§The digestive system is responsible for
breaking down food we eat into smaller components so that nutrients
can be easily absorbed by the body and the waste discarded.
§There are two types of digestion. Mechanical
digestion is the physical breakdown of large pieces of food into smaller pieces
through, chewing (mastication). While chemical digestion uses enzymes to break
down this food mass further into small molecules which the body can separate
§Saliva in our mouths plays a key role
in initial digestion by moistening the food to help with the mechanical chewing
and swallowing process. Saliva also contains an enzyme which starts the
chemical digestion of starchy foods.
§Our salivary glands produce around 1.5
liters of saliva each day!
§Bolus is the name of the small round
slurry mass produced for swallowing as a result of chewing and starch
§The pharynx, at the back of the throat,
has a flap of tissue called the epiglottis that closes during swallowing to
prevent food going down the trachea (windpipe).
§Once swallowed, bolus (food) travels
down through the oesophagus to the stomach, taking about 7 seconds to get
§Muscles in the oesophagus tighten and
relax to create a wave-like process called peristalsis which pushes food down
the small tube, which is why your food never falls back out if you happen to be
eating and swallowing upside down!
§Enzymes called proteases break
down proteins within the stomach and small intestine. While in saliva,
amylases break down carbohydrates and lipases break down fats.
§The adult stomach has a very small
volume when empty but can expand to hold up to 1.5 liters of food when full.
§The inner wall of the stomach secretes
hydrochloric acid to help kill bacteria and, along with proteases enzymes, aids
in the digestion of food. To protect itself from the corrosive acid, the
stomach lining must create a thick coating of mucus.
§Stomach rumblings (borborygmi) are
caused by wave-like muscular contractions (peristalsis) at the walls of the
stomach and small intestine. These are normal digestion movements, however the
process is louder and more noticeable when the stomach is empty as the sound is
§Some animals such
as cows, giraffes and deer have stomachs with multiple
compartments (not multiple stomachs as is commonly believed). While others like
seahorses, lungfishes and platypuses have no stomachs at all.
§The small intestine is composed of a
duodenum, jejunum, and ileum.
§Most of the digestion and absorption of
food nutrients actually takes place in the small intestine. The stomach passes
on a thick liquid called chyme and enzymes continue to break this down in the
small intestine which absorbs the nutrients into the blood stream.
§The pancreas secretes enzymes for use
by the small intestine.
§On average, the human adult male's
small intestine is 6.9 m (22 ft 6 in) long, and the female's 7.1 m (23 ft 4
§The large intestine includes the cecum,
appendix, colon, and rectum. It is the final part of the digestive system. It
absorbs water from the remaining indigestible food matter, and passes any
un-needed waste from the body.
§The large intestine is approximately
1.5 m (4.9 ft) long.
§The liver produces bile for the
digestive system and processes the nutrients.
§The gall bladder stores the bile used
to break down dietary fat.
§Your digestive system has its own