How the Body Controls Its Calcium
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.
Evolutionary scientists, for their part, find skulls of different animals, which not only protect the brain from injury, but also have openings for the eyes, nose, and mouth. However, without considering what it takes to produce and maintain these structures, they claim that skulls arose unguided by purely natural processes, demonstrating the validity of Darwinian theory.
In the last few articles in this series, I have shown that the production and maintenance of the human skeleton requires multiple coordinated parts and process. It needs cells called osteoblasts and osteoclasts, the movement of calcium back and forth from the blood as the bone acts as a reservoir for the calcium needs of the body through its tissue fluid, and the presence of activated Vitamin D to bring in enough calcium from the gastrointestinal system. In addition, the body must have Ca++ ions in the blood for clotting. It needs calcium pumps in the cells to keep the Ca++ ion concentration of the cytosol ten thousand times less than the blood so it can signal proper nerve, gland, heart, and all other muscle function. When anyone looks at a skeleton, this is what they should know before they try to figure out where it came from.
But even that's not enough when taking into account how the bones relate to the body's calcium metabolism. For when it comes to life, real numbers have real consequences. Clinical experience teaches that not just any Ca++ ion concentration in the blood will do. It has to be the right amount. The normal blood level for calcium is between 8 to 10 units and if it rises above or drops below this range by more than 30 percent, the result is often lethal. So how does the body maintain control of its calcium?
As we've discussed in the past, the first thing you need to take control is a sensor that can detect what needs to be controlled. The cells of the four parathyroid glands that are embedded in the four corners of the thyroid gland have sensors that can detect the level of calcium in the blood.
The second thing you need to take control is something to integrate the data by comparing it to a standard, decide what must be done, and send out a message. When the calcium level in the blood drops, the parathyroid gland cells send out more parathormone (PTH) and when it rises they send out less PTH. Due to being broken down by enzymes, the metabolic effect of a given amount of PTH, like for most other hormones, only lasts several minutes, allowing the body to maintain moment to moment control.
The third thing you need to take control is an effector that can do something about the situation. The calcium blood level is determined by how much calcium moves in and out of the bone, how much is lost through the filtering of blood by the kidneys, and how much is brought into the body through the gastrointestinal system with the help of calcitriol (activated Vitamin D). Vitamin D is activated when the liver adds a hydroxyl group (OH) to its 25th carbon, followed by the kidney adding another one to its first carbon to produce calcitriol. If the kidney adds the OH to its 24th carbon instead, it results in an inactive form of Vitamin D.
PTH travels in the blood and attaches to specific PTH receptors on the bone cells and tells the osteoclasts to breakdown more bone to release more calcium and the osteoblasts to take in less calcium by making less bone. PTH also attaches to specific PTH receptors on the cells of the kidney tubules and tells them to take back more calcium from the urine that is presently in production. Finally, PTH attaches to specific PTH receptors on specialized cells in the kidneys and tells them to put OH on the first carbons of more 25 OH Vitamin D than on its 24th carbon, producing more calcitriol.
The combined effect of PTH is to increase the blood level of calcium by promoting its release from the bone, reuptake by the kidneys, and absorption into the body by the gastrointestinal system by increasing the production of calcitriol. When the blood level of calcium drops, the parathyroid glands send out more PTH to make the level rise back toward normal and when the level rises, they send out less PTH so it drops back toward normal. Due to the absolute need for the body to control its blood level of calcium, the absence of PTH or PTH receptors makes life impossible.
An abnormally high calcium level (hypercalcemia) is usually due to having too much PTH released by one or more of the parathyroid glands or widespread cancer. Since calcium is directly related to the development of bone, hypercalcemia can often result in weakening of the bone with increased pain and even fractures. Calcium also is connected with nerve function and hypercalcemia can cause anxiety, depression, and difficulties with concentration. This can progress to confusion, lethargy, coma, and death. Calcium is also important for heart function and hypercalcemia can cause rhythm disturbances and problems with heart function. However, one of the commonest problems encountered early on with hypercalcemia is the formation of kidney stones, because the increased blood calcium increases the amount of calcium in the urine, which can join with phosphate and come out of solution to form calcium phosphate crystals. This happens particularly when the person with hypercalcemia is dehydrated and is making very concentrated urine. For our earliest ancestors, this would have led to recurrent kidney infections and compromised kidney function.
An abnormally low calcium level (hypocalcemia) is usually due to low parathyroid gland function. This is often related to previous central neck surgery or radiation, severe Vitamin D deficiency, or chronic renal failure. Since calcium plays a major role in nerve and muscle function, the commonest early complaints of hypocalcemia are tingling and numbness of the hands and feet and around the mouth, in addition to muscle twitching and spasm. This can progress to seizures, difficulty breathing, and life-threatening cardiac rhythm problems.
The system the body uses to control its blood level of calcium requires calcium sensors on the parathyroid gland cells, the ability for these cells to produce PTH, properly adjusted release of PTH to the change in the calcium blood level, enzymes to limit the effect of PTH, and specific PTH receptors on the bone cells, tubule, and specialized cells of the kidneys. Without any one of these five components being present and doing what they're supposed to do, the whole system would fail and calcium control would be lost.
But for our earliest ancestors to have survived, like all other living creatures, not only would they have needed this irreducibly complex system but, in addition, it would have had natural survival capacity to make sure the blood level of calcium stayed within the right range. In other words, the systems the body uses must do the right thing at the right time and they must do these well enough to survive under the laws of nature. In any realistic perspective, this casts serious doubt on the idea that life came about by chance and nature's laws alone.
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