Stomach

• Stomach function

  • The stomach is a highly dilated portion of the alimentary canal and is concerned with thestorage and digestion of food
  • localized in the epigastric region.
  • The stomach has two surfaces - anterior and posterior, which meet one to another in lesser and greater curvatures and two orifices – cardiac and pyloric. 
• Location and orifices

  • Location: The stomach is an intraperitoneal organ located in the epigastric region, situated between the esophagus and the small intestine. It lies mainly on the left side of the body, under the diaphragm.
  • Orifices:
  • Cardiac orifice: This is where the stomach connects to the esophagus, located near the lower esophageal sphincter. It is the entry point for food into the stomach.
  • Pyloric orifice: The opening between the stomach and the duodenum . It is regulated by the pyloric sphincter, which controls the release of chyme (partially digested food) into the duodenum.
• layers of stomach

  1. Tuncia mucosa

  • lamina epithelialis
  • lamina propria
  • lamina muscularis mucosae

  2. Tela Submucosa

  3. Tunica muscularis

  4. Tunica Adventitia and serosa
• Lamina epithelialis of the stomach

  • Simple columnar epithelium lining the lumen
  • mucous-secreting but...
  • nuclei: elongated and centrally located as no mucous granules in cytoplasm due to constant secretion.
  • : Surface epithelial cells and mucous neck cells secrete mucus that is rich in bicarbonate ions (HCO₃⁻)- for protection and neutralising HCl
  • Features:
  • Contains gastric pits that open into gastric glands.
  • The surface mucous cells secrete mucus to protect the lining from acid and digestive enzymes.
• Lamina propria of the stomach

  •  Loose connective tissue made up of largely of reticular fibers with associated fibroblasts and smooth muscle that houses blood vessels, lymphatics, and immune cells.
  • Gastric glands are embedded here.
  • Fundus/Body: simple Branched tubular glands.
  • Pylorus: Contain pyloric glands simple branched tubular that are predominantly mucous-secreting and include gastrin-producing cells
  • cardiac region: cardiac glands Simple tubular
• Parietal cells of gastric glands

  • in the neck of the fundic glands, among the mucous neck cells
  • They are large pyramid-shaped cells, The nucleus is spherical and the cytoplasm stains intensely with eosin=numerous mitochondria
  • responsible for the production of hydrochloric acid (HCl) and intrinsic factor secretion.
  • intrinsic factor is a glycoprotein can bind to vit B12
  • Secretion of HCl
• what is secretion in parietal cell driven by

  • driven by the activity of an H+, K+, ATPase coupled with an Na+
  • broad base produce H+/Cl-
  • invagination to increase SA of membrane as Hcl formed in lumen
  • H+ ions formed by carbohydrate H20 +Co2-> H2CO3-> H+ + HCO3-
• Chief cells of gastric gland

  • Found in the base of the glands, they secrete 

  pepsinogen, which is converted into the active enzyme pepsin when it comes in contact with stomach acid.

  • They are cuboidal or lowcolumnar cells that line the lower half of the glands. The rER in their apical poleaccounts for the basophilia, which allows for easy identification of these cells in H&E sections
• cells of gastric glands

  1. Mucous neck cells: Secrete mucus.

  • 2. Parietal cells (Oxyntic cells): Secrete hydrochloric acid (HCl) and intrinsic factor (important for B12 absorption).
  • 3. Chief cells : Secrete pepsinogen (converted to pepsin in the acidic environment to help digest proteins).
  • 4.Enteroendocrine cells (G cells): Secrete gastrin, which regulates gastric acid secretion,cck, histamine (histamine stimulates hcl secretion)
  • histamine, which acts locally on parietal cells to stimulate the secretion of hydrochloric acid (HCl)
  • 5.non differentiated stem cells
• mucous.cells/mucous neck cells of gastric gland

  -lose to cervix ((neck)

  -Found near the opening of the gastric pits. These cells secrete mucus to protect the stomach lining.

  -spherical nucleus and cell is columnar in shape
• Non differentiated stem cells

  regeneration of epithelium
• neuroendocrine cells/enteroendocrine cells

  • endocrine function
  • secretion gastrin which regulates gastrin secretion (HCl) by parietal cells and emptying of duodenum
  • release cck
  • histamine stimulates hcl secretion by acting on histamine secretors
  • histamine has paracrine role: acts locally on parietal cells to stimulate the secretion of hydrochloric acid (HCl). histamine only affects nearby parietal cells in the stomach lining
• Cadiac glands

  • Found in the cardiac region of the stomach, near the gastroesophageal junction.
  • Simple tubular mucous glands.
  • located within the lamina propria of the mucosa.
  • Function: Secretion of mucus to protect the stomach lining and esophagus .which contains bicarbonate ions to help neutralize stomach acid .
  • helps protect the oesophageal epithelium against gastric reflux.
  • The mucous cells show flattened nucleus and the apical cytoplasm is typically filled with mucin granule
• Pyloric Glands

  • Located in the pyloric antrum (the lower part of the stomach near the pyloric sphincter)
  • primarily secrete mucus and gastrin, a hormone that stimulates the secretion of gastric acid by the parietal cells.
  • Gland Type: They are simple tubular glands, but the glands here are often branched (compound tubular) in some areas.
• muscularis mucosae  of Tunica mucosa of stomach

  This thin layer of smooth muscle helps to move and facilitate secretion in the mucosa, ensuring the glands stay open and function properly.

   inner circular: controls the narrowing of the stomach and mixing of contents.

  outer longitudinal: controls the shortening of the stomach and propulsion of food through the gastrointestinal tract.
• submucosa of the stomach

  consists of dense connective tissue containing variable amount of adipose

  tissue, larger blood vessels and lymph vessels, nerves and submucosal glands.

  • Submucosal Plexus (Meissner's Plexus): Found within the submucosa, it regulates the secretion from glands and controls blood flow to the mucosa.
• tunica muscularis

  3 layers

  • Inner oblique layer (unique to the stomach, helps churn food).
  • Middle circular layer: significantly thickened at the pyloric region, forming the pyloric sphincter.
  • Outer longitudinal layer.: contract
  • Myenteric Plexus (Auerbach's Plexus): Located between the inner circular and outer longitudinal layers, it regulates muscle contractions (peristalsis) and gastric motility.
• musculus sphincter pylori

  • a thickening of the  inner circular layer of the tunica muscularis of the stomach
  •  inner circular layer of smooth muscle becomes significantly thickened at the pyloric region, forming the pyloric sphincter.
  • This sphincter regulates the passage of chyme from the stomach into the duodenum- acts as a valve to allow one way passage
  • It prevents reflux of intestinal contents back into the stomach.
  • blocks food coming from duodenum
• serosa of the stomach

  outer layer

  no adventitia

  Simple squamous flat epithelium (mesothelium) with connective tissue.
• Pylorus of the stomach

  muscle is the thickest- Thickened middle circular layer forming pyloric sphincter

  Pyloric glands(branched tubular, mucus-secreting)
• role of HCO3-

  neutralise HCl and protect the stomach
• Basophillic cell

  as you go down basophilic cell: chief cell - release enzymes and RER (latter giving basophilic appearance)
• Difference between pylorus and fundus of the stomach

  • Fundus & Body: Mainly involved in acid and enzyme secretion.
  • Pylorus: Functions in mucus production and hormone regulation, especially gastrin secretion.