The stomach is an organ of the digestive system, specialized in the accumulation and digestion of food. Its anatomy is quite complex; it consists of four parts, two curvatures and receives its blood supply mainly from the celiac trunk. Innervation is provided via the vagus nerves and the celiac plexus.
Thanks to our stomachs, every human is technically capable of corroding metal and picking up new hobbies, such as competitive eating. These are possible due to the extremely potent hydrochloric acid and the expandable nature of this organ.
Anteriorly: diaphragm, liver (left lobe), and anterior abdominal wall
Posteriorly: omental bursa (lesser sac), pancreas, left kidney and adrenal gland, spleen, and splenic artery
Superiorly: esophagus and diaphragm
Inferiorly and laterally: transverse mesocolon
Cardia, fundus, body, pyloric part
Mnemonic: Cows Find Bulls Passionate
|Functions||Mechanical and chemical digestion, absorption, hormone secretion|
Mucosa, submucosa, muscularis externa and serosa
|Blood supply||Gastric arteries, gastroomental arteries, short gastric arteries, posterior gastric arteries, gastroduodenal artery|
Parasympathetic: vagus nerve (CN X)
Sympathetic: celiac plexus (T5-T12)
|Lymphatics||Gastric, gastroomental, and pyloric lymph nodes|
|Clinical point||Hiatal hernia|
In this article we’ll explore every aspect of the stomach mentioned above, including the precise position of the stomach within the abdominal cavity.
- Microscopic anatomy
- Blood vessels
- Hiatal hernia
The stomach is the most dilated part of the digestive system, lying between the esophagus and duodenum. More precisely, the stomach spans the region between the cardiac and pyloric orifices of the gastrointestinal tract. It is covered and connected to other organs by peritoneum. The lesser omentum connects the stomach to the liver and then extends around the stomach. The greater omentum then continues inferiorly from the stomach, hanging from it like a curtain.The peritoneum has a convoluted course that requires visualization for a complete understanding, so study the following resources to avoid taking a wrong turn. They trace the trajectory of the peritoneum and provide you with an overview of the entire digestive system, including labeling worksheets and a study unit:
The stomach is located inside the abdominal cavity in a small area called the bed of the stomach, onto which the stomach lies when the body is in a supine position, or lying face up. It spans several regions of the abdomen, including the epigastric, umbilical, left hypochondriac, and left flank regions. The stomach also has some precise anatomical relations and comes in contact with several neighboring structures.
|Anteriorly||Diaphragm, liver (left lobe), and anterior abdominal wall|
|Posteriorly||Omental bursa (lesser sac), pancreas, left kidney and adrenal gland, spleen, and splenic artery|
|Superiorly||Esophagus and diaphragm|
|Inferiorly and laterally||Transverse mesocolon|
The stomach consists of several important anatomical parts. The four main sections of the stomach are the cardia, fundus, body, and pyloric part. As the name implies, the cardia surrounds the cardiac orifice, which is the opening between the esophagus and the stomach. It is the first section that ingested food passes through, representing the inflow part. The fundus is the superior dilation of the stomach, which is located superiorly relative to the horizontal plane of the cardiac orifice.
Next, we have the corpus, or gastric body, which is the largest part of the organ. Finally, the pyloric part represents the outflow section of the stomach, passing stomach contents into the duodenum. The pylorus is further divided into two distinct areas – the pyloric antrum connected to the stomach and the pyloric canal connected to the duodenum. The contents of the pyloric canal enter into the duodenum via the pyloric orifice, the opening and closing of which are controlled by the pyloric sphincter (pylorus), a circular layer of smooth muscle.
As you might notice in the stomach diagram illustrated above, the organ has a characteristic J-shape created by two unequal curvatures. The longer and convex curvature located on the left of the stomach is called the greater curvature, this starts from the cardiac notch that is formed between the esophageal border and fundus. In contrast, the shorter concave curvature found to the right is the lesser curvature. The latter contains a small notch called the angular incisure which marks the line of intersection between the body and pyloric part of the stomach.
You might be wondering if there's an easy way to remember the parts of the stomach. Of course there is and we're about to tell you! Just remember the phrase ' Cows Find Bulls Passionate', which stands for:
Now to cement your newly acquired knowledge about the parts of the stomach take a look at the following study unit!
The main function of the stomach involves mechanical and chemical digestion of ingested food. Ingested food enters the stomach from the esophagus via the cardiac orifice, falling into gastric juice produced by the stomach. Repetitive muscle contractions physically churn food particles, breaking them into smaller fragments which are mixed with the gastric juice. The various enzymes and hydrochloric acid (pH 1-2) in the gastric juice break food down even more, forming a semi-liquid substance called chyme. This ultimately passes into the duodenum through the pyloric orifice by a process called gastric peristalsis. Being a muscular organ, the stomach can distend quite a lot, accumulating anywhere between 2 and 3 liters of food.
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In addition to digestion, this organ is also involved in a small degree of absorption. Specifically, it can absorb water, caffeine, and a small proportion of ingested ethanol. The stomach also plays a role in controlling secretion and motility within the digestive tract by releasing several hormones such as gastrin, cholecystokinin, secretin, and gastric inhibitory peptide.
