Calcium's Role in the Body -- and a Note on the Origin of This Series
Howard Glicksman
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.
museum of natural history and you are likely to see human skeletons displayed next to those of other animals. Often, without any explanation as to the molecular and cellular structure of bone or its impact on calcium metabolism, this is intended to convince visitors that chance and the laws of nature alone are responsible for the origin of human life.
In contrast, visit a museum of science and technology and you are likely to see the remains of many different inventions, starting with the prototypes followed by the developmental models in between and ending with the most modern versions. Often, by explaining the science behind the technology, describing the intellectual hurdles that had to be overcome, and displaying the equations, calculations, and blueprints, they show the observer the ingenuity of the inventors.
About a dozen years ago I woke in the middle of the night with a thought. It was that if people understood what makes up bones and their relationship with the calcium metabolism and how it impacts their survival, they would cease to believe in the theories of evolutionary biologists and realize that we are the product of intelligent design. This series has resulted from that middle of the night awakening. The next several articles will put flesh to the bones of this skeletal notion.
We live in a world made from matter. Matter is made up of atoms and molecules that follow the laws of nature. All life is made up of atoms and molecules that are organized into cells. Our body has trillions of them. Calcium is a chemical element that is vital for life.
Everyone knows that we must eat food and drink liquids that contain calcium to have strong bones. Most people realize that it is the digestive system that brings calcium into the body and puts it into the blood so it can be used to build up the skeleton. Some people know that the digestive system controls how much calcium enters the body and that the kidneys regulate how much calcium goes out of the body through the urine. But what most people do not understand and appreciate is how, in addition to strengthening the bones, calcium plays a major role in clotting and heart, nerve, gland, and muscle function.
The body must make sure it has enough calcium, not only inside the bones, but within the blood and its cells too. Having the right amount of calcium in the right places is not as simple as eating food or drinking liquids that contain calcium. Nor is it as simple as having properly working digestive and cardiovascular systems, bones, and kidneys. Without the body's ability to
control the amount and location of calcium within it, life as we know it would be impossible. The proof of this is that when our body loses control of its calcium, we die. In other words, control is the key to life. But how does the body do it? Let's first look at the cellular and molecular structure of bones and their relationship with the calcium content of the body.
There are over two hundred bones in the human body. Look at a complete skeleton and you will see a skull, two clavicles, twenty-four ribs, a sternum, and the bones that make up the pelvis, the upper and lower extremities, and the spinal column. The bones provide support and protection for many important organs. The skull protects the brain, the vertebrae protect the spinal cord, and the ribs and sternum protect the heart and lungs from external injury. The bones also contain the marrow tissue that makes the blood cells, like red blood cells to carry oxygen, white blood cells to fight infection, and platelets to prevent bleeding.
The bones are the frame to which the muscles are attached by tendons. This allows us to breathe, move around, and manipulate things. There are many joints in the body where two or more bones come together that can be moved in one or more directions by muscular contraction. The bones in these joints are held together by strong bands of tissue called ligaments. In addition, where the ends of each bone meet, there is a specialized tissue called cartilage. Cartilage acts both as a shock absorber to cushion the bones within the joint and to reduce friction, allowing the bones to glide across each other smoothly. The upper body has the shoulders, elbows, wrists, and joints of the hands and the lower body has the hips, knees, ankles, and joints of the feet. There are many other joints between the vertebrae in the spinal column, both ends of the ribs,
and even the jaw and temporal bone so we can open the mouth to talk and eat.
Bone is a specialized connective tissue formed by living cells containing organic material and minerals. There are mainly two types of bone cells directly involved in the formation, growth, and turnover of bone. These cells live within the bone itself. To make bone, the osteoblast lays down a firm organic mesh, called osteoid, which is mainly made up of protein. It then mineralizes the osteoid by depositing calcium crystals into it. It is the calcium in our bones that gives them the strength to withstand the forces of nature, so if we fall, gravity usually won't shatter them like glass. The other bone cell is the osteoclast, which reverses what the osteoblast does by removing the calcium crystals and the osteoid from the bone tissue.
Although bone is a very solid and rigid material, it nevertheless has a very dynamic metabolism. All of the bones in the body continually undergo a process of turnover called remodeling. The osteoclasts break down bone and then osteoblasts build it back up again. The remodeling of bone usually involves anywhere from 5 to 20 percent of the body's total bone mass each year. The remodeling of bone is thought to allow the skeleton to adapt to ongoing changes in mechanical stress, from weight-bearing and multi-directional movements that take place with everyday activities. A person who leads a very sedentary life or is forced to remain in a chair or bed for prolonged periods of time may lose significant amounts of bone mass. In fact, astronauts have been shown to experience loss of bone mass as a result of prolonged weightlessness in space unless they undergo exercise programs. Despite its present knowledge of what happens during bone remodeling, medical science has a very limited understanding of what factors control this process.
About 99 percent of the calcium in the body is located within our bones. And about 99 percent of the calcium within our bones is in crystalline form called calcium hydroxyapatite. Because it's a solid, the calcium within these calcium crystals is not available to the rest of the body.
The remaining 1 percent of the calcium inside our bones is dissolved as calcium phosphate in the bone tissue fluid that surrounds the bone cells. The bone tissue fluid is in direct contact with the capillaries and in communication with the body through circulation. From the calcium phosphate dissolved in this pool of bone tissue fluid, the osteoblasts take calcium to make the calcium crystals needed for bone. Calcium is deposited in this pool of bone tissue fluid as calcium phosphate when the osteoclasts remove the calcium crystals from the bone. The body is able to supply the bone and itself with its calcium needs through this bone tissue fluid. In other words, through its tissue fluid and circulation, the bones act as a reservoir for the body's calcium metabolism.
Now that you understand the molecular and cellular structure of bone and its relationship with the body's content of calcium, you are ready to explore the roles that calcium plays within the fluid inside and outside the cell. Maybe natural history museums could better educate the public about the origin of life by adding what you've learned here about the relationship between bones and the calcium metabolism to their skeletal displays. Visitors might then see how
life actually works and not just how it looks.
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