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2.2 T1: The endocrine system > T1 L2: Thyroid hormone physiology > Flashcards

T1 L2: Thyroid hormone physiology Flashcards

1
Q

What is the arterial blood supply to the thyroid gland?

A

2 arteries:

  • Superior thyroid artery branch of the external carotid artery
  • Inferior thyroid artery from the thyrocervical trunk branch of the first part of the subclavian artery
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2
Q

What is the venous drainage of the thyroid gland?

A

3 veins:

  • Superior thyroid vein drains to the internal jugular vein
  • Middle thyroid vein drains to the internal jugular vein
  • Inferior thyroid vein drains to the innominate veins
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3
Q

What are the innominate veins?

A

It’s another word for brachiocephalic veins

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4
Q

What is the lymphatic drainage of the thyroid gland?

A

To the pretracheal and prelaryngeal then to the deep cervical, supraclavicular and medistinal lymph nodes

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5
Q

Describe the cellular composition of the thyroid gland

A

Composed of follicles each consisting of a monolayer of epithelial cells enclosing a large core of viscous, homogenous colloid

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6
Q

What is the colloid for?

A

It acts as a reservoir for the thyroid hormone

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7
Q

What is Tri-iodothyronine also known as?

A

T3

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8
Q

What is Tetraiodothyronine also known as?

A

T4

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9
Q

What are the 3 primary hormones secreted by the Thyroid gland?

A

T3, T4, and calcitonin

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10
Q

How is T3 produced?

A

Iodine and Tyrosine form Monoiodotyrosine (MIT) and Diiodothyronine (DIT).

DIT plus MIT create T3

Alternatively, T4 can be broken down by iodothyronine deiodinase in tissues to create T4

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11
Q

How is T4 produced?

A

Iodine and Tyrosine form Monoiodotyrosine (MIT) and Diiodothyronine (DIT).

DIT plus DIT create T4

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12
Q

What % of thyroid hormone leaves the thyroid gland in the form of T4 (thyroxine)?

A

95%

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13
Q

What degrades MIT and DIT and why?

A

Halogenases to free the iodine, which is then re-utilised by combination with thyroglobulin

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14
Q

What is reverse T3 (rT3)?

A

The biologically inactive form of triiodothyronine (T3)

T3 and rT3 have the same structure but is just arranged differently

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15
Q

Where are receptors for thyroid hormones found?

A

They’re intracellular (in the nucleus) just like for other steroid hormones

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16
Q

What effect do thyroid hormones have on the cell when they bind to receptors?

A

They influence gene expression and thus protein synthesis

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17
Q

Which hormones control rate at which chemicals are taken up by cells in the body?

A

Thyroid hormones

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18
Q

What is the main effect of thyroid hormones?

A

To increase basal metabolic rate

19
Q

What are 3 ways to increase the basal metabolic rate?

A
  • Increase carbohydrate metabolism
  • Increase synthesis, metabolism, and degradation of lipids
  • Increase protein synthesis
20
Q

How can you accurately measure the basal metabolic rate at the bedside?

A

By measuring the basal heart rate

21
Q

Which cells produce Calcitonin?

A

Parafollicular ‘C’ cells

22
Q

What is TRH?

A

Thyrotropin releasing hormone

23
Q

What is TSH?

A

Thyroid stimulating hormone

24
Q

Which is more biologically active, T4 or T3?

A

T3

It’s about 40x more active than T4

25
Q

What is the plasma half-life of T3 and T4?

A

T3 - 1 day

T4 - 6-8 days

26
Q

Which 3 proteins does Thyroxine bind to while circulating in the blood?

A

Thyroxine binding globin
Thyroxine binding Albumin
Thyroxine binding Prealbumin

27
Q

What inhibits the release of TSH directly and how?

A

T3 and T4 inhibit TSH by supressing the release of TRH

It all creates a cycle with T3 and T4 creating a negative feedback loop for themselves

28
Q

What do hypothalamic releasing hormones do?

A

They control the secretion of ganadotropes, somatotropes, lactotropes, corticotropes, and thyrotropes

29
Q

How does the body get rid of T3 and T4?

A

T3 and T4 is conjugated and excreted as bile

30
Q

What is a Derbyshire neck?

A

A goitre formerly endemic to Derbyshire because the area is deficient in iodine

31
Q

What makes an area deficient in Iodine?

A

Being far away from the sea because iodine is abundant in seaweed and the fish

32
Q

Why can the body become deficient in iodine during pregnancy?

A

Because the requirements for iodine go up

33
Q

How can Hyperthyroidism be treated?

A

By reducing thyroid hormones with drugs or removing the thyroid by surgery or radioactive iodine

34
Q

How can hypothyroidism be treated?

A

Replacement therapy

35
Q

What is Levothyroxine used to treat? How does it work and how can it be administered?

A

Hypothyroidism by supressing TSH secretion. Can be given by mouth or injection

36
Q

What are some adverse effects of Levothyroxine?

A 
Palpitations
Arrhythmias
Diarrhoea
Insomnia
Tremor
Weight loss
37
Q

What is the drug Carbimazole used to treat? How does it work?

A

Treats hyperthyroidism

It’s converted into Methimazole upon absorption which prevents peroxidase iodinating the tyrosine residues on Thyroglobulin. This reduces the levels of T3 and T4

38
Q

What are some adverse drug effects of Carbimazole?

A

Rashes and Pruritus are common but can be treated with antihistamines. Can cause Neutropenia and agranulocytosis. It’s tetragenic

39
Q

What is Pruritus?

A

Itchy skin

40
Q

What is Neutropenia?

A

Few to no white blood cells

41
Q

What is Agranulocytosis?

A

Few to no granulocytes

42
Q

What is the drug Propylthiouracil used to treat? How does it work?

A

Treatment for Hyperthyroidism for pregnancy

It inhibits thyroperoxidases which normally act in thyroid hormone synthesis

43
Q

What are some adverse effects of Propylthiouracil?

A

Rashes and Prutirtus that can be treated with antihistamines. Can cause agranulocytosis and risk or serious liver damage including liver failure and death. Is not tetragenic

44
Q

What effect does iodine have on radiation?

A

It blocks absorption of radiation

2.2 T1: The endocrine system (23 decks)

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