Functions and Disorders of the Thyroid Gland

Question 1

What is the thyroid gland?

Answer 1

Shield shaped gland in neck, sits under Adam’s apple, in front of trachea, with parathyroid glands sitting above and below

Question 2

What are the effects of iodine deficiency?

Answer 2

TSH drives thyroid to produce more thyroxine –> goitre

Question 3

What are the actions of thyroid hormones?

Answer 3

growth, development, basal metabolic rate control, thermogenesis (brown adipose), active mental processes

Question 4

What are thyroxine (T4) and triiodithyroxine (T3) made from?

Answer 4

iodinated tyrosine residues

Question 5

Which of T4 and T3 is active?

Answer 5

T3 (has lost one iodine to become active)

Question 6

Outline basic thyroid secretion

Answer 6

hypothalamus (TRH) –> anterior pituitary (TSH) –> thyroid (T4, T3) –> tissues

Question 7

What is the structure of the thyroid gland?

Answer 7

made of many follicles, inside is colloid - hormones made here

Question 8

Within the follicular colloid which molecule is processed with in the presence of H2O2 and thyroid peroxidase (TPO) ?

Answer 8

thyroglobulin

Question 9

Thyroglobulin enters the follicular cell to be

Answer 9

cleaved to produce T4 and T3

DIT and MIT are recycled

Question 10

How does TSH impact T4 and T3 synthesis?

Answer 10

speeds up the cycle by stimulating via cAMP/calcium action by binding a GPCR

Question 11

Why must thyroxine be carried in the blood?

Answer 11

it’s not water-soluble

Question 12

What are the proteins that carry thyroxine?

Answer 12

T4-binding globulin (70%)
transthyretin (20%)
albumin (10%)

Question 13

How is T3 produced?

Answer 13

conversion of T4 via deiodinase 1 and 2

Question 14

How is rT3 produced?

Answer 14

conversion of T4 via deiodinase 1 and 3

Question 15

What are the clinical aspects of hyperthyroidism?

Answer 15

weight loss, appetite, fatigue, heat intolerance, sweating, GI disturbance

Question 16

How does Graves’ Disease lead to hyperthyroidism?

Answer 16

Ab stimulate TSH receptor to produce T4/T3

Question 17

What are the clinical features of Graves?

Answer 17

large smooth goitre
technetium scan - hotspots over thyroid
50% have ophthalmopathy (retracted eyelids, lid lag, proptosis, redness, gritty sensation, swelling, blurred vision, vision loss)

Question 18

How does Graves lead to ophthalmopathy?

Answer 18

Ab binding to TSH receptors on orbital fibroblasts –> production og glycosaminoglycans and fat which causes swelling of muscles and tissues behind the eye

Question 19

How is Graves treated?

Answer 19

Carbimazole - inhibits TSH synthesis
radioiodine (high hypothyroidism risk)
thyroidectomy
beta blockers good for symptomatic control
steroids for immunosuppression

Question 20

What are the clinical features of multinodular goitre?

Answer 20

large, lumpy nodules
technetium scan show fewer hotspots
can block trachea if very big
increased thyroid hormones occur at later stages

Question 21

How is multinodular goitre/single toxic nodule treated?

Answer 21

radioiodine
surgery (esp. if tracheal compression)
long-term carbimazole

Question 22

How does thyroiditis lead to temporary hyperthyroidism?

Answer 22

autoimmune disruption of tissue in thyroid
Any TSH stored is released from colloid
treatment not required as thyroid gland not overactive, so TSH stops being released eventually

Question 23

What are the clinical features of hypothyroidism?

Answer 23

weight gain, tired, cold intolerance, muscle stiffness, constipation, hyperlipidaemia, dry hair/skin

Question 24

What are common causes of hypothyroidism?

Answer 24

hashimoto's (autoimmune)
- Ab attack thyroid
- permanent
iatrogenic 
- post-op
- radioactive iodine
spontaneous atrophy
temporary thyroiditis
- viral, post-partum

Question 25

What are some uncommon causes of hypothyroidism?

Answer 25

hypopituitarism (not enough TSH - secondary hypothyroidism)
congenital
iodine deficiency
drugs

Question 26

What is used to treat hypoparathyroidism?

Answer 26

oral thyroxine