Thyroid Gland
The thyroid gland is a very vascular organ that is located in the neck. It consists of two lobes, one on each side of the trachea, just below the larynx or voice box. The two lobes are connected by a narrow band of tissue called the isthmus. Internally, the gland consists of follicles, which produce thyroxine and triiodothyronine hormones. These hormones contain iodine.
About 95 percent of the active thyroid hormone is thyroxine, and most of the remaining 5 percent is triiodothyronine. Both of these require iodine for their synthesis. Thyroid hormone secretion is regulated by a negative feedback mechanism that involves the amount of circulating hormone, hypothalamus, and adenohypophysis.
If there is an iodine deficiency, the thyroid cannot make sufficient hormone. This stimulates the anterior pituitary to secrete thyroid-stimulating hormone, which causes the thyroid gland to increase in size in a vain attempt to produce more hormones. But it cannot produce more hormones because it does not have the necessary raw material, iodine. This type of thyroid enlargement is called simple goiter or iodine deficiency goiter.
Calcitonin is secreted by the parafollicular cells of the thyroid gland. This hormone opposes the action of the parathyroid glands by reducing the calcium level in the blood. If blood calcium becomes too high, calcitonin is secreted until calcium ion levels decrease to normal.
Parathyroid Gland
Four small masses of epithelial tissue are embedded in the connective tissue capsule on the posterior surface of the thyroid glands. These are parathyroid glands, and they secrete parathyroid hormone or parathormone. Parathyroid hormone is the most important regulator of blood calcium levels. The hormone is secreted in response to low blood calcium levels, and its effect is to increase those levels.
Hypoparathyroidism, or insufficient secretion of parathyroid hormone, leads to increased nerve excitability. The low blood calcium levels trigger spontaneous and continuous nerve impulses, which then stimulate muscle contraction
In hypocalcemia, the calcium level in blood is too low. A low calcium level may result from a problem with the parathyroid glands, as well as from diet, kidney disorders, or certain drugs. As hypocalcemia progresses, muscle cramps are common, and people may become confused, depressed, and forgetful and have tingling in their lips, fingers, and feet as well as stiff, achy muscles. Usually, the disorder is detected by routine blood tests.
Calcium and vitamin D supplements may be used to treat hypocalcemia.
Hypocalcemia most commonly results when too much calcium is lost in urine or when not enough calcium is moved from bones into the blood. Causes of hypocalcemia include the following:
Lack of response to a normal level of parathyroid hormone (pseudohypoparathyroidism)
Kidney dysfunction, which results in more calcium excreted in urine and makes the kidneys less able to activate vitamin D
Inadequate consumption of calcium
Disorders that decrease calcium absorption
Certain drugs, including rifampin (an antibiotic), antiseizure drugs (such as phenytoin and phenobarbital), bisphosphonates (such as alendronate, ibandronate, risedronate, and zoledronic acid), calcitonin, chloroquine, corticosteroids, and plicamycin
The calcium level in blood can be moderately low without causing any symptoms. If levels of calcium are low for long periods, people may develop dry scaly skin, brittle nails, and coarse hair. Muscle cramps involving the back and legs are common. Over time, hypocalcemia can affect the brain and cause neurologic or psychologic symptoms, such as confusion, memory loss, delirium, depression, and hallucinations. These symptoms disappear if the calcium level is restored.
An extremely low calcium level may cause tingling (often in the lips, tongue, fingers, and feet), muscle
aches, spasms of the muscles in the throat (leading to difficulty breathing), stiffening and spasms of muscles (tetany), seizures
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Measurement of calcium level in the blood
Hypocalcemia is often detected by routine blood tests before symptoms become obvious. Doctors measure the total calcium level (which includes calcium bound to albumin) and the albumin level in blood to determine whether the level of unbound calcium is low.
Blood tests are done to evaluate kidney function and to measure magnesium, phosphate, parathyroid hormone, and vitamin D levels. Other substances in blood may be measured to help determine the cause.
Calcium supplements
Sometimes vitamin D
Calcium supplements, given by mouth, are often all that is needed to treat hypocalcemia. If a cause is identified, treating the disorder causing hypocalcemia or changing drugs may restore the calcium level.
Once symptoms appear, calcium is usually given intravenously. Taking vitamin D supplements helps increase the absorption of calcium from the digestive tract.
Sometimes people with hypoparathyroidism are given a synthetic form of parathyroid hormone.
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