The human digestive tract seamlessly adapts to any of the wide variety of foods that people eat. It has evolved to break down foods into their component nutrients and excrete waste efficiently. With many different organs playing a role in digestion, the humble digestive tract is actually a complex system.
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Sterile Before Birth
The bacteria that populate the digestive tract and help in nutrient absorption are not present in the fetus. Babies acquire bacteria from the mother and the environment during birth and in the days after being born.
Outside the Body
Technically, the digestive tract is not inside the body but outside the body. It is considered a canal that allows food in and waste out, but the food has to pass through the digestive wall to get into the body proper.
Liver-Esophagus Vein Connection
Veins that take blood from the digestive organs to the liver can back up the liver has a problem. These liver veins also connect with veins in the esophagus. When liver problems cause a backup of blood, the esophageal veins swell and may burst, causing severe bleeding.
Sonic Hedgehog Gene
Human embryos have a simple digestive tube before the various parts of the digestive system develop. The oddly named sonic hedgehog gene is the driving force behind the development of the primitive digestive tube into the various digestive organs. This gene cues the activation of a variety of other genes in different parts of the primitive digestive tube.
Taste Ability Varies
The taste buds in the mouth vary in concentration among people. According to the medical textbook "Histology," 25 percent of people are "supertasters," with lots of taste buds. Another 25 percent are "nontasters," with a reduced ability to discriminate among certain tastes.
Frequent Gas Expulsion
Gas in the digestive tract comes from swallowed air and bacterial production. Some swallowed air is absorbed in the intestine. Passed gas, or flatus, is a mixture of nitrogen, carbon dioxide, hydrogen and methane. People normally pass gas up to 20 times per day, according to the medical text "Kumar and Clark's Clinical Medicine."
The stomach has sensory receptors that send information through the vagus nerve to the brainstem, the bottom part of the brain. If the information indicates the presence of toxins, the brainstem triggers nausea and vomiting.
The salivary glands in the mouth produce approximate 1.2 liters of saliva daily, according to "Histology." In addition to lubricating the mouth, saliva also contains enzymes that break down starches and kill certain potentially dangerous bacteria. It also provides calcium and phosphate to keep the teeth strong.
Esophageal Lining Changeable
The cells lining the esophagus differ from those lining the stomach, as stomach cells must protect against acid. Severe gastroesophageal reflux disease, which causes stomach acid to repeatedly gets into the esophagus, can stimulate the cells of the lower esophagus to change into cells like those of the stomach lining as a protective mechanism.
Bacteria May Cause Inflammation
A 2013 review in the journal "Pediatric Gastroenterology, Hepatology and Nutrition" states that the various types of bacteria in the intestine influence certain types of immune system cells. Research is ongoing to determine possible ways that digestive system bacteria might contribute to the development of certain diseases, such as inflammatory bowel disease.