The Thyroid Gland

Question 1

Diagram of the thyroid

Answer 1

Moves up when swallowing

30% of people have the extra pyramid

Colloid contains mucus and extracellular fluid

Question 2

Diagram of thyroid gland

Answer 2

Parathyroid glands embedded in thyroid (produces calcium)

Left recurrent laryngeal nerve run close (supplies vocal chords)

Question 3

Embryology of thyroid gland

Answer 3

Question 4

Thyroid histology

Answer 4

Red blood vessels - red

White line/dots - where hormones are being made

Question 5

Production of hormone in thyroid gland

Answer 5

TSH - thyroid stimulating horme

TG - Thyroglobulin (made by binding of TSH)

TPO - Thyroid peroxidase enzyme (made by binding TSH)

Question 6

Chemical reactions in the thyroid gland

Answer 6

Question 7

What happens during deiodination of triiodothyronine

Answer 7

Thyroxine (T4-prohormone) deiodinated to triiodothyronine (T3) - bioactive form

Deiodinated in a different position to produce reverse T3 (inactive)

T4 is converted by deiodinase enzyme

T3 - 80% from deiodination 20% from thyroidal secretion

T3 provides almost all the thyroid hormone activity

Question 8

How is T3 and T4 transported in the blood

Answer 8

Bound to plasma proteins (inactive)

1. Thyroid-binding globulin: TBG (70-80%)
2. Albumin (10-15%)
3. Prealbumin

Only 0.05% T4 and 0.5% T3 is unbound (bioacitve components

Question 9

What does T3 do

Answer 9

Alter gene expression by binding onto thyroid hormone receptor

Question 10

What is the TSH in newborns

Answer 10

Heel-prick test

Question 11

What is untreated congenital hypothyroidism called

Answer 11

Cretinism

Question 12

Why is thyroid essential for fetal

Answer 12

Growth and development

CNS

Question 13

What action does thyroid homrones have

Answer 13

T4 - 7-9 days

T3 - 2 days

Question 14

What is the Wolff Chaikoff effect

Answer 14

Ingest high levels of iodine to reduce thyroid hormone

Question 15

How do you control thyroid hormone production

Answer 15

Negative feedback

Question 16

Who is more predisposed to thyroid

Answer 16

Women 4:1

Question 17

How does hypothyroidism arise

Answer 17

Hashimoto’s thyroditis disease

Graves’ disease (rarely)

Presence of one autoimmune disease increases risk of others

Question 18

Symptoms of primary hypothyroidism

Answer 18

Eventual myxoedema coma

Cold intolerance

Question 19

WHat is levothyroxine and how can it help

Answer 19

It replaces T4

Hyperthyroidism (by blocking the production of T3 and T4 and replacing it)

Common dose 100 mg

Administered orally

Might get weight loss or headache, heart attack and rapid HR

Question 20

Why isn’t a T3 drug used

Answer 20

Because it has no effect

More expensive

Question 21

Using a combination of T4/ T3 reports what

Answer 21

Improvement in wellbeing

May have complications of toxicity - palpitations, tremor, aniety - surpresses TSH

Question 22

What are causes of hyperthyroidism

Answer 22

Graves disease - gland is smoothly enlarged and overactive

Toxic multinodular goitre

Solitary toxic nodule

Question 23

Symptoms of hyperthyroidism

Answer 23

Question 24

What happens in graves disease

Answer 24

Antibodies bind and sitmulate TSH receptor in thyroid

Other antibodies bind to muscles behind eye which causes exopthalmos - bulging of the eye, sore

Other antibodies stimulate growth of soft tissue of shins - pretibial myxoedema