Thyroid Hormones

Question 1

Thyroid gland anatomy

Answer 1

follicles: thyroglobulin solution-filled lumen surrounded by thyroid cells; parathyroid cells b/w follicles synthesize calcitonin

Question 2

What element is needed for thyroid hormone synthesis

Answer 2

IODIDE

Question 3

Iodide transport

Answer 3

Stimulated by TSH= Actively transported into thyroid cells through NA/I symporter; I- is transported from the cell to the follicular lumen via pendrin

Question 4

Na/I symporter

Answer 4

transports Na and I into thyroid cells (TSH stimulated)

Question 5

Pendrin

Answer 5

causes I to move from the thyroid cell into the follicular lumen

Question 6

Thiocyanate and perchlorate

Answer 6

BLOCK NIS transport of iodide

Question 7

How would renal disease affect the thyroid gland?

Answer 7

affect the reabsorption of iodide

Question 8

Production of T3 and T4

Answer 8

thyroglobulin produced by thyroid cells is excreted into lumen and iodine in lumen it reacts with the tyrosine’s (generating MIT) then sequentially DIT; coupling of MIT/DIT generates T3 and T4

Question 9

MIT and DIT

Answer 9

are precursors to T3 and T4 and are biologically inactive

Question 10

Thyroid peroxidase

Answer 10

Uses H2O2 to oxidize I-; also couples MIT and DIT molecules

Question 11

Organification of the Iodide

Answer 11

menas the iodide is added to the tyrosine of the thyroglobulin molecule

Question 12

T4 is formed by

Answer 12

2 DIT molecules

Question 13

T3 is formed by

Answer 13

1 MIT and 1 DIT molecules

Question 14

Propylthiouracil

Answer 14

inhibits the thyroperoxidases (TP); treatment for hyperthyroidism

Question 15

Wolff-Chaikoff Effect

Answer 15

Excessive extracellular iodide is counteracted by an inhibition of organification (H2O2) of the iodide in the thyroid follicles, therefore inhibiting T3 and T4 production

Question 16

Storage of Thyroid hormones

Answer 16

Large amounts stored in follicle attached to thyroglobulin

Question 17

Body cannot store iodide so it stores

Answer 17

thyroid hormones in excess to circumvent a iodide shortage

Question 18

Secretion of thyroid hormone

Answer 18

TSH-dependent megalin receptor causes endocytosis of thyroglobulin by thyroid cells; lysosomes fuse and cleave T3 and T4

Question 19

Megalin

Answer 19

receptor that mobilizes the thyroglobulin colloid droplet from the lumen

Question 20

Cathepsin

Answer 20

lysosomal enzyme that cleaves T3 and T4 from thyroglobulin

Question 21

T4 is solely made by the

Answer 21

thyroid gland

Question 22

T3 is made by

Answer 22

the thyroid gland and the liver cleaves T4 to T3

Question 23

5’-deiodinase (D1, D2, D3 depending on location)

Answer 23

D1 in the liver; removes iodine from T4 to make T3

Question 24

D1 deiodinase (removes iodide from outer ring)

Answer 24

liver and kidney and thyroid

Question 25

D2 deiodinase (removes iodide from outer ring)

Answer 25

CNA and placenta

Question 26

D3 deiodinase (removes iodide from inner ring)

Answer 26

peripheral tissue; reverses T3 producing inactive rT3

Question 27

Deiodinases TYPE I that activate T3 are inhibited by

Answer 27

fasting, severe illness, high glucocorticoids, drugs, fetuses

Question 28

Why doesn't TSH stimulate more thyroid hormone production when fasting is inhibiting T3 production?

