1. Thyroid
Peer Support 2014

2. What hormones are secreted by the thyroid gland?
T4 (thyroxine)
T3 (tri-iodothyronine)
These are referred to as the thyroid hormones and are derivatives of tyrosine
Calcitonin (don’t worry about this for now, it will reappear in Block 4!)

3. What are the 6 steps of thyroid hormone synthesis?
Thyroglobulin synthesis
Uptake and concentration of iodide (I-)
Oxidation of iodide (I-) to iodine (Io)
Iodination of thyroglobulin
Coupling of 2 iodinated tyrosine molecules to form T4 or T3
Secretion

4. Hypothalamus
TRH
Anterior pituitary
TSH
Thyroid
T3 T4

5. Transport of thyroid hormones
Are lipophilic so hard to dissolve in blood and so are transported bound to proteins
70% by TBG (thyroxine binding globulin)
30% by albumin
Transported as T4
Converted by deiodinases to T3 to effect on the cells.

6. Hyperthyroidism Caused by thyrotoxicosis (high T3T4)
Signs and symptoms link to HIGH metabolic rate
Weight and muscle loss
Increased appetite
Heat intolerance and sweating
Anxiety/irritability

7. Grave’s Disease Autoimmune disease
Body’s immune system produces Thyroid Stimulating Antibodies that act on the thyroid to increase T3/T4.
Exopthalmos

8. TSH T3 T4 TRH Hypothalamus
High T3T4 levels result in inhibition of TSH and TRH
TRH
Anterior pituitary
TSH
Thyroid
T3 T4

9. Hypothyroidism Low T3/T4
Signs and symptoms relate to a lowered metabolic rate
Weight gain
Lethargy
Alopecia
Sensitive to cold
Slow movements

10. Causes of hypothyroidism
Autoimmune disease: Hashimoto’s Disease
Iodine deficiency
Previous surgery/treatment that have damaged the thyroid
Radioactive iodine therapy
Thyroidectomy

11. Goitre Enlarged thyroid gland Causes: Tumour Graves disease
Hashimoto’s disease
Iodine deficiency
Will result in hypothyroidism

12. Thyroid function quiz
Peer support

13. Question 1 A woman, 43, presents with:
weight loss of a stone over the last few weeks associated with an increase in appetite
sweating, exophthalmus and goitre
What type of thyroid disease might you be expecting (hyper or hypo)?
Hyperthyroidism

14. Question 1b
What would you want to measure to diagnose the hyperthyroidism?
TSH, T3 and T4 levels in the circulating blood (called a Thyroid Function Test (TFT)).

15. TSH T3 T4 TRH This patient has: Hypothalamus Low TSH, high T3 and T4
A history of autoimmune diseases
What is your primary differential?
Hypothalamus
TRH
Anterior pituitary
TSH
Grave’s –
autoimmune hyperthroidism
Thyroid
T3 T4

16. TSH Antibodies T3 T4 TRH Hypothalamus
High T3T4 levels result in inhibition of TSH and TRH
TRH
Anterior pituitary
TSH
Antibodies
Grave’s where Thyroid stimulating immunoglobulin (TSI) stimulates the thyroid to produce T4 and 3 – these feedback to the hypothalamus and pituitary to suppress TSH
Thyroid
T3 T4

17. TSH T3 T4 TRH TUMOUR If instead the TFTs showed: Hypothalamus
high T4 and T3
elevated TSH
where might the issue in the hormone axis be?
Hypothalamus
TRH
Anterior pituitary
TUMOUR
TSH
Hypothalamus or pituitary
Thyroid
T3 T4

18. Question 2 A 37 year old man presents with:
Weight gain (with poor appetite)
Slow and lethargic
Feeling cold
What type of thyroid disease would you expect from these symptoms?
Hypothyroidism

19. TSH T3 T4 TRH Hypothalamus You find:
The patient had throat cancer 1yr ago that was successfully treated with external beam radiation
High TSH, low T3 and T4
What has caused the hypothyroidism?
TRH
Anterior pituitary
TSH
Thyroid
Damage from radiation to the thyroid gland
T3 T4

21. Any questions?