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Endocrine > Thyroid function in health and disease > Flashcards

Thyroid function in health and disease Flashcards

1
Q

What are the two major functions of the thyroid gland?

A

Secrete thyroid hormones to regulate metabolism

Secrete calcitonin to regulate calcium levels

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2
Q

Describe the histology of the thyroid gland?

A

Follicle = colloid surrounded by follicular cells

C cells in interstital spaces

Capillaries in interstital spaces

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3
Q

What is contained in the colloid?

A

Glycoprotein mix containing thyroglobulin

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4
Q

What do the C cells in the thyroid gland secrete?

A

Calcitonin

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5
Q

Where in the thyroid gland are thyroid hormones synhtesised?

A

Colloid (where thyroglobulin is)

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6
Q

Describe the process of thyroid hormone synthesis?

A
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7
Q

Where in the thyroid gland is thyrogobulin synthesised?

Where is it stored?

A

Synthesised in follicular cells

Stored in colloid

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8
Q

How is iodine transported into follicular cells and colloid for thyroid hormone synthesis?

A

Na-I symporter brings I and Na into follicular cell from blood

Pendrin transporter moves I into colloid from follicular cell

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9
Q

Describe what happens to iodine once it enters the colloid?

A

Iodine added to tyrosine > MIT

Iodine added to MIT > DIT

MIT added to DIT> T3

DIT added to DIT > T4

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10
Q

What happens to thyroglobulin after the thyroid hormones have been added to it?

A

Reabsorbed into follicular cells

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11
Q

How are the thyroid hormones released from thyroglobulin?

A

Enzymes in follicular cells separate T3 and T4 from thyroglobulin

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12
Q

How do T3 and T4 enter the circulation?

A

Lipophilic > diffuse from follicular cells

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13
Q

How are T3 and T4 carried in the blood?

Why?

A

Thyroid binding globulin

Albumin

Transthyretin

Because they are lipophilic

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14
Q

Describe the structure of thyroid hormones?

A

T4: tetraiodothyronine

T3: triodothyronine

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15
Q

Where is most T3 derived from?

A

80% from T4: deiodinase

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16
Q

Describe the thyroid hormone control pathway?

A
17
Q

Describe the half life of the thyroid hormones?

A

T4: 6-7 days

T3: 1 day

18
Q

Describe the factors that affect the release of thyroid hormones?

A

Tonic release

19
Q

Where is the receptor for thyroid hormones located?

A

Nuclear receptor on most cells and tissues

20
Q

Describe the actions of thyroid hormones?

A

Increase BMR and oxygen consumption

Modulate metabolism

Sympathomimetic effect

Growth promoting

Nervous system development

21
Q

Describe the hormone levels in primary hypothyroidism?

Is a goiter present? Why?

A

Low T3 and T4, high TSH (no negative feedback)

Goiter present , as high TSh stimulates growth of thyroid

22
Q

Describe the hormone levels in secondary hypothyroidism?

Is a goiter present? Why?

A

Low T3 and T4

Low TRH and/or TSH (hypothalamic or pituitary failure)

No goiter, as there is not any TSH present to drive growth

23
Q

What is the most common cause of hypothyroidism?

A

Iodine deficiency

24
Q

List the causes of congenital hypothyroidism?

A

Maternal iodine deficiency

Fetal thyroid dysgenesis

Inborn errors of thyroid hormone synthesis

Maternal antithyroid antibodies (cross placenta)

Fetal pituitary hypothyroidism

25
Q

Describe the hormone levels in primary hyperthyroidism?

Is a goiter present? Why?

A

High T3 and T4

Low TSH (negative feedback from T3 and T4)

Goiter present, as stimulating auto-Ab encourgaes growth

26
Q

Describe the causes of primary hyperthyroidism?

A

Autoimmune: Grave’s disease, thyroid stimulatin immunoglobulin

27
Q

Describe the hormone levels in secondary hyperthyroidism?

Is a goiter present? Why?

A

Due to hypothalamic or pituitary excess: high T3 and T4, high TRH and/or TSH > goiter (TSH)

Due to hypersecreting tumour: high T3 and T4, low TSH (negative feedback) > low goiter (low TSH)

28
Q
A

Endocrine (17 decks)

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