- 1 Definition | Location | shape & size | capacity | External features | Blood supply | lymphatics drainage | Nerve supply | interior of the stomach | functions of the stomach | Histology
- 2 The gross anatomy of the stomach
- 3 Definition of Stomach
- 4 Location:
- 5 Shape:
- 6 Size and Capacity:
- 7 External features
- 8 Two Offices:
- 9 Two Curvatures:
- 10 Two Surfaces:
- 11 Two parts Subdivided into Four:
- 12 Cardiac Part
- 13 Pyloric Part
- 14 Peritoneal Relations
- 15 Visceral Relations
- 16 Blood Supply:
- 17 Lymphatic drainage
- 18 Nerve Supply
- 19 The anterior gastric nerve divides into:
- 20 Interior of the stomach
- 21 Features
- 22 Functions of Stomach
- 23 Microscopic anatomy of the stomach
- 24 Cardiac End
- 25 Fundus and Body of Stomach
- 26 Pyloric part
- 27 Conclusion
Definition | Location | shape & size | capacity | External features | Blood supply | lymphatics drainage | Nerve supply | interior of the stomach | functions of the stomach | Histology
The gross anatomy of the stomach
The stomach is a muscular, J-shaped organ located in the upper abdomen, between the esophagus and the small intestine. It plays a vital role in the digestive system by breaking down food into smaller particles that can be further digested and absorbed by the small intestine.
The stomach is composed of four main parts: the cardia, the fundus, the body, and the pylorus. The cardia is the region where the esophagus connects to the stomach, while the fundus is the uppermost part of the stomach that lies above the cardia. The body is the largest and central part of the stomach, and the pylorus is the lower part that connects to the small intestine.
The stomach has two openings: the cardiac orifice at the top, which receives food from the esophagus, and the pyloric orifice at the bottom, which empties the stomach’s contents into the small intestine. The pylorus is controlled by a sphincter muscle that regulates the release of stomach contents into the small intestine.
The stomach is lined with a thick layer of specialized cells that secrete gastric juice, a mixture of hydrochloric acid and enzymes, including pepsinogen, that breaks down proteins. The stomach also produces mucus to protect its lining from the acidic gastric juice.
The stomach’s muscular walls contract rhythmically to churn and mix the food with the gastric juice, creating a semi-liquid mixture called chyme. The chyme is then slowly released into the small intestine, where it is further digested and absorbed.
The blood supply to the stomach is provided by the celiac artery, which branches off from the aorta, and the venous drainage is carried by the hepatic portal vein, which carries nutrient-rich blood to the liver.
Definition of Stomach
The stomach, a muscular, J-shaped organ in the upper abdomen, plays a crucial role in the digestive system by mechanically and chemically breaking down food. Specialised cells line the inside of the stomach, which secretes gastric juice that contains enzymes and hydrochloric acid to break down meal proteins into smaller parts. The stomach also generates mucus to shield its lining from the stomach juice’s acidity. The cardia, the fundus, the body, and the pylorus are the stomach’s four primary structural components. The cardiac orifice and the pyloric orifice control how much of the stomach’s contents are released into the small intestine. In addition to aiding in digestion, the stomach also helps to control hunger and satiety by secreting hormones.
The stomach is a muscular sac located in the upper part of the abdomen. It is situated between the esophagus and the small intestine. The stomach is positioned obliquely, occupying the epigastric, umbilical, and left hypochondriac regions of the abdomen.
Anatomically, the stomach is divided into four parts:
The cardia is the area where the esophagus connects to the stomach, while the pylorus is the opening through which food exits the stomach and enters the small intestine.
The stomach is partially covered by the left costal margin and the ribs, providing protection to the organ. The left kidney and spleen are also in close proximity to the stomach.
The shape of the stomach is not fixed and can vary depending on several factors. The degree of its distension, the amount of food and fluid present in it, and the position of the surrounding organs like the colon, liver, and spleen all influence its shape.
