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.

By only considering DNA and the molecules that derive from it, evolutionary biologists only talk about how life looks, not how it actually works within the laws of nature to survive. It’s like explaining how all the parts of the Saturn V came together as a functioning rocket without showing how it developed the capacity to overcome the Earth’s gravitational pull to boost the Apollo XI into space.

In previous articles in this series I have shown that life does not exist within a vacuum or in the imagination of evolutionary biologists, but within the laws of nature. Those laws state that heat is the transfer of energy from one object to another, whereas temperature is a measure of the random motion within an object or its internal energy. The body must control its core temperature because if it isn’t just right it can adversely affect enzyme function and the integrity of the plasma membrane and other cellular structures.

The core temperature is directly related to how much heat the body’s metabolism releases, whether at complete rest (basal metabolic rate, or BMR) or with activity, and how much heat it loses to, or gains from, its surroundings. The BMR represents the minimum amount of heat the body produces and is mainly controlled by thyroid hormone activity. The exact mechanism of how thyroid hormone affects the metabolism of the cell is as yet poorly understood. However, studies indicate that it binds to a specific receptor in the nucleus of all of the body’s cells to stimulate protein synthesis and cellular respiration, causing an increase in oxygen consumption and heat production.

We saw in a previous article that thyroid hormone production is controlled by the hypothalamus and the pituitary, both of which can detect its level in the blood. If the level is too low, the hypothalamus sends out more thyrotropin-releasing factor (TRF) and the pituitary sends out more thyroid-stimulating hormone (TSH). If it is too high, they send out less of the hormones. The more TRF is sent to the pituitary, where it attaches to specific receptors, the more TSH it releases, and vice versa. And the more TSH sent to the thyroid gland, where it attaches to specific receptors, the more thyroid hormone it releases, and the less sent, the less it releases. Clinical experience shows that the normal blood level for thyroid hormone is 60-140 units and for TSH, 0.4-4.2 units.

When your car isn’t working properly, you can appreciate why all the different parts must be present and in good working order for it to function right. The same can be said for your body. Medical science’s attention is usually brought to bear when the body is suffering from a condition that is affecting its ability to function properly. So, knowledge and appreciation for what thyroid function accomplishes in the body may best be viewed through the lens of dysfunction. Let’s look at what happens to the body when the real numbers regarding thyroid function don’t add up right.

Along with diabetes mellitus, diseases that affect thyroid function are one of the commonest endocrine disorders. In general, if the hypothalamus and pituitary are working normally, when the thyroid produces too much, or not enough hormone the blood level of thyroid hormone and TSH are outside the normal range. If the thyroid hormone level goes too low (hypothyroidism) there normally is a compensatory rise in the TSH as the pituitary tries to make the thyroid make more. And if the thyroid hormone level goes too high (hyperthyroidism) there normally is a drop in TSH, often approaching zero, as the pituitary tries to turn off the thyroid’s excessive production.

Hypothyroidisminvolves a major drop in the production of thyroid hormone. World-wide, the commonest cause is a deficiency in iodine which, like iron for hemoglobin, is an important element for thyroid hormone production. The normal daily intake of iodine is about 150 micrograms, but there are many areas in the world where it may be as low as 20 micrograms. Most developed countries add iodine to salt and flour to prevent deficiency. The commonest cause for hypothyroidism in these countries is Hashimoto’s thyroiditis, an autoimmune disease that produces antibodies that attack thyroid tissue, causing inflammation and tissue injury. Over time, as enough of thyroid tissue is destroyed, the thyroid gland is rendered incapable of producing adequate amounts of thyroid hormone to meet the body’s normal metabolic needs.

Hypothyroidism causes all of the cells in the body to function slower than normal, use less energy, consume less oxygen, and give off less heat. All of this results in a major drop in the basal metabolic rate and every organ in the body is affected. People with hypothyroidism usually experience weight gain, despite eating less than usual, severe fatigue, muscle weakness, dry skin, loss of hair, increased sensitivity to cold, constipation, a slower heart rate, and may even have problems with concentration, memory, and depression. A person with severe hypothyroidism may even develop myxedema in which all of the tissues of the body become swollen. If not diagnosed and treated in time, these people can slip into a coma. Congenital hypothyroidism takes place in about 1 in 4,000 newborns and if not quickly diagnosed and treated can lead to permanent growth problems and intellectual deficiency.

Hyperthyroidism involves a major rise in the production of thyroid hormone activity and the commonest cause is Grave’s Disease. This is also an autoimmune disease, but instead of causing inflammation and destruction of tissue, the antibodies stimulate the TSH receptors on the thyroid gland, making it produce more thyroid hormone. In this setting, the usual control mechanisms for thyroid hormone production are no longer working right, since the formation of these antibodies has nothing to do with the hypothalamus or the pituitary. Since these antibodies and their effect on the TSH receptors are not under hypothalamic and pituitary control, the thyroid gland becomes over-stimulated. This causes it to swell up and form a goiter and release increased amounts of thyroid hormone.

Hyperthyroidism causes all of the cells in the body to function faster than normal, use more energy, consume more oxygen and give off more heat. All of this, results in a major rise in the basal metabolic rate and every organ in the body is affected. People with hyperthyroidism usually experience weight loss, despite often eating more than usual, severe fatigue, muscle weakness, excessive sweating, nervousness, tremors, increased sensitivity to heat, diarrhea, and a faster heart rate that can sometimes lead to palpitations and life-threatening rhythm problems. Occasionally a person with hyperthyroidism may experience a thyrotoxic crisis where the core temperature rises above 105^oF (41^oC), and becomes confused, restless, and agitated which, if not diagnosed and treated can quickly progress to lethargy or a coma.

When it comes to thyroid hormone real numbers have real consequences. Not only is the total absence of thyroid hormone incompatible with human life, but for our earliest ancestors to have survived, not just any amount would have been sufficient. c The system the body uses to control the blood level of thyroid hormone demonstrates irreducible complexity. But, this article has shown that this is not enough for human life to survive within the laws of nature. Just like the systems the body uses to control oxygen, carbon dioxide, hydrogen ion, hemoglobin, iron, water, sodium, potassium, respiration, heart rate, and blood pressure, the one for thyroid function must have natural survival capacity, because it seems to know what the normal range is and then, using an irreducibly complex system, achieves it.

However, the control of thyroid hormone and the basal metabolic rate represents only one part of what the body must do to control its core temperature. After all, life is a dynamic process and the body must stay very active within an environment to which it can lose heat, or gain from it. In the next article, I will review what it takes for the body to control its core temperature and what happens when the numbers just aren’t right.

Image: Thyroid gland, by Uwe Gille [GFDL, CC-BY-SA-3.0 or CC BY-SA 2.5-2.0-1.0], via Wikimedia Commons.