2.  Thyroid hormones are synthesized in the thyroid gland.  Iodination and coupling of two molecules of tyrosine.  Monoiodotyrosine and diiodotyrosine.  T3 and T4 are formed, incorporated in thyroglobulin in the colloid.  Thyroglobulin is taken by the follicular cells, proteolytic enzymes break it and T3 and T4 released into the circulation.

3.  TSH controls the whole process.  More than 99% of plasma T3 and T4 are bound to thyroid binding globulin (TBG) and albumin.  The free is the active form.  Deiodination of T4 peripherally produces T3.  Some rT3 is also formed (inactive).  T3 is more active than T4.

4.  Affect metabolic processes  Increases oxygen consumption  Change the expression of some genes.  Essential for normal growth, mental development and sexual maturation.  Increase the sensitivity to catecholeamines.

5.  T4 inhibits TSH.  TRH stimulates TSH secretion.

6.  Free T4 vs total  Free T3 (hyperthyroidism)  TSH

7.  Increased :  High estrogen  Inherited excess  Decreased:  Severe illness  Loss of proteins  Androgens  Inherited deficiency

8.  Autoimmune  Toxic nodules  Ingestion of thyroid hormones

9.  Increased metabolic rate

10.  High T3 and T4  Low TSH

11.  Primary, Congenital, autoimmune, overtreatment of hyperthyroidism  Secondary, pituitary disease

12.  Goiter  Slow metabolic rate

13.  Primary: low T4, high TSH  Secondary: Low T4, low TSH  Low HB  Cholesterol  CK

14.  Thyroxine

16.  Congenital hypothyroidism  Short stature  Mental retardation  Preventable  Screen by TSH from cord or heel blood.