When the stomach is empty, it appears somewhat J-shaped or vertical. As it begins to fill with food and fluid, it gradually assumes a more rounded, pyriform shape. In obese individuals, the stomach may be more horizontal due to the increased volume of abdominal fat.
In medical practice, the shape of the stomach can be assessed through various diagnostic imaging techniques. For example, radiographic examination after giving a barium meal is a common method used to evaluate the shape and function of the stomach. During this procedure, the patient swallows a liquid containing barium, which makes the stomach and intestines visible on X-rays.
Size and Capacity:
The stomach is a highly distensible organ that can expand to accommodate varying amounts of food and fluid. The size and capacity of the stomach can vary significantly between individuals and can also change throughout a person’s lifetime.
At birth, the stomach is relatively small, with a mean capacity of about one ounce or 30 milliliters. As a child grows and develops, the stomach gradually expands in size and capacity. By the time a person reaches puberty, the average capacity of the stomach is around one liter or 1000 milliliters.
In adults, the size and capacity of the stomach can vary widely, depending on factors such as body size, gender, and eating habits. On average, the stomach is about 25 centimeters or 10 inches long. The capacity of the stomach in adults can range from 1.5 to 2 liters or more.
The stomach’s ability to expand is due to its muscular walls, which can stretch to accommodate larger volumes of food and fluid. The walls of the stomach are composed of smooth muscle fibers that contract and relax to mix the contents of the stomach and propel them towards the small intestine.
The anatomy of the stomach mainly begins with the external features of the stomach. The stomach annexe two orifices or openings, two curvatures or borders and two surfaces.
The stomach has two openings or orifices that are responsible for controlling the flow of food and fluids into and out of the stomach. These orifices are known as the cardiac orifice and the pyloric orifice.
The cardiac orifice is located at the top of the stomach and is connected to the lower end of the esophagus. It is positioned behind the left 7th costal cartilage, about 2.5 centimeters from its junction with the sternum at the level of vertebra T11. Although there is physiological evidence of sphincteric action at this site, a true anatomical sphincter cannot be demonstrated.
The pyloric orifice is located at the bottom of the stomach and opens into the duodenum, which is the first part of the small intestine. In an empty stomach and in the supine position, it lies 1.2 centimeters to the right of the median plane at the level of the lower border of vertebra L1, also known as the transpyloric plane. The position of the pyloric orifice is indicated on the surface of the stomach by a circular groove known as the pyloric constriction.
The pyloric constriction is produced by the underlying pyloric sphincter or pylorus, which acts as a gate guard and controls the flow of food and fluids from the stomach into the small intestine. The pyloric sphincter feels like a large firm nodule and can be felt by gently palpating the abdomen in the region of the lower right quadrant.
Another important landmark in the region of the pyloric orifice is the prepyloric vein of Mayo. This vein lies in front of the pyloric constriction and is an important anatomical reference point for surgeons performing procedures in this region of the abdomen.
In summary, the stomach has two important openings or orifices – the cardiac orifice and the pyloric orifice – that are responsible for controlling the flow of food and fluids into and out of the stomach. The pyloric sphincter acts as a gate guard and controls the flow of contents from the stomach into the small intestine, while the prepyloric vein of Mayo is an important anatomical reference point in this region of the abdomen.
The stomach has two curvatures that define its shape and orientation within the abdomen. These are the lesser curvature and the greater curvature.
The lesser curvature is located on the right side of the stomach and is concave in shape. It forms the right border of the stomach and provides attachment to the lesser omentum, which connects the stomach to the liver. The most dependent part of the lesser curvature is marked by a distinct indentation known as the angular notch or incisura angularis. This landmark is important for surgical procedures in the region of the stomach.
The greater curvature, on the other hand, is located on the left side of the stomach and is convex in shape. It forms the left border of the stomach and 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 esophagus. The greater curvature is approximately five times longer than the lesser curvature and is an important landmark for identifying the anatomical location of various regions of the stomach.
