Thyroid Disease

Thyroid gland - anatomy:




Function of thyroid hormones:
- Increase heat production
- Increase oxygen consumption
- Increase metabolism of proteins, fats and carbohydrates
- Promote normal growth
- Required for normal CNS function

Plasma thyroid hormones:
- T3 is metabolically 4 times more active than T4
- Half Life of T4 is 9 days whereas T3 has a half life of 1.5 days
- T4 can readily be converted to T3 in most tissues particularly liver
- Conversion of T4 to T3 reduced in systemic illness and by drug ex.
Propranolol

Thyroid hormone binding proteins:




Binding proteins:
- Thyroxine binding globulin (TBG): 70%
- Albumin: 20%
- Prealbumin: 10%

Thyroid hormones: regulation
- Negative feedback control of T4 and T3
- Free and not total [T4/T3] determine feedback
- Thyroid stimulating hormone (TSH) and thyroid
releasing hormone (TRH) involved in feedback
- Plasma [TSH] is 0.3-30mU/L