The human stomach is the main reservoir for storing body food. If the body did not have such a capacity as the stomach, we would eat constantly, and not just several times a day. It also secretes a mixture of acid, mucus, and digestive enzymes that help digest and sanitize our food during storage.
Macroscopic anatomy
What kind of stomach does a person have? It is a rounded, hollow organ. Where is a person’s stomach? It is located below the diaphragm on the left side of the abdominal cavity.
The structure of human organs is such that the stomach is located between the esophagus and the duodenum.
The stomach is the crescent-shaped enlarged part of the gastrointestinal tract. Its inner layer is full of wrinkles, known to us as wrinkles (or folds). It is these folds that allow him to stretch so that large portions of food can fit into it, which subsequently calmly moves during digestion.
In form and function, the human stomach can be divided into four parts:
1. The esophagus connects to the stomach in a small area called the cardia. This is a narrow, tube-like part that goes into a wider cavity - the body of the stomach. The cardia consists of the lower sphincter of the esophagus, as well as a group of muscle tissue that contracts to hold food and acid in the stomach.
2. The cardiac section passes into the body of the stomach, which forms the central and largest part of it.
3. Slightly above the body is a domed area known as its bottom.
4. Below the body is the pylorus. This part connects the stomach to the duodenum and contains the pyloric sphincter, which controls the flow of partially digested food (chyme) from the stomach and into the duodenum.
Microscopic anatomy of the stomach
Microscopic analysis of the structure of the stomach shows that it is made of several separate layers of tissue: mucous, submucous, muscle and serous.
Mucous membrane
The inner layer of the stomach consists entirely of the mucous membrane, which is a simple epithelial tissue with many exocrine cells. The small pores, called the gastric fossa, contain many exocrine cells that produce digestive enzymes and hydrochloric acid in the stomach. Mucous cells located throughout the mucous membrane and gastric fossa secrete mucus to protect the stomach from its own digestive secrets. Due to the depth of the gastric fossae, the mucous membrane can thicken, which cannot be said about the mucosa of other organs of the gastrointestinal tract.
In the depths of the mucous membrane is a thin layer of smooth muscles - the muscle plate. It forms folds and increases the contact of the mucosa with the contents of the stomach.
Around the mucous membrane there is another layer - the submucosa. It consists of connective tissue, blood vessels and nerves. Connective tissues support the structure of the mucous membrane and connect it to the muscle layer. The submucosal blood supply provides nutrients to the walls of the stomach. Nervous tissue in the submucosa controls the contents of the stomach and controls smooth muscle and digestive secretion.
Muscle layer
The muscle layer of the stomach surrounds the submucosa and makes up a greater amount of the mass of the stomach. The muscle plate consists of 3 layers of smooth muscle tissue. These layers of smooth muscles allow the stomach to contract to mix food and move it through the digestive tract.
Serous membrane
The outer layer of the stomach surrounding the muscle tissue is called the serous membrane, which is made of simple squamous epithelial and loose connective tissue. The serous layer has a smooth, slippery surface and releases a liquid, watery secret, known as serous fluid. The smooth, wet surface of the serous membrane helps to protect the stomach from friction, during its constant expansion and contraction.
The anatomy of the human stomach is now more or less understood. Everything that is described above will be considered a little later on the diagrams. But first, we’ll figure out what the functions of a person’s stomach are.
Storage
In the oral cavity, we chew and moisturize solid food until it becomes a homogeneous mass in the form of a small ball. When we swallow each ball, it slowly passes through the esophagus to the stomach, where it is stored along with the rest of the food.
The volume of a person’s stomach can vary, but on average it is able to contain 1-2 liters of food and a liquid that helps digestion. When the stomach is stretched with large amounts of food, it can store up to 3-4 liters. A distended stomach makes digestion difficult. Since the cavity cannot easily contract to mix food properly, this leads to a feeling of discomfort. The volume of a person’s stomach also depends on the age and condition of the body.