Both curvatures of the stomach are important for the movement and function of the stomach. They are the sites where the longitudinal and circular muscle layers of the stomach meet and form the muscular sphincters that regulate the flow of food and fluids through the stomach. Additionally, the curvatures provide attachment sites for various ligaments and connective tissues that support the stomach within the abdomen.
The stomach has two surfaces – the anterior or anterosuperior surface and the posterior or posteroinferior surface. These surfaces are important for the anatomical description of the stomach and provide attachment sites for various structures.
The anterior or anterosuperior surface of the stomach faces forwards and upwards towards the diaphragm. This surface is covered by peritoneum, a layer of serous membrane that lines the abdominal cavity. The peritoneum forms a fold known as the lesser omentum, which attaches the stomach to the liver. The anterosuperior surface of the stomach is also in contact with the left lobe of the liver, the diaphragm, and the anterior abdominal wall. It is an important surgical landmark for procedures that involve accessing the stomach through the anterior abdominal wall.
The posterior or posteroinferior surface of the stomach faces backwards and downwards towards the retroperitoneal structures of the abdomen. This surface is in contact with the pancreas, the left kidney, the left suprarenal gland, the transverse colon, and the left colic flexure. The posterior surface of the stomach also provides attachment to the greater omentum, which hangs from the greater curvature and drapes over the small intestine. The posterior surface of the stomach is an important anatomical landmark for procedures that involve accessing the posterior aspect of the stomach or the retroperitoneal structures of the abdomen.
Two parts Subdivided into Four:
The stomach is divided into two main parts – the cardiac and pyloric parts – by a line that is drawn downwards and to the left from the incisura angularis. The cardiac part is the larger of the two and is further subdivided into the fundus and body. The pyloric part is smaller and is subdivided into the pyloric antrum and pyloric canal.
The fundus is the dome-shaped uppermost part of the stomach, which lies above the level of the cardiac orifice. It serves as a reservoir for food and gas that is released during the digestive process. The body is the central part of the stomach, located between the fundus and the pyloric antrum. It is the site where most of the digestion occurs.
The pyloric antrum is the distal part of the stomach, located between the body and the pyloric canal. It is responsible for grinding and mixing the food with gastric juices to form chyme. The pyloric canal is a narrow channel that connects the pyloric antrum to the duodenum, the first part of the small intestine.
The division of the stomach into these four parts is important for understanding the digestive process and the movement of food through the gastrointestinal tract. Each part of the stomach has a specific function, and disruptions in these functions can lead to digestive problems and other health issues.
In summary, the stomach is divided into two parts – the cardiac and pyloric parts – which are further subdivided into four parts: the fundus, body, pyloric antrum, and pyloric canal. Each part has a specific function in the digestive process and plays a critical role in the movement of food through the gastrointestinal tract.
The cardiac part of the stomach is the initial section of the stomach and is situated just below the esophagus. The lower esophageal sphincter (LES) acts as a gateway to the cardiac part and allows food boluses to pass through to the stomach. The cardiac orifice is a ring-like structure formed by the LES and marks the boundary between the esophagus and the stomach.
- The fundus of the stomach is the uppermost part of the stomach and is situated above a horizontal line drawn at the level of the cardiac orifice. This dome-shaped structure projects superiorly and to the left, forming a noticeable bulge under the left dome of the diaphragm. It is distended with gas and can be visualized clearly on a radiographic examination. The fundus does not contain any gastric glands but is important in storing undigested food and gases.
- The body of the stomach lies between the fundus and the pyloric antrum. It is a muscular sac that can stretch and expand enormously along the greater curvature to accommodate food. The gastric glands are present in the fundus and body of the stomach and produce gastric juice, which is a mixture of hydrochloric acid, pepsinogen, and mucus. The gastric glands are made up of three types of secretary cells, namely mucous cells, chief cells, and parietal cells.
