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MEH > The Thyroid Gland > Flashcards

The Thyroid Gland Flashcards

1
Q

Where is the thyroid gland located?

A

Around the front larynx and trachea
Below the thyroid cartilage

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2
Q

What is the name of the bridge that joins the 2 lobes of the thyroid gland?

A

Isthmus

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3
Q

Describe the embryological development of the Thyroid gland

A

An epithelial proliferation in the floor of the pharynx at the base of the tongue

Descends down the Thyroglossal duct and migrates downwards passing in front of the hyoid bone

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4
Q

What are thyroid follicles?

A

When follicular cells are arranged in spheres

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5
Q

What do the thyroid follicles contain?

A

Colloid

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6
Q

What is colloid?

A

It’s made up of deposits of Thyroglobulin

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7
Q

Is colloid Intracellular or extracellular?

A

Extracellular even though it is inside the follicle

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8
Q

What is Thyroglobulin?

A

A protein where thyroid hormone is synthesised

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9
Q

What are parafollicular cells and where are they found in thyroid histology?

A

Cells that produce Calcitonin which is important in calcium metabolism

They are found not producing the spheres/ thyroid follicles

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10
Q

What is the only use of iodine in the body?

A

Synthesis of Thyroid hormones

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11
Q

What do thyroid hormones consist of?

A

Iodinated tyrosine

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12
Q

What does T3 (Triiodothyronine) consist of?

A

2 tyrosines linked together with iodine at 3 positions on the aromatic rings

MONOiodotyrosin + DIiodotyrosine

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13
Q

What does T4 (Tetraiodothyronine) or Thyroxine consist of?

A

2 tyrosines linked together with iodine at 4 positions on the aromatic rings

DIiodotyrosine + DIiodotyrosine

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14
Q

Why is Thyroglobulin important in thyroid hormone synthesis?

A

It acts as a scaffold

It contains the tyrosine residues that will be iodinated
Tyrosine residues on the thyroglobulin protein get iodinate
They also then get coupled to form T3 or T4

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15
Q

What happens to the thyroglobulin protein that holds the coupled tyrosine residues, so T3 or T4 when the thyroid hormones need to be released?

A

It gets degraded (proteolysis)

The colloid that got taken back into the cell fuses with a lysosome which degrades thyroglobulin

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16
Q

What is the key enzyme involved in the synthesis of thyroid hormones?

A

Thyroid Peroxidase

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17
Q

What are the 3 key roles of Thyroid peroxidase?

A

-Oxidation of iodide to iodine (needs H2O2)

-Addition of Iodine to tyrosine residues

-Coupling of MIT or DIT to generate T3 or T4 in the Thyroglobulin protein

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18
Q

What form must iodine be converted into before it can be absorbed into the body?

A

Iodide (I-)

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19
Q

What is an Iodine trap?

A

The sodium iodide symporter found in thyroid epithelial cells which take up iodide from the blood

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20
Q

Which enzyme oxidises Iodide to iodine in the thyroid epithelial cell so it can be released into the colloid?

A

Thyroid peroxidase

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21
Q

What happens to the thyroid gland in response to iodine deficiency?

A

Enlarges
Goitre

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22
Q

How are the thyroid hormones stored?

A

Within the thyroglobulin proteins

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23
Q

How does colloid containing Thyroglobulin protein with thyroid hormones stored in it enter back into the thyroid follicular cell?

A

Pinocytosis

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24
Q

Out of T3 and T4, which one is more biologically active?

A

T3

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25
Q

Which is the main thyroid hormone which is secreted?

A

T4 but T3 is more active

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26
Q

What is the name of the protein which T3 and T4 are transported bound to in the blood?

A

Thyroxine-binding globulin

27
Q

How is thyroid hormone secretion regulated?

A

Negative feedback

28
Q

Describe the negative feedback Regualtion of thyroid hormone secretion

A

Too much thyroid hormone stops anterior pituitary releasing TSH
Too much thyroid hormone inhibits Hypothalamus producing TRH

29
Q

What type of hormone is Thyroid Stimulating Hormone?

A

Glycoprotein

30
Q

Why are all glycoprotein hormones similar?

A

They have the same alpha subunit

31
Q

How does TSH trigger thyroid hormone release?
What does it stimulate?

