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 the stomach, 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.
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.
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.
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:
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.
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.
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.
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.
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.
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.
These groups drain into the celiac nodes which drain through the intestinal lymphatic trunk into the cisterna chyli (if present) and from there flow into the thoracic duct. Some drainage will often occur from the stomach to the splenic and superior mesenteric nodes.
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.
a mnemonic to remember the contents of the Tarsal tunnel from anterior to posterior is "Tom, Dick and Harry". or alternatively "Tom, Dick (and very nervous) Harry" if the artery, vein, and nerve are included.
The order of structures in the femoral triangle is important in the embalming of bodies, as the femoral artery is often exposed and used to pump embalming fluids into the body. The order of this neurovascular bundle can be remembered using the mnemonic, "NAVY":
An alternate to this mnemonic is "NAVEL" for Nerve, Artery, Vein, Empty Space and Lymph, to include the deep inguinal lymph nodes located medial to the Femoral vein. 2b1af7f3a8