有关大脑 part4 Hints: liquidizer enzymes hydrochloric acid small intestine bile 因音频不完整，最末句后三个单词是: tendency to twitch

The first scheduled stop is the stomach. It's essentially a biological liquidizer. Its lining is covered in delicate folds which allow it to expand with each mouthful. Inside a mixture of enzymes and hydrochloric acid start to digest your food. And very probably your dinner is still in there, it churns away for about four hours. Soon it will be released into your small intestine and at a cue from your brain, bile will be added. This will help you break down fats. You will be carrying tonight's dinner for about 24 hours, so I hope you liked it. When it does finally leave you, it will take around 25 grams of dead cells from your gut with it.
But don't worry, you are constantly replacing cells from head to toe.
Your brain is managing the body's workforce of approximately 50, 000 billion cells and most of them don't last more than a few years. Cells are constantly dying and being replaced by new ones. Up to a billion new cells for old every hour. What this really means is that most parts of your body are in fact a good deal younger than you are. But remarkably these cells aren't replaced and they are particularly special.Each one has a natural tendency to twitch.

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