Editor’s note: Physicians have a special place among the thinkers who have elaborated the argument for intelligent design. Perhaps that’s because, more than evolutionary biologists, they are familiar with the challenges of maintaining a functioning complex system, the human body. With that in mind, Evolution News is delighted to offer this series, “The Designed Body.” For the complete series, see here. Dr. Glicksman practices palliative medicine for a hospice organization.

Just like a car needs the energy, in the form of gasoline, to run properly, the body needs the energy in glucose to survive. When we haven’t eaten for a while, our blood glucose level drops and our stomach is empty, causing the hunger center in our brain to tell us to eat or drink something with calories. As I have explained in my last couple of articles, the complex molecules that are in what we eat and drink enter the gastrointestinal system, where digestive enzymes break them down into simpler molecules so the body can absorb them. Carbohydrates are broken down into simple sugars, like glucose, which are then absorbed into the blood. Tissues, such as the brain and other organs, rapidly absorb some of this glucose, to be used for their immediate energy needs.

However, the amount of glucose absorbed after a meal is usually much more than what the tissues can use right away, causing excess. The body is able to chemically link these excess glucose molecules together to form a carbohydrate called glycogen. Most of the glycogen in the body is made and stored in the liver, with smaller amounts in the muscles, kidneys, and other tissues. Once the liver and other tissues have filled up their glycogen stores, any excess glucose is stored as fat, apparently without limit. These tissues can use this stored energy in between meals, during exercise, and fasting overnight, when there aren’t any new supplies of glucose coming into the body. However, the brain cannot store glucose and is mostly dependent on the glucose in the blood for all of its energy needs.

One way the body makes sure the brain receives enough glucose during fasting is to have the liver release glucose from its glycogen stores into circulation. The liver has the capacity to store enough glucose to meet all of the body’s energy needs for about 24 hours. In addition, when necessary, the liver can take certain proteins and fats and convert them into glucose and other molecules, called ketones, that the brain can use for energy as well. This is partly why we don’t have to eat food as often as we have to breathe or drink water. But clinical experience teaches that not just any blood level of glucose will do for human survival. Real numbers have real consequences and the brain always needs a certain amount of glucose. Even though the body may be physically at rest, the brain is always working hard. It must keep us awake, monitor what’s going on inside and around us, and control vital functions like breathing and circulation.

Between meals, the blood glucose level usually runs between 70-90 units. Several hours after we eat, when the blood glucose level starts to drop towards 70 units, our hunger center warns us to eat something. If the blood glucose drops below 50 units, symptoms of brain malfunction, like weakness, dizziness, and problems with concentration occur. If it drops below 40 units, you’ll probably start experiencing problems speaking, confusion, and drowsiness. Below 30 units, seizures and coma result, and below 20 units, brain death is certain. Being able to control the blood glucose is important for human survival and it doesn’t just happen because we eat and drink things that have sugar in them. It requires the body to know when to store glucose and when to release it so the brain is always receiving what it needs. Here’s how the body does it.

As we’ve seen in this series, the first thing you need to take control is a sensor that can detect what needs to be controlled. The pancreas is not only an exocrine gland that, as noted in the previous articles, sends fluid containing various chemicals and enzymes into the intestine to help digest food. It is also an endocrine gland that sends hormones into the blood to help control the blood glucose. Scattered throughout the pancreas are small clumps of cells that make up what is called the islets of Langerhanswhich perform this endocrine function. These cells have glucosensors,allowing them to detect the blood level of glucose.

The second thing you need to take control is something to integrate the data, decide what needs to be done, and then send out a message. There are two different types of gland cells in the islets of Langerhans that together control the blood glucose. One is the beta cell,which sends out a hormone called insulin,made up of 51 amino acids joined together in a specific order. After a meal, the more the blood glucose rises above 70 units (it normally peaks at about 110 units), the more insulin the beta cells release into the blood. However, several hours after eating, as the blood glucose drops toward 70 units and below, the beta cells reduce the levels of insulin they send out. The other cell is the alpha cell, which sends out a hormone called glucagon,made up of 29 amino acids joined together in a specific order. Several hours after a meal, when the blood glucose drops toward 70 units and below, the more glucagon the alpha cells send out and after a meal, the more the blood glucose rises above 70 units, the less glucagon the alpha cells send out.

