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.

Visit a museum of natural history and you are likely to encounter a human skeleton or two. Next to them you might find an exhibit showing a famous paleontologist unearthing human bones from antiquity along with a commentary that confirms evolutionary biologists’ claim that life came about by chance and the laws of nature alone.

What you will not find is an explanation of the cellular and molecular basis for the bones you are looking at nor how they related to the calcium metabolism of the body in which they were housed. It would be like visiting the Kennedy Space Center and seeing all the different rockets there without an explanation of the ingenuity it took to build and launch them into space.

In the last two articles in this series, I showed that although bone is a solid tissue, it nevertheless has a dynamic metabolism in which cells called osteoblasts deposit calcium into the protein meshwork they lay down and others called osteoclasts remove it. Ninety-nine percent of the body’s calcium content is located in bone and 99 percent of that is in crystalline form. The remaining 1 percent of bone calcium is dissolved as Ca++ ions in the tissue fluid surrounding the bone cells. This bone tissue fluid is in direct contact with the circulation through the capillaries. This means that bones act as reservoirs for the calcium metabolism of the body.

As important as calcium is in helping to form the bones to protect the organs and provide attachment for muscles so we can breathe, move around, and handle things, it also works in the blood to help clotting and acts as a chemical signal within cells to bring about nerve, gland, heart, and all other muscle function. To accomplish the job of cell signaling, the Ca++ ion concentration in the cytosol must be in the order of ten thousand times less than it is in the fluid outside the cell. Just as the cell uses the sodium-potassium pump to maintain its proper chemical content, it uses the calcium pump to push Ca++ ions out to maintain this ten thousand-fold difference.

Now, don’t you think natural history museums should provide this sort of information about how life actually works and not just how it looks? After all, it isn’t rocket science.

So far we have seen how calcium can move in and out of the bone and other cells. In addition, since there are Ca++ ions dissolved within the blood, this means that they are filtered out of the body through the kidneys. What still needs to be explained is how the body gets the calcium it needs in the first place. Nobody ever tells us to be sure we take in enough sugar or salt. In fact, we’re usually told to be careful not to take in too much or else we’ll get fat and develop diabetes or high blood pressure. The gastrointestinal system readily absorbs all the sugar and salt we take in and deals with it later through various hormones and the kidneys. But that’s not the case for calcium. Without some sort of chemical assistance, the intestine can only absorb about 10 percent of the calcium it encounters, which is why we have to make sure we take in enough calcium to have strong bones. So what does the body need to help the gastrointestinal system bring in enough calcium so it can survive within the laws of nature.

Calcium is a mineral that is naturally present in foods like milk products, eggs, nuts, fruits, and green leafy vegetables. However, without Vitamin D, our earliest ancestors wouldn’t have been able to absorb enough calcium to build up their bones and survive within the laws of nature. Vitamins are essential chemicals that the body generally does not produce but are needed for certain metabolic reactions and must therefore be obtained from the diet or supplements. The body can make its own Vitamin D when exposed to sunlight. However, since Vitamin D deficiency can lead to significant debility and even death, we generally increase our intake through supplements and fortified foods such as milk, orange juice, and cereals. However, the Vitamin D we make ourselves and bring in from our diet does not help in the absorption of calcium from the gastrointestinal system until it becomes activated by the body.

Vitamin D, like iron and thyroid hormone, does not dissolve well in the blood and must attach to a specific carrier protein made in the liver to be transported throughout the body. The liver begins the activation process of Vitamin D by adding a hydroxyl (OH) group to its 25th carbon. Then it is transported to the kidneys, where another OH group is added. Depending on the calcium needs of the body, the OH is added to either the 24th carbon, keeping it relatively inactive or to the 1st carbon which activates it to become calcitriol. Calcitriol is activated Vitamin D which then attaches to specific Vitamin D receptors in the nucleus of the intestinal cells and signals them to absorb more calcium. In a normal diet, this can increase the calcium absorption from 10 to 30 percent and in ones with very low calcium up to 90 percent.

It is clear that the body’s ability to form strong bones and have the right amount of calcium inside and outside its cells is an irreducibly complex process, requiring several different properly working components. If you are comparing human and other animal bones to confirm the validity of Darwinism, shouldn’t you educate people about this as well?

But we aren’t finished yet! Even though we have explained how the calcium pump works to keep the Ca++ ion level low in the cell, how Vitamin D becomes activated and allows the gastrointestinal system to absorb enough calcium, and how the bone cells take calcium from or deposit it into its tissue fluid, we have not explained how the body controls its blood level of calcium. For it is a matter of life and death. That’s what we’ll look at next time.

Photo credit: Chedid [GFDL, CC-BY-SA-3.0 or CC BY-SA 2.5-2.0-1.0], via Wikimedia Commons.