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Endocrine > EXAM #1: NORMAL BIOCHEMISTRY AND PHYSIOLOGY > Flashcards

EXAM #1: NORMAL BIOCHEMISTRY AND PHYSIOLOGY Flashcards

1
Q

What is the precursor of the thyroid hormones?

A

Tyrosine

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2
Q

What is the active form of thyroid hormone? Which is more active?

A

T3* and T4

*T3 is more active

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3
Q

What are the biologicaly inactive forms of the thyroid hormones?

A

T2 and rT3

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4
Q

Where are thyroid hormones synthesized?

A

Thyroid follicle

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5
Q

What direction does the apical side of the follicular cell face? Basal?

A

Apical= colloid

Basal= bloodstream

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6
Q

What is the platform for T3 and T4 synthesis?

A

Thryoglobulin

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7
Q

What is exogenous substance is required for the synthesis of thyroid hormones?

A

Iodine

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8
Q

What has virtually eliminated iodine deficiency in the US?

A

Iodized salt

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9
Q

How is iodine transported into the thyroid follicle?

A

Na+-I cotransporter (symporter)

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10
Q

What is organification?

A

Adding iodine to thyroglobulin

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11
Q

What is the site of organification?

A

Exocytotic vesicles in the colloid

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12
Q

Outline the process of organification.

A

Thyroid peroxidase oxidizes and attaches iodide to the tyrosyl residues

*Uses hydrogen peroxide

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13
Q

What is the outcome of organification?

A

Formation of MIT and DIT

*MIT= 1 iodine 
DIT= 2x iodine
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14
Q

What is the next step after organification?

A

Coupling

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15
Q

What enzymes is responsible for coupling?

A

Thyroid peroxidase (TPO)

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16
Q

How is thyroglobulin released via the lysosomal pathway?

A

1) Endocytosis
2) Hydrolysis in the lysosome/ proteolysis
3) Diffusion into the circulation

17
Q

What happens to thyroglobulin after cleavage of T3 and T4 during release?

A

1) Recycled to colloid

2) Transcytosis into the circulation

18
Q

Describe the composition of TRH.

A

Pyroglutamul-histidyl-proline residues

19
Q

What is the mechanism of TRH signaling in the anterior pituitary?

A

GPRC via

  • PLC
  • IP3
  • Ca++
20
Q

What is the mechanism of TSH signaling in the thyroid gland?

A

GPRC via

- cAMP protein kinases

21
Q

Specifically, what does TSH stimulate?

A

1) Iodide transport
2) Transcription of thyroglobulin
3) Transcruption of tyroid peroxidase (TPO)

22
Q

What thyroid hormone is preferentially bound to serum proteins?

A

T4

23
Q

What enzymes catalyze the metabolism of T3 and T4?

A

Deiodinases

24
Q

What are the functions of deiodinases?

A

1) Formation of active T3 from T4

2) Deactivation of T3 and T4 when their concentrations are too high

25
Q

What form of deiodinase is active against T3?

A

Type III

*Thus, this is the major enzyme that deactivates thyroid hormones

26
Q

What is the function of Type I deiodinase?

A

Outer/ inner ring vs. T4

27
Q

Where is Type I deiodinase located?

A

Liver, kidney, thyroid

28
Q

What are the products of Type I deiodinase?

A

T3 or rT3

29
Q

What is the function of Type II deiodinase?

A

Outer ring vs. T4

30
Q

What is the location of Type II deiodinase?

A

Diffuse

31
Q

What is the product of Type II deiodinase?

A

Intracellular T3

32
Q

What is the function of Type III deiodinase?

A

Inner ring vs. T4 and T3

33
Q

Where is Type III deiodinase located?

A

Brain and placenta

34
Q

What are the products of Type III deiodinase?

A

rT3 and T2

35
Q

Describe the mechanism of action of the thyroid hormones in the nucleus.

A

1) TR binds DNA with RXR
2) TR/RXR recruits HDAC, repressing transcription
3) Binding of T3 or T4 displaces HDAC for HAT*

HAT complex turns target genes ON

36
Q

What is stimulated by T3/T4 in regards to cellular metabolism?

A

1) Increased oxygen consumption/ heat production
2) Increased adipose tissue lipolysis
3) Increased glycogenolysis and gluconeogenesis

Endocrine (34 decks)

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