- Mucous cells secrete mucus, which forms a protective layer on the stomach lining and prevents acid from corroding the stomach walls.
- Chief cells, also known as zymogenic cells, secrete pepsinogen, which is converted into pepsin in the acidic environment of the stomach. Pepsin is a proteolytic enzyme that breaks down proteins into smaller peptides and amino acids.
- Parietal cells, also known as oxyntic cells, secrete hydrochloric acid (HCl), which creates an acidic environment in the stomach. HCl helps to activate pepsinogen to pepsin and also kills bacteria and other harmful pathogens that may enter the stomach.
The pyloric part of the stomach is located at the distal end of the stomach and is responsible for regulating the flow of partially digested food into the small intestine. The pyloric sphincter acts as a gateway to the duodenum and controls the release of chyme, which is the mixture of food and gastric juice, from the stomach into the small intestine.
- The pyloric antrum is the initial portion of the pyloric part and is separated from the pyloric canal by an inconstant sulcus, the sulcus intermedius, which is present on the greater curvature. It is about 7.5 cm long and is characterized by the presence of numerous pyloric glands, which are richest in mucous cells. These cells secrete a thick, protective mucus that helps to protect the lining of the small intestine from the acidic gastric juice.
- The pyloric canal is a narrow and tubular section that connects the pyloric antrum to the pylorus, the final portion of the pyloric part. It is approximately 2.5 cm long and contains fewer pyloric glands than the antrum. The cells in the pyloric canal secrete gastrin, a hormone that stimulates the release of gastric juice from the gastric glands in the fundus and body of the stomach.
- The pylorus is the final portion of the pyloric part and is situated at the distal end of the stomach, just before the duodenum. The pylorus contains a thick ring-like muscle called the pyloric sphincter, which regulates the flow of chyme into the small intestine. The pyloric sphincter opens and closes in response to signals from the nervous system and the hormones released by the cells in the pyloric canal. This helps to ensure that the small intestine is not overwhelmed by the acidic gastric juice, allowing for optimal digestion and absorption of nutrients.
The stomach is a vital organ that is lined by peritoneum on both its surfaces. The peritoneal relations of the stomach are important to understand as they help to define its anatomical boundaries and relationships with other abdominal structures.
- The lesser curvature of the stomach is where the layers of peritoneum lining the anterior and posterior surfaces meet and become continuous with the lesser omentum. The lesser omentum is a double layer of peritoneum that extends from the liver to the lesser curvature of the stomach. It provides a pathway for vessels and nerves to enter and exit the stomach.
- Along the greater curvature of the stomach, the two layers of peritoneum meet to form the greater omentum. The greater omentum is a large apron-like fold of peritoneum that extends from the greater curvature of the stomach and drapes over the intestines. It contains adipose tissue and lymph nodes and serves as a protective layer for the abdominal organs.
- Near the fundus of the stomach, the two layers of peritoneum meet to form the gastrosplenic ligament. The gastrosplenic ligament connects the spleen to the stomach and contains vessels and nerves that supply both organs.
- Near the cardiac end of the stomach, the peritoneum on the posterior surface is reflected onto the diaphragm as the gastrophrenic ligament. The gastrophrenic ligament attaches the stomach to the diaphragm and provides stability to the stomach during contraction. 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 known as the bare area of the stomach.
- The greater and lesser curvatures of the stomach are also bare along the peritoneal reflections. These areas lack the protective layer of the peritoneum and are in direct contact with the adjacent structures.
The stomach, located in the upper abdomen, is related to various neighboring structures on its anterior and posterior surfaces.
On the anterior surface of the stomach, the liver, diaphragm, transverse colon, and anterior abdominal wall are located. The diaphragm separates the stomach from the left pleura, pericardium, and the sixth to ninth ribs. The costal cartilages are separated from the stomach by the transversus abdominis muscle. Deep to the peritoneum, gastric nerves and vessels ramify. Traube’s space, the area between the left costal margin and the lower edge of the left lung on the stomach, is a notable landmark. Normally, percussion over this space results in a resonant note, but in cases of splenomegaly or pleural effusion, a dull note can be detected.
