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Endocrinology > Thyroid > Flashcards

Thyroid Flashcards

1
Q

Where does the thyroid sit?

A

Lies in front of the trachea and larynx

Below thyroid cartilage and cricoid cartilage

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2
Q

What joins the two lobes?

A

Isthmus

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3
Q

What is the histology of thyroid tissue?

A

Follicular cells arranged in spheres called thyroid follicles

Follicles filled with colloid (extracellular)

Parafollicular cells around follicles

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4
Q

What is colloid?

A

A deposit of thyroglobulin

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5
Q

What do follicular cells produce?

A

Thyroid hormone

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6
Q

What do parafollicular cells produce?

A

Calcitonin

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7
Q

What are the thyroid hormones?

A

T3 - triiodothyronine

T4 - tetraiodothyronine (thyroxine)

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8
Q

What is the structure of thyroid hormones?

A

2 tyrosines linked together with iodine at 3 or 4 positions on the aromatic rings

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9
Q

What is the function of thyroglobulin?

A

Acts as a scaffold for formation of thyroid hormones

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10
Q

What is thyroid peroxidase?

A

Membrane bound enzyme that regulates reactions involving iodine

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11
Q

Which reactions does thyroid peroxidase regulate?

A
  1. Oxidation of iodide to iodine (requires h2o2)
  2. Addition of iodine tyrosine acceptor residues on thyroglobulin
  3. Coupling of MIT or DIT to generate thyroid hormones
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12
Q

How is dietary iodine absorbed?

A

Reduced to iodide before absorption in small intestine

Iodide taken up from blood by thyroid epithelial cells
- sodium-iodide symporter

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13
Q

How is T4 converted to T3?

A

Thyroid secretes T4

Converted to T3 in liver and kindeys

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14
Q

How are T4/T3 transported in blood?

A

Thyroxine-binding globulin

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15
Q

What is TSH?

A

Thyroid stimulating hormone

Glycoprotein hormone

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16
Q

What is the effect of TSH?

A

Trigger for thryoid hormone release

Stimulates

  • iodide uptake
  • iodide oxidation
  • thyroglobulin synthesis
  • thyroglobulin iodination
17
Q

What are the general actions of thyroid hormone?

A

Increase in basal metabolic rate

  • increase number + size of mitochondria
  • stimulate synthesis of enzymes in respiratory chain

Stimulation of metabolic pathways

  • lipid metabolism - stimulate lipolysis + β-oxidation of fatty acids
  • carb metabolism - increase gluconeogenesis + glycogenolysis

Increase cell response to catecholamines

18
Q

What are the cardiovascular actions of thyroid hormone?

A

Increases heart’s responsiveness to catecholamines

  • increase cardiac output
  • increase heart rate
  • increase force of contraction
  • increase peripheral vasodilation
19
Q

What are the nervous system actions of thyroid hormone?

A

Increase myelination of nerves

Increase development of neurons

20
Q

What is goitre?

A

Enlargement of thyroid gland

21
Q

What causes hypothyroidism?

A 
Failure of thyroid
TSH/TRH deficiency 
Inadequate dietary iodine 
Autoimmunity
Post-surgery
22
Q

What are the hormone levels in hypothyroidism?

A

Low T3
Low T4
High TSH

23
Q

What are the general symptoms of hypothyroidism?

A 
Obesity 
Lethargy 
Intolerance to cold
Bradycardia
Constipation
24
Q

What happens in infants with hypothyroidism?

A

Cretinism

  • dwarfed stature
  • mental deficiency
  • poor bone development
  • GI disturbances
25
Q

What happens in adults with hypothyroidism?

A

Myxoedema

  • thick puffy skin
  • muscle weakness
  • slow speech
26
Q

What is Hashimoto’s disease?

A

Autoimmune destruction of thyroid follicles

Cause of hypothyroidism

27
Q

Who is Hashimoto’s disease more common in?

A

Women

28
Q

What is the treatment for Hashimoto’s disease?

A

Oral thyroxine

29
Q

What causes hyperthyroidism?

A

Autoimmune (Graves’)
Toxic multinodular goitre
Drugs (amiodarone)
Thyroid carcinoma

30
Q

What are the general symptoms of hyperthyroidism?

A 
Weight loss
Irritability 
Heat intolerance
Tachycardia
Fatigue

Bulging eyes
Goitre

31
Q

What is Graves’ disease?

A

Autoimmune disease resulting in hyperthyroidism

Production of TSI

32
Q

What are the hormone levels in hyperthyroidism?

A

High T3
High T4
Low TSH

33
Q

What are the symptoms of Graves’ disease?

A 
Increase in basal metabolic rate
Excessive sweating 
Weight loss
Muscle weakness
Palpitations 
Bulging eyes
34
Q

What is thyroid scintigraphy?

A

Imaging of thyroid using technetium-99

35
Q

What is used to treat hyperthyroidism?

A

Anti-thyroid drugs - carbimazole

Prevents thyroid peroxidase from coupling an iodinating tyrosines of thyroglobulin

Endocrinology (13 decks)

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