The stomach is an expanded section of the digestive tube between the esophagus and small intestine. It's characteristic shape is shown, along with terms used to describe the major regions of the stomach. The right side of the stomach shown above is called the greater curvature and that on the left the lesser curvature. The most distal and narrow section of the stomach is termed the pylorus - as food is liquefied in the stomach it passes through the pyloric canal into the small intestine.
The wall of the stomach is structurally similar to other parts of the digestive tube, with the exception that the stomach has an extra, oblique layer of smooth muscle inside the circular layer, which aids in performance of complex grinding motions. In the empty state, the stomach is contracted and its mucosa and submucosa are thrown up into distinct folds called rugae ; when distended with food, the rugae are "ironed out" and flat.
The image to the right shows rugae on the surface of a dog's stomach. Inheritance 5. Genetic Modification 4: Ecology 1. Energy Flow 3. Carbon Cycling 4. Climate Change 5: Evolution 1. Evolution Evidence 2. Natural Selection 3. Classification 4. Cladistics 6: Human Physiology 1. Digestion 2. The Blood System 3. Disease Defences 4. Gas Exchange 5. Homeostasis Higher Level 7: Nucleic Acids 1.
DNA Structure 2. Transcription 3. Translation 8: Metabolism 1. 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.
The contraction of this muscle helps to expel the contents of the gastric glands. The muscularis externa layer has three layers of muscle. An innner oblique layer , a middle circular and an external longitudinal layer. The contraction of these muscle layers help to break up the food mechanically. Now look at this eMicroscope showing the layers. This image may also be viewed with the Zoomify viewer. The structure of the oesophagus was covered in the topic 'oral'.
The oesophagus forms a junction with the stomach , which is called the oesophageo-gastric junction.
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