Thyroid function in health and disease Flashcards Preview

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Flashcards in Thyroid function in health and disease Deck (28)
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1

What are the two major functions of the thyroid gland?

Secrete thyroid hormones to regulate metabolism

Secrete calcitonin to regulate calcium levels 

2

Describe the histology of the thyroid gland?

Follicle = colloid surrounded by follicular cells

C cells in interstital spaces 

Capillaries in interstital spaces 

3

What is contained in the colloid?

Glycoprotein mix containing thyroglobulin 

4

What do the C cells in the thyroid gland secrete?

Calcitonin

5

Where in the thyroid gland are thyroid hormones synhtesised?

Colloid (where thyroglobulin is)

6

Describe the process of thyroid hormone synthesis?

7

Where in the thyroid gland is thyrogobulin synthesised?

Where is it stored?

 

Synthesised in follicular cells

Stored in colloid 

8

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

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

Pendrin transporter moves I into colloid from follicular cell

9

Describe what happens to iodine once it enters the colloid?

Iodine added to tyrosine > MIT

Iodine added to MIT > DIT

MIT added to DIT> T3

DIT added to DIT > T4

10

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

Reabsorbed into follicular cells

11

How are the thyroid hormones released from thyroglobulin?

Enzymes in follicular cells separate T3 and T4 from thyroglobulin

12

How do T3 and T4 enter the circulation?

Lipophilic > diffuse from follicular cells

13

How are T3 and T4 carried in the blood?

Why?

Thyroid binding globulin

Albumin

Transthyretin 

Because they are lipophilic 

14

Describe the structure of thyroid hormones?

T4: tetraiodothyronine

T3: triodothyronine

15

Where is most T3 derived from?

80% from T4: deiodinase 

 

16

Describe the thyroid hormone control pathway?

17

Describe the half life of the thyroid hormones?

T4: 6-7 days

T3: 1 day

18

Describe the factors that affect the release of thyroid hormones?

Tonic release 

19

Where is the receptor for thyroid hormones located?

Nuclear receptor on most cells and tissues 

20

Describe the actions of thyroid hormones?

Increase BMR and oxygen consumption

Modulate metabolism

Sympathomimetic effect

 

Growth promoting

Nervous system development

21

Describe the hormone levels in primary hypothyroidism?

Is a goiter present? Why?

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

Goiter present , as high TSh stimulates growth of thyroid

22

Describe the hormone levels in secondary hypothyroidism?

Is a goiter present? Why?

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

What is the most common cause of hypothyroidism?

Iodine deficiency

24

List the causes of congenital hypothyroidism?

Maternal iodine deficiency

Fetal thyroid dysgenesis

Inborn errors of thyroid hormone synthesis

Maternal antithyroid antibodies (cross placenta)

Fetal pituitary hypothyroidism

 

25

Describe the hormone levels in primary hyperthyroidism?

Is a goiter present? Why?

High T3 and T4 

Low TSH (negative feedback from T3 and T4)

Goiter present, as stimulating auto-Ab encourgaes growth

26

Describe the causes of primary hyperthyroidism?

Autoimmune: Grave's disease, thyroid stimulatin immunoglobulin 

27

Describe the hormone levels in secondary hyperthyroidism?

Is a goiter present? Why?

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