I learned this today. Our bodies make energy from food by breaking it down and converting the chemical energy that is stored in it.
Our bodies need energy to move and to exercise, but we also need energy just to live. Even when we think we are perfectly still, our bodies are burning energy so that we can breathe, our cells can carry out their functions, our hearts can pump blood, our bodies can maintain their temperature, and our brains can think. Our brains use more energy than any other muscle in our body, up to 20% of the body’s total energy consumption. This energy usage is called the base metabolic rate. It is the number of calories you burn just performing life-sustaining functions. This rate varies depending on gender, age and body size.
What do we mean by energy? The energy that our cells use comes from a molecule called adenosine triphosphate (ATP). All of our cells need ATP to work. If you want to pick up a pencil, your muscles, your brain, and every other cell in between need ATP to make it happen.
ATP is needed by cells because it is able to store potential energy in its phosphate bonds. In our cells, there is an enzyme called ATPases that breaks the ATP down into Adenosine Diphosphate (ADP). When this happens, the potential energy that is stored in the ATP is released and your cells can use it to do work.
We are able to make ATP from carbohydrates, proteins, and fats. The first step is to get these things into our bodies. When you eat something, you chew it and your saliva starts to break down the starches and helps wash the chewed food down into your stomach. In your stomach, the food is mixed with digestive juices. These juices are produced by glands in the stomach, and they contain acid and enzymes that break down the food.
The dissolving food then passes into the small intestine where it mixes with juices from the stomach and with juices from the pancreas, liver, and intestines. The digestive juice from the pancreas breaks down carbohydrates, fats, and proteins. The digestive juice from the liver is called bile and breaks down fats and some vitamins. The food breaks down even further as it moves along the small intestine and the large intestine. The walls of the intestines absorb fluid that contains minerals and nutrients from the food mixed into it. These minerals and nutrients pass straight into the blood stream.
When the carbohydrates are broken down, they become glucose, which our bodies can use or store. The body needs insulin to move the glucose out of the blood stream. If there is no insulin, for example in people with diabetes, the glucose will stay in the blood, pushing blood sugar levels to dangerous heights.
Insulin is made in the pancreas, and it travels round the blood telling the glucose where to go. Each cell has an insulin receptor, and when insulin attaches to this, it tells the cell to draw glucose out of the bloodstream. As more of the glucose moves from the blood into cells, the blood sugar level starts to drop, and insulin production slows down. Insulin aims to keep blood sugar at between 70 and 140 milligrams per deciliter.
Once the insulin has got the glucose into a cell, a process called aerobic metabolism starts. This is where oxygen is drawn into the cell and used to burn the glucose into heat energy and ATP. The energy in the ATP can then be used by the cell.
This is how our food becomes energy, but often we eat far more energy than we need. When that happens, our body has two ways of dealing with it. It can expel it or store it. Sometimes, if the blood sugar level is too high, the kidneys will try to expel the glucose and make you urinate more. That is one of the reasons why you feel thirsty if you eat a lot of carbohydrates.
However, the energy is more likely to be stored. Insulin can turn the glucose into larger packages of glucose that are called glycogen. Glycogen can be stored in the liver and the muscles. Your body can also store this excess energy as fat. We have specialized fat cells called adipose tissue that are basically huge stores of energy. We hate the way they make us look, but we’d be grateful for them if we got lost in a forest for a week.
So, we eat food, break it down into nutrients and sugars, convert the sugars to glucose, insulin tells the cells to absorb the sugars, which are then converted into ATP to release their stored potential energy. And that is what I learned today.
Photo by Jonathan Borba: https://www.pexels.com/photo/hamburger-and-fries-photo-2983101/
Sources:
https://www.metabolics.com/blog/how-does-the-body-produce-energy
https://www.livestrong.com/article/444740-how-does-the-food-we-eat-actually-give-us-energy/
https://www.universityworldnews.com/post.php?story=20130509171737492
https://en.wikipedia.org/wiki/Adenosine_triphosphate
https://www.lion.co.jp/en/oral/role/03.htm
https://www.niddk.nih.gov/health-information/digestive-diseases/digestive-system-how-it-works
https://www.livestrong.com/article/25939-glucose-provide-energy/