Stomach Anatomy (Advanced)

The stomach is:

1. A storage area.
2. The site of mechanical and chemical breakdown of proteins.
3. Where food is rendered down to chyme before leaving the stomach.

Physical features of the stomach:

1. When the stomach is empty, it collapses its large longitudinal folds called rugae.

2. Food enters the stomach from the esophagus through the cardiac sphincter (gastroesophageal sphincter).

3. Chyme leaves the stomach through the pyloric sphincter into the small intestine.

4. The stomach regions are the fundus, body and pylorus.

5. The lateral surface of the stomach (convex side) is called the greater curvature.
 The medial surface of the stomach (concave side) is called the lesser curvature.

6. The peritoneum associated with the stomach is called the greater omentum. It comes off the greater curvature of the stomach. The lesser omentum comes off the lesser curvature of the stomach.

• The greater omentum is a double layer sheet. The potential space is filled with fat (for protection).
• It also contains a large collection of lymph nodules. An infection (peritonitis) causes the peritoneal coverings to stick together to keep the infection localized while the lymphatics work to address the infection.
• The portion of the greater omentum that connects the stomach and spleen is called the gastrosplenic ligament.
• The lesser omentum extends from the lesser curvature of the stomach to the liver and a portion of duodenum.

7. The stomach has the 4 basic tunics of the alimentary canal - the mucosa, submucosa, muscularis, serosa (except the muscular layer is modified).
      a) The mucosa has 3 layers: The top layer is epithelium is all columnar cells that produce lots of mucus. It is interspersed with gastric glands that produce digestive enzymes and other *specialized secretory cells (more below) and gastric pits that sink into the deeper layers and from which flows gastric juice. The middle layer is lamina propria made of loose connective tissue, smooth muscle and lymph tissues. The deep layer is muscularis mucosa made up of smooth muscle.
      b) The submucosa is dense connective tissue supporting blood vessels and lymphatic tissue.
      c) The muscularis layer, which is usually just a circular and longitudinal layer in the rest of the digestive tract, has amn additional third innermost layer of smooth muscle that runs obliquely. This allows the stomach to create mixing action for breaking food down.
      d) The serosa is the outer layer of the stoamch made up of serous membrane.

*Most chemical digestion occurs in the fundus and body of the stomach. The glands here have the following types of secretory cells.

• Chief Cells: The are found at the base of the gastric gland and produce pepsinogen (the enzyme that digests protein).
• Parietal Cells: secretes HCL to kill bacteria in food and makes it acidic for enzyme action. They also secrete intrinsic factor, which is a glycoprotein required to absorb Vitamin B12 in the small intestine.
• Mucous Neck Cells: found in the neck region of the gastric glands among the parietal cells, they produce alkaline mucus that protects the stomach wall from HCL.
• Enteroendocrine Cells: found in the pyloric region of the stomach, they secrete hormone-like products directly into the lamina propria which diffuse into the blood and regulate stomach secretions and contractions.

After reading about stomach anatomy and studying the diagram. Take the Stomach Anatomy - Short Answer Quiz.