structure and function of digestive organs; Mouth, oesophagus, stomach, intestines, rectum, anus-4

Stomach

In the upper left area of the abdominal cavity, below the diaphgram in the epigastric, umbilical, and left hypogastric sections of the abdomen, is the stomach, an extended J-shaped organ. The stomach functions as a digestive organ, churn, and storage pouch. It can be made to carry enough food and fluids to fill a half-gallon. The duodenum, the first segment of the small intestine, is joined to the esophagus by the stomach.

Associated Organs with the Stomach

• Anteriorly
  • Liver's left lobe and the front of the abdomen
• Posteriorly
  • Pancreas, spleen, left kidney, adrenal gland, and abdominal aorta
• Superiorly
  • Esophagus, liver's left lobe, and the diaphragm
• Inferior
  • Small intestine and the transverse colon
    • Spleen and diaphragm are to the left.
    • Duodenum and liver are to the right.

Structure of the Stomach

The cardiac sphincter and the pyloric sphincter connect the stomach to the esophagus and the duodenum, respectively. Greater and lesser curvatures make up its two different curves. The greater curvature of the stomach is found in the left-facing arch (convex lateral border), while the lesser curvature is found on the right surface (concave medial border). A muscular ring, or sphincter, guards each end of the stomach and allows substances to pass through only in one direction. The lower esophageal sphincter is located between the esophagus and the stomach (LES). Because it divides the esophagus from the portion of the stomach close to the heart, this valve is also known as the cardiac sphincter. We occasionally recognize the presence of this sphincter, but occasionally it does not relax as it should, leaving us with the impression that we cannot swallow any further. The pyloric sphincter is located halfway between the small intestine and the distal, or far, end of the stomach.

There are four primary areas of the stomach:

• Cardia
  • The cardia encircles the stomach's superior opening.
• Fundus
  • The fundus is the rounded portion of the stomach that is above and to the left of the cardia.
• Body
  • The body is the largest portion of the stomach and lies below the fundus.
• Pylorus
  • The pylorus, a part of the stomach that joins to the duodenum, plays a crucial role in controlling how quickly food enters the small intestine.

Walls of the Stomach

With some modifications, the stomach wall is made up of the same four basic layers as the rest of the alimentary canal.

• Serous Layer
  • It completely envelops the organ and is generated from the visceral peritoneum. Simple squamous epithelium and areolar connective tissue make up its structure.
• Muscular Layer
  • It is located right underneath the serous coat, to which it is closely related. It comprises of longitudinal, circular, and oblique sets of smooth muscle fibers. The most superficial fibers are the longitudinal fibers, which run parallel to those of the esophagus. Under the longitudinal fibers, the stomach is uniformly covered in circular fibers. They are most numerous and organized in a circular ring at the pylorus. Together, they make up the esophagus's round fibers. The pyloric sphincter is formed by the circular layer's internal oblique fibers thickening around the end of the pylorus.
• Submucous Layer
  • Connects the mucous and muscle layers with a loose, areolar tissue.
• Mucous Membrane
  • When the stomach is bloated, is thick and has a smooth, soft, and velvety surface. Rugae are the numerous irregular folds that form when the stomach is empty. This layer is made up of mucus cells, parietal cells, and the chief cell, which are all simple columnar epithelial cells.

Function of the Stomach

• Before food is sent into the small intestine, the stomach acts as a temporary storage space for it, giving the digestive enzymes and pepsins time to do their jobs.
• The bacteria is killed by the gastric juice's hydrochloric acid content, which is secreted by the stomach.
• Pepsin, which starts the chemical digestion of proteins, is released.
• It conceals the intrinsic component required for the terminal ileum to absorb vitamin B12.
• It causes the hormone gastrin, which stimulates gastric juice secretion, to be released into the blood.
• To create chyme, it combines saliva, food, and stomach juice. Chyme is the term for the semi-liquid combination of food and stomach juice.
• Although the small intestine is where iron is absorbed, the stomach prepares the iron for absorption when HCL is present.
• A small amount of water, alcohol, and some medications that are liquid soluble are absorbed in the stomach wall.

Blood Supply of the Stomach

• The gastroepiploic arteries, a branch of the celiac artery, the left gastric artery, and the right gastric artery all supply arterial blood. The portal vein is reached by venous drainage through the veins with the matching nomenclature.

Nerve Supply of the Stomach

• The stomach is supplied by the sympathetic and parasymphetic nerves.

Gastric Juice and Secretions

The mucous membrane that makes up the inner lining of the stomach is thick, and on its surface are numerous small openings known as gastric pits that are situated at the ends of the gastric glands. There are three different types of secretory cells in the stomach, which are found in the gastric glands. Gastric juice is created by the combination of these cells' secretions.

• Mucus-secreting cells are present in the necks of glands close to the entrances of the gastric pits.
• Digestive enzymes pepsinogen and gastric lipase are secreted by chief cells, also known as peptic cells, in deeper regions.
• Hydrochloric acid and intrinsic factor are produced by parietal cells or oxyntic cells.

The inactive enzyme precursor pepsinogen is secreted by the chief cells. It quickly decomposes into pepsin when it comes into touch with hydrochloric acid, which is released by parietal cells. All dietary protein types are broken down by pepsin into polypeptides. When there is HCL in the stomach juice, it is most active in an acidic environment. Additionally, gastric juice has an enzyme called gastric lipase that breaks down fat molecules into fatty acids. Because pepsin can breakdown the proteins in stomach tissues, mucous cells secrete a viscous, alkaline fluid that coats the inside of the stomach wall and stops the stomach from digesting itself. For vitamin B12 to be absorbed from the small intestine, intrinsic factor, which is released by parietal cells, is necessary.

Additionally, the G cell that secretes gastrin is found in the gastric gland, which is situated in the pyloric antrum of the stomach. Gastrin is a hormone that causes parietal cells to release HCl when stimulated. A hormone called gastrin causes parietal cells to secrete HCL.

Composition of Gastric Juice

• Water
  • 99.5%
• Solids
  • 0.5%
• Organic
  • Gastric lipase, rennin, urease, mucus, gastric lipase, gelatinase, and intrinsic factors
• Inorganic
  • HCO3, Cl-, PO4, SO4, HCI, Na", Ca", K",