It is in the mouth, that the Thanksgiving feast begins its journey through the
fabulous digestive system. It is here that the lips, cheeks and tongue,
carefully position the food that the teeth will chew. This chewing process
breaks up the food, this being a part of mechanical digestion. While the teeth
grind up the turkey and tasty stuffings, the salivary glands begin emitting
enzymes, these enzymes being contained in saliva. This saliva helps to dissolve
some foods, and adds mucus to make the food's passage through the digestive
system a little more "speedy". The saliva also attacks dangerous
microorganisms which enter the mouth. Saliva also contains an enzyme which helps
to break down carbohydrates into sugars. As the food is being ground and coated
with saliva, it's passed over the taste buds, which in turn send messages to the
brain. The brain uses this information to decide whether or not the food should
be swallowed. The food is then gathered into a ball, called a bolus, and it is
pushed down into the pharynx by way of the tongue. This bolus of
"Thanksgiving meal" is then passed down the esophagus, the esophagus
being a 24cm long tube which connects the pharynx and stomach. Lining the walls
of the esophagus are rings of muscle which contract in waves, pushing the bolus
down the length of the esophagus. At the base of the esophagus, where the
esophagus and stomach join, a thick ring of muscle called a sphincter, is found.
This sphincter acts like a valve, as it allows food to pass into the stomach but
does not permit it to pass back up through the esophagus. The stomach, which is
in the essence a large muscle sack, contains three sets of glands which produce
gastric fluids. One set produces mucus which coats the food, making it slippery,
and it protects the stomach walls from being digested by its own secretions. The
second set of manufactures hydrochloric acid, which aids in the
"break-down" of foods. In conjuction with hydrochloric acid, pepsin,
which aids in the "break-down" of protein into smaller polypeptides,
begins the process of protein digestion. The stomach's muscular walls move
around the "food" and mucus, mixing them with the gastric fluids
produced. The "food" becomes a pasty substances referred to as chyme,
after about 2 or 3 hours of grinding within the stomach. The pyloric valve, or
gateway between the stomach and small intestine, opens. The chyme contained in
the stomach is then forced down into the small intestine by a process called
persitalsis. The chyme is then forced along the entire 20ft of small intestine,
where the process of breaking down the "food", and taking out its
vitamins, minerals, etc., is continued. These vitamins and minerals will be used
throughout the rest of the body, once they have been placed into the
bloodstream. After making its way through the small intestine, the chyme is
passed on through the colon, or large intestine. The colon proceeds to remove
water from the chyme passing through it, reducing it into solid waste, or feces.
Again, through the process of persitalsis, the fecal matter is passed through
the colon, where it will then gather at the end of the colon, in rectum. Muscles
located in the colon prevent the feces from being released until it becomes
convenient for us to expel them from the body, by way of the anus.