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Endocrinology > Thyroid Physiology > Flashcards

Thyroid Physiology Flashcards

1
Q

Thyroid means

A

shield

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2
Q

What are two clinical properties that distinguish the thyroid gland from the other endocrine glands?

A
  • Can be seen and palpated during routine physical.

- Has a trace element, iodine

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3
Q

Microscopic stucture of thyroid gland

A

Follicular cells surrounding Colloid in circular patterns. In between layers of follicular cells you have parafollicular cells.

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4
Q

What does Colloid contain

A

Thyroglobulin

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5
Q

What do parafollicular cells generate

A

calcitonin

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6
Q

The six steps of thyroid hormone synthesis

A

1) Iodide uptake by Na/I symporter
2) Thyroblobulin synthesis and release into the follicular lumen
3) Iodination of tyrosine residues in thyroglobulin
4) Endocytosis of iodinated thyroglobulin into follicular cells
5) Generatin and secretion of T3 and T4
6) Iodide recycling

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7
Q

Iodide is present in most of our food

A

true

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8
Q

Iodide travels from the gut into the bloodstream, through the bloodstream to the thyroid gland and comes into the follicular cells of the thyroid gland through what?

A

Na-Iodide symporter on the basolateral side of the cell (the side facing the blood vessel)

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9
Q

What can inhibit the uptake of iodide?

A

CIO4, TcO, SCN….I dont know what any of that is

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10
Q

What carries iodide from the apical side of the follicular cell into the colloid lumen?

A

Pendrin

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11
Q

THyroglobulin is made where?

A

In the Colloid

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12
Q

What is the surface of the colloid layer coated in>

A

Thyroid Peroxidase

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13
Q

What is the purpose of thyroid peroxidase

A

oxidizes iodide to iodine

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14
Q

Iodine then does what to thyroglobulin

A

reacts with the tyrosine residues to “iodinate them”

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15
Q

Internal rearrangement of two iodinate tyrosyl residues results in

A

Iosothyronine. This is catalyzed by thyroid peroxidase

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16
Q

As long as T3 and T4 are attached to the thyroglobulin backbone,

A

they are inactive

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17
Q

At the appropriate time, a droplet of colloid is endocytosed into the follicular cell

A

ok

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18
Q

This endocytosed colloid fuses with what

A

a native lysosome forming a lysoendosome

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19
Q

What happens inside the lysoendosome

A

Enzymes inside the lyso-endosome hydrolyze the tyrosine residues and you get active T3 and T4….THIS IS BIG

T3 and T4 get released into the blood

20
Q

Iodide is recycled?

A

Yes

21
Q

90% of what is released into the bloodstream is

A

T4, 10% T3….KNOW THIS

22
Q

Once in the bloodstream, the thyroid hormones are immediately bound by

A

Plasma proteins like albumin or thyroid binding globulin (most attached to this)

23
Q

What kinds of things decrease the amount of Thyroid Binding Hormone TBG?

A

Steroid Use

24
Q

What kinds of things increase the amount of TBG?

A

Pregnancy, heroin use

25
Q

Which is more active, T3 or T4?

A

T3

26
Q

What must you have in the inner ring of thyroid hormone for it to be considered active?

A

Two iodines

27
Q

The lack of iodine in the inner ring of what type of T3 molecule makes it inactive

A

Reverse T3

28
Q

What is the enzyme responsible for the conversion of T4 to T3

A

5/3- Deiodinase

29
Q

What are the two types of 5/3-Deiodinase?

A

Type 1 and type 2

30
Q

Type 1 deiodinase is found where?

A

Liver, Kidney, Thyroid

31
Q

Type 2 deiodinase is found where?

A

Pituitary, CNS, Placenta

32
Q

Which Deiodinase is mainly responsible for the amount of free T3 found in the blood?

A

Type 1

33
Q

Thyroid hormone is a peptide

A

KNOW

34
Q

All peptide hormones have what type of Receptor? EXCEPT THYROID

A

ALL have a plasma membrane receptor except thyroid

35
Q

Thyroid hormone has what type of receptor

A

nuclear

36
Q

Thyroid hormone receptor (THR) forms a dimer with Retinoid X Receptor (RXR) and does what

A

Acts directly on the DNA to regulate transcription

37
Q

Why does hyperthyroidism (physiologically) increase metabolism

A

Directly increases oxygen consumption and when oxygen consumption goes up, the amount of heat generated by the cells goes up

38
Q

Increases in TRH lead to increases in TSH

A

truth

39
Q

TRH acts on what cells where

A

Thyrotrophs in the anterior pituitary…generates the secretion and release of TSH

40
Q

How are TRH and TSH levels controlled

A

Feedback mechanism involving T4 and T3. As free T4 and T3 levels rise, TRH goes down via direct and indirect mechanisms

41
Q

WHat is the indirect method of TRH control

A

High T4 and T3 levels cause the downregulation of TRH receptors on Thyrotrophs

42
Q

What is the direct method of regulation

A

Low amounts of TSH released from Thyrotrophs

43
Q

Know the slide about TSH regulation of thyroid function

A

ok

44
Q

What is Cretinism

A

Dwarfism caused by endemic thyroid deficiency during development.
- Mental retardation
- short stature
- delayed motor development
Treatment within a few days of birth restores normal development
Treatment after this time restores physical development bu tnot mental development

45
Q

Hashimoto thyroiditis

A

Anti-thyroid antibodies that block and destroy thyroid function
Presentation: Painless goiter, edema, headache

46
Q

Graves Disease

A

Hyperthyroidism. Caused by Ig Antibodies that mimic Thyroid Stimulating hormone.
Antibodies continually bind to TSH receptors on the thyroid and continualy drive thyroid hormone production.
Wt loss, sweating, diarrhea, fatigue
Eyeball protrusion, dry epithelial layers, ulceration of the eye

Endocrinology (33 decks)

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