Digestion is the process by which

the gastrointestinal system

retrieves important nutrients for

the body, and chemically changes

the unused food into waste.

Mastication, or the chewing of food

in the mouth, is the first step

of digestion.

Saliva initiates digestion, and changes

the chewed food into a soft mass

or bolus.

Saliva makes the bolus slippery

making it easier to be swallowed and slide

down the back of the throat and esophagus.

The bolus passes through the

esophageal sphincter before it enters the

stomach.

Inside the stomach, hydrochloric acid is

released.

Breaking down large food molecules into

smaller ones, and liquifying the bolus.

The liquified bolus, now called chyme

then passes through the pyloric sphincter

and enters the duodenum,

the first section of the small intestine.

It is here that enzymes released from the

pancrease, liver, and gall bladder

further break down chyme into elements

that can be easily absorbed and used

by the body.

The small intestine is lined with a

heavily folded inter mucosa, and small

finger-like projections called villi.

The villi enable digested food to enter

the blood stream.

It is here in the small intestine

where all nutrients and vitamins are absorbed.

Chyme can travel through up to

20 feet of small intestine

before it passes through the ileocecal valve

to enter the large intestine.

Very little digestion occurs in the large

intestine.

Undigested chyme that enters the large

intestine is considered waste.

The waste becomes more and more solid

as it passes through the large intestine

because water is continuously being

re-absorbed from the waste.

Waste collects in the rectum, or

end of the large intestine, until the brain

signals for it to be expelled from the body.