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| stomach with digestion, but the liver, our largest and busiest organ, is even more important. People can survive without stomachs but no one survives without a liver. |
| The "small" in its name makes the small intestine sound insignificant, but this is where digestion really takes place. Food broken down by hydrochloric acid and stomach enzymes is completely transformed during its journey through this 23-foot tube by bile from the gallbladder and enzymes from the pancreas, releasing most of its nutrients to the intestine's blood-rich lining. What's left exits into the large intestine. |
| The large intestine absorbs water, excretes mucus and (under normal conditions) hosts large numbers of beneficial bacteria which complete the digestive process by absorbing some nutrients and releasing others. As food residue travels through the large intestine and its water is absorbed, it becomes more compact and is eventually expelled. When the diet is rich in fiber, the resulting stool is large, soft and easy to eliminate, taking harmful bacteria, toxins and other waste material with it. |
| Evolution and the Human Digestive Tract |
| Anthropologists tell us that human beings have been evolving for 4 million years. Even if theories of more recent evolution are correct, placing today's humans on the planet for only 50,000 to 75,000 years, it's obvious that our species evolved on a diet very different from our own. The first significant shift in human diet followed the agricultural revolution, when people domesticated plants, then animals. For the first time, a stable and reliable supply of food could be grown in one place, gradually shifting us from the truly omnivorous fare of nomadic hunter/gatherers, who had no choice but to eat whatever the earth provided, to the more selective diet of a settled people who produced more than they could eat. This made it possible to stay in one place and, even more important, to prevent starvation by setting the surplus aside for future use. Because grains store well, farmers developed effective methods for growing them and they became a staple |
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