincter's relaxation during the chyme movement.
Sympathetic innervation is provided by the celiac plexus via the greater splanchnic nerves from the sixth to eleventh thoracic spinal nerves (T6-T9).
Opposite the parasympathetic system, the sympathetic system inhibits the secretion and motility and provides the pyloric sphincter's constriction.
Gastritis characterizes by inflammation and irritation of the inner lining of the stomach wall. The most common cause for gastritis includes various infections, alcohol consumption, and nonsteroidal anti-inflammatory drug usage.
It can develop suddenly, and then it is called acute gastritis, or it can develop slowly and gradually over time. In this case, it is called chronic gastritis, and it can be present for years without proper treatment.
Mild gastritis can present without symptoms, or gastritis can result in burning sensation and pain in the upper abdomen. Nausea and vomiting can be present. Sometimes patients complain of the fullness feeling in the upper part of the stomach after eating. Abdominal bloating, regular hiccups, loss of appetite also can be a sign of gastritis. More severe cases can present with black stool and blood vomiting or vomiting substance that looks like coffee grounds.
There are many risk factors causing gastritis:
- older age,
- a large amount of alcohol consumption,
- regular usage of nonsteroidal anti-inflammatory drugs (ibuprofen, aspirin),
- stomach injury,
- tobacco usage,
- bacterial infections (H.pylori),
- parasitic infections,
- viral infections (HIV),
- autoimmune disorders (autoimmune gastritis),
- sarcoidosis, Crohn's disease.
Diagnosis and prognosis
Most cases are self-limiting, although untreated gastritis can result in bleeding and ulcers, rarely in cancer.
Gastritis diagnosis is made by physical examinations, blood, stool tests, endoscopy, and biopsy depending on the causing factor.
Treatment depends on the causing agent and factor (for example, antibiotics in H.pylori infection), including acid-reducing medications, proton pump inhibitors, antacids, and probiotics.
Smaller portions and more frequent meals during the day and the avoidance of spicy, fatty, and acidic food, alcohol, and tobacco can relieve the symptoms and promote recovery. Reduced nonsteroid anti-inflammatory drug usage also has a beneficial effect on gastritis.
Peptic ulcers characterize by open sores and erosions developing in stomach wall layers, most common in the mucosa, but it can affect all layers.
A peptic ulcer can occur in the stomach, duodenum, and lower esophagus part and is a pretty common condition.
The most common risk factors include H. pylori infection and nonsteroidal anti-inflammatory drug usage. When a peptic ulcer develops in the stomach, it is called a gastric ulcer.
Risk factors are very similar to gastritis risk factors, and they are:
- bacterial infections (H.pylori),
- nonsteroidal anti-inflammatory drug and pain killer usage,
- pain killer usage together with other medication such as anticoagulants,
- female gender,
- older age,
- excessive alcohol consumption,
Early stages can present without any symptoms. Symptoms include burning sensation and pain, abdominal bloating and fullness feeling, heartburns, nausea, and vomiting. Abdominal pain gets worse during the night and between meals or when the stomach is empty. The pain usually locates in the upper abdomen between the navel and the ribcage. Pain can irradiate to the chest. It slowly disappears when eating.
The ulcer can present with blood in the vomit or vomit looking like coffee grounds in more severe cases. It can cause black or tarry stools, weight loss, appetite loss, changes in it, and difficulty breathing.
When peptic ulcers are left untreated, they can lead to severe complications. The most common complication is bleeding. More severe complications include stomach wall perforation and cancer. The ulcer can leave scar tissues making it more difficult for food to travel through.
Treatment and prevention
Treatment is very similar to gastritis treatment, and it depends on the causing factors. Still, it includes medications blocking the acid production or reducing it, medications that neutralize the stomach acid. Opposite to gastritis, peptic ulcers need treatment, and they usually don't go away independently.
Avoidance of spicy, fatty, and acidic food, alcohol, and tobacco can promote recovery. Reduced nonsteroid anti-inflammatory drug and alcohol usage is essential in peptic ulcer prevention. Avoidance of alcohol when taking medication is vital for peptic ulcers.