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Gabe's Endocrinology > Thyroid function in health and disease > Flashcards

Thyroid function in health and disease Flashcards

1
Q

What comprises the thyroid gland?

A
  • Follicular cells surrounding colloid
  • Colloid (glycoprotein mix) contains thyroglobulin (Tg)
  • C cells in interstitial spaces secrete calcitonin
    • Calcium metabolism
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2
Q

How is thyroid hormone synthesised?

A
  1. Follicular cell synthesises enzymes and thyroglobulin for colloid.
  2. A Na+-I- symporter brings I- into the follicular cell. The pendrin transporter moves I- into the colloid.
  3. Enzymes add iodine to tyrosine to make T3 and T4
  4. Thyroglobulin is taken back into the cell in vesicles.
  5. Intracellular enzymes separate T3 and T4 from the protein
  6. Free T3 and T4 enter the circulation
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3
Q

Which is the most potent of the thyroid hormones?

A

T3

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4
Q

What is 80% of T3 (tetraiodothyronine) derived from?

A

T4

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5
Q

Which enzyme converts T4 to T3?

A

Deiodinase

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6
Q

What do thyroid hormones bind to in the circulation?

A

Plasma proteins - because they’re lipophilic

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7
Q

What is the difference between T3 and T4?

A
  • T3: 2 tyrosines and 3 iodides.
  • T4: 2 tyrosines and 4 iodides.
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8
Q

What stimulates all steps in thyroid hormone synthesis?

A

TSH

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9
Q

What is the only known factor to increase TRH?

A

Cold in infants

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10
Q

What decreases TRH?

A

Stress

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11
Q

What is the target receptor for thyroid hormones?

A

Nuclear receptor

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12
Q

What are the whole body tissue actions of thyroid hormones?

A
  • Increased oxygen consumption (thermogenesis)
  • Protein catabolism in adults but anabolism in children.
  • Normal development of nervous system
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13
Q

What is the action of thyroid hormones at the cellular level?

A

Increases activity of metabolic enzymes and Na+-K+-ATPase

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14
Q

What are the sympathomimetic effects of thyroid hormones?

A

Increased heart rate and cardiac output

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15
Q

What are the actions of thyroid hormones?

A
  • Increased BMR & oxygen consumption: calorigenic / heat producing effects
  • Modulate metabolism
  • Sympathomimetic effect; increased heart rate, cardiac output
  • Not essential for life but essential for child growth & development
  • Growth promoting
    • Fetal life
    • After birth essential for GH & IGFs actions
  • Nervous system development
    • Before & after birth
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16
Q

What is primary hypothyroidism?

A
  • Failure of the thyroid.
  • Decreased T3, T4 and increased TSH, leading to goitre.
17
Q

What will decreased dietary iodine lead to?

A
  • ↓T3, T4
  • ↑TSH
  • Goitre
18
Q

What is secondary hypothyroidism?

A
  • Hypothalamic or anterior pituitary failure/tumor.
  • ↓ T3, T4, TRH ± ↓ TSH.
  • No goitre!
19
Q

What is cretinism?

A

Congenital birth defect from iodine insufficiency leading to dwarfism and mental retardation.

20
Q

What is the most common of all the endocrine illnesses?

A

Hypothyroidism - iodine deficiency most common cause.

21
Q

What are the causes of congenital hypothyroidism?

A
  • Maternal iodine deficiency
  • Foetal thyroid disease
  • Inborne errors of thyroid hormone synthesis
  • Maternal antithyroid antibodies that cross the placenta
  • Foetal hypopituitary hypothyroidism
22
Q

What are the physiological effects of hypothyroidism?

A
  • Decreased BMR & O2 consumption, decreased energy, increased weight
  • Cold intolerance
  • Sympathetic effects, decreased heart rate
  • Central effects, decreased mentation & reflexes, fatigue
  • Decreased protein synthesis, accumulate mucopolysaccharides under skin = puffy appearance of myxoedema
23
Q

What is the treatment for hypothyroidism?

A
  • Replace thyroid hormone
  • Adequate dietary iodine
24
Q

What is primary hyperthyroidism?

A
  • Grave’s disease, autoimmune problem.
  • ↑ T3 and T4, decreased TSH.
  • Goitre
  • Thyroid stimulating immunoglobulin (TSI) targets TSH receptors.
25
Q

What is secondary hyperthyroidism?

A
  • Hypothalamic or anterior pituitary excess.
  • ↑ T3, T4 TRH ± TSH
  • Goitre
26
Q

What is hypersecreting tumour hyperthyroidism?

A
  • ↑T3 and T4
  • ↓TSH
  • No goitre
27
Q

What is thyroid-stimulating immunoglobulin?

A
  • From B lymphocytes
  • Targets TSH receptors
28
Q

What are the physiological effects of hyperthyroidism?

A
  • ↑BMR and O2 consumption.
  • ↑ appetite, weight loss, muscle weakness heat intolerance
  • ↑ Heart rate
  • ↑ Alertness, irritability and hyperexcitability
  • Grave’s disease: exophthalmos
29
Q

What is exophthalmos due to?

A

Water retaining carbohydrates behind the eyes.

30
Q

What is the treatment for hyperthyroidism?

A
  • Remove thyroid/tumour.
  • Use radioactive iodine to destroy gland.
  • Anti-thyroid drugs - block TH synthesis or conversion of T4 to T3.
31
Q

When does goitre occur?

A

In hyperthyroidism and hypothyroidism

32
Q

What occurs in hypothyroidism due to low iodine?

A

See image.

33
Q

What occurs in hyperthyroidism due to Grave’s disease?

A

See image.

Gabe's Endocrinology (17 decks)

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