On the posterior surface of the stomach lies the stomach bed, which is separated from the stomach by the cavity of the lesser sac. The stomach bed consists of various structures such as the diaphragm, left kidney, left suprarenal gland, pancreas, transverse mesocolon, splenic flexure of the colon, and splenic artery. Occasionally, the spleen may also be included in the stomach bed, but it is typically located in the cavity of the greater sac, not the lesser sac. The peritoneum on the posterior surface of the stomach is reflected onto the diaphragm as the gastrophrenic ligament near the cardiac end. This ligament separates the bare area of the stomach, a small part of the posterior surface of the stomach in direct contact with the left crus of the diaphragm, from the rest of the peritoneal surface.
The structures are:
- Left kidney
- Left suprarenal gland
- Transverse mesocolon
- Splenic flexure of the colon
- Splenic artery Sometimes the spleen is also included in the stomach bed, but it is also included in the stomach by the cavity of the greater sac (and not of the lesser sac). Gastric nerves and vessels ramify deep to the peritoneum.
The stomach is a muscular organ located in the upper abdomen and is involved in the digestion of food. Adequate blood supply is essential for the normal functioning of the stomach. The blood supply to the stomach is provided by several arteries and veins.
The lesser curvature of the stomach is supplied by two main arteries:
- Left gastric artery: The left gastric artery arises from the celiac trunk, which is a major branch of the abdominal aorta, and runs along the lesser curvature towards the cardiac region of the stomach.
- Right gastric artery: The right gastric artery is a branch of the proper hepatic artery, which is also a branch of the celiac trunk. It supplies blood to the pyloric region of the stomach.
The greater curvature of the stomach is supplied by two arteries:
- Right gastroepiploic artery: The right gastroepiploic artery is a branch of the gastroduodenal artery, which is also a branch of the hepatic artery. It runs along the greater curvature of the stomach and supplies blood to the pyloric region.
- Left gastroepiploic artery: Left gastroepiploic artery is a branch of the splenic artery and supplies blood to the greater curvature of the stomach.
The fundus, which is the upper part of the stomach, is supplied by 5 to 7 short gastric arteries, which are branches of the splenic artery. These arteries supply blood to the upper part of the stomach and the lower part of the esophagus.
The veins of the stomach drain into the portal vein, which is a major vessel that carries blood from the digestive organs to the liver. The superior mesenteric vein and the splenic vein are two main veins that drain blood from the stomach. The right and left gastric veins drain into the portal vein, while the right gastroepiploic vein and the short gastric veins terminate in the splenic vein.
In conclusion, the stomach receives blood supply from various arteries, including the left gastric, right gastric, right gastroepiploic, left gastroepiploic, and short gastric arteries. The veins of the stomach drain into the portal vein, superior mesenteric vein, and splenic vein. Adequate blood supply to the stomach is crucial for its normal functioning, and any disruption in blood supply can lead to various digestive disorders.
The lymphatic system plays an important role in the immune system and is responsible for draining excess fluids and waste products from tissues. In the stomach, lymphatic drainage is divided into four territories, each with its own specific drainage pattern.
- The upper part of the left 1/3rd of the stomach drains into the pancreaticosplenic nodes, which are located along the splenic artery at the back of the stomach. The lymphatic vessels from these nodes travel along the splenic artery to reach the celiac nodes, which are located near the celiac trunk.
- The right 2/3rd of the stomach drains into the left gastric nodes, which are located along the artery of the same name. These nodes also receive lymph from the abdominal part of the esophagus. Lymph from these nodes drains into the coeliac nodes.
- The lower part of the left 1/3rd of the stomach drains into the right gastroepiploic nodes, which are located along the artery of the same name. The lymphatic vessels arising in these nodes drain into the sub pyloric nodes, which are located in the angle between the first and second part 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.
