Anatomy and Physiology of Stomach: Definition, Function, Structure, Diagram, & Facts

Stomach

The stomach is attributable to the larger gastroenterology system and has the functionality of efficiently breaking food and preparing it for the absorption process. Located between the oesophagus and the small intestine, the stomach performs mechanical digestion by the contraction of muscles and chemical digestion accompanied by compounds formed from gastric secretions. This knowledge does not only help in understanding simple aspects of life but also forms a basis for other related diseases and treatments.

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Anatomy Of The Stomach

The anatomy of the stomach is listed below-

Location And Structure

Thus, the stomach is situated in the upper left quadrant of the abdominal cavity between the oesophagus and the small intestines. It is located sub-diaphragmatic and is positioned ventral to the spleen and pancreas.

External Anatomy:

• Greater Curvature: left The longer, convex and more prominently placed curve from the termination of the fundus to the level of the umbilicus.

• Lesser Curvature: One of two curves; the short, inverted ‘U’ shaped portion of the right side of the stomach.

• Fundus: That segment of the stomach that enlarges above the level of the lower border of the oesophagus.

• Body: The middle part of the stomach which has the responsibility of grinding and mechanically integrating the food in the stomach with the stomach acid.

• Pylorus: The two muscular rings near the junction of the stomach and the first part of the small intestine through which the partially broken-down and mixed food is allowed into the latter

Diagram: External Structure Of The Stomach

Histology Of The Stomach Wall

Four Layers:

• Mucosa: The deepest one is covered by that simple columnar epithelium that is responsible for the secretion of gastric juice and mucus. It is composed of the following lined with gastric pits and gastric glands.

• Submucosa: A layer of connective tissue that is rich in blood supply, nerves and lymphatics which supply the mucosa with nourishment.

• Muscularis Externa: Including three layers of smooth muscles which comprise oblique muscles inner circular muscles and outer longitudinal muscles to churn the food.

• Serosa: The fourth layer is the layer of connective tissue covered by a layer of mesothelium this layer acts as a protective layer that minimizes abrasion between the stomach and other organs.

Diagram: Histological Structure Of The Stomach Wall

Gastric Glands And Cells

Types of Cells:

• Parietal Cells: They are found in the gastric glands and release hydrochloric acid permanently intrinsic factor which plays a great role in the digestion of proteins and absorption of vitamin B12.

• Chief Cells: Another cell found in the gastric glands seems to secrete pepsinogen which turns into pepsin an enzyme that helps in protein digestion.

• Mucous Cells: These cells secrete the mucus which coats the stomach lining preventing it from being burnt by acid and mechanical breakdown.

• G Cells: G cells are located largely in the pyloric region of the stomach although some may be found in the fundic glands as well; they release gastrin which excites the secretion of HCl and the contractions of the stomach.

Physiology Of The Stomach

The Physiology of the stomach includes:

Mechanical Functions

• Churning and Mixing of Food: One should also understand that the mechanical aspect of the stomach is to churn and mix the food with the help of some substances known as gastric juice to form a partially digested matter known as chyme. It aids in the mechanical digestion of the food particles and combines them with the chemical means for digestion.

• Role of Muscularis Externa in Peristalsis: The muscularis externa is made up of an inner layer of oblique muscles, a middle circular layer of muscles, and an outer layer of longitudinal muscles whose primary function is peristalsis; the wave-like contractions, which propel the chyme through the stomach and towards the pyloric sphincter.

Chemical Functions

• Secretion of Gastric Juices: Several types of gastric juices are secreted by the stomach to help in digestion and they include:

• Hydrochloric Acid (HCl): Secrete by parietal cells, HCl brings about an acidic nature that influences protein uncoiling and transformation of pepsinogen to pepsin.

• Pepsinogen: This inactive enzyme is released by chief cells and is converted into the active one called pepsin once it is in an acidic environment and initiates protein digestion.

• Mucus: Produced by mucous cells, mucus does not allow the acidic content of the stomach to come into direct contact with the stomach lining and also shields the stomach lining from mechanical.

Role of Hydrochloric Acid in Digestion: It also causes a drop of pH in the stomach which assists in the breakdown of proteins to smaller peptides and a favorable environment for pepsin.

Activation of Pepsinogen to Pepsin: HCl also activates Pepsinogen which is the inactive form of pepsin. It is then digested by the pepsin enzyme and this splits proteins into smaller peptides for digestion.

Regulation Of Gastric Function

Phases of Gastric Secretion:

• Cephalic Phase: Activated by sight, the smell or the mere thought of food and by stimulating nerves it brings out the secretion of gastric juices.

• Gastric Phase: Started by the presence of food in the stomach, promotes the secretion of more gastric juices and subsequently the movement of the stomach.

• Intestinal Phase: Concerned with the regulation of gastric secretion especially as a result of chyme in small intestines and involves feedback mechanisms for digestion efficiency.

Hormonal Regulation:

• Gastrin: secreted by G-cells, gastrin promotes the production of gastric acid and increases the contractions of the stomach.

