Thyroid Physiology Trivia Quiz

Answer: Auto-immunity

Auto-immunity, in which the immune system mistakes one or more thyroid proteins for foreign proteins, such as those associated with bacteria or viruses, is the main cause of thyroid disease in the US. Auto-immunity can cause the thyroid to be underactive (hypothyroid), or overactive (hyperthyroid). It can cause widespread enlargement resulting in a goiter or regional enlargement leading to thyroid nodules.

Iodine deficiency is almost unheard of in the US because most salt is fortified with sodium iodide.

Thyroid cancer does occur, but is much less common than breast, lung, or colon cancer, and can be successfully treated in a majority of cases.

Radiation exposure can cause thyroid disease, but is also uncommon. In regions downwind from Chernobyl, however, rates of hypothyroidism, and both cancerous and benign thyroid nodules occured at much higher rates than usual for many years after the accident.

Answer: The pituitary gland

The pituitary gland monitors circulating levels of thyroid hormones and increases or decreases the amount of TSH, or Thyroid Stimulating Hormone, in order to control the amount of thyroid hormone synthesized and secreted by the thyroid gland.

Answer: Nucleus

Thyroid hormone receptors are found in the cell nucleus. When thyroid hormone binds to these receptors, they act as promoters or repressors for the expression of a wide range of genes.

Answer: Heart pounding and racing

Constipation, unusually dry skin, and puffiness around the eyes are frequently seen in hypothyroid individuals. However, instead of having their hearts pound and race, hypothyroid individuals tend to have a slow heartbeat.

Answer: Feeling cold all the time

Increased appetite, shakiness or tremors, and sweats are commonly reported in hyperthyroid individuals. Feeling hot, rather than cold, when others are comfortable is another common symptom of hyperthyroidism.

Many people associate weight loss with hyperthyroidism. While this is often true, hyperthyroid individuals can actually gain weight because of their increased appetite.

Answer: The number of iodine atoms per molecule.

T3 has 3 iodine atoms per molecule; T4 has 4.

Both have a heavily modified tyrosine molecule as a backbone, and thus both consist of a single amino acid. T3 has a molecular weight of 651 Daltons (0.65 kD); T4 has a molecular weight of 776 Daltons (0.78 kD). The difference is the 125 Daltons contributed by the extra iodine atom in T4.

Answer: one

Normally, a person has one thyroid gland. The thyroid gland is made up of two lobes, one on either side of the trachea, which are connected by a thin bridge of tissue in front of the trachea called the isthmus. Despite having these different regions, the thyroid gland is considered to be one gland.

Answer: Bound to a carrier protein

Most thyroid hormone is bound to thyroid binding globulin or to albumin. Less than 1% is found as "free" (unbound) T4 or T3. It does not form dimers or hexamers.

Answer: Calcitonin

Calcitonin (occasionally referred to as thyrocalcitonin), is made by a distinct population of cells within the thyroid called parafollicular cells or C-cells. One known action of calcitonin is to lower calcium levels in the bloodstream, but individuals who have had their thyroid removed do not have trouble with high calcium levels.

Thyrotropin is another name for TSH/Thyroid Stimulating Hormone, which is made in the pituitary gland and controls the thyroid. Leptin and adiponectin are hormones involved in fat cell metabolism.

Answer: Potassium iodide

When uranium decays, radioactive isotopes of iodine are formed. If a person ingests significant amounts of these isotopes, the radioactive iodine concentrates in the thyroid gland, and the energy given off as it decays can cause damage to proteins and nucleic acids within the cells. A large amount of radioactive iodine can do enough damage to kill the thyroid, and there is no increased risk of cancer. An insignificant amount of radioactive iodine causes negligible damage, and there is no measurable increased risk of cancer. Somewhere in between, the thyroid receives what is termed a "sublethal dose" - not enough to kill, but enough to cause significant damage. This damage may lead to errors or mutations in the DNA that are sufficient to cause a cell to transform (become cancerous) immediately or make it more likely to do so in the future.

Flooding the body with "cold" (nonradioactive) iodine protects the thyroid in two ways. First, the radioactive iodine represents a smaller proportion of the total iodine pool, so that less gets into the thyroid. Second, in order to prevent the thyroid gland from suddenly making too much thyroid hormone when there is excess iodine available, the thyroid gland stops taking up iodine temporarily when there is a sudden increase in iodine levels in the blood. Therefore, taking potassium iodide reduces both the total amount of iodine absorbed by the thyroid after an exposure, and the proportion of absorbed iodine that is radioactive.