The Thyroid gland

Question 1

What is the Thyroid made up of?

Answer 1

• Follicles - the colloid surrounded by follicular cells

- Parafollicular cells

Question 2

What lies embedded behind each lobe of the thyroid?

Answer 2

Superior parathyroid gland

Inferior parathyroid gland

Question 3

Which nerve runs close to thyroid?

Answer 3

Left recurrent laryngeal nerve runs close - supplies vocal cords

Question 4

How is the thyroid formed? ( Embryology )

Answer 4

• Midline outpouching from floor of pharynx
• Development of Thyroglossal duct
• Divides into 2 lobes
• Duct disappears leaving foramen caecum
• Final position by week 7
• Thyroid gland then develops

Question 5

What Happens in the Thyroid Gland?

What reactions occur in the colloid?

How do the hormones leave the Thyroid gland?

Answer 5

• TSH binds to TSH-R on follicular cell membrane
• Iodide Ions get transported into follicular cell from Sodium Iodide

The TSH creates TG which going into colloid
The TSH creates TPO (enzyme) which going into colloid
Iodide gets turned into Iodine in colloid ( iodination )

In Colloid:

TPO + hydrogen peroxide acts as an enzyme for the following reaction - Iodine + TG = MIT = DIT

DIT + MIT ( coupling reaction ) also using TPO as enzyme
= T3 / T4

These bind to TG - enter back into follicular cell, they are separated by TG by lysosomes and released into bloodstream

Question 6

What is Iodination of tyrosine?

Answer 6

Iodine reacted with TG creates MIT (Monoiodotyrosine) and DIT ( 3,5 Diiodotryrosine)

MIT + DIT = T3/T4

DIT + DIT = Thyroxine

Question 7

What is Deiodination

Answer 7

• Most T3 is made this way

T4 is the main hormone product of thyroid gland

Question 8

How does T3 alter gene expression?

Answer 8

Can bind and

Question 9

How does T3 alter gene expression?

Answer 9

Can bind and

Question 10

What does Thyroid hormone do (Fetal) ?

Answer 10

Fetal growth and development in particular the CNS

Question 11

What are the characteristics of Cretinism

Answer 11

Congenital hypothyroidism

Baby born without thyroid hormone or gland that functions

Question 12

How is TSH measured in new born infants?

Answer 12

Heel-prick test on day 5

Question 13

What does the thyroid hormone to do metabolims?

Answer 13

Increases basal metabolic rate
Increases protein, carb, fat metabolism

Sympathetic N system = cardiac output

Affect GI tract

Maturation of CNS

Question 14

What controls the thyroid hormone production

Answer 14

Hypothalamic-pituitary-thyroid axis

TRH–>TSH–>Thyroid–> T3+T4

Negative feedback from T3 and T4 turning TRH off in hypothalamus

Question 15

What is the Wolff-chaikoff effect?

Answer 15

Iodine in large quantities it can inhibit T3 T4 production

Question 16

Why are women predisposed to thyroid disorders

Answer 16

Autoimmunity tends to affect thyroid

When pregnant women are exposed to antigens and so their immune systems are more likely to develop autoimmune thyroid disorders

Question 17

What does autoimmune thyroid damage do?

Answer 17

Thyroxine levels decline
TSH levels climbs

( negative feedback )

Question 18

What is Hypothyroidism

Answer 18

Thyroxine levels decline
TSH levels climbs

( negative feedback )

Question 19

What disease is linked to hyper

Answer 19

Graves’ disease

Question 20

What disease is linked to hyperthyroidism?

Answer 20

Graves’ disease

Question 21

What are the signs and symptoms of hypothryroidism?

Answer 21

• Enlarged thyroid gland
• Fatigue, memory impairment, depression
• Swollen face
• Deepening voice
• Cold intolerance
• Weight gain
  reduced appetite
• Bradycardia
• Constipation
• Eventual myxoedema coma

Question 22

What therapeutics can be given to patients with an underactive thyroid?

What is the dosage based on?

Answer 22

Levothyroxine

It mimics the role of the thyroid by producing T4 which gets changed into T3

Dose: according to TSH
( 100 mg )

Side effects - Weight loss and headache – Heart attack

*Sometimes you can give it for hyperthyroidism ( block and replace )

Question 23

What is hyperthyroidism?

Answer 23

Thyroid makes too much thyroxine
TSH levels drop

Toxic multinodular goitre
Solitary toxic nodule

( causes include Graves disease )

Question 24

What are the characteristics of Graves’ disease?

Answer 24

Autoimmune disease

Antibodies bind to TSH receptor in thyroid

Smooth Goitre - enlargement of thyroid

Exophthalmos - antibodies bind to muscles behind eyes
: severe eye complications

Antibodies stimulate growth of soft tissue of shins - Pretibial myxoedema

Question 25

What are the signs and symptoms of hyperthryroidism?

Answer 25

nervousness, Insomnia, Depression
Weightloss
Hunger
Fragile fingernails
Warm moist skin 
Myopathy
Mood swings
Diarrhoea
Tremor of hands
Palpitations
Sore eyes, goitre
Hairloss 
Increased heart rate
High blood pressure