Thyroid 1

Question 1

What does the thyroid gland secrete?

Answer 1

Thyroxine (T4), Tri-iodothyronine (T3), Calcitonin

Question 2

What do the parathyroid glands secrete?

Answer 2

PTH

Question 3

What structure makes up the thyroid gland?

Answer 3

Follicles

Question 4

What makes up follicles?

Answer 4

Follicular cells and inner colloid

Question 5

What is the colloid?

Answer 5

Tyrosine containing thyroglobulin filled spheres enclosed by follicular cells

Question 6

What do parafollicular C cells secrete?

Answer 6

Calcitonin

Question 7

What happens in iodide sequestration?

Answer 7

Inorganic iodide is trapped by the gland by an enzyme dependent system, oxidised and incorporatd into the glyco protein thyroglobulinto form mono and diiodotyrosine, thyroid hormone precursors.

Question 8

What coupling occurs after the production of MIT and DIT, and where are they stored?

Answer 8

MIT+DIT (T3), AND 2 DITs(T4) which are stored in colloid thyroglobulin till required

Question 9

How much of the thyroid hormones secreted is T4?

Answer 9

~90%

Question 10

How many times more potent is T3 than T4?

Answer 10

Roughly 4x

Question 11

What organs convert T4 to T3?

Answer 11

Liver, kidney, (and muscle)

Question 12

How do T3 and T4 move from the colloid to follicular cell?

Answer 12

Pinocytosis

Question 13

Why do T3 and T4 bind to plasma proteins when released from follicular cells?

Answer 13

As they are hydrophobic and lipophilic

Question 14

What plasma proteins do T3 and T4 bind to in the blood stream?

Answer 14

Thyroxine binding globulin (around 70%), Thyroxine binding prealbumin (TBPA around 20%), albumin (around 5%)

Question 15

In what form at T3 and T4 biologically active?

Answer 15

Unbound

Question 16

How much less avidly is T3 bound by TBG and TTR than T4?

Answer 16

10-20x less avidly by TBG, and not significantly at all by TTR

Question 17

What does an increased /decreased TBG level cause?

Answer 17

Increased/decreased total T4 but not free T4

Question 18

What are some causes of an increased TBG?

Answer 18

Pregnancy, newborn state, oestrogen sources, Tamoxifen, Hep A

Question 19

What are some causes of decreased TBG?

Answer 19

Androgens, large doses glucocorticoids, Cushings S, active acromegaly, severe systemic illness

Question 20

What do carbimazole and propylthiouracil inhibit in the treatment of hyperthyroidism?

Answer 20

Iodine attachment to tyrosine residues to form MIT and DIT

Question 21

What do thyroid hormones do the basal metabolic rate and thermogenesis?

Answer 21

Increase them

Question 22

What do thyroid hormones do to carbohydrate metabolism?

Answer 22

Increase blood glucose, and increase insulin-dependent glucose uptake into cells

Question 23

What do thyroid hormones do to lipid metabolism?

Answer 23

Mobilise fats from adipose tissue, increase fatty acid oxidation in tissues

Question 24

What do thyroid hormones do to protein metabolism?

Answer 24

Increase protein synthesis

Question 25

Why are thyroid hormones important in growth?

Answer 25

GHRH production and secretion, glucocorticoid-induced GHRH release and GH/somatomedins require thyroid hormones or the presence of them for activity

Question 26

How do thyroid hormones effect development of foetal and neonatal brain?

Answer 26

Myelinogenesis & axonal growth require thyroid hormones

Question 27

What are the effects of thyroid hormone on the sympathetic nervous system?

Answer 27

Increased catecholamine sensitivity and B-adrenergic receptor numbers in heart, skeletal muscle, adipose cells and lymphocytes, and decrease cardiac alpha-adrenergic receptors

Question 28

What are the effects of thyroid hormone on the CVS?

Answer 28

Increases HR and CO

Question 29

What stimulates TSH release from anterior pituitary?

Answer 29

Thyrotrophin releasing hormone (TRH) from hypothalamus

Question 30

What do low temperatures do to thyroid hormone regulation?

Answer 30

In babies/young children, cold environments stimulate TRH release, stimulates TSH release so increases T3 and T4 release

Question 31

What does stress do in thyroid hormone regulation?

Answer 31

Inhibits TRH and TSH

Question 32

What is the circadian rhythm in thyroid hormone production?

Answer 32

Highest late at night, lowest in morning

Question 33

What subfamily of enxzymes are important in the activation/deactivation of thyroid hormone at tissue level?

Answer 33

Delodinase enzymes (Type 1,2,3)

Question 34

How do delodinase enzymes make thyroid hormone inactive?

Answer 34

Addition or removal of an iodine atom in outer ring

Question 35

What delodinase enzyme activates T4 to T3 in tissues?

Answer 35

D2

Question 36

Where is D1 found?

Answer 36

Commonly in liver and kidney

Question 37

Where is D2 found?

Answer 37

Heart, skeletal muscle, CNS, fat, thyroid, pituitary

Question 38

Where is D3 found?

Answer 38

Fetal tissue, placenta, brain (except pituitary)

Question 39

What are the most common types of thyroid cancer?

Answer 39

Papillary (76%), follicular (17%)

Question 40

What hormone drives DTC?

Answer 40

TSH

Question 41

iS DTC more commen in men or women?

Answer 41

Women

Question 42

What are the differentiated thyroid cancers?

Answer 42

Papillary and follicular

Question 43

How does papillary thyroid cancer spread and where to?

Answer 43

Via lymphatics-local spread. Haematogenous spread to lungs, bone, liver and brain

Question 44

What thyroid condition is papillary thyroid cancer associated with?

Answer 44

Hashimoto's thyroiditis

Question 45

What is the prognosis of papillary thyroid cancer?

Answer 45

Good-better if young and female

Question 46

How does follicular carcinoma tend to spread?

Answer 46

Haematogenously to lung and bone.

Question 47

What is the prognosis of follicular carcinoma?

Answer 47

Good

Question 48

What investigations are required in DTC?

Answer 48

After initial thyroid tests, US guided FNA, can involve excision biopsy of LN

Question 49

What is the usual management of DTC?

Answer 49

Surgery- lobectomy with isthmusectomy, sub-total or total thyroidectomy