After the stomach cavity was filled with food, it persists for another 1-2 hours. At this time, the stomach continues the digestive process, which began in the mouth, and allows the intestines, pancreas, gall bladder and liver to prepare to complete the procedure.
At the end of the stomach, the pyloric sphincter controls the movement of food into the intestines. Typically, it usually closes to retain food and stomach secretions. Once the chyme is ready to leave the stomach, the pyloric sphincter opens to allow a small amount of digested food to pass into the duodenum. Within 1-2 hours, this process is slowly repeated until all the digested food leaves the stomach. The slow release rate of chyme helps to decompose it into components and maximize digestion and absorption of nutrients in the intestine.
Secretion
The stomach produces and stores several important substances to control the digestion of food. Each of them is produced by exocrine or endocrine cells located in the mucous membrane.
The main exocrine product of the stomach is gastric juice - a mixture of mucus, hydrochloric acid and digestive enzymes. Gastric juice mixed with food in the stomach to aid digestion.
Specialized exocrine cells of the mucous membrane are mucous cells that store mucus in the folds and pits of the stomach. This mucus spreads through the surface of the mucous membrane to cover the stomach lining with a thick, acid and enzyme-resistant barrier. The mucus of the stomach is also rich in bicarbonate ions, which neutralize the pH of gastric acid.
Parietal cells located in the pits of the stomach produce 2 important substances: Castle's internal factor and hydrochloric acid. The intrinsic factor is a glycoprotein that combines with vitamin B12 in the stomach and helps it to be absorbed into the small intestine. Vitamin B12 is an essential nutrient for the formation of red blood cells.
The acid in the human stomach protects our body by killing the pathogenic bacteria that are present in food. It also helps to digest proteins, turning them into an expanded form that is easier to process with enzymes. Pepsin - an enzyme that digests protein, is activated only under the influence of hydrochloric acid in the stomach.
The main cells, also in the pits of the stomach, produce two digestive enzymes: pepsinogen and gastric lipase. Pepsinogen is the preceding molecule of a very powerful protein-digesting enzyme, pepsin. Since pepsin would destroy the main cells that produce it, he hid in the form of pepsinogen, where it is harmless. When pepsinogen comes into contact with the acidic pH that is found in stomach acid, it changes shape and becomes the active enzyme of pepsin, which converts proteins into amino acids.
Gastric lipase is an enzyme that digests fats by removing fatty acid from a triglyceride molecule.
G-cells of the stomach - endocrine cells located at the base of the fossae of the stomach. G cells synthesize the hormone gastrin into the bloodstream in response to many stimuli, such as signals from the vagus nerve, the presence of amino acids in the stomach from digested proteins, or stretching of the walls of the stomach with food. Gastrin passes through the bloodstream to various receptor cells throughout the stomach, and its main task is to stimulate the gland and muscles of the stomach. The effect of gastrin on the glands leads to an increase in the secretion of gastric juice, which improves digestion. Gastrin stimulation of smooth muscles contributes to stronger contractions of the stomach and the opening of the pyloric sphincter to move food into the duodenum. Gastrin can also stimulate cells in the pancreas and gall bladder, where it increases the secretion of juice and bile.
As you can see, human stomach enzymes perform very important functions in digestion.
Digestion
Digestion in the stomach can be divided into two classes: mechanical and chemical digestion. Mechanical digestion is nothing more than a physical separation of the mass of food into smaller portions, and chemical digestion is the transformation of larger molecules into smaller molecules.
• Mechanical digestion occurs due to the mixing action of the walls of the stomach. Its smooth muscles contract, due to which portions of food are mixed with gastric juice, which leads to the formation of a thick liquid - chyme.
• While food is physically mixed with gastric juice, the enzymes present in it chemically break down large molecules into smaller subunits. Gastric lipase breaks down triglyceride fats into fatty acids and diglycerides. Pepsin breaks down proteins into smaller amino acids. The chemical decomposition started in the stomach does not end until the chyme enters the intestines.
