Sunday, April 3, 2011

The miracle of the tube

By Richard P. Holm, M.D.

By the 16th day after conception, the human embryo has grown into a hollow ball of cells. Then a fold develops on the underside of the sphere, and it pushes inward until the sides wrap around the bend and become a cylinder that starts at a primitive head and extends down to what looks like a tail.

The resulting pipe is called the primitive gut, and it is evolving into what later will become the mouth, esophagus, stomach, and both the small and large intestines. Eventually this tube will extend about 26 feet from lips to anus. During development, pouches budding out from this food tube will also form the lungs, liver, gallbladder, and pancreas.

Once the embryo fully develops and is born, the gastrointestinal (or GI) tract begins performing the marvelous act of digestion. When food is shoved into the mouth, it is gummed or chewed until the tongue pushes it down. Food is swallowed as a small ball – doctors call it a bolus – and it passes the entrance to the lungs where a fleshy a trapdoor called the epiglottis protects the lungs and helps move the food into the esophagus.

The esophagus is a toothpaste-tube-type apparatus that moves the bolus into the stomach. There, acid not only helps break down the food, but it also kills most of the microorganisms that enter with food. Now liquefied, food then moves into the small intestine where tiny, shag-carpet-like fingers provide a surface area that’s about the same size as a football field. All that space is needed, and those tiny fingers work together to absorb nutrients.

The leftover liquid material finally moves to the large intestine, or colon, and this organ works mainly to reclaim water. The colon also harbors colonies of good bacteria that work on the leftover material and produce an important vitamin. That vitamin subsequently is absorbed and the body uses it to prevent bleeding.

The tube from lips to anus may not receive the respect it deserves, but it is an engineering masterpiece that humbly nourishes our lives.

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