Endocrine System

 TSH made by pituitary gland  T 3 and T 4 in thyroid, duh!

 Hormones that act like steroid hormones  Triiodothyronine  3 iodines added = T 3  Thyroxine  4 iodines added = T 4

 Go through plasma membrane and directly activate transcription in the nucleus  So… it’s a TRANSCRIPTION FACTOR!!! Now you know!

 Hypothalamus triggers the release of TSH which activates thyroid to secrete T3 or T4

Thyroid stimulating hormone is released from pituitary gland when T4 falls too low When T4 is too high, pituitary will NOT release TSH Metabolism stabilizes

 T 3 stops metabolism  So your body would digest slower  Hypothyroidism: low levels of thyroid hormones weight gain  T 4 stabilizes metabolism  So keeps digestion at normal range  Increases O 2 consumption in all tissues  Hyperthyroidism: high levels of thyroid hormones weight loss elevated BMR Nervousness Voice changes Puffy appearance

 Disease causes hyperthyroidism  Immune system produces antibodies that bind to receptor TSH  Activates sustained T3 and T4 production  Negative feedback destroyed  Symptom= protruding eyes

 Not enough iodine?  Thyroid cannot produce T4  Thyroid enlarges to keep up with demand for thyroid hormone production  T4 levels in blood fall drastically  This triggers the TSH to release  But without iodine, thyroid still cannot produce hormone  Thyroid swells  Can cause choking, and difficulty swallowing and breathing