Thyroid Gland

Question 1

Metabolically active hormones of thyroid gland

Answer 1

Thyroxine 93% T4
Triiodothyronine T3 4x as potent but less
Calcitonin

Question 2

Major constituent of colloid of thyroid glands

Answer 2

thyroglobulin containing thyroid hormones

Question 3

Amount of iodine ingested each year for hormone formation

Answer 3

50mgc

1mg/wk

Question 4

Thyroid hormone formation:

Answer 4

iodide trapping
formation and secretion of thyroglobulin
oxidation of iodide ion
iodination of tyrosine and formation of thyroid hormones aka organification 
storage of thyroglobulin
release of T4 and T3

Question 5

First stage in formation of thyroid hormone
Transport of iodide from blood to thyroid cells

via this symporter

Answer 5

Iodide trapping

Sodium-iodide symporter

Question 6

Sodium-iodide symporter co transports

Answer 6

1 iodide ion
2 sodium ions

from the lon Na gradient by Na-K ATPase

Question 7

Rate of iodide trapping is influenced by

Answer 7

TSH concentration

Question 8

Iodide is transported out of the thyroid cell into the follicle by the counter transporter

Answer 8

pendrin

chloride-iodide ion countertransporter

Question 9

Major substrates in thyroglobulin that combine with iodine to form hormone

Answer 9

tyrosine AA

Question 10

First essential step in formation of thyroid hormones

Answer 10

Conversion of iodide ions to iodine (I0 or I3) aka oxidation which is capable of combining with tyrosine

Question 11

Oxidation of iodine is promoted by the enzymes

Answer 11

Peroxidase with

hydrogen peroxide

Question 12

Binding of iodine with tyrosine in thyroglobulin is called

Answer 12

organification

Question 13

Final formation of two important hormones

Answer 13

1 tyrosine iodized to monoiodotyrosine and to diiodotyrosine
2 more iodotyrosine coupled (diiodo)

2 mol diiodo T4
1 mol monoiodo with 1 mol diiodo T3

Question 14

During release of T3 and T4, thyroglobulin is cleaved via

Answer 14

proteases

Question 15

Remaining iodine trapped with unreleased thyroglobulin is cleaved by to be recycled

Answer 15

deiodinase enzyme

Question 16

Once released in blood, T4 and T3 combine with

Answer 16

TBG
Thyroxine binding prealbumin
Albumin

Question 17

T4 is released slowly into target tissues every

While T3 is released bec of lower affinity in about

Answer 17

6 days with long latent period

1 day

Question 18

General effect of thyroid hormones are to

this is done by

Answer 18

activate nuclear transcription of large numbers of genes

removing one iodide from all thyroxine forming T3 which has affinity to about 90% of peripheral receptors

Question 19

on the DNA to activate nuclear receptors, the hormone forms a heterodimer with

Answer 19

RXR
retinoid X receptor at thyroid hormone response elements

Transcription initiated
Translation then formation of hundreds of intracellular proteins

Question 20

T4 is converted into T3 by

Answer 20

Iodinase

Question 21

Effect of thyroid hormone on metabolic activity

Answer 21

Increased by 60-100

Inc protein synth and cata

Question 22

TH on mitochondria

Answer 22

Increase in size and number

Inc rate of ATP formation

Question 23

TH on active transport of ions

Answer 23

Inc activity of Na/KATpase

Question 24

TH on growth

Answer 24

Increased

Important in brain development in fetal life

Question 25

TH on carbohydrate metabolism

Answer 25

Inc uptake, glycolysis, gluconeogenesis, rate of absorp, insulin secretion

Question 26

Effect of TH on fat

Answer 26

Inc mobilization Inc FA conc in plasma and oxidation Dec conc of chole, phospholipid and TAG in plasma despite FA inc

Question 27

Excess in TH may cause

Answer 27

vitamin deficiency

Question 28

TSH effect on thyroid gland

Answer 28

1 inc proteolysis of thyroglobulin 2 inc activity of iodide pump 3 inc iodination of tyrosine 4 inc size and secretory activity of thyroid cells 5 inc number of thyroid cells plus change from cuboidal to columnar

Question 29

TSH activation

Answer 29

TSH binding with receptor on thyroid gland Activation of adenylate cyclase Inc cAMP formation (as 2nd messenger) Mult phosphorylations

Question 30

TRH acts to produce TSH by

Answer 30

binding to TRH receptors in anterior pituitary Activating PLC Cascade of Ca ions + DAG TSH release

Question 31

Thiocyante, perchlorate and nitrate ions dec thyroid secretion by

Answer 31

decreasing iodide trapping by competitive inhibition of NIS no effect on thyroglobulin Inc TSH -> goiter

Question 32

PTU, Methimazole and Carbimazole dec thyroid supression by

Answer 32

Preventing formation of thyroid hormones from iodides and tyrosine Blocking of peroxidase for iodination of tyrosine and coupling of two iodinated tyrosine No effect on thyroglobulin Inc TSH -> goiter

Question 33

Iodides dec thyroid activity by

Answer 33

Decreasing all phases of thyroid activity esp at release of thyroid hormones Dec size of thyroid gland utilized preop