But the functions of the human stomach are not limited to digestion.
Hormones
The activity of the stomach is controlled by a number of hormones that regulate the production of stomach acid and the release of food into the duodenum.
• Gastrin, produced by G-cells of the stomach itself, increases its activity, stimulating an increase in the amount of produced gastric juice, muscle contraction and gastric emptying through the pyloric sphincter.
• Cholecystokinin (CCK) is produced by the mucous membrane of the duodenum. It is a hormone that slows down gastric emptying by reducing the pyloric sphincter. CCK is secreted in response to a meal rich in proteins and fats, which are very difficult to digest by our body. CCK allows food to be stored in the stomach longer for more thorough digestion and gives time to the pancreas and gall bladder to release enzymes and bile that improve digestion in the duodenum.
• Secretin - another hormone secreted by the duodenal mucosa, reacts to the acidity of the chyme entering the intestines from the stomach. Secretin passes through the bloodstream to the stomach, where it slows down the production of gastric juice by the exocrine glands of the mucous membrane. Secretin also stimulates the production of pancreatic juice and bile, which contain acid neutralizing bicarbonate ions. The purpose of secretin is to protect the intestines from the harmful effects of chyme acid.
Human Stomach: Structure
Formally, we have already become familiar with the anatomy and functions of the human stomach. Let's use illustrations to examine where a person’s stomach is and what it consists of.
Picture 1:
This figure shows the human stomach, the structure of which can be considered in more detail. Indicated here:
1 - the esophagus; 2 - lower esophageal sphincter; 3 - cardia; 4- the body of the stomach; 5 - the bottom of the stomach; 6 - serous membrane; 7 - a longitudinal layer; 8 - a circular layer; 9 - oblique layer; 10 - large curvature; 11 - folds of the mucous membrane; 12 - the pyloric cavity of the stomach; 13 - the pyloric canal; 14 - the pyloric sphincter of the stomach; 15 - duodenum; 16 - the gatekeeper; 17 - small curvature.
Figure 2:
The anatomy of the stomach is clearly visible in this image. The numbers mark:
1 - the esophagus; 2 - the bottom of the stomach; 3 - the body of the stomach; 4 - large curvature; 5 - cavity; 6 - the gatekeeper; 7 - the duodenum; 8 - small curvature; 9 - cardia; 10 - gastroesophageal compound.
Figure 3:
It shows the anatomy of the stomach and the location of its lymph nodes. The numbers correspond to:
1 - the upper group of lymph nodes; 2 - pancreatic group of nodes; 3 - pyloric group; 4 - the lower group of pyloric nodes.
Figure 4:
This image shows the structure of the wall of the stomach. Here are marked:
1 - serous membrane; 2 - longitudinal muscle layer; 3 - circular muscle layer; 4 - the mucous membrane; 5 - a longitudinal muscle layer of the mucous membrane; 6 - circular muscle layer of the mucous membrane; 7 - glandular epithelium of the mucous membrane; 8 - blood vessels; 9 - gastric gland.
Figure 5:
Of course, the structure of human organs in the last figure is not visible, but the approximate position of the stomach in the body can be considered.
This image is quite interesting. It does not depict the anatomy of the human stomach or anything like that, although some parts of it can still be considered. This figure shows what heartburn is and what happens with it.
1 - the esophagus; 2 - lower esophageal sphincter; 3 - contractions of the stomach; 4 - stomach acid, together with its contents, rises into the esophagus; 5 - burning sensation in the chest and throat.
In principle, the picture clearly shows what happens with heartburn and no further explanation is required.
The human stomach, the pictures of which were presented above, is a very important organ in our body. You can live without it, but this life is unlikely to replace a full one. Fortunately, in our time you can avoid many problems by simply periodically visiting a gastroenterologist. Timely diagnosis of the disease will help get rid of it faster. The main thing is not to delay the trip to the doctor, and if something hurts, then you should immediately contact a specialist with this problem.