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Thyroid and Parathyroid Hormones

January 24, 2022

The thyroid gland releases triiodothyronine (T3) and thyroxine (T4). These hormones play an important role in regulation of your weight, energy levels, internal temperature, skin, hair, nail growth, metabolism and is an important part of the endocrine system. 

Although it gets less attention than thyroid hormones, the parathyroid hormone is still important in the body. Parathyroid hormone is connected to blood calcium levels in the bones, intestines and kidneys. Parathyroid hormone comes from four parathyroid glands in the neck, just behind the thyroid. These glands receive feedback from blood calcium levels to determine when they need to secrete the hormone. The hormone plays a role in regulating blood calcium levels, helping the body maintain adequate calcium stores in the bloodstream to protect bone health.

Calcitonin is a hormone that the C-cells in the thyroid gland produce and release. It opposes the action of the parathyroid hormone, helping to regulate the blood’s calcium and phosphate levels. Calcitonin works to control calcium and potassium levels. It does this by inhibiting the activity of the osteoclasts, the cells that break down bone. When the osteoclasts break down bone tissue, the calcium enters the bloodstream. By preventing the breakdown of bone, calcitonin lessens the amount of calcium in the blood. The hormone also seems to decrease the amount of calcium the kidneys can re-absorb, lowering levels further.

Secretion of this hormone is controlled directly by the blood’s calcium levels. When the levels start to increase, the body responds with increased calcitonin levels. When calcium levels drop, so do calcitonin levels.

What can go wrong with calcitonin?

Calcitonin is a unique hormone, because its importance is not well known. While doctors know what it does, they do not understand why we have it, and few symptoms occur if levels are high or low. The body appears to function normally, even with high or low levels of this thyroid hormone. In fact, patients who have had their thyroids removed will have virtually no calcitonin levels, but they show no resulting symptoms.

Sometimes high calcitonin levels can point to a rare type of medullary thyroid cancer. This cancer, which starts in the C-cells, can be connected to multiple endocrine neoplasia type 2b and multiple endocrine neoplasia type 2a. However, the calcitonin levels do not cause the cancer.

If you have blood work done that indicates high or low calcitonin levels, you may wish to talk to your doctor about the problem to determine if there is an underlying cause or issue with your thyroid. Specifically, if your levels are high, consider asking why or requesting further testing to rule out cancer. Otherwise, high or low calcitonin levels have little affect on your overall health. Still, if you have concerns, talk to an endocrinologist to ensure you are getting support from a hormone specialist.

What is T4?

Thyroxine (T4) is produced by the thyroid gland under regulation from the hypothalamus and pituitary gland. The feedback loop signals to the hypothalamus in to release thyrotropin-releasing hormone, which then stimulates the pituitary gland to release the thyroid stimulating hormone.

What is T3?

T3 is a second thyroid hormone that is produced by the thyroid gland, but also in other tissues through deiodination (enzymatic conversion) of T4. T3 helps maintain muscle control, brain function and development, heart and digestive functions. It also plays a role in the body’s metabolic rate and the maintenance of bone health.

Problems Associated with T3 and T4?

Having too much T3 in the bloodstream is referred to as thyrotoxicosis. This condition often results from overactivity in the thyroid gland, or hyperthyroidism. Hyperthyroidism occurs in conditions such as Graves’ disease, inflammation of the thyroid or a benign tumor. Signs of thyrotoxicosis include weight loss, increased appetite, palpitations, irregular menstrual cycle, tiredness, irritability, and hair thinning. Hyperthyroidism can also occur when supplements with T3 are ingested.

Hypothyroidism is a condition that occurs if the thyroid gland does not produce enough of the thyroid hormone. This may be due to autoimmune conditions, such as Hashimoto’s thyroiditis or certain medications. Hypothyroidism can also occur in pituitary dysfunction, such as pituitary tumors or inflammation.

Hypothyroidism tends to run in families and more common in adults, as well as women. Symptoms may include tiredness, mental depression, feeling cold, weight gain, dry skin, constipation, and menstrual irregularities. Consider asking your healthcare provider:

  • Are my thyroid hormone levels normal?
  • What test should I have to check my thyroid function?
  • Could my symptoms be due to thyroid hormone abnormalities?
  • If my thyroid hormone levels are too high or too low - What are the treatment options?
  • Should I see a thyroid specialist or endocrinologist?

Thyroxine is a hormone the thyroid gland secretes into the bloodstream. Once in the bloodstream, thyroxine travels to the organs, like the liver and kidneys, where it is converted to its active form of triiodothyronine. Thyroxine plays a crucial role in heart and digestive function, metabolism, brain development, bone health, and muscle control. It affects almost all of the body's systems, which means proper thyroxine levels are vital for health. This is why many doctors will test T4 levels along with the more common T3 levels when testing for thyroid disorders.

What Can Go Wrong with Thyroxine?

Having too little thyroxine or too much thyroxine can cause health problems. If your body releases too much thyroxine, you will suffer a condition called thyrotoxicosis. This can cause a goiter, which is a swelling of the neck because of an enlarged thyroid gland. Thyrotoxicosis can also cause menstrual irregularities, an increase in bowel movements, weight loss, heat intolerance, fatigue, and irritability. Thyrotoxicosis is commonly caused by hyperthyroidism, tumors in the thyroid gland, or thyroid inflammation.

The body can also produce too little thyroxine, a condition known as hypothyroidism. Low thyroxine levels cause problems with development if it occurs when an individual is young. In adults, thyroxine deficiency will lower the metabolic rate, causing weight gain, memory problems, infertility, fatigue, and muscle stiffness.

If you are struggling with symptoms of a thyroid disorder and suspect thyroxine deficiency, it's crucial that you talk with an endocrinologist. You will need a series of blood tests to determine whether or not your thyroid hormone levels are where they should be. As you discuss your thyroid health with your doctor, consider asking these questions:

  • Is thyroid function causing my symptoms?
  • What could have caused my thyroid to stop functioning properly?
  • How can I regain proper levels of thyroxine and other thyroid hormones?
  • What type of monitoring will I need while on thyroid medication?
  • How long will I need thyroid medication?

Parathyroid hormone helps prevent low calcium levels by acting on the bones, intestine, and kidneys. In the bones, the hormone triggers the release of calcium stores from the bones to the blood. This can lead to bone destruction. In the intestines, parathyroid hormone helps with vitamin D metabolism. This, in turn, allows the body to absorb more of the calcium it digests from food. In the kidneys the hormone stops the release of calcium through the urine, while also increasing vitamin D production.

Potential Problems with Parathyroid Hormone Function

Because the function of parathyroid hormone directly impacts blood calcium levels, improper balance of parathyroid hormone can cause an imbalance of calcium levels in the blood.

Having too much of the hormone can cause a condition known as hypercalcaemia, which increases blood calcium levels. This does not cause obvious symptoms in mild cases, but if levels rise too high, it can cause digestive upset, constipation, depression, lethargy, weakness, joint pain, and excessive thirst. Hypercalcaemia is typically discovered during routine blood testing. Too little parathyroid hormone causes a rare condition called hypoparathyroidism, which leads to low blood calcium levels. This is fairly easy to treat using vitamin D and oral calcium tablets, once it is discovered.

Because parathyroid hormone problems rarely cause symptoms at the beginning of the condition, be sure to ask your doctor about parathyroid hormone levels when having routine blood work done. If calcium levels are too low or too high, consider asking your healthcare team about parathyroid hormone.

  • Are parathyroid levels to blame for my calcium levels?
  • How can I treat this?
  • What are the dangers of improper calcium levels?

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