As you can see, both the beta and alpha cells have glucosensors, but they respond to changes in blood glucose in opposite ways. Normally, the higher the blood glucose rises above 70 units, the more insulin the beta cells send out and the less glucagon the alpha cells send out. And when the blood glucose drops toward 70 units and below, the less insulin the beta cells send out and the more glucagon the alpha cells send out.

The third thing you need to take control is an effector that can do something about the situation. After a meal, the blood glucose rises because the amount of glucose brought into the blood is more than what the body can use right away. As noted above, the beta cells react to this rise in blood glucose by sending out more insulin. Insulin travels in the blood and locks onto specific receptors within target organs, especially the liver, and tells them to absorb glucose for energy and store what is left over. In general, insulin is an anabolic hormone, e.g. it promotes the formation of more complex molecules from simpler ones. Not only does insulin promote the formation of glycogen from glucose in the liver and muscles, it also tells some cells to take in amino acids to form proteins and others to take in fatty acids to form fats. In other words, insulin tells the body “We’ve just been fed and we’ve got more than we need right now. Store up the excess for later use.”

In contrast, several hours after a meal, the blood glucose falls as the body takes glucose out of the blood and uses it for its energy needs without new supplies coming in through the gastrointestinal system. As I noted, the alpha cells react to this drop in blood glucose by sending out more glucagon. Glucagon travels in the blood where it locks onto specific receptors on target cells, mainly in the liver, and tells them to release the glucose from within glycogen and other forms of stored energy. In general, glucagon is a catabolic hormone, which promotes the breakdown of more complex molecules into simpler ones. Not only does glucagon cause glucose to be released from the glycogen stores, it also tells cells to break down certain proteins and fats into glucose and ketones, so the brain can be use them for energy. In other words, glucagon tells the body “We haven’t been fed for a while. Release the energy we stored up before.”

Once again, you can see that insulin and glucagon order the liver and other cells to do things that are opposed to each other. Insulin tells the body when it is fed and must take glucose out of the blood and store it in the liver and fat cells for later use. Glucagon tells the body when it is in starvation mode and must release glucose and other chemicals from the liver and fat cells into the blood so the brain will have enough energy. It is important to note that due to the breakdown by enzymes, the metabolic effect of a given amount of insulin or glucagon only lasts a few minutes and along with the ratio of insulin and glucagon this allows for moment-to-moment blood glucose control within the body.

There are twenty different amino acids that make up the proteins in the body. Since insulin consists of 51, and glucagon, 29 amino acids arranged in a specific order, this means that the chances of one molecule of each of them coming into being at random is one in 10⁶⁶ for insulin and one in 10³⁸ for glucagon. It was this extremely high improbability of any one of the thousands of biologically significant molecules, such as insulin and glucagon, being formed by chance and the laws of nature, which alerted scientists that the cells must have an intelligent agent telling them how to make them.

This is what first motivated scientists to search for and find the DNA molecule. However, paradoxically, evolutionary biologists see all of the information packed into the DNA molecule and still conclude that it all came about by chance and the laws of nature alone rather than through a mind at work. In other words, scientists, using their ability to detect intelligence, recognized that there had to be an intelligent agent inside the cell instructing it on how and when to produce these complex and vital molecules, but after finding it, concluded that this intelligent agent itself had come about by chance and the laws of nature alone.

Alternatively, many people now believe nature itself was the intelligent agent that, through evolution, brought about DNA and all of the innovations needed for life, because that was what was needed. They seem to forget that, by definition, evolution, as defined by its modern Darwinist proponents, is a blind process that has no goals.

By taking control to follow the rules,the system the body uses to control its blood glucose, involving insulin and glucagon, seems to know what it’s doing. But, as noted above, regarding having too low of a blood sugar, real numbers have real consequences. Next time, we’ll look at what can take place when the system isn’t working right and the body experiences too high a level of blood sugar instead.

Image credit: © Monkey Business / Dollar Photo Club.