How is fat generated in human body?

Bharat Kalluri / 2020-12-22

Biology is an interesting subject. Recently I've started to make an effort to understand how fat gets stored and why fat gets generated in our body. This is what I understood from my little research experiment.

Digestion

It all starts from eating. Raw food is chewed by the mouth and then sent through the oesophagus into the stomach. Stomach releases a bunch of chemicals (including HydroChloric acid, some enzymes etc.. ) to form a uniform mixture called chyme. This chyme is sent down to duodenum(the first part of the small intestine). Bile (from liver) and pancreatic juice (from pancreas) are mixed here, these work together here since the pH of the mixture is already high.

Now, this mixture of chyme, bile and pancreatic juice is sent down to the small intestines. Small intestines will aid in breaking down this mixture into simpler molecules. For example, Fat in your food breaks into glycerol and fatty acids. Proteins into amino acids and Carbohydrates into Glucose. These are then transferred into the blood stream by using Villi tubes of the small intestines. So essentially, small intestines exist so that they can give the mixture enough time to process and then push the processed results out into the blood (since they have a huge amount of surface area).

Regulation of Glucose levels. Understanding what is the role of Insulin and Glucagon

Now that the food is digested and pushed into the system. The Glucose levels in the body shoot up. The normal Glucose level for a human body is 80-120 milligrams/deciliter of blood. Since the Glucose levels are going up, the body decides to initiate the production of something which reduces the Glucose levels in the blood stream. This is where Insulin comes into play.

Insulin is a hormone whose job is to either convert Glucose into Glycogen (A temporary storage form of Glucose) or to make cells use Glucose.

Apparently when the cells need Glucose, they "signal" Insulin and Insulin attaches itself to the cell and in turn opens some receptor pathways to push the Glucose inside for cell energy. This is also called as Facilitated diffusion. This is one part of what Insulin does.

After some time, cells will reach a equilibrium and will not be requiring more Glucose. At this point, Insulin will start converting Glucose to short term storage. Glycogen. Glycogen now gets stored in liver and muscles. After some more time, all the Glycogen stores will be full and the cells no longer require new Glucose. Now Insulin starts converting the excess Glucose into lipids (fats). This is how fats are generated in our body.

These generated fats are stored in different places in the body like liver, thighs, abdomen, arms and legs etc..

There are pieces to this which I do not fully understand. Here are some questions I have

  • How does the body understand that the Glucose levels are in the safe zone of 80-120 mg/dl?
  • How do the cells "signal" for the production of Insulin when required?
  • How does Insulin understand that all the cells are satisfied and the blood Glucose levels are in the safe zone and then decide to convert Glucose into Glycogen?
  • How does Insulin understand that all the Glycogen stores (muscles, organs etc..) are saturated and the go into long term fat conversion mode for the extra Glucose in the blood?

I think there are deeper bio-chemical explanations which I do not fully understand as of yet. I will be looking into these topics sometime later.

The next part of the discussion could be around how fat burns during any intense work. I will explore that topic in another piece.

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