Thyroid and Parathyroid Disorders
Overview of the Thyroid Gland
The thyroid gland covers the anterior surfaces of the second to fourth tracheal rings. It comprises a right and left lobe, separated in the middle by an area called the isthmus. It is surrounded with a fibrous capsule. The posterior layer contains four parathyroid glands.
The thyroid consists of loose tissue in the formation of grape-like clusters with many blood vessels. Microscopic analysis reveals follicle walls that are surrounded by cuboidal epithelial cells. The follicle cells produce a glycoprotein called thyroglobulin. With the incorporation of dietary iodine, thyroglobulin is further processed to form a variety of thyroid hormones, most importantly triiodothyronine, commonly referred to as T3, and thryroxine (tetraiodothyronine), commonly referred to as T4.
T3 and T4 Hormones
- T3, the most active thyroid hormone, is produced in small amounts from the thyroid, and is converted in the liver and kidneys from T4.
- T4 secretion is controlled by the pituitary secretion of TSH (thyroid-stimulating hormone). Like many other endocrine systems, its regulation works by a negative feedback loop.
- Both T3 and T4 have the same function: they increase oxygen availability in virtually all tissues.
- T3 also functions in maintaining metabolic rate, growth and development.
Iodine
The trace mineral iodine is a chief component of the thyroid hormones.
Iodine deficiency has been known to cause hypothyroidism, and has also been associated with increased cholesterol levels, atherosclerosis, fibrocystic breast disease, and breast cancer.
Iodine deficiency can also be devastating to the developing brain, causing a mental retardation known as cretinism.
Found primarily in sea life, iodine is absorbed through the body through the consumption of sea vegetables and seafood, such as fish and shellfish, and iodized sea salt, and is also found in some legumes, vegetables, dairy and eggs provided that the soil contains sufficient amounts of iodine, and the dietary sources of the animal.
Selected Clinical Studies and Literature Review
For a comprehensive review of iodine deficiency research and thyroid disorders, see Guy E. Abraham , Jorge D. Flechas, and John C. Hakala, “Orthoiodosupplementation: Iodine Sufficiency of the Whole Human Body,” in Selected Clinical Studies and Literature Reviews.
Overview of the Parathyroid Gland
The parathyroid glands lie posterior to the thyroid. It is a highly vascular tissue that secretes parathormone, and consists of two pairs of small button-shaped tissues located above and below the back of the thyroid gland. Like most endocrine tissue, these glands are highly vascular. They secrete parathyroid hormone (PTH) that increases plasma calcium levels.
Parathormone
- PTH maintains calcium levels throughout the body by stimulating bone breakdown, freeing calcium ions.
- Reduced PTH will result in low calcium levels manifesting as muscle stiffness, cramps, spasms, and convulsions.
- Up to 30-40% of essential hypertension may be due to excessive parathyroid factor (PHF), another hormone produced by the parathyroid gland.
- PTH levels are modulated via a negative feedback loop by serum calcium ion levels. Normal muscle activity and blood clotting depend on normal calcium levels and, below certain levels, causes muscle stiffness, cramps, and convulsions.
