THYROID By Joshua BowerEaster Revision 2014J.Bower@warwick.ac.uk

What hormones does the thyroid gland produce?

• Thyroxine (T4)• Tri-iodothyronine (T3)• Calcitonin

List the SIX steps in thyroid hormone synthesis [6]1. Thyroglobulin synthesised from tyrosine2. Uptake and concentration of iodide3. Oxidation of iodide to iodine4. Iodination of thyroglobulin5. Coupling of 2 iodinated tyrosine molecules to form T4 or T36. Secretion

MIT and DITmono-, di-iodotyrosine

hydrolysis

Secretion T3 & T4

Follicular Lumen(COLLOID)

Blood

Follicle cell

Thyroglobulin chain (tyrosine residues)

Conjugation MIT and DIT T3 and T4

Thyroid Hormone synthesis (3)

pendrin

Iodide (I-)

iodine(Io)TPO

NIS

Thyroglobulin synthesis

Describe the HPT axis

How do thyroid hormones travel?• 70% bound to thyroxin binding globulin (70%)• 30% bound to albumin• TBG has higher affinity for T4 – readily available reserve

Which hormone is the active one?• T3• T4 is converted by deiodinases to T3, to bind to T3R and have an

effect

List FOUR physiological actions of TH [4]• Affects BMR• Maturation and differentiation of bone, lung, brain etc• Synapse formation• Myelinogenesis• Neuronal outgrowth• Growth (regulated by GH, but needs T3/T4)

By what week of development does the foetus make its own T3/T4?

• Week 12• After trimester 1, not enough TSH or T4/T3 can cross placenta

What is cretinism?• Impaired physical and neurological development due to iodine

deficiency during foetal or postnatal development• Irreversible after first 2 years of life• TSH levels tested for in heel prick test

List THREE signs/symptoms of hyperthyroidism [3]

What would the blood test results show in hyperthyroidism?• Inc’d T3/T4

• Inc’d TSH (if fault in or above pituitary gland)• Dec’d TSH (if fault with thyroid gland)

What is Grave’s disease?• Auto-antibody (TSI) for the TSH receptor• Causes hyperthyroidism• Causes goitre as TSI is stimulating thyroid gland, even if TSH levels low

List THREE signs/symptoms of hypothyroidism [3]• Slow• Lethargic• Overweight/obese• Alopecia• Goitre

What would the blood test results show in hypothyroidism?• Dec’d T3/T4

• Inc’d TSH (usually)

List THREE possible treatments for thyroid issues [3]• Drugs (inhibit production or replace hormone)• Radioactive iodine (131I) to destroy gland• Surgery

List THREE complications associated with thyroid gland surgery [3]

• General surgery issues• Vocal cord nerve damage• Bleeding• Parathyroid gland damage

QUESTIONS?By Joshua BowerEaster Revision 2014J.Bower@warwick.ac.uk