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The liver is the largest internal organ and gland in the body, and has the very important role of controlling the blood-sugar levels in our bodies. It ensures the body has enough energy levels, and does this by storing and releasing glucose into the bloodstream.
The main function of the liver is to convert the food we eat into energy that can be used by our muscles and organs. To fully understand how this is done, it is important to know what happens when food is digested, so I suggest you take a look at the intestines and how nutrients are absorbed into the bloodstream before reading on.

After eating a typical meal high in carbohydrates, the breakdown products (mainly glucose) are absorbed into the bloodstream via the walls of the small intestine. There is a vein, called the hepatic portal vein, which carries the glucose to the liver where one of a number of things may happen:

  • the glucose may be used by the liver to provide energy for the liver itself
  • it may be stored in the liver or muscles, as glycogen, for later use
  • it may continue to circulate in the bloodstream where it is readily available for organs and muscles to use as energy
  • too much glucose is converted to fat and stored around the body.

If the glucose levels in the blood drop below normal, such as when a person does exercise or doesn't eat for a long time, the glycogen stored in the body can be converted back to glucose, and used as a source of energy. This, however, is only a short-term energy supply, which provides glucose for body cells for only about six hours if no other supply is available. If more energy is required, the energy reserves in stored fat are tapped.

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Pancreas: The pancreas has two main functions:

  • Exocrine function: The pancreas excretes various fluids into the pancreatic duct. Daily, it produces between one and four litres of pancreatic juice, which is essential for the digestive process. It contains enzymes that help break down protein, fats and carbohydrates. 
  • Endocrine function: The pancreas is also a gland involved with the hormones insulin and glucagon.

Gall bladder: Bile is formed by the liver. It is stored and concentrated in the gall bladder.

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So, what exactly does the liver do?

The liver maintains the level of sugar, or glucose, in the blood. This glucose is a source of energy which can be used by our muscles and organs. We get this glucose from the foods we eat. If we eat too much, it is then converted to fat and stored around the body.

A person eats a meal and it is converted to glucose. The liver determines what will happen to it, according to the activity of the body and the blood sugar levels. It may get used by the liver, stored in the muscles, remain in the bloodstream, or stored as fat.

Then this person decides to go for a 10km run. What happens to their body? It requires more energy, because a lot of it is being used up during exercise. So the glycogen in the muscles is converted back to glucose, and this provides the muscles with more energy. However, this is not enough. This person is really busting a move! So, the energy stored in fat is converted back to glucose, and this is used by the muscles as energy. This is actually an example of homeostasis.

If a person eats more than they exercise, they become overweight. You could say they are putting more in than they are putting out. And if a person eats very little, but exercises a lot, they may become very skinny. They are putting more out than they are putting in.

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