Question

What are the target cells of TH? What are the effects of TH in humans? What other hormone action is influenced by TH?

What are the symptoms of hypothyroidism? Hyperthyroidism? What are some causes of each?

How is the effect of hypothyroidism different if its onset is from infancy rather than in adulthood?

What is a goiter? Name 3 circumstances when a person might develop a goiter.

Answer 1

1. a. It is likely that all cells in the body are targets for thyroid hormones. While not strictly necessary for life, thyroid hormones have profound effects on many physiologic processes, such as development, growth and metabolism, and deficiency in thyroid hormones is not compatible with normal health.

b. In adults, TH primarily controls the basic metabolic rate (BMR).

c. Growth hormone (GH) is influenced by TH.

2. a. Common symptoms of hypothyroidism arising after early childhood include lethargy, fatigue, cold-intolerance, weakness, hair loss and reproductive failure. If these signs are severe, the clinical condition is called myxedema. In the case of iodide deficiency, the thyroid becomes inordinantly large and is called a goiter.

b. Common signs of hyperthyroidism are basically the opposite of those seen in hypothyroidism, and include nervousness, insomnia, high heart rate, eye disease and anxiety.

c. Hypothyroidism can be from a defective thyroid gland, or insufficient TRH or TSH, or insufficient amounts of iodine.

Hyperthyroidism can be the result of hyper-secretion of either TRH, TSH, or an autoimmune disease (Graves' disease).

d. If hypothyroidism occurs in infancy, it leads to cretinism which will have profound effects on growth and development, especially of the nervous system. If not treated, their disorder leads to mental retardation, impaired growth, low body temperatures, and abnormal bone formation.

In adulthood, it leads to myxedema. The characteristics of this disease are edema, low blood levels of T3 and T4, weight gain, cold intolerance, fatigue, depression, muscle or joint pain, and sluggishness.

3. a. Goiter is an enlargement of the thyroid gland.

b. 3 circumstances when a person might develop a goiter are:

i. Not enough dietary iodine.

ii. Hyper-secretion of TRH or TSH.

iii. Graves' disease, which is an autoimmune disease in which thyroid stimulating immunoglobulins (TSI) over stimulate the thyroid gland to hypersecrete TH.