DAE - Stomach and Accessory Organs Lesson

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Stomach and Accessory Organs

The stomach.

Although the mouth performed some minimal chemical digestion, this process really gets started in the stomach. The stomach is a sac-like organ of the alimentary canal connecting the esophagus to the first part of the small intestine (duodenum). While many people think that the stomach is located near the umbilicus (belly button), it is actually located on the left side of the abdominal cavity tucked under the liver and diaphragm. Two sphincters keep the contents of the stomach contained: the lower esophageal sphincter and the pyloric sphincter.  

Sonya "The Black Widow" Thomas weighs less than 100 lbs, but she has won numerous competitive eating contests. She was the first champion of the Nathan's Hot Dog Eating Content for Women, eating 40 hot dogs in 10 minutes.Even though the stomach is relatively fixed in place, it is a highly active structure continually changing position and size. Its thick muscular walls are able to contract and relax. This action moves food around and helps break it into smaller pieces. An empty stomach is approximately the size of a fist but can stretch to hold as much as 4 liters of food and fluid. This is more than 75 times its volume when empty!  

A person's size or body weight does not correlate to stomach size. Rather, when you eat greater quantities of food you stretch the stomach more than when you eat less. For example, even though Sonya "The Black Widow" Thomas weighs less than 100 lbs., she has won numerous competitive eating contests. She was the first champion of the Nathan's Hot Dog Eating Contest for Women, eating 40 hot dogs in 10 minutes.

Anatomy

There are four main regions in the stomach: the cardia, fundus, body, and pylorus.

 

The anatomy of the stomach.

Download the "Anatomy of the Stomach" note outline here Download here. Use the image below to fill in the diagram in the note outline.

The anatomy of the stomach.

Digestion 

A common misconception is that the stomach is the location where all digestion takes place. While water, salt, and simple sugars can be absorbed here, most other substances are broken down further in the small intestine before they are absorbed.  

The digestive anatomy at the cellular level.Mechanical digestion begins in the stomach when a bolus of chewed-up food enters through the esophagus through the lower esophageal sphincter. Within a few moments, a unique form of peristalsis called mixing waves occurs. These waves function to mix and soften the food with gastric juices to create chyme.

Gastric juices are responsible for chemical digestion within the stomach. These secretions occur when food enters the stomach causing the release of the hormone gastrin, but could also be triggered by just smelling, tasting, seeing, or thinking about food. Gastric juices include both acid and enzymes which are made by specialized cells found in the protective mucous membrane covering the entire stomach. Two main cells responsible for the creation of gastric juices are parietal and chief cells. Parietal cells produce gastric acid (HCl), while chief cells produce a precursor to pepsin (an enzyme that breaks down proteins) and gastric lipase (an enzyme that breaks down lipids). Up to 3 quarts of this digestive fluid is produced daily.

The mucous membrane functions to protect the stomach from the low pH of the acid. An ulcer can occur if the mucous membrane becomes damaged. Normally, ulcers heal on their own. However, some may become perforated, where a hole goes all the way through the stomach wall.  

The pyloric sphincter controls the opening between the stomach and duodenum. When the small intestine is empty, the muscle relaxes allowing small amounts of chyme to pass from the stomach into the duodenum. The contents of the stomach are emptied into the duodenum within 2 to 4 hours after eating a meal. Some types of foods take longer to process than others. For example, foods heavy in carbohydrates empty very quickly, while fatty foods take longer to process (6 hours or longer) since the enzyme for these macromolecules is found in the small intestine. Full digestion typically takes 24 to 72 hours from start to finish.

Review the anatomy of the stomach in the learning object below.

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