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The Physiology of Insulin: The Poison of Plenty

example of physiology of insulin

 

Physiology of Insulin

The importance of diet has been an obsession of popular culture for many decades. However, amidst the passionate arguments that each health guru brings to the table, people fail to ask a simple question: how does the body burn fat? For example, all the weight watchers advocate low calorie diets. But does the body know how to count calories? By digging deeper into the biology, we must determine exactly what “language” the body speaks. This quest ultimately leads us to the ultimate solution: the physiology of insulin. 

Food and Hormones: The Language of Life

In order to understand why this is the case, we must first understand how the body sends messages to different organs. In essence, what “language” does the body speak in? Well, let’s think about it: what makes you tired, hungry, or happy? The correct answer is melatonin, ghrelin, and dopamine, respectively. In short: hormones are the messengers that carry commands that tell your body to do things. So, what hormone is associated with eating food? The answer is insulin. We need to understand the physiology of insulin.

Why Insulin?

The physiology of insulin explains why this hormone is essential for fat gain and loss. Essentially, whenever insulin is high in the blood, our body is constantly sending the message “store fat, there is enough food”. In order to accomplish this, our bodies have insulin receptors that tell fat cells to stop releasing fat due. This makes sense since high insulin usually means lots of energy is already present in the blood. Thus, when lots of food is coming in through the mouth, insulin stops the body from accessing fat, saving it for times of famine. This understanding of the physiology of insulin leads us to another question: if energy storage is essential for life, what stops us from eating to the point of death? This question brings us to the next character in our metabolic performance: leptin.

Feeling Stuffed…with Leptin

If you are reading this, odds are that you have experienced the feeling of being stuffed. I am talking about the feeling you get after eating a ton of food, where just thinking of eating something else makes you nauseous. This feeling may actually stay with you throughout the day and maybe even the next morning! If the body is an energy monger, this is a shocking development. An organism that needs constant energy to fuel the brain has natural eating limitations. How does the body send us this long term signal? 

The answer is leptin. This hormone is released when fat cells expand, telling the body that it is getting too fat. Why does the body limit how much we eat? The answer is because being too fat is not a survival advantage. After a certain point, excess fat will slow you down and affect the rest of your body in a negative way. Leptin thus counters insulin by lowering appetite and reducing the amount of sugar in the blood since the organism will not eat. This implies that less insulin will be needed when leptin is active.  Taken together, these two hormones create a negative feedback loop that maintains the body weight through appetite.

Now…back to the original question: what is the issue with calorie counting? 

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The Concentration Gradient: Transport of Molecules

examples of the concentration gradient

What is the Concentration Gradient?

We have discussed equilibrium in organisms through the topic of homeostasis. However, as per usual, the evolution of complex life derives its properties from fundamental laws of the universe. In this post, we will be discussing the force that is responsible for everything from nerve impulses to energy production: the concentration gradient.

The concentration gradient stems from the basic law of expansion that drives the universe. Instead of looking at expansion from a macroscopic view, we can see how it affects the chemical properties of molecules. These properties, in turn, are harnessed by living organisms to their advantage. This property enables almost every process in your body to occur. For example, let’s look at breathing.

The Physics of Breathing and Respiration

What is happening when you inhale? Your lungs are expanding, increasing the amount of space inside them. Because of this increase in volume, the surrounding air, constantly seeking to expand, moves to fill the new area. Once the air is inside the lungs, it interacts with the small blood vessels known as capillaries.

These capillaries are filled with carbon dioxide rich and oxygen poor blood. Once again both gases, seeking to expand, fill the space where there is less of its kind: the oxygen enters the blood as carbon dioxide leaves in an attempt to level off the concentration gradient and reach equilibrium. Essentially, equilibrium is the point where the law of expansion is exerting its maximum force on a system.

Circulation

Next, the blood is pumped by the heart to the rest of the body. So how does the heart pump blood? By contracting its chambers, the volume of the heart decreases. In order to make use of the space in the vessels, blood squeezes into the arteries with each beat. Upon reaching its destination, the oxygen and carbon dioxide swap near the cells as the try to bridge the concentration gradient and the blood travels back to the heart and lungs, restarting the cycle.

As you can see, the importance of this phenomenon cannot be overstated. So what is the concentration gradient? We know that every molecule in the universe wants to spread out as much as possible. This means gases will spread out to take up as much space as is given and things dissolved in water will be evenly distributed. In addition, large molecules have trouble following these rules because of barriers to expansion or due to counter-forces like gravity.

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