How does the metabolic system work?

Our bodies are complex, powerful machines. All machines need energy to do work. Every single cell in our body serves some function, and each cell needs this energy in order to fulfill their unique function. How we utilize this energy is through our metabolism; it is how we take the energy from the food we eat (and drink) and convert it into energy that our bodies can use. The main source of energy in the human body is glucose. 

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 Major players in the human metabolic system include: 

  • The gastrointestinal tract is a long, hollow tube with specialized sections that each serve different functions. It begins at the mouth and ends at the anus. The mouth manually breaks down food, the stomach begins to digest and chemically break down food, the small intestine finishes digesting and begins absorbing food, and the large intestine absorbs the final nutrients, water, and sends the waste to the anus for excretion. 
  • The pancreas provides the enzymes needed for the GI tract to digest different macronutrients. The pancreas also produces several essential hormones, two of which are glucagon and insulin. Glucagon is released when our blood sugars are low (when we are fasting). It tells our bodies that we need energy, and begins breaking down fat, muscle, and glycogen (the short-term storage form of glucose) to use for energy. Insulin is the opposite; it is produced when we are in a fed state. It tells our bodies that we are full, and to store the excess glucose (as glycogen or fat). 
  • The liver is a multifunctional organ. It stores and breaks down glucose (in glycogen or triglyceride form), produces bile (the fluid needed to absorb cholesterol), produces and breaks down proteins, manages the cholesterol, triglycerides and lipoproteins (transporters of fat) found in our blood, detoxifies, and stores several vitamins, among many other functions.
  • The gallbladder stores and excretes the bile that was produced in the liver. Bile is essential to digest and absorb fats. 
  • The thyroid produces T3 and T4, the hormones that affect the rate of our metabolism. 
  • The cardiovascular system delivers blood (with nutrients) to all of the cells in our body. The heart pumps the blood, the veins and arteries are the highways that deliver the blood throughout the body, and the capillaries disperse the blood to each individual cell. 
  • The hypothalamus receives the hormonal signals that alarm us when we are hungry or full. Leptin tells us that we are full and speeds up our metabolic rate. Ghrelin tells us that we are hungry and prompts us to eat; it also slows down our metabolic rate. 

When any of these major players are not working harmoniously, our metabolic health is affected. Non-alcoholic fatty liver disease, high LDL levels, plaque formation in the arteries, and insulin blockage of the leptin pathway are all examples of metabolic disharmony. 

Want to learn more? Check out What is Metabolic Syndrome and Why are Children Getting It?


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