Welcome to this edition of the First Aid Show.
Now, we have had the odd questions on how the human body works and one of the questions
we got asked recently was how does the digestive system work? In this edition, we are going
to have a brief look at what happens when you eat food. The digestive system is a complex system and
when running correctly is very effective in processing food to feed the body and get rid
of waste out of the body. Digestion is defined as the process where food is broken down,
ready to be absorbed into the bloodstream and distributed around the body. Food enters
the digestive system through the mouth, where it is broken down into small pieces as it
is chewed before swallowing. And then the food passes through the oesophagus into the
stomach and the small intestine where it is digested and absorbed into the bloodstream.
The small intestine has a very large surface area, as it is covered by very small finger-like
villi, which stick out to give the surface area. These are very thin, just about one
cell thick to allow nutrients to pass through them into the bloodstream quickly. Excess
water is absorbed back into the body in the large intestine. Any undigested food passes
out of the body through the anus. The liver and pancreas play an important part
in the digestive process, as the liver produces bile, which helps in digesting fats and oils.
The pancreas produces biological catalysts called digestive enzymes, which are used to
speed up the digestive process. Enzymes are not living things, they are special proteins
which are able to break down large molecules into small molecules. And there are so many
different types of enzyme, which break down different nutrients. Carbohydrate enzymes
break starch down into sugar, which actually starts in the mouth as saliva contains Amylase
which is a starch-digesting enzyme. Lipase enzymes are used to turn fats and oils into
fatty acids and glycerol. Digestion of fat is helped by bile; this is made in the liver.
Bile breaks fat into small droplets that make it easier for the Lipase enzymes to work.
The bile itself is not an enzyme. Protease enzymes are used to break down proteins into
amino acids. Digestion of proteins is assisted by the acid in the stomach, which also helps
to kill micro-organisms that may be in the food. Vitamins, minerals and water are already small
enough to be absorbed into the body without needing to be broken down in the digestive
process. The only thing the body cannot digest is dietary fibre, which is passed out of the
body. Fibre is important to encourage digestive transit through the body. There are lots of
bacteria in the digestive system; about half of the dry weight of faeces consists of bacteria.
Bacteria are important as they digest substances that cannot be digested, such as certain carbohydrates.
They produce some vitamins, such as vitamin K and vitamin B, and they reduce the chance
of harmful bacteria multiplying which may cause disease.