Thyroid gland

Question 1

Describe the location of the thyroid gland.

Answer 1

Sits on the trachea,joined by isthmus

Question 2

What are the dimensions and weight of the thyroid gland?

Answer 2

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

Question 3

When is the thyroid gland enlarged?

Answer 3

• during pregnancy
• lactation
• adolescence
• later portion of menstrual cycle

Question 4

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

Answer 4

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

Question 5

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

Answer 5

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

Question 6

What are the functions of the thyroid hormones?

Answer 6

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

Question 7

What is the active unit of the thyroid gland?

Answer 7

A follicle( composed of follicular cells)

Question 8

Which cells secrete calcitonin?

Answer 8

parafollicular or ‘C’ cells of the thyroid gland

Question 9

Why is T4 converted to T3 in the periphery?

How is this conversion brought about?

Answer 9

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

Question 10

What is Hashimoto’s thyroditis?

Answer 10

• Autoimmune disease

- antibodies to thyroglobulin or thyroid peroxidase

Question 11

hat is the function of thyroid perixidase?

Answer 11

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

Question 12

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

Answer 12

Forms monoiodotyrosine/diiodotyrosine.
MIT+DIT=T3
DIT+DIT=T4

Question 13

How can hypothyroidism be caused?

Answer 13

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

Question 14

How can we treat hypothyroidism?

Answer 14

• 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

Question 15

What is the dietary iodine requirement

Answer 15

150ug/day

Question 16

What amount of iodine intake signifies an iodine deficiency?

Answer 16

<50ug/day

Question 17

Define goitrogen

Answer 17

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

Question 18

What causes hyperthyroidism( thyrotoxicosis)?

Answer 18

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

Question 19

What are some of the features of graves disease?

Answer 19

• thyrotoxicosis
• Goitre
• weight loss
• tachycardia
• diarrhoea
• Exophthalmos and upper lip retraction
• pretibial myxoedema

Question 20

What is the treatment for Hyperthyroidism?

Answer 20

• 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.