- The pyloric part of the stomach drains in different directions into the pyloric, hepatic, and left gastric nodes, which in turn drain into the coeliac nodes. It is important to note that lymph from all areas of the stomach ultimately reaches the coeliac nodes. From here, it passes through the intestinal lymph trunk to reach the cistern chyli.
The stomach is innervated by both sympathetic and parasympathetic nerves, which play a crucial role in regulating its various functions. The sympathetic nerves are derived from the thoracic six to ten segments of the spinal cord and travel via the greater splanchnic nerves and coeliac and hepatic plexuses. These nerves have several important functions, including vasomotor control, motor control of the pyloric sphincter, and transmission of pain sensations from the stomach.
These nerves are:
- Motor to the pyloric sphincter, but inhibitory to the rest of pyloric sphincter, but inhibitory to the rest of the gastric musculature.
- The chief pathway for pain sensation from the stomach.
The parasympathetic nerves are derived from the vagus nerves and travel through the oesophageal plexus and gastric nerves to innervate the stomach. The anterior gastric nerve is composed mainly of left vagal fibers, while the posterior gastric nerve is composed mainly of right vagal fibers. These nerves play an important role in stimulating gastric secretions and motility.
The sympathetic nerves primarily have a vasoconstrictor effect on the blood vessels of the stomach, reducing blood flow to the organ. They also have a motor effect on the pyloric sphincter, causing it to open and close, and they are the primary pathway for pain sensation from the stomach.
On the other hand, the parasympathetic nerves have a vasodilator effect on the blood vessels of the stomach, increasing blood flow to the organ. They also stimulate the production of gastric secretions and motility, including the peristaltic contractions that mix and propel the stomach contents.
Nerve supply of the stomach:
(a) Anterior gastric nerve and
(b) The posterior gastric nerve.
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 antrum and another for the pylorus.
The anterior gastric nerve is a branch of the vagus nerve that innervates the stomach. It plays an important role in regulating the gastric functions, such as motility and secretion. The anterior gastric nerve divides into several gastric branches, which innervate the anterior surface of the fundus and body of the stomach. These branches transmit signals that stimulate gastric motility and secretion.
In addition to the gastric branches, the anterior gastric nerve also divides into two pyloric branches. One of these branches innervates the pyloric antrum, while the other innervates the pylorus. The pyloric branches are responsible for regulating the opening and closing of the pyloric sphincter, which controls the flow of chyme from the stomach into the duodenum.
The innervation of the pyloric sphincter is important for the regulation of gastric emptying. When the stomach is full, the pyloric sphincter remains closed, allowing the stomach to mix and break down the food. As the food becomes more liquid and the stomach is empty, the pyloric sphincter gradually opens to allow the chyme to pass into the duodenum. The pyloric branches of the anterior gastric nerve play a crucial role in this process by controlling the opening and closing of the sphincter.
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 secretomotor 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.
The posterior gastric nerve, which is one of the branches of the vagus nerve, plays a vital role in regulating the motor and secretory functions of the stomach. It divides into several smaller branches that supply the posterior surface of the fundus, the body, and the pyloric antrum. These branches contain parasympathetic fibers that stimulate the secretion of gastric juice by the stomach glands, which is rich in hydrochloric acid and pepsin, as well as increase the motility of the stomach muscles.
In addition to these gastric branches, the posterior gastric nerve also gives rise to larger coeliac branches that supply the coeliac plexus, a network of nerve fibers that innervates the abdominal organs. These fibers also have a parasympathetic origin and play a crucial role in regulating the digestive processes of the stomach.
When the parasympathetic nerves are stimulated, they cause relaxation of the pyloric sphincter, allowing the contents of the stomach to pass into the small intestine. This action is necessary for the process of digestion to continue. Additionally, the parasympathetic fibers stimulate the production of digestive enzymes and other secretions in the stomach, which are essential for the digestion of food.