So far, we’ve seen the external, macroscopic structure of the stomach. Let’s dive deeper to see its internal and microscopic structure. The stomach consists of four histological layers called, from interior to exterior, mucosa, submucosa, muscularis externa, and serosa.
When the stomach is empty or contains very small quantities of food, it is in a contracted, shrunken state. The mucosa has a wrinkled aspect, consisting of ridges called gastric folds, or rugae. During distension of the organ, the gastric folds disappear. Along the lesser curvature of the stomach, a temporary, continuous furrow called gastric canal is formed between the gastric folds. This facilitates the passage of saliva and fluids during swallowing.
The mucosa is lined by simple columnar epithelium which is covered by a protective, alkaline mucous layer. The epithelial layer contains numerous invaginations, called gastric pits, that extend deeper into structures called gastric glands. Depending on the part of the stomach, these glands consist of various cell types. Mucous neck cells produce the mucous layer, while parietal cells secrete hydrochloric acid. Chief cells release pepsinogen, an inactive precursor that will transform into the active pepsin enzyme in a low pH environment. In turn, neuroendocrine cells release various hormones mentioned previously.
Moving externally, the next layer is the submucosa. It consists of loose connective tissue containing blood vessels and nerves.
The third layer is called muscularis externa and consists of three smooth muscle sub-layers. From internal to external, they are called inner oblique, middle circular, and external longitudinal. The inner oblique layer is located throughout the entire organ and works in unison with the other layers to produce the physical motion and contractions of the stomach required for digestion. The middle circular layer is located concentrically to the long axis of the stomach throughout the organ and plays an important role in forming the pyloric sphincter. The external longitudinal layer is situated in the two curvatures of the stomach in a longitudinal fashion. Last but not least, the serosa consists of the visceral peritoneum that covers the stomach.
You can easily remember the layers of the stomach wall using a mnemonic. ' M.S.M.S', which stands for:
- Muscularis externa
The overall blood supply of the stomach originates from the abdominal aorta and is provided from two anastomotic systems along the curvatures and several direct branches. The anastomosis along the lesser curvature is created by the union of the right and left gastric arteries which originate from the common hepatic artery and celiac trunk respectively. The greater curvature anastomosis is formed by the union of the right and left gastroomental arteries (gastroepiploic), which originate from the gastroduodenal and splenic arteries respectively.
The splenic artery also sends out short and posterior gastric arteries, which directly supply the fundus and upper body of the stomach. The pyloric part receives arterial blood from the gastroduodenal artery, which stems from the common hepatic artery.The veins draining the stomach follow the course and nomenclature of the arteries very closely. They ultimately drain into three large vessels called the hepatic portal, splenic, and superior mesenteric veins. Do you want to find out how every blood vessels twists and turns as it snails towards its respective gastric portion?
The stomach receives involuntary innervation by the autonomic nervous system (ANS). Parasympathetic innervation originates from the anterior and posterior vagal trunks, which stem from the left and right vagus nerves (CN X), respectively. The anterior vagal trunk mainly supplies a portion of the anterior surface of the stomach, as well as the pylorus. The larger posterior vagal trunk innervates the remaining anterior surface, as well as the entire posterior surface. Parasympathetic innervation is responsible for inducing gastric secretion and motility, as well as relaxation of the pyloric sphincter during gastric emptying. The vagus nerves also carry sensations of pain, fullness, and nausea from the stomach.
In contrast, sympathetic innervation is provided by the celiac plexus. The nerve impulses originate from the fifth to twelfth thoracic spinal nerves (T5-T12) and travel to the celiac plexus via the greater splanchnic nerves. Sympathetic innervation is responsible for inhibiting gastric motility and constricting the pyloric sphincter, thus preventing gastric emptying.
Lymph is drained from the stomach by lymph vessels that empty into the gastric and gastroomental lymph nodes. They are located along the arteries of the lesser and greater curvatures of the stomach. The pyloric part is drained by the superior and inferior pyloric lymph nodes. Subsequently, lymph vessels drain these sets of lymph nodes into the celiac lymph nodes, which are located around the celiac trunk.For more details about the lymphatic drainage of the stomach take a look at the following resources:
A hiatal hernia is a protrusion of part of the stomach into the mediastinum through the esophageal hiatus of the diaphragm. Any gastric part can be involved, but the most common situation is a protrusion of the gastroesophageal junction (sliding hiatal hernia), accounting for 95% of cases. The fundus of the stomach (paraesophageal hiatal hernia), multiple parts, or even the entire organ can herniate into the mediastinum, making the pathology quite varied.
There are several causes of hiatal hernias, such as trauma, congenital malformations, and previous surgery. Perhaps the most common, however, is advanced age which results in weakening of the diaphragm and widening of the esophageal hiatus, facilitating protrusions.
Patients suffering from hiatal hernias are mostly asymptomatic but can complain of non-specific symptoms like heartburn (pyrosis), regurgitation, dysphagia, epigastric discomfort, postprandial fullness, and nausea. Due to their asymptomatic nature, hiatal hernias are mostly diagnosed incidentally during upper endoscopy or imaging performed for other specific reasons.
Asymptomatic hiatal hernias are treated conservatively, managing the symptoms of gastroesophageal reflux disease for instance. Symptomatic hernias, however, require surgical intervention.