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Clinical Biochem > Thyroid Disease > Flashcards

Thyroid Disease Flashcards

1
Q

What are the functions of thyroid hormones ?

A
  • increase heat production
  • increase oxygen consumption
  • increase metabolism of proteins, fats & carbs
  • promotes normal growth
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2
Q

What are the thyroid hormones?

A
  • thyroxine = T4
  • Tri-iodothyronine = T3
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3
Q

Describe the conversion of T4 into T3

A
  • occurs in most tissues - particularly the liver
  • conversion of T4 to T3 is reduced in systemic illness & drugs
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4
Q

What are the reference ranges for Total & Free T4 ?

A

Total = 60-150 nmol/L
Free = 9-26 pmol/L

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5
Q

What are the references ranges for total & free T3 ?

A

Total = 1.2-2.9 nmol/L
Free = 3.0-8.8 pmol/L

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6
Q

Describe the regulation of thyroid hormones

A
  • negative feedback control of T4 & T3
  • free T3 & T4 determines feedback
  • thyroid stimulating hormone & thyroid releasing hormone also involved
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7
Q

What 2 hormones are involved in regulation ?

A
  • Thyroid stimulating hormone
  • Thyroid releasing hormone
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8
Q

Describe the beginning of thyroid hormone synthesis

A
  • dietary iodide absorbed by small intestine
  • 1/3 of this iodide is concentrated in thyroid glad & rest is excreted
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9
Q

What is the main binding protein for T3 & T4 ?

A
  • thyroxine binding globulin
    (albumin secondly)
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10
Q

What happens to the iodide in the thyroid gland?

A
  • iodide is oxidised to iodine in thyroid follicular cells
  • iodination of tyrosines on colloid thyroglobulin forms monoiodotyrosine(MIT) & diiodotyrosine (DIT)
  • coupling forms t4 (DIT+DIT) & T3 (DIT+MIT)
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11
Q

How are thyroid hormones stored?

A
  • attached to colloid thryoglobulin
  • thyroglobulin is taken up by follicular cells via pinocytosis
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12
Q

How are stored thyroid hormones released ?

A
  • lysosomes fuse with stored droplet & proteases digest thyroglobulin to release the thyroid hormones
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13
Q

What is the incidence of hypothyroidism in the UK?

A
  • Men = 0.2%
  • Women =2.0%
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14
Q

What age group is most affected by hypothyroidism ?

A
  • 50/60 year olds
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15
Q

What are some of the primary causes of hypothyroidism ?

A
  • Hashimoto’s thyroiditis
  • post- thyroidectomy
  • anti-thyroid drugs
  • iodine deficiency
  • congenital hypothyroidism
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16
Q

What is a secondary cause of hypothyroidism ?

A
  • pituitary/hypothalamic effect
17
Q

What are some of the clinical features of Hypothyroidism ?

A
  • weight gain
  • puffy face, hands & feet
  • reduced appetite
  • bradycardia
  • cold intolerance
  • menstrual abnormality
  • deep hoarse voice
18
Q

What are some ways to manage hypothyroidism ?

A
  • Replacement therapy with T4
  • monitoring of therapy with TSH
19
Q

What are some pros to T4 replacement therapy ?

A
  • readily available
  • safe
  • inexpensive
20
Q

Define hypothyroidism

A

Under active thyroid gland

21
Q

Define hyperthyroidism

A

overactive thyroid gland

22
Q

What’s the incidence of hyperthyroidism ?

A

1% female
0.1% male

23
Q

What are some common causes of hyperthyroidism ?

A
  • graves disease
  • toxic nodules
  • thyroid hormone intake
24
Q

What are some rare causes of hyperthyroidism ?

A
  • ectopic thyroid tissue
  • ash secreting tumours
25
Q

What are the clinical features of hyperthyroidism ?

A
  • weight loss
  • increased sweating
  • tachycardia
  • heat intolerance
  • menstrual abnormalities
26
Q

How can hyperthyroidism be managed ?

A
  • anti thyroid drugs = carbimazole
  • radioiodine therapy - 131 I therapy
  • thyroidectomy
27
Q

Describe T3 & T4 in hypothyroidism

A
  • Free T4 is low
  • Free T3 can be normal
28
Q

Describe T3 & T4 in hyperthyroidism

A
  • Free T4 is high
  • Free T3 is highly raised
29
Q

Describe Thyroid Stimulation hormone in hypo/hyper-thyroidism

A
  • high in hypothyroidism
  • low in hyperthyroidism
30
Q

Describe Non-thyroidal Illness

A

(Sick euthyroid syndrome)
- thyroid regulation& metabolism disturbed in systemic illness
- increased conversion of T4 to reverse T3
- TSH may be normal or low
- wait till patient recovers from illness before testing thyroid function

31
Q

Describe T3 Toxicosis

A
  • patients have very high T3 but T4 is within ref range
  • TSH often very low or undetectable
  • often presents with clinical hyperthyroidism

Clinical Biochem (13 decks)

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