Some patients with HPT axis problems develop a goiter Descib

Some patients with HPT axis problems develop a goiter. Descibe two different conditions where a goiter would be present and explain physiologically why and how the goiter occurs. Make sure to include axis feedback in your answer.

Solution

Lithium causes hypothyroidism which leads to goitre leads to lithium induced hypothyroidism. Lithium is concentrated in thyroid gland and thyroidal iodine uptake. Iodotyrosine coupling is inhibited and thyroid secretion is inhibited. Lithium interferes with the deiodination of T4 to T3 by inhibiting type-II deiodinase in the brain. Lithium alters cellular responsiveness to thyroxine, and influences thyroid hormone receptor gene expression . Inhibition of thyroid hormone release, a process mediated by cyclic adenosine monophosphate, appears to be the critical mechanism in the development of lithium-induced hypothyroidism. Bipolar disorder - patients with bipolar disorder causes hypothyroidism . Release of thyroid hormone is seen in treatment of patients who take treatment for bipolar depression. HPT axis is regulated by many feedback mechanisms. Free T3 or T4 inhibits TRH release from hypothalamus and anterior poitutary to inhibit TSH. Neurotransmitters and hormones either promote or inhibit release of TRH and TSH . TSH and TRH levels are induced by stress responsive elements.