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BRS > The thyroid gland > Flashcards

The thyroid gland Flashcards

1
Q

What can be found in the thyroid?

A

Parathyroid glands (4 in total- superior and inferior on each side)

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2
Q

What nerve runs close to the thyroid gland?

A

Left recurrent laryngeal nerve

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3
Q

Describe the embryology of the thyroid gland

A
  1. Midline out pouches from floor of pharynx (originates from base of tongue)
  2. Development of thyroglossal duct
  3. Duct divides into 2 lobes
  4. Duct disappears leaving foramen caecum
  5. Final position by week 7 of gestation
  6. Thyroid gland then develops
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4
Q

What hormones does the thyroid gland secrete?

A

tri-iodothyronin (T3)

thyroxine (T4)

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5
Q

How does the thyroid release T3 and T4 into circulation?

A
  1. Thyroid stimulating hormone (TSH) binds to TSH receptor on follicular cell in thyroid- causes production of thyroglobulin and thyroid peroxidase (TPO)
  2. Iodine ions travel from blood through Na+/I- transporters into follicular cell then into colloid
  3. Iodine ion oxidised to iodine (iodination)- TPO ad H2O2 catalyse iodination
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6
Q

How are T3 and T4 made from thyroglobin?

A
  1. Iodination of thyroglobin (thyroglobulin + iodine catalysed by TPO and H2O2) results in formation of mono-iodothyronine (MIT) and di-iodothyronine (DIT)
  2. Coupling of MIT and DIT forms tri-iodothyronine (T3), coupling of DIT and DIT gives thyroxine (T4)
  3. T3 and T4 released into bloodstream
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7
Q

What is the importance of tyrosine?

A

Found in Thyroglobulin

Can bind to iodine

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8
Q

What happens to T4?

A

T4 is the main product of thyroid gland and is converted into T3 (the bioactive form) by deiodinase enzyme
T4 can also be deiodinated in a different position to form reverse T3
T3 provides almost all of the thyroid hormone activity in target cells

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9
Q

How is thyroid hormone transported around the blood?

A 
Mostly bound to plasma proteins:
Thyroid- binding globulin: TBG (70- 80%)
Albumin (10 - 15%)
Prealbumin (aka transthyretin)
A very small amount of T3 and T4 in unbound
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10
Q

How does thyroid hormone effect gene expression?

A

T3/T4 enter cell through respective receptors
T4 is deiodinated to T3
T3 acts on nuclear receptor to alter gene

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11
Q

What is the function of thyroid hormone?

A
  1. Essential for growth and development, particularly CNS- if there is untreated congenital hypothyroidism you get cretinism (baby can’t produce thyroid hormone)
  2. In pregnancy foetus takes thyroid hormone from mother
  3. Increases basal metabolic rate
  4. Needed for carbohydrate, protein and fat metabolism
  5. Potentiate actions of catecholamines
  6. Effects on CNS, GI and reproductive system
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12
Q

How do we measure TSH in a new-born?

A

Heel- prick test

High TSH level result suggests baby has congenital hypothyroidism

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13
Q

What is the half-life of T3 and T4?

A

T4: ~7-9 days
T3: ~2 days

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14
Q

How is thyroid hormone production controlled?

A

TRH in hypothalamus stimulates release of TSH in anterior pituitary gland which stimulates release of thyroid hormone
High levels of thyroid hormone lead to less TSH and TRH secretion (negative- feedback)

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15
Q

What is primary hypothyroidism?

A

Autoimmune damage to the thyroid
Thyroxine levels decline
TSH levels increase

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16
Q

What are the 2 commonest forms of autoimmune thyroid diseases?

A

Hashimoto’s thyroiditis (undereactive thyroid)

Grave’s disease (overreactive thyroid)

17
Q

What are symptoms and signs of primary hypothyroidism?

A 
Deep voice
Depression and tiredness
Cold intolerance
Weight gain and reduced appetite 
Constipation
Bradycardia
Eventual myxoedema coma
18
Q

How do you diagnose primary hypothyroidism?

A

Thyroid function tests: FT4, FT3 and TSH

19
Q

What is hyperthyroidism?

A

Thyroid makes too much thyroxine
Thyroxin levels rise
TSH levels drop

20
Q

What are causes of hyperthyroidism?

A

Grave’s disease
Toxic multinodular goitre
Solitary toxic nodule

21
Q

What is Grave’s disease?

A

Autoimmune disease where antibodies bind to and stimulate TSH receptor in the thyroid
Associated with smooth goitre
Other antibodies bind to muscles behind eye: exophthalmos
Other antibodies stimulate growth of soft tissue on shins: pretibial myxoedema

22
Q

What are symptoms of hyperthyroidism?

A 
Heat intolerance 
Weight loss and increased appetite
Myopathy
Palpitations (Tachycardia)
Mood swings
diarrhoea
Tremor of hands
Sore eyes
23
Q

What are 2 treatment options for hypothyroidism and hyperthyroidism?

A

Levothyroxine

Combination thyroid hormone replacement

24
Q

What is levothyroxine?

A

Drug for both hypothyroidism and hyperthyroidism
Common dose is 100mg but dose adjusted accordingly
Commonly administered orally

25
Q

What is combined thyroid hormone therapy?

A

Combination T3/T4
Some report improvement in wellbeing
Complicated by symptoms of toxicity: palpitations, tremors and anxiety- often combination therapy supresses TSH

BRS (60 decks)

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