Interior of the stomach
The interior of the stomach is a complex and important part of its anatomy. To fully understand it, one should begin by opening the stomach along the greater curvature and examining the mucous membrane with a hand lens. This will reveal the rugae, which are the folds in the stomach that allow it to expand and contract as needed. By stripping the mucous membrane from one part, the internal muscle coat can be exposed. This coat consists of several layers of muscle fibers, including the outer longitudinal, middle circular, and inner oblique fibers.
To further explore the pyloric region, it is necessary to feel the thickened pyloric sphincter, which is responsible for controlling the flow of food from the stomach into the duodenum. One can also incise the beginning of the duodenum to examine both the duodenal and pyloric aspects of the pyloric sphincter. By doing this, one can see the intricate network of muscle fibers that make up the sphincter and how they function to regulate the passage of food.
It is also important to note the presence of gastric pits and glands, which are responsible for the secretion of gastric juice, rich in pepsin and HCL, as well as other important enzymes and hormones. These pits and glands are located throughout the mucous membrane of the stomach and play a vital role in the digestive process.
In addition to these features, the interior of the stomach also contains blood vessels and nerves that are important for its functioning. The blood vessels provide oxygen and nutrients to the stomach, while the nerves control its movement and secretions. Understanding the complex anatomy of the stomach’s interior is crucial for understanding its overall function and how it contributes to the digestive process.
The stomach is a muscular organ located in the upper abdomen that plays a critical role in digestion. Its internal structure is complex and includes several layers that are responsible for the stomach’s function. Let’s explore these features in more detail:
- The mucosa of the stomach is the innermost layer, which is made up of several folds called gastric rugae. These folds increase the surface area of the stomach, allowing it to expand as it fills with food. When the stomach is empty, the rugae are more pronounced, but they flatten out as the stomach fills up. The mucosal layer also contains miniature depressions called gastric pits, which lead to the gastric glands. These glands secrete digestive enzymes, hydrochloric acid, and mucus, which are essential for digestion. The part of the lumen that lies along the lesser curvature of the stomach is called the gastric canal or magenstrasse, which allows rapid passage of swallowed liquids along the lesser curvature directly to the lower part before it spreads to the other part of the stomach.
- The submucosa is a layer of connective tissue, arterioles, and nerve plexus located beneath the mucosa. It provides support to the mucosal layer and helps transport nutrients and waste products in and out of the stomach.
- The muscularis layer is the thickest layer of the stomach, composed of three layers of smooth muscle fibers that work together to move food through the digestive system.
- The outermost layer of the muscularis is made up of longitudinal fibers that are mainly located along the curvatures of the stomach.
- The middle layer of the muscularis is composed of circular fibers that encircle the body of the stomach.
- The innermost layer of the muscularis is made up of oblique fibers that loop over the cardiac notch and spread throughout the fundus and body of the stomach. Some of these fibers form a well-developed ridge on each side of the lesser curvature, creating the gastric canal for the passage of fluids.
- The outermost layer of the stomach is the serous coat, which consists of the peritoneal covering. This layer helps protect the stomach from injury and infection.
It is important to note that the stomach has a complex structure that is vulnerable to injury and disease. Gastric ulcers, for example, can occur when the gastric rugae and mucosal layer are damaged, often due to prolonged use of nonsteroidal anti-inflammatory drugs or infection with Helicobacter pylori. Therefore, it is essential to take care of your digestive system by maintaining a healthy diet and avoiding habits that can damage your stomach.
Functions of Stomach
The stomach is an important organ of the digestive system that performs several functions to facilitate the process of digestion. Here are some ways in which the stomach functions:
- Reservoir for Food: The stomach acts as a reservoir for food, storing and releasing it to the small intestine at a controlled pace.
- Mixing Food: The stomach mixes food with gastric juices by its peristaltic movements, breaking it down into smaller particles that are easier to digest.
- Production of Gastric Juices: Gastric glands in the stomach produce gastric juices, which contain enzymes that break down proteins and other nutrients.
