Thyroid Hormone Physiology

Question 1

Blood supply to thyroid?

Answer 1

Superior thyroid from external carotid artery.

Inferior thyroid branch of subclavian artery.

Thyroidea ima artery, branch of arch or brachiocephalic trunk

Question 2

Venous drainage of thyroids?

Answer 2

Superior thyroid, middle thyroid vein and inferior thyroid vein. Superior and middle from internal jugular vein and inferior from innominate veins

Question 3

How does lymph drainage?

Answer 3

Prelaryngeal and pretracheal, deep cervical supraclavicular, and mediastinal lymph nodes

Question 4

What is the major problem with thyroid surgery?

Answer 4

You could cause damage to recurrent laryngeal nerve

Question 5

Where does recurrent laryngeal nerve do loop?

Answer 5

Right loops under subclavian artery and left under arch of aorta

Question 6

What is thyroid made of?

Answer 6

Follicles-mono layer of epithelial cells enclosing a large core of viscous homogenous colloid (reserve of thyroid hormone).

Question 7

Thyroid hormones?

Answer 7

T3, t4 and calcitonin

Question 8

After halogenase frees iodide from MIT and DIT what happens?

Answer 8

It is reutilised by combining with thyroglobulin

Question 9

How much thyroid hormone leaves gland?

Answer 9

95% in t4 form

Question 10

Which hormone is more active?

Answer 10

T3 is 40x more active than T4

Question 11

Which enzyme converts t4 to t3?

Answer 11

Deiodinase

Question 12

What makes calcitonin?

Answer 12

Parafollicular c cells

Question 13

How much t4 is converted to reverse t3?

Answer 13

20%

Question 14

Plasma half life?

Answer 14

6-8 days for T4

And 1 day for T3

Question 15

Circulating thyroid hormones?

Answer 15

Thyroxine binding globulin T4, thyroxine binding albumin T3 and thyroxine binding prealbumin

Question 16

What does median eminence release?

Answer 16

Small peptides and dopamine

Question 17

How is t4 and t3 excreted?

Answer 17

Conjugated and excreted in bile

Question 18

Myxedema signs?

Answer 18

Relative obesity and stature. Lots of blubber, looks dopey

Question 19

Derbyshire neck due to?

Answer 19

Enlarged goitre- Places far away from sea, require iodine.

Question 20

Hyperthyroidism treatment?

Answer 20

Carbimazole,propythiouracil, thyroid surgery, radioactive iodine

Question 21

Hypothyroidism treatment?

Answer 21

Replacement therapy T4

Question 22

Core drug to treat thyroid deficiency?

Answer 22

Levothyroxine
Oral bioavailability- 100%
Half life - 7 days
Excretion- 20-40% in urine

At excessive doses you will get palpitations, arrhythmia, diarrhoea, insomnia, tremor, weight loss

Can be used to suppress TSH secretion in the treatment of some thyroid tumours

Question 23

Core drug for hyperthyroidism?

Answer 23

Carbimazole:
After absorption converted to methimazole. Prevents peroxidase iodinating the thyrpglobulin, so less t3 and t4

over 90% oral bioavailability
Half life 6.4 hours
Excretion-90% in urine as metabolites

Adverse effects - rashes priorities, neutropenia, agranulocytosis

Question 24

Carbimazole rare side effect?

Answer 24

Neutropenia and agranulocytosis

Common-pruritis and rashes

Question 25

Drug for pregnancy?

Answer 25

Propylthiouracil, in first semester

Works by inhibiting thyroperoxidase, hence inhibiting thyroid hormone production

Serious liver injury/ agranulocytosis, rashes pruritis

Question 26

Why are thyroid hormones important?

Answer 26

Increased carbohydrate metabolism, increased synthesis mobilisation and degradation of lipids and increased protein synthesis, myelination of nerve fibres

Question 27

Side effects of levothyroxine?

Answer 27

Palpatations, diarrhoea, tremor, weight loss, insomnia, and arrhythmias

Question 28

Thyroid hormone production?

Answer 28

Iodine and tyrosine
Equal monoiodinetyrosine
And diiodotyrosine

MIT and DIT equal T3
DIT and DIT equal t4

Question 29

By what is t4 converted into t3 in tissue?

Answer 29

Iodothyronine deiodinase

Question 30

How are MIT and DIT degraded to release free iodine?

Answer 30

By halogenase and then the free iodide can be reused to combine with thyroglobulin

Question 31

What is main effect of thyroid hormone in increasing basal metabolic rate?

Answer 31

Increase in carbohydrate metabolism, lipid synthesis, mobilisation and degradation
And increased protein synthesis

Question 32

Which cells release calcitonin?

Answer 32

Parafollicular c cells