Lingual lipase then begins breaking down triglycerides into free fatty acids, and mono- and diglycerides. The breakdown of protein begins in the stomach through the actions of HCl and the enzyme pepsin. During infancy, gastric glands also produce rennin, an enzyme that helps digest milk protein. Its numerous digestive functions notwithstanding, there is only one stomach function necessary to life: the production of intrinsic factor. The intestinal absorption of vitamin B 12 , which is necessary for both the production of mature red blood cells and normal neurological functioning, cannot occur without intrinsic factor.
People who undergo total gastrectomy stomach removal —for life-threatening stomach cancer, for example—can survive with minimal digestive dysfunction if they receive vitamin B 12 injections. The contents of the stomach are completely emptied into the duodenum within 2 to 4 hours after you eat a meal. Different types of food take different amounts of time to process. Foods heavy in carbohydrates empty fastest, followed by high-protein foods.
Meals with a high triglyceride content remain in the stomach the longest. Since enzymes in the small intestine digest fats slowly, food can stay in the stomach for 6 hours or longer when the duodenum is processing fatty chyme. However, note that this is still a fraction of the 24 to 72 hours that full digestion typically takes from start to finish.
The stomach participates in all digestive activities except ingestion and defecation. It vigorously churns food. It secretes gastric juices that break down food and absorbs certain drugs, including aspirin and some alcohol.
The stomach begins the digestion of protein and continues the digestion of carbohydrates and fats. It stores food as an acidic liquid called chyme, and releases it gradually into the small intestine through the pyloric sphincter. Answer the question s below to see how well you understand the topics covered in the previous section.
Skip to main content. Module 7: The Digestive System. Search for:. The Stomach Learning Objectives By the end of this section, you will be able to: Label on a diagram the four main regions of the stomach, its curvatures, and its sphincter Identify the four main types of secreting cells in gastric glands, and their important products Explain why the stomach does not digest itself Describe the mechanical and chemical digestion of food entering the stomach.
Watch this animation that depicts the structure of the stomach and how this structure functions in the initiation of protein digestion.
This view of the stomach shows the characteristic rugae. What is the function of these rugae? Critical Thinking Questions Explain how the stomach is protected from self-digestion and why this is necessary. Describe unique anatomical features that enable the stomach to perform digestive functions. Show Answers The mucosal barrier protects the stomach from self-digestion. It includes a thick coating of bicarbonate-rich mucus; the mucus is physically protective, and bicarbonate neutralizes gastric acid.
Epithelial cells meet at tight junctions, which block gastric juice from penetrating the underlying tissue layers, and stem cells quickly replace sloughed off epithelial mucosal cells. The stomach has an additional inner oblique smooth muscle layer that helps the muscularis churn and mix food.
The epithelium includes gastric glands that secrete gastric fluid. The gastric fluid consists mainly of mucous, HCl, and the enzyme pepsin released as pepsinogen. The lesser and greater curvatures are on the right and left sides, respectively, of the stomach. The mucosal lining of the stomach is simple columnar epithelium with numerous tubular gastric glands. The gastric glands open to the surface of the mucosa through tiny holes called gastric pits.
Food can stay in the stomach for 2 hours or more. Food is broken down chemically , by gastric juice , and mechanically , by contraction of the three layers of smooth muscle in the muscular externa layer. The broken up food at the end of this process is called chyme. Gastric juice is secreted by gastric mucosal glands , and contains hydrochloric acid, mucu s, and proteolytic enzymes pepsin which breaks down proteins , and lipase which breaks down fats. When the stomach is empty, and not distended, the lining is thrown up into folds called rugae.
After eating, these folds flatten, and the stomach is able to distend greatly. The pyloric region ends at the pyloric sphincter. This sphincter relaxes when the formation of chyme is completed, and the chyme is squirted into the duodenum. When you've worked through the three regions of the stomach, test your knowledge. This shows an image through the wall of the body of the stomach at low power. You should be able to identify the three major layers seen here - the mucosa, submucosa and muscularis externa.
The mucosa is full of gastric glands and pits, and there is a prominent layer of smooth muscle - the muscularis mucosa. Mucous Neck Cells or Foveolar Cells —. They are smaller in size compared to the surface mucus cells having round nuclei and apical secretory granules.
These cells are involved in the secretion of mildly alkaline mucus which is different from the mucus secreted by the epithelial mucus cells. They are found in the isthmus and neck of the glands. Stem Cells —. They are found in the isthmus or neck of the gland. These cells are involved in the replacement of damaged cells. Parietal Cells or Oxyntic Cells —. These cells are round, large, or pyramidal in shape having rounded nuclei at the center. Oxyntic cells secrete Hydrochloric acid HCl which is the most important component of gastric acid, that activates other enzymes.
These cells also secrete intrinsic factors which helps in Vitamin B12 absorption. These are highly acidophilic that is, they stain pink colour.
They are found in the Fundic glands and the walls of the tubes. Chief Cells or Zymogenic Cells —.
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