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Physiology > Thyroid Gland > Flashcards

Thyroid Gland Flashcards

1
Q

Metabolically active hormones of thyroid gland

A

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

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2
Q

Major constituent of colloid of thyroid glands

A

thyroglobulin containing thyroid hormones

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3
Q

Amount of iodine ingested each year for hormone formation

A

50mgc

1mg/wk

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4
Q

Thyroid hormone formation:

A 
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
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5
Q

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

via this symporter

A

Iodide trapping

Sodium-iodide symporter

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6
Q

Sodium-iodide symporter co transports

A

1 iodide ion
2 sodium ions

from the lon Na gradient by Na-K ATPase

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7
Q

Rate of iodide trapping is influenced by

A

TSH concentration

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8
Q

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

A

pendrin

chloride-iodide ion countertransporter

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9
Q

Major substrates in thyroglobulin that combine with iodine to form hormone

A

tyrosine AA

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10
Q

First essential step in formation of thyroid hormones

A

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

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11
Q

Oxidation of iodine is promoted by the enzymes

A

Peroxidase with

hydrogen peroxide

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12
Q

Binding of iodine with tyrosine in thyroglobulin is called

A

organification

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13
Q

Final formation of two important hormones

A

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

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14
Q

During release of T3 and T4, thyroglobulin is cleaved via

A

proteases

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15
Q

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

A

deiodinase enzyme

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16
Q

Once released in blood, T4 and T3 combine with

A

TBG
Thyroxine binding prealbumin
Albumin

17
Q

T4 is released slowly into target tissues every

While T3 is released bec of lower affinity in about

A

6 days with long latent period

1 day

18
Q

General effect of thyroid hormones are to

this is done by

A

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

19
Q

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

A

RXR
retinoid X receptor at thyroid hormone response elements

Transcription initiated
Translation then formation of hundreds of intracellular proteins

20
Q

T4 is converted into T3 by

A

Iodinase

21
Q

Effect of thyroid hormone on metabolic activity

A

Increased by 60-100

Inc protein synth and cata

22
Q

TH on mitochondria

A

Increase in size and number

Inc rate of ATP formation

23
Q

TH on active transport of ions

A

Inc activity of Na/KATpase

24
Q

TH on growth

A

Increased

Important in brain development in fetal life

25
Q

TH on carbohydrate metabolism

A

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

26
Q

Effect of TH on fat

A

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

27
Q

Excess in TH may cause

A

vitamin deficiency

28
Q

TSH effect on thyroid gland

A

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

29
Q

TSH activation

A

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

30
Q

TRH acts to produce TSH by

A

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

31
Q

Thiocyante, perchlorate and nitrate ions dec thyroid secretion by

A

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

32
Q

PTU, Methimazole and Carbimazole dec thyroid supression by

A

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

33
Q

Iodides dec thyroid activity by

A

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

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