• Somatostatin: Being produced by D cells, somatostatin strongly suppresses gastric acid secretion and regulates the function of the stomach to avoid the overproduction of acid.

Nervous Regulation:

• Vagus Nerve: Acts to stimulate parasympathetic nerves – gastric acid, stimulating movements/contraction.

• Enteric Nervous System: A picking network of neurons contained in the distinct system of the digestive tract that is capable of regulating gastrointestinal functions apart from the CNS.

Role Of The Stomach In Digestion

The stomach plays a major role in the:

Protein Digestion

• Breakdown of Proteins by Pepsin: In the stomach, proteins are firstly digested by pepsin which is secreted by the chief gland in the form of an inactive precursor the pepsinogen, which is activated by HCl. Pepsin cleaves large protein molecules into smaller peptides which are then further split in the small intestine.

• Formation of Chyme: As proteins are digested, the muscles of the stomach work to mechanically break down the food into a semiliquid consistency with the help of gastric juices. It increases the protein’s digestibility in the small intestine and readies it for even further digestion in the small intestine.

Absorption In The Stomach

• Limited Absorption: The function of digestion is primarily carried by the stomach but it does secrete few substances. Liquids such as alcohol and certain medicines like aspirin can be ingested through the lining of the stomach. Nevertheless, the larger quantity of most nutrients is taken by the small intestine.

• Mechanisms of Absorption: Some vitamins are absorbed through the simple diffusion that takes place mainly in the stomach. Some drugs and alcohol dissolve and cross the stomach’s cells known as the epithelial lining and enter the bloodstream. The rate of such substances’ absorption depends on the rate of gastric emptying as well as the presence of food in the stomach.

Protection Of The Stomach Lining

• Role of Mucus and Bicarbonate: The stomach lining has a layer of mucus produced by mucous cells that are on the lining and create a shield from the acidic environment. Bicarbonate ions are also released to compensate for any acid that manages to diffuse through the mucus barrier and thus the surface of the stomach lining is slightly alkaline.

• Mechanisms Preventing Self-Digestion: To avoid self-digestion there are various strategies that the stomach employs:

• The gentle movement of the organs through gallbladder contractions, and the release of mucus and bicarbonate to write down the high acidic environment.

• The short lifecycle which is about three to five days of the epithelial cells of the area.

• The fact that epithelial cells are connected with tight junctions does not allow the leakage of enzymes present in the digestive juices to the surrounding tissues.

Common Disorders Of The Stomach

The common disorders of the stomach include:

Gastritis

Causes: For instance, gastritis is the inflammation of the stomach lining and it can be attributed to;

• Infection: More frequently this is caused bacterium Helicobacter pylori However.

• Medication: Long-term smoking, the use of alcohol and x-ray procedures, the regular use of aspirin and non-steroidal anti-inflammatory (NSAIDs).

• Alcohol: Alcohol consumption if taken in large quantities can irritate the stomach lining.

• Stress: The husband added that psychological stress has a certain role in the development of gastritis.

• Autoimmune Conditions: IgA where the immune system targets tissues of the lining of the stomach.

Symptoms: The symptoms that it shares with other diseases are: abdominal ache or discomfort, nausea or vomiting, lack of appetite and even haemorrhage. As the condition progresses to the chronic form, only feelings of bloating and fullness can be deemed as symptoms of the disease.

Treatment: Treatment of gastritis may vary depending on the cause and may involve:

• Medications: Gastroesophageal reflux diseases; antacids agents, H2 receptor blockers, and proton pump inhibitors.

• Antibiotics: To prevent gastric cancer in patients with Helicobacter pylori infection.

• Avoiding Irritants: Such as NSAIDs, alcohol and foods with the following ingredients: üufenin, salsolinol and hydroxyhomospermidine.

• Dietary Changes: Refusing foods that contain spices and acids, respectively.

Peptic Ulcers

Causes: Peptic ulcers are open sores that develop on the lining of the stomach, the top part of the small intestine or the oesophagus. Key causes include:

• Infection: Some of the local pathogens include; Helicobacter pylori bacteria which play a central role in the formation of peptic ulcers.

• NSAIDs: Misuse of non-steroidal anti-inflammatory drugs creates ulcers Non-steroidal anti-inflammatory drugs when used over a long period cause the action of ulcers.

• Excessive Acid Production: They observed that stress and particular foods which lead to the production of Le histamine cause ulcers due to high stomach acidity.

Symptoms: The signs and indications of this ailment can entail burning stomach pain, bloated abdomen, sickness with vomiting, and in extreme instances, Blood. It develops a burning pain in the upper abdomen that begins between meals or at night and can be dulled by eating or taking antacids.

Treatment: Management of this condition involves the reduction of acid secretion, eradication of H. pylori and promotion of ulcer formation.

• Medications: PPIs, H2-receptor antagonists and antibiotics for H. pylori infection, if any.

• Lifestyle Changes: Not taking NSAIDs, quitting smoking and limiting alcoholic drinks.

• Dietary Adjustments: To reduce the occurrence of hives eating smaller portions of food throughout the day and avoiding triggering foods.

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