THYROIDPeer Support 2014

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!)

What are the 6 steps of thyroid hormone synthesis?

1. Thyroglobulin synthesis

2. Uptake and concentration of iodide (I-)

3. Oxidation of iodide (I-) to iodine (Io)

4. Iodination of thyroglobulin

5. Coupling of 2 iodinated tyrosine molecules to form T4 or T3

6. Secretion

Hypothalamus

Anterior pituitary

Thyroid

TRH

TSH

T3 T4

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.

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

Grave’s Disease

• Autoimmune disease

• Body’s immune system produces Thyroid Stimulating Antibodies that act on the thyroid to increase T3/T4.

Exopthalmos

Hypothalamus

Anterior pituitary

Thyroid

TRH

TSH

T3 T4

High T3T4 levels result in inhibition of TSH and TRH

Hypothyroidism• Low T3/T4

• Signs and symptoms relate to a lowered metabolic rate• Weight gain• Lethargy• Alopecia• Sensitive to cold• Slow movements

Causes of hypothyroidism

• Autoimmune disease: Hashimoto’s Disease

• Iodine deficiency

• Previous surgery/treatment that have damaged the thyroid• Radioactive iodine therapy• Thyroidectomy

GoitreEnlarged thyroid gland

Causes:• Tumour

• Graves disease

• Hashimoto’s disease

• Iodine deficiency

Will result in hypothyroidism

THYROID FUNCTION QUIZPeer support

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

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)).

Hypothalamus

Anterior pituitary

Thyroid

TRH

TSH

T3 T4

This patient has:

• Low TSH, high T3 and T4

• A history of autoimmune diseases

• What is your primary differential?

Grave’s – autoimmune hyperthroidism

Hypothalamus

Anterior pituitary

Thyroid

TRH

TSH

T3 T4

High T3T4 levels result in inhibition of TSH and TRH

Antibodies

Hypothalamus

Anterior pituitary

Thyroid

TRH

TSH

T3 T4

If instead the TFTs showed:

high T4 and T3elevated TSHwhere might the issue in the hormone axis be?

Hypothalamus or pituitary

TUMOUR

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

Hypothalamus

Anterior pituitary

Thyroid

TRH

TSH

T3 T4

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?

Damage from radiation to the thyroid gland

Any questions?• D.white.1@warwick.ac.uk