Summary

The thyroid_gland sits in the neck and makes t3 and t4, controlled by tsh from the pituitary. hypothyroidism: low hormones, slow metabolism, fatigue, weight gain, cold intolerance, dry skin. hyperthyroidism: high hormones, fast metabolism, weight loss, heat intolerance, palpitations, tremor. Common causes: hashimoto_thyroiditis and graves_disease. Key tests: tsh, free_t4, total_t3, thyroid_antibodies. Typical findings: high tsh in hypothyroidism; low tsh in hyperthyroidism. Treatment options to remember: levothyroxine, antithyroid_drugs, radioactive_iodine, surgery.