Final answer:
Primary hypothyroidism is the adult hypothyroid condition characterized by low T4 and T3 levels, causing increased TRH and TSH due to a feedback mechanism. It is the result of a malfunction within the thyroid gland itself, which fails to produce enough thyroid hormones.
Step-by-step explanation:
The type of adult hypothyroidism characterized by low levels of T4 and T3, which causes an increase in TRH (thyrotropin-releasing hormone) and TSH (thyroid-stimulating hormone) as a result of the feedback mechanism, is known as primary hypothyroidism.
In primary hypothyroidism, the problem resides within the thyroid gland itself, which fails to produce adequate amounts of thyroid hormones necessary for regulating metabolism. This condition often leads to symptoms such as fatigue, weight gain, and cold intolerance. In response to low thyroid hormone levels, the hypothalamus releases TRH, which then prompts the pituitary gland to secrete TSH, stimulating the thyroid to produce more hormones.
If the thyroid gland is unable to respond appropriately due to disease, damage, or other factors like iodine deficiency, TSH levels continue to rise in a futile attempt to accelerate hormone production, but without successful elevation of T3 and T4 levels.