Hypothyroidism is characterized by low levels of which hormone and high levels of which hormone?

Hypothyroidism is primarily characterized by low levels of thyroid hormones, specifically thyroxine (T4), which is the principal hormone produced by the thyroid gland. In response to the low levels of T4, there is an increase in thyroid-stimulating hormone (TSH) levels, produced by the pituitary gland, in an attempt to stimulate the thyroid to produce more hormones. Therefore, the correct answer is the one that indicates low T4 and high TSH, reflecting the physiological feedback mechanism that occurs in cases of hypothyroidism.

Thyroid hormones, T3 and T4, play crucial roles in regulating metabolism, growth, and development. When thyroid hormone production is inadequate, the body compensates by increasing TSH, which signals the thyroid gland to produce more thyroid hormones. However, in hypothyroidism, the thyroid is unable to respond adequately, leading to persistently low T4 and elevated TSH levels.

The other options do not accurately represent the typical hormonal findings in hypothyroidism, which is why they do not fit the profile of the condition. Understanding the relationship between T4, TSH, and the thyroid gland's function is essential to recognizing the endocrine patterns associated with hypothyroidism.