0:00:01.473,0:00:03.715
Digestion is the process by which

0:00:03.715,0:00:05.712
the gastrointestinal system

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retrieves important nutrients for

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the body, and chemically changes

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the unused food into waste.

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Mastication, or the chewing of food

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in the mouth, is the first step

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of digestion.

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Saliva initiates digestion, and changes

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the chewed food into a soft mass

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or bolus.

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Saliva makes the bolus slippery

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making it easier to be swallowed and slide

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down the back of the throat and esophagus.

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The bolus passes through the

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esophageal sphincter before it enters the

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stomach.

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Inside the stomach, hydrochloric acid is

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released.

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Breaking down large food molecules into

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smaller ones, and liquifying the bolus.

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The liquified bolus, now called chyme

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then passes through the pyloric sphincter

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and enters the duodenum,

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the first section of the small intestine.

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It is here that enzymes released from the

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pancrease, liver, and gall bladder

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further break down chyme into elements

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that can be easily absorbed and used

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by the body.

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The small intestine is lined with a

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heavily folded inter mucosa, and small

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finger-like projections called villi.

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The villi enable digested food to enter

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the blood stream.

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It is here in the small intestine

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where all nutrients and vitamins are absorbed.

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Chyme can travel through up to

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20 feet of small intestine

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before it passes through the ileocecal valve

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to enter the large intestine.

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Very little digestion occurs in the large

0:01:50.686,0:01:51.472
intestine.

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Undigested chyme that enters the large

0:01:54.620,0:01:56.613
intestine is considered waste.

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The waste becomes more and more solid

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as it passes through the large intestine

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because water is continuously being

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re-absorbed from the waste.

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Waste collects in the rectum, or

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end of the large intestine, until the brain

0:02:13.157,0:02:16.040
signals for it to be expelled from the body.