- Hydrochloric Acid Production: The gastric glands also produce hydrochloric acid, which helps to kill harmful bacteria and other microorganisms present in the food.
- Protection of Gastric Mucosa: The lining cells of the stomach produce mucus, which protects the stomach lining from the corrosive effects of the hydrochloric acid.
- Absorption of Substances: Some substances, such as alcohol, water, salt, and some drugs, are absorbed in the stomach.
- Production of Intrinsic Factor: The stomach produces intrinsic factor, a protein that helps in the absorption of vitamin B12.
Microscopic anatomy of the stomach
At the cardiac confine of the stomach, the stratified epithelium of oesophagus abruptly changes to simple columnar epithelium of the stomach.
- Mucous Membrane: The innermost layer of the digestive tract is the mucous membrane, also known as the mucosa. It consists of a layer of simple columnar epithelial cells that secrete mucus to lubricate and protect the digestive tract. The mucous membrane also contains small tubular glands that produce digestive enzymes and other substances.
- Submucosa: The submucosa is a layer of loose connective tissue that contains blood vessels, lymphatic vessels, and Meissner’s plexus of nerves. Meissner’s plexus helps to regulate the movements of the digestive tract and controls the secretion of digestive juices.
- Muscularis Externa: The muscularis externa is a layer of smooth muscle that surrounds the submucosa. It is composed of two layers of muscle fibers: an outer longitudinal layer and an inner circular layer. Between these two layers is the myenteric plexus or Auerbach’s plexus of nerves, which helps to control the contractions of the muscles that propel food through the digestive tract.
- Serosa: The outermost layer of the digestive tract is the serosa. It is lined by a single layer of squamous cells and serves to protect the digestive tract from damage by surrounding organs and structures.
Fundus and Body of Stomach
The stomach is a specialized organ of the digestive system that is responsible for the storage, mixing, and breakdown of food. Here are some additional details about the structure and function of its different layers:
- Mucous Membrane: The mucous membrane of the stomach contains tall, simple, tubular gastric glands that are composed of various cell types. The upper one-third of the gland is responsible for conducting secretions, while the lower two-thirds is involved in secretion. The different cell types present in the gastric glands include chief or zymogenic cells, which secrete digestive enzymes; oxyntic or parietal cells, which secrete hydrochloric acid; and mucous neck cells, which produce mucus to protect the stomach lining.
- Muscularis Mucosae and Submucosa: The muscularis mucosae and submucosa of the stomach are similar in structure and function. The muscularis mucosae is a layer of smooth muscle that contracts to help mix and propel food through the stomach. The submucosa is a layer of loose connective tissue that contains blood vessels, lymphatic vessels, and nerves.
- Muscularis Externa: The muscularis externa of the stomach is composed of three layers of smooth muscle: an outer longitudinal layer, a middle circular layer, and an inner oblique layer. The oblique layer allows for more efficient mixing and churning of food.
- Serosa: The serosa is the outermost layer of the stomach, which is lined by a single layer of squamous cells. It is continuous with the serosa of the esophagus and duodenum, and serves to protect the stomach from damage by surrounding structures.
Mucous membrane: There are pyloric glands which consist of basal one-third as mucous secretory component and upper two-third as conducting part. Muscularis mucosae are built of two layers of fibres. The submucosa is same as in the cardiac end.
Muscularis external comprises a thick layer of circular fibres forming the pyloric sphincter. The serosa is same as of the cardiac end
In conclusion, the stomach is a vital organ in the digestive system, responsible for breaking down food into nutrients that can be absorbed by the body. Its anatomy includes various layers of tissues, each with a specific function, including the mucous membrane, submucosa, muscularis externa, and serosa. The stomach also has specialized regions, such as the fundus, body, and pylorus, each with unique structures and functions. The understanding of the anatomy of the stomach and its functions is crucial for the diagnosis and treatment of various gastrointestinal disorders.