Thyroid Flashcards
(23 cards)
How does iodine enter the thyroid follicular cell?
From the blood, via an iodine/sodium symporter
How does iodine enter the follicle colloid?
It diffuses across the thyroid follicular cell and enters to colloid through the Pendrin transporter
Once in the colloid, how are thyroid hormones formed from iodine?
Iodide is oxidised to iodine
Iodine then combines with thyroglobulin via the action of thyroid peroxidase, to produce MIT and DIT
- mono/di-iodinated tyrosine
MIT and DIT thyroglobulin are then endocytosed into the cell
Proteolysis occurs to breakdown the thyroglobulin
MIT and DIT = T3
DIT and DIT = T4
In what form are thyroid hormones normally secreted?
Pro-hormone (T4)
T3 is the active hormone and is secreted in very low quantities
If T3 is the active hormone, why is T4 secreted in larger quantities from the thyroid gland?
T4 is converted to T3 by peripheral 5’-deiodination
T3 is very unstable and acts quickly so can’t be circulated
What are the functions of the thyroid hormones?
Negative feedback on TRH and TSH
Increased metabolism
Growth and development
Increased catecholamine effect
What are the normal thyroid hormone concentrations in the blood?
Free T4 (used in diagnostic testing) - 9-21pmol/l
Total T4 - 60-160nmol/l
Free T3 - 0.9-2.5pmol/l
Total T3 - 1.2-2.6nmol/l
What is the medical treatment for hypothyroidism?
Levothyroxine - synthetic T4 75-150mcg per day
Name some of the causes of hypothyroidism,
Thyroidectomy Post radioactive iodine ablation Autoimmune - thyroiditis - silent - Hashimoto's Blocking TSH receptor antibodies Congenital hypothyroidism Hypopituitarism
What happens to babies if the mother has hypothyroid disease?
Neonatal hypothyroidism
- cretinism
- coarse facial features
- macroglossia
- umbilical hernia
- mottled, cool and drug skin
- developmental delay
- pallor
- myxoedema
- goiter
What are the most common causes of congenital hypothyroidism?
Thyroid dysgenesis - TSH receptor Dyshormonogenesis - thyroid peroxidase - thyroglobulin - sodium/iodide symporter - pendrin (pendred syndrome)
What investigations would you perform on someone with suspected hyperthyroidism?
TSH Free T4 Free T3 TSH receptor antibodies TPO - thyroid peroxisomal antibody 123 I uptake scan - radiolabelled iodine
What is the treatment for hyperthyroidism?
Beta blockers - symptom management Carbimazole - prodrug of methimazole - prevents iodination of thyroglobulin (prevents coupling of thyroid peroxidase enzyme) Propylothiouracil 131 I - radioactive iodine Thyroidectomy
Describe the aetiology of Graves Disease.
Autoimmune disease - associated diseases in family
Genetic suscpetibility (HLA, TG and thyroid receptor)
Environmental - iodine, tobacco smoke
Immune modulating treatment - IFN, alemtuzemab
Name some causes of hyperthyroidism.
Pituitary adenoma Other hormones acting as TSH - HcG Autoimmune - thyroiditis acute early phase - activating TSH receptor antibodies Thyroid adenoma
How does amiodarone affect the thyroid?
200mg of amiodarone releases 6mg of iodine
Name the types of amiodarone thyroid disease.
Type 1 - autoimmune thyrotoxicosis - treated with high dose carbimazole Type 2 - destructive thyroiditis - treated with glucocorticoids
What are the effects of oral contraceptive pill on thyroid function?
It increases the amount of binding proteins available
- the level of total T4 increases
What are the different types of tumour that can occur in the thyroid gland?
Follicular cell - papillary cancer - follicular cancer - anaplastic cancer - poorly differentiated Thyroid C cell - medullar cancer
How are thyroid carcinomas diagnosed?
Fine needle aspirate of nodules
How are thyroid carcinomas treated?
Surgical removal Therapeutic radioiodine TSH suppression (papillary cancers depend on TSH stimulation for growth) Monitor thyroglobulin Multikinase inhibitors
Name some diseases related to mutation of RET protooncogene.
Familial medullary thyroid cancer
Multiple endocrine neoplasia type 2 and 3
Hirschprungs
What is thyroid eye disease?
Muscles and soft tissues of the eye socket swell
- associated with problems with thyroid gland (commonly overactive, but can occur in both)