Answer 28

Because fasting only inhibits type I, type II deiodinase in the CNS is still active and therefore the pituitary still recognizes a higher level of T3 hormone

Question 29

T3 and T4 are bound (except 1%) to transport proteins

Answer 29

only free hormone is active

Question 30

Thyroid hormone transport proteins:

Answer 30

Thyroxine-binding globulin (TBG), albumin, thyroxine-binding pre-albumin

Question 31

Production of TBG alters

Answer 31

the amount of free vs bound T3 and T4

Question 32

Thyroid hormones effects

Answer 32

T3 (T4 little direct effect) increases O2 consumption, ATP synthesis, causes PM to become for permeable to solutes, enhances mito conversion of substrates to energy, and induces protein synthesis of mito enzymes

Question 33

Thyroid hormone results in

Answer 33

thermogenesis and heat production, increased metabolism, and O2 consumption

Question 34

Which tissues do not have effects of T3 and T4

Answer 34

brain, spleen, anterior pituitary, and gonads

Question 35

A major contributor to the heat production is

Answer 35

Na/K ATPase which generates ADP, stimulates O2 consumption and heat production

Question 36

Thermogenin

Answer 36

protein induced by T3 that uncouples OX PHOS and ATP generation to produce heat without generating ATP

Question 37

Metabolic effects of thyroid hormones

Answer 37

increases Carb, Fat and protein metabolism

Question 38

Thyroid hormones are permissive to

Answer 38

EPI, GH, and Insulin

Question 39

Thyroid hormone effect son the heart

Answer 39

to increase HR, SV, and CO by increasing the adrenergic activity and increasing transcription of beta receptors, Ca-ATPases, G proteins, A.C.

Question 40

Why would a beta blocker work to treat hyperthyroidism

Answer 40

to decrease HR, SV, and CO and MAP caused by increased T3

Question 41

Thyroid hormone effect on respiration

Answer 41

increased rate of ventilation, increased RBC production

Question 42

Thyroid hormone effect on brain

Answer 42

NO EFFECT on metabolism; but important for brian development

Question 43

Thyroid hormone effect on growth

Answer 43

permissive to GH, necessary for normal growth and development in children

Question 44

Metabolism of thyroid hormones

Answer 44

de-iodination and excretion through feces

Question 45

TRH stimulates and SS inhibits

Answer 45

TSH release from the anterior pituitary; TSH enhances Iodine trapping, T3/T4 liberation, and thyroid tissue growth

Question 46

T3 and T3 negative feedback

Answer 46

inhibits anterior pituitary and hypothalamus (reducing TRH and TRH receptor #) increases SS to inhibit TSH secretion

Question 47

Why would you see a goiter in hyperthyroidism?

Answer 47

TSH is overstimulated, TSH is trophic meaning it causes growth of the thyroid gland

Question 48

What would the labs look like for hypersecretion of T3 and T4

Answer 48

increased T3 and T4

Question 49

What would the labs look like for hypersecretion of TSH or secondary hypersecretion of T3 and T4

Answer 49

increased TSH and T3 and T4

Question 50

What would the labs look like for hypersecretion of TRH

Answer 50

increased TRH, TSH, and T3 and T4

Question 51

What would the labs look like for inability of thyroid

Answer 51

increased TRH and TSH, decreased T3 and T4

Question 52

Estrogens increase TBG, effect?

Answer 52

increased total serum concentration of T3 and T4 and also increases TRH sensitivity

Question 53

Age effect thyroid function?

Answer 53

T4 serum levels remain constant, BUT T3 declines with age

Question 54

GLUCOCORTICOIDS effect thyroid?

Answer 54

DEPRESS pituitary secretion of TSH (cortisol and dexamethasone)

Question 55

Severe illness effects thyroid hormones

Answer 55

increases rT3 and peripheral metabolism of T4, generating inactive thyroid hormones to slow "sick hypothyroidism"

Question 56

Acute iodine deficiency

Answer 56

T4 plasma levels decrease, TSH increases, and T3 is being generated in the thyroid at higher rates (T3 requires less I and is more potent)

Question 57

Chronic iodine deficiency

Answer 57

T3 and T4 levels fall and TSH is chronically active causing hypertrophy of the thyroid gland (goiter)

Question 58

Tumor in AP that secretes TSH

Answer 58

cause increased levels of T3 and T4 and TSH

Question 59

Atrophy of AP

Answer 59

increased TRH, decreased TSH, T3, and T4

Question 60

Abnormal stimulation of the thyroid gland

Answer 60

increased T3 and T4, decreased TSH

Question 61

destruction of thyroud gland

Answer 61

decreased T3 and T4 despite high levels of TSH

Question 62

Systemic illness

Answer 62

decreased T3, and NORMAL TSH and T4

Question 63

acute iodine deficiency

Answer 63

Increased TSH, normal T3, low T4