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Visibly Human Health and Disease in the Human Body

The Digestive System

THE DIGESTIVE SYSTEM The gastrointestinal system breaks down the foods we consume into simpler substances in order to acquire essential nutrients that the body cannot produce on its own. The digestive process involves many specialized organs that include the mouth and teeth, stomach, gallbladder, spleen, pancreas, liver and small and large intestines.

Digestion begins in the mouth with mastication, in which the teeth chew and break up food into smaller pieces for easier swallowing. Saliva moistens food and contains digestive enzymes that initiate the chemical breakdown of complex food molecules into smaller, simpler molecules that the body can use, such as converting complex starches into sugars.

Food moves from the throat to the esophagus and the stomach via peristalsis. The peristaltic action slowly moves the chewed food (bolus) toward the stomach. If the food bolus is not chewed into smaller pieces it may block the airway (trachea) causing asphyxia (lack of oxygen).

The stomach is an expandable reservoir that holds food for further processing. Cells in the stomach release hydrochloric acid and pepsin that further break down complex molecules to simple molecules. The mucous lining of the stomach prevents the acid from harming the stomach wall.

Food empties into the small intestine, where the major part of digestion and nutrient absorption occurs. The duodenum comprises the first 10 to 12 inches of the small intestine which has a total length of approximately 18 to 21 feet and a diameter of 1 to 2 inches. In the duodenum, bile (produced in the liver and stored in the gallbladder) and digestive enzymes (produced by the pancreas) break down the complex carbohydrate, fat and protein molecules. The released nutrients, water, vitamins and minerals are absorbed through the intestinal wall by millions of tiny protrusions called villi.

normal stomach plastinated
Normal stomach, plastinated. .
NMHM 1998.0033.037
esophagus bolus
Asphyxiation due to bolus
Tongue (top) and trachea (bottom) showing a bolus (large piece of steak) obstructing the airway. The development of the Heimlich maneuver, a method of dislodging objects caught in the throat buy compressing the victim’s diaphragm, has reduced the number of deaths from choking. NMHM 1990.0003.768
Trichobezoar
Trichobezoar
This is a trichobezoar that was removed from the stomach of a 12-year-old girl who ate her hair for six years. The hair took the shape of her stomach. Trichotillomania is defined as the self-pulling of body hair. Hair is resistant to human digestion and when eaten excessively it can form a bezoar (undigested mass) in the stomach. M- 906252
mega colon
Megacolon
An abnormally enlarged colon may be a congenital or an acquired trait. Congenital megacolon is due to a functional loss of the nerves in a segment of the colon. Damage to the nerves that normally help pass undigested matter through the intestine results in obstruction and enlargement of the colon. Acquired megacolon may be associated with chronic constipation, leading to marked enlargement caused by obstruction. This megacolon was removed from a 19-year-old man with a history of constipation.
Leather Bottle stomach
"Leather Bottle" stomach (aka Brinton disease)
Thickening of the stomach wall caused by spread of scirrhous carcinoma. The lining of the stomach becomes rigid and inflexible. Other causes of this condition include syphilis and Crohn’s disease. AFIP 49460