How
food can go from a sandwich and salad and be turned into the energy
needed to hit a home run is amazing. The food will pass through more
than 22 feet of tubing, be mixed with chemicals from four different
glands, be separated between useful and not useful elements and the
whole process could take more than 14 hours! Digestion really has
TWO missions:
1. Break
down the food we eat into parts so tiny, that the useful elements
of food can actually be absorbed into our bloodstream and sent throughout
our body.
2. Get rid
of any leftover parts of the food that our body can’t use.
Our digestive system goes through 9 basic
steps:
Teeth- Digestion starts here.
The job of the teeth is to start tearing and crushing the food down
into small enough pieces so that it can fit down our throats.
Saliva- The salivary gland in
located underneath the back of our tongue. It creates our saliva or
spit. This helps soften the food in the mouth so that it is easier
to swallow. Saliva is also the first of several chemicals that start
to break down foods into simpler forms.
Tongue-
The tongue is a muscle that works with the food and saliva to form
a "ball" that can be swallowed. Of course, the tongue also
contains taste buds that helps us tell the difference between salty,
sour, sweet, and bitter foods.
Esophagus- The esophagus is simply
a transportation tube from the mouth to the stomach. When we swallow,
what we are really doing is closing a trap door in our throat called
the epiglottis. This sends food down the esophagus and prevents
food from going down the trachea (or windpipe) and into our lungs.
Food moves down the esophagus using muscles not gravity.
Stomach- The first stop after
the esophagus is the stomach. Once the food gets to the stomach the
stomach uses chemicals to try to make the food tinier. These chemicals
are called gastric juices and the include hydrochloric acid and enzymes
(chemicals that break down food). The food is moved around in the
stomach and mixed with the chemicals for about 3 or 4 hours. When
it is done in the stomach, the food is now a cream-like liquid call
chyme. The food is still not small enough the get into our
blood stream and it has not provided the body with anything useful
yet. Now a valve at the end of the stomach opens sending the food
past the liver.
Liver/Gall Bladder- At this point,
our food is hit with more chemicals. The liver makes a chemical called
bile but bile is not stored in the liver. Instead it is stored
in the gall bladder. When the gall bladder mixes bile with our food,
it does an important job: breaking down the fat (from milk, butter,
cheeses) into tiny droplets. This fat will supply us with much energy
later.
Pancreas- The pancreas also adds
a digestive chemical as the food leaves the stomach. This digestive
juice works on breaking down the carbohydrates (from breads, potatoes,
etc.) and the proteins (from meats, cereals, peanut butter)
Small Intestine- The small intestine
is the real hero of the digestive system. The small intestine is a
tube that is about 22 feet long! This is where the real digestion
takes place. As the food passes through, it is mixed with the new
chemicals and soon our "food" is now digested small enough
to be put to use by the body. Along the walls of the intestine are
thousands of tiny fingers called villi.. Blood vessels (capillaries)
in the villi can absorb the tiny food molecules and send them off
to the rest of our body through the blood.
Large Intestine- Whatever the
body cannot put to use is sent to the large intestine. Many plants,
for example, contain cellulose which cannot be digested. The big job
of the large intestine is to remove water. Water has been necessary
up until now but it is no longer needed and in the large intestine
water is sent into the blood stream . Food spends about 12 hours in
the large intestine where it become feces and later leaves the body
through the anal opening when we go to the bathroom.
