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Flashcards in Thyroid gland Deck (20)
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Describe the location of the thyroid gland.

Sits on the trachea,joined by isthmus


What are the dimensions and weight of the thyroid gland?

Each lobe is:
2.5-4cm long
1.5-2cm wide
1-1.5cm thick
adult gland weighs 10-20g


When is the thyroid gland enlarged?

-during pregnancy
-later portion of menstrual cycle


Where does the blood supply to the thyroid gland come from?

-The thyroid gland has a rich blood supply from the external carotid and subclavian arteries via the superior and inferior thyroid arteries


Where does the thyroid gland arise from and what is it's blood flow?

external carotid artery
subclavian artery
blood flow is 4-6ml/min/g of tissue


What are the functions of the thyroid hormones?

-neural development in foetus
-growth in the young child
-controls BMR
Concentrates iodine for incorporation into thyroid hormones
Contains 60-65% of body iodine


What is the active unit of the thyroid gland?

A follicle( composed of follicular cells)


Which cells secrete calcitonin?

parafollicular or 'C' cells of the thyroid gland


Why is T4 converted to T3 in the periphery?
How is this conversion brought about?

T3 is more potent than T4 at thyroid receptors. T3 acts on the thyrotrophs to decrease release of TSH and to decrease release of TRH from the hypothalamus. This conversion of T4 to T3 is brought about by deiodination


What is Hashimoto's thyroditis?

-Autoimmune disease
-antibodies to thyroglobulin or thyroid peroxidase


hat is the function of thyroid perixidase?

In the presence of hydrogen peroxidase, it allows for organification of iodine.


What does addition of iodine to tyrosine formed? How are T3 & T4 subsequently formed

Forms monoiodotyrosine/diiodotyrosine.


How can hypothyroidism be caused?

-Hashimoto's thyroiditis
-radiotheraphy or surgery for hyperthyroidism
-failure of delivery of thyroid hormones in the foetus i.e cretinism


How can we treat hypothyroidism?

-T4; has a half life of 6days;effects last 14 days
-Liothyronine(sodium salt of T3) has a half life of 2-4 days,effects last 8 days


What is the dietary iodine requirement



What amount of iodine intake signifies an iodine deficiency?



Define goitrogen

substances that suppress hormone secretion, so increase TSH secretion, leading to a goitre


What causes hyperthyroidism( thyrotoxicosis)?

-GRAVES' DISEASE (diffuse toxic goitre): autoimmune disease with abnormal antibodies( TSAb(LATS)-produces prolonged stimulation of TSH receptors


What are some of the features of graves disease?

-weight loss
-Exophthalmos and upper lip retraction
-pretibial myxoedema


What is the treatment for Hyperthyroidism?

-antithyroid drugs
-carbimazole( converted to methimazole in the body)
-propyl thiouracil (This inhibits thyroid peroxidase and prevents peripheral conversion of T4 to T3; takes 4-8 weeks to become euthyroid and then u reduce to maintenance dose and treat for 12-18months. Side effects include neutropenia and angranulocytosis)
-Beta blockers (propanolol blocks sympathetic effects of hormones )
-Radioiodine( mass no=131 Iodine). This is taken up into follicular cells and irradiates them. Beta and gamma emitter. Beta particles kills cells while gamma passes through without causing any damage. Half life=8days and in 2months there's complete decay.
-Surgery (partial thyroidectomy)
-Iodine in LUGOL'S solution ( 5% iodine and 10% potassium iodide is given prior to surgery to reduce vascularity.