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Endocrine > The Thyroid Gland > Flashcards

The Thyroid Gland Flashcards

1
Q

What is the function of thyroid hormone generally

A

Regulate basal metabolic rate

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2
Q

What are the cell types of the thyroid gland

A

C -cells

Follicular cells

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3
Q

What do C cells do

A

Secrete CALCITONIN (Ca2+ regulating hormone).

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4
Q

What do follicular cells do

A

Make the enzymes that make thyroid hormones

Make thyroglobulin, a large protein

Actively concentrate iodide from the plasma and transport it into the colloid

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5
Q

What is the enzyme that make thyroid hormones called

A

Thyroid peroxidase

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6
Q

What is important about thyroglobulin

A

Rich in tyrosine residues

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7
Q

What are thyroid follicles

A

Thyroid follicles are spherical structures whose walls are made of follicular cells.

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8
Q

What is centre of a follicle filled with

A

Colloid (sticky glycoprotein matrix)

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9
Q

How much thyroid hormone does the colloid contain

A

Contain 2-3 mths supply of TH (in precursor form)

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10
Q

What the process of concentration of iodine in the follicles

A

Iodide enters the follicular cells from the plasma via a Na+/I- transporter (symport).

It couples to Na+ enabling the follicular cells to take up iodide against a concentration gradient.

Iodide is then transported into the colloid.

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11
Q

What the name of the transporter of the iodide into the colloid

A

Pendrin transporter

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12
Q

What does the thyroid peroxidase do once secreted into the colloid

A

Catalyses the oxidation of Iodide to Iodine

Adds iodine to tyrosine residues

Conjugates MIT and DIT

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13
Q

What is added to tyrosine to create Monoiodotyrosine

A

1 iodine added

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14
Q

What is added to tyrosine to create diiodotyrosine

A

2 iodine added

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15
Q

What is made when MIT + DIT

A

triiodothyronine or T3

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16
Q

What is made when DIT + DIT

A

tetraiodothyronine (Thyroxine T4)

17
Q

What stimulates thyroid hormone release into the blood

A

Thyroid stimulating Hormone

18
Q

What happens when the thyroid is stimulated by Thyroid stimulating Hormone

A

Portions of the colloid are taken back up into the follicular cell by endocytosis.

Within the cells they are packaged into vesicles containing proteolytic enzymes that cut the thyroglobulin to release thyroid hormones

Both T3 and T4 are lipid soluble and so pass across the follicular cell membrane into the plasma where they bind to plasma proteins

19
Q

Why are thyroid hormones bound to thyroglobulin

A

The hormones are attached to thyroglobulin in order to remove their lipophilic nature and keep them in the follicle

20
Q

What are the plasma proteins that bind thyroid hormones

A

Thyroxine-binding globulin.

21
Q

What kind of hormones are thyroid hormones

A

Thyroid hormones are amine hormones but act like steroid hormones

22
Q

What % of of thyroid hormones released from the thyroid gland is normally thyroxine

A

93%

23
Q

What % of of thyroid hormonesreleased from the thyroid gland is normally thrioiodine

A

7%

24
Q

How do the half life of T4 and T3 differ and why

A

TBG has a higher affinity for T4 meaning it releases it slowly into the plasma (preventing it from degradation and prolonging its half life)

25
Q

What thyroid hormone is used in the cells

A

T3

26
Q

How is T4 converted to T3

A

T4 is deiodinated to T3 by deiodinase enzymes

27
Q

Where T4 is deiodinated to T3 by deiodinase enzymes

A
  • Around half the T4 is deiodinated in plasma,

- The rest is deiodinated inside target cells.

28
Q

What controls thyroid release

A

Thyroid releasing hormone from the hypothalamus.

29
Q

What increases the Thyroid releasing hormone from the hypothalamus.

A

Cold
Exercise
Pregnancy

30
Q

What can inhibit Thyroid releasing hormone from the hypothalamus.

A

Glucocorticoids

Somatostatin (GHIH)

31
Q

How does glucocorticoid inhibit TH release

A

Inhibits TSH and conversion of T4 to T3

32
Q

How does Somatostatin inhibit TH release

A

Inhibits TSH (TH required for GH action so if we are wanting to stop the effects of GH (purpose of GHIH release) then it makes sense that it also inhibits TSH.

33
Q

What are the specific functions of thyroid hormones

A

Raises metabolic rate and promotes thermogenesis

Increase hepatic gluconeogenesis

Net increase in proteolysis
Net increase in lipolysis

Critical for growth -
stimulates GH receptor expression

Essential for brain development in utero

Endocrine (14 decks)

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