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Endocrinology > The Thyroid gland and Iodothyronines > Flashcards

The Thyroid gland and Iodothyronines Flashcards

1
Q

How many lobes in the thyroid gland?

A

2

Left and Right

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2
Q

What does thyroid tissue consist of?

A

Follicles which consist of a central colloid, surrounded by follicular cells surrounded by parafollicular cells

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3
Q

What is between the 2 lobes of the thyroid?

A

Isthmus

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4
Q

Where is the thyroid?

A

Infront of the trachea

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5
Q

What is the thyroid shaped like?

A

A butterfly

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6
Q

TSH secreted from anterior pituitary stimulates Thyroid gland

A

TSH binds to TSH receptor on follicular cells, stimulating various processes

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7
Q

What processes are stimulated by the binding of TSH to thyroid follicular cells?

A

Uptake of iodide
Synthesis of Thyroglobulin
Iodination of thyroglobulin
Coupling reaction

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8
Q

How and why is iodide taken in by the thyroid?

A

Need iodide for thyroid hormones
Taken up from blood through sodium-iodide symporters
Iodide transported into colloid

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9
Q

What is thyroglobulin?

A

Protein made of AAs

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10
Q

What is iodination of Thyroglobulin?

A

Add iodide to Tyrosine residues in Thyroglobulin

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11
Q

What catalyses iodination of Thyroglobulin?

A

Thyroperoxidase (TPO)

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12
Q

What can be produced from iodination of Thyroglobulin?

A

+1 Iodide = Mono-iodo-tyrosine (MIT)

+2 Iodides = Di-iodo-tyrosine (DIT)

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13
Q

What is produced in a coupling reaction of MIT + DIT?

A

T3

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14
Q

What is produced in a coupling reaction of DIT + DIT?

A

T4

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15
Q

After production in the colloid, where are T3 and T4 taken?

A

Back into follicular cells

Secreted into blood when required

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16
Q

What is the predominant hormone secreted by the Thyroid?

A

T4

Thyroxine

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17
Q

Iodothyronines

A

Thyroid hormones

18
Q

How are iodothyronines mainly transported?

A

Bound to plasma proteins in blood

19
Q

What are the proportions of binding of iodothyronines?

A

Thyroid binding globulin (TBG)= 70-80%
Albumin= 10-15%
Prealbumin= Small %

20
Q

Percentages of unbound iodothyronines

A
  1. 05% T4

0. 5% T3

21
Q

How is T3 different to T4?

A

T3 is the bioactive form of Thyroid hormone

22
Q

What is formed from de-iodination of T4?

A

T3

Occurs in target tissues

23
Q

A little T3 is made in Thyroid

A

Majority of T3 made in peripheral tissue from de-iodination of T4

24
Q

T4 can be de-iodinated in a different position

A

Produces reverse T3

inactive form

25
Q

Mechanism for main action of T3

A

T3 binds to Thyroid hormone receptor

Which stimulates transcription of genes, leading to protein synthesis (in nucleus)

26
Q

T3 May also have non-nuclear actions

A

Bind to ion channels on cell surface membrane

27
Q

Thyroid hormone effects

A

Fetal growth and development

Basal metabolic rate

28
Q

Congenital hypothyroidism

A

=Cretinism

So TH & TSH measured in heel prick test

29
Q

Hyperthyroidism

A

Increases basal metabolic rate (protein, carbs, fat)
Potentiates actions of catecholamines- Tachycardia
Effects on GI, CNS, Reproductive system

30
Q

What effects does hyperthyroidism on GI, CNS and Reproductive system?

A

GI= Diarrhoea
CNS= Agitation
Reproductive system= Irregular periods

31
Q

Latent periods of thyroid hormones

A 
T3= 12 hours
T4= 72 hours
32
Q

Half-lives of thyroid hormones

A 
T3= 2 days
T4= 7-9 days
33
Q

Hyperthyroidism TSH levels

A

Expect low levels TSH

34
Q

Hypothyroidism TSH levels

A

Expect high levels TSH

35
Q

What does TRH stimulate?

A

TSH

36
Q

What does TSH stimulate?

A

Production of T3 and T4

37
Q

What is the negative feedback loop in Thyroid hormone production?

A

T3 and T4 inhibit production of TRH and TSH

38
Q

What is the Wolff-Chaikoff effect?

A

Iodide itself may inhibit Thyroid hormone release

39
Q

What hormone may stimulate TRH production?

A

Oestrogen

40
Q

What may suppress TRH production?

A

Glucocorticoids

Endocrinology (12 decks)

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