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 & Views is delighted to present this series, “The Designed Body.” For the complete series, see here. Dr. Glicksman practices palliative medicine for a hospice organization.

We live in a world made of matter that must follow the laws of nature. Our body consists of trillions of cells that are made up of atoms and molecules that must obey these laws as well. Nature demands that our cells have enough energy, and be provided with enough of the chemicals they need, to allow them to do what they need to do to survive. Moreover, since our body is a multi-cellular organism, where the survival of each cell is dependent upon others, our survival also requires that the function of our vital organ systems stay within specific limits. This means that our body must have mechanisms in place to take control of its internal environment so it can stand up to the laws of nature.

Remember that to take control in a military operation requires the coordinated activity of a reconnaissance team, headquarters, and the soldiers in the field. Similarly, to take control in the body requires that there be a sensor, to detect what needs to be controlled, an integrator, to receive the sensory data, analyze it, make a decision, and send out orders, and an effector, to receive the orders from the integrator and take appropriate action. One of the most important sets of molecules in the body that let it take control are the hormones and neurohormones. Here’s how they work.

Hormones are protein molecules that are sent out by specific gland cells into the blood to help regulate specific functions of the body. The hormones are chemical messengers sent out by gland cells just like the orders sent out by army headquarters. The gland cells have sensors on their surface that can detect how much of a specific chemical (for example, glucose) is present in the blood. So the gland cells have their own reconnaissance team that can detect a specific chemical (again, glucose) that the body must control to survive. The gland cells take the information from their sensors, analyze it, and then send the right amount of a specific hormone into the blood.

The gland cells act as the integrator, just like army headquarters, to send out orders to direct activities in the field. These actions, performed at a distance from the gland cells, are designed to achieve a specific goal: the control of a specific chemical so the body can stay alive. The hormones from the different gland cells travel in the blood to specific target organs to pass on their orders. The cells in these organs act as the effector, which, like the soldiers in the field, receive the orders and perform a specific action. This effect, at the direction of the integrator, helps to control the specific chemical (once more, in our example, glucose) that was sensed by the gland cells that sent out the hormone in the first place.

But hormone systems may take several minutes to get the job done, and sometimes the body has to act faster. For example, when it comes to managing falling blood pressure on standing up, causing dizziness that can lead to unconsciousness, the body must react much more quickly, usually within seconds, to maintain the blood supply to the brain. The force of gravity waits for no one.

Nerve cells can transmit messages much faster than gland cells, literally in a split second or two. Just like gland cells, nerve cells release chemicals, called neurohormones, that stimulate or inhibit muscles, glands, or other nerve cells. The neurohormones are chemical messengers sent out by nerve cells that are just like the orders sent out by army headquarters. Specialized nerve cells, located in strategic places in the body, have sensors on their surface to detect certain physical parameters (for example, blood pressure). In other words, the nervous system has its own reconnaissance team that can detect a specific physical parameter that the body must control to survive. The data from these sensory nerve cells is sent rapidly along nerves to the brain where it is analyzed. The brain then sends out other nerve messages to the target tissues.

The nerve cells in the brain act as the integrator, just like army HQ, sending out orders to direct activities in the field. These actions, performed at a distance from the sensory nerve cells, are designed to achieve a specific goal: the control of a specific physical parameter (again, blood pressure) so the body can function properly and stay alive. The specific messages from the brain travel along specific nerves that release specific neurohormones in the specific target organs to pass on their orders. The cells in these organs act as the effector, which, like the soldiers in the field, receive the orders and perform a specific action. This effect, at the direction of the integrator, helps to control the specific physical parameter (blood pressure) that was sensed by the sensory nerve cells in the first place.

However, army HQ must send out different orders to different soldiers telling them to do different things. So too, the body’s gland and nerve cells must send out different messages to different target cells to get different things done. And just as the soldiers can’t take just any message or do whatever they want, the target cells must respond to the right message and do the right thing. The way the body ensures that the right target cells receive the right orders, so they can do the right thing, is for them to have specific receptors.

The receptors in the target cells are proteins with a special shape that allows them to attach to specific molecules when they come in contact with them. Think of it like a key fitting into a lock. When the hormone from the gland, or the neurohormone from the nerve, locks on and attaches to its specific receptor, this tells the target cell to do something. And what the target cell does directly affects the specific chemical (for example, glucose) or physical parameter (for example, blood pressure) that the sensor in the gland or nerve cell detected in the first place.

If the body doesn’t have just the right level of, e.g., oxygen, or glucose, or water, or salt, or calcium, or red blood cells, or white blood cells, or blood pressure, or temperature, then it can’t stand up to the laws of nature and it dies. Moreover, each of the systems that allow the body to maintain control of these vital factors has their own sensors, integrators, and effectors. If any one of these three components were to be absent, or not functioning properly, then control of that vital factor would be lost and death could take place. This is the whole basis of medical practice.

Now that you understand what your body needs to do to overcome the laws of nature to live, grow, and work properly, let’s look at each of these vital chemicals and physiological parameters one at a time. Keep in mind that in order to take control, not only must your body have a sensor, an integrator, and an effector, it must also have what appears to be an inherent knowledge of what is needed for you to stay alive. For who among us, other than cooperating when prompted to do so, by breathing, drinking, and eating what we’re supposed to, can say that we are directly responsible for being able to survive in the world?

Image by Ministry of Information Photo Division Photographer [Public domain], via Wikimedia Commons.