8 Stomach
Stomach overview:
After exiting the esophagus food enters the stomach, a J-shaped organ which lies between the esophagus and the entry of the small intestine in the upper left abdominal area.
The stomach is like a blender, grinding down ingredients into a smaller, more fluid liquid called chyme.
Its function is to receive the food bolus from the esophagus which enters through the lower esophageal sphincter (commonly known as the cardiac sphincter).
The stomach has several identifiable features, containing several folds of the mucosa layer, called rugae. Further, the stomach can be divided into 5 areas:
- Cardia-the top section (located the near the heart, hence the name cardia)
- Fundus-The rounded part under the diaphragm
- Body-The largest part just below the fundus
- Antrum-Lies beneath the body and stores food to be sent to the duodenum (we’ll get to that later)
- Pylorus-The very bottom and distal part of the stomach which contains the pyloric sphincter(which excretes food stuffs to the duodenum)
The image below represents the structural locations of the various parts of the stomach:
Stomach function
The stomach has several functions which we will cover briefly. The stomach’s main job is to break down foodstuffs mechanically through involuntary muscular contraction and chemically through enzymes.
Mechanically, the stomach breaks down food through rhythmic contractions known as peristaltic contractions. This is facilitated from the smooth muscle from the fundus to the pylorus.
Chemically the stomach produces several secretions from several types of cells to aid in digestion:
Note how there are no enzymes specific to breaking down carbohydrates. The process of breaking down carbs initiates in the mouth and continues in the small intestine. Yet another enzyme released in the stomach is gastric lipase which breaks down lipids.
Stomach Digestion:
Like the esophagus the stomach also facilitates digestion via peristalsis as depicted below. The stomach’s smooth musculature aids in this rhythmic contraction to churn food into chyme:
When food enters the stomach it should leave through the pyloric sphincter as an acidic, semi digested chyme.