A

Iodide uptake
Iodide oxidation
Thyroglobulin synthesis
Thyroglobulin iodination
Colloid pinocytosis
Proteolysis of thyroglobulin

32
Q

What are the general actions of thyroid hormone?

A

Increase Basal metabolic rate and heat production

Stimulates metabolic pathways

Sympathomimetic effects

33
Q

How does thyroid hormone stimulate the metabolic rate?

A

Increase number and size of mitochondria

Stimulate synthesis of enzymes in respiratory chain

34
Q

What metabolic pathways are generally stimulated by thyroid hormones?

A

Catabolic:
Lipolysis and B-oxidation of fatty acids

Gluconeogenesis, glycogenolysis

35
Q

What is the sympathomimetic effect of thyroid hormone?

A

Increases number,of Catecholamines receptors (adrenaline) on target cells

36
Q

How does thyroid hormone specifically effect the CVS?

A

Increases hearts responsiveness to Catecholamines

Increased cardiac output = chronotropy (inc Heart rate) and inotropy (stronger contraction)

Peripheral vasodilation = more heat to body surface

37
Q

How does thyroid hormone specifically effect the nervous system?

A

Increased myelination of nerves and development of Neurons

38
Q

How do thyroid hormone receptors act when no thyroid hormone is bound?

So how does Thyroid hormone act?

A

They bind to DNA when the hormone isn’t present preventing transcription/gene expression

Regulates gene expression

39
Q

How does binding of the thyroid hormone to its receptor activate transcription?

A

Causes conformational change to the receptor so it is no longer bound to the DNA allowing it to be transcribed

40
Q

Where is the thyroid hormone receptor actually located?

A

Inside the nucleus actually on the DNA

41
Q

What is the part of DNA that has the Thyroid Hormone Receptor bound to it called?

A

Thyroid Response element

42
Q

So what is a hormone response element? (HRE)

A

A region of DNA which a hormone receptor binds/is bound to

43
Q

What is Goitre?

A

Enlargement of the thyroid gland

44
Q

When can goitre be present?

A

Hypothyroidism
Hyperthyroidism (when gland is overstimulated)

45
Q

What can cause Hypothyroidism?

A

Failure of thyroid gland
TSH or TRH deficiency
Iodine deficiency
AUTOIMMUNITY
Post surgery
Anti thyroid drugs

46
Q

What are the general symtoms of Hypothyroidism?

A

Obesity
Lethargy
Slow reflexes
Intolerance to cold
Brady cardia

47
Q

In Hypothyroidism what hormones are low and what are high?

A

Low T3 and T4
High TSH

48
Q

What condition can Hypothyroidism cause in adults?

A

Myxedema

49
Q

What are the signs of Myxedema in Adults due to Hypothyroidism?

A

Thick puffy skin (waxy swollen skin)
Muscle weakness
Slow speech
Metal deterioration
Intolerance to cold

50
Q

What is congenital hypothyroidism caused by in infants?

A

Iodine deficiency

51
Q

Signs of Congenital hypothyroidism

A

Mental deficiency
GI disturbances
Poor bone development
Slow pulse muscle weakness

52
Q

What is Hashimotos disease?

A

An Autoimmune disease which leads to the destruction of thyroid follicles causing hypothyroidism

53
Q

In Hashimotos disease, what hormone levels will be low and which hormone will be high?

A

Low T3
Low T4
High TSH

54
Q

How is Hashimotos disease treated?

A

Give oral thyroid hormone

55
Q

What are some causes of Hyperthyroidism?

A

Autoimmune Graves’ disease
Excessive T3 or T4 therapy
Drugs amiodarone
Ectopic thyroid tissue

56
Q

What are the general symptoms of Hyperthyroidism?

A

Weight loss
Irritability
Heat intolerance
Tachycardia
Increased appetite
Tremors

57
Q

What is Exophthalmos?

A

Bulging eyes

58
Q

Can some hyperthyroidisms cause Exophthalmos (bulging eyes)?

A

Yes but not all

59
Q

How does Graves Disease cause Hyperthyroidism?

A

TSI (Thyroid stimulating immunoglobulin) is produced

This binds to TSH receptors mimicking the actin of TSH stimulating Thyroid hormone production

60
Q

What hormone levels will be high and low in Graves Disease?

A

High T3
High T4
Low TSH

61
Q

What does Graves Disease cause?

A

Increased BMR
Sweating
Decrease body weight
Muscle weakness
Heart palpitations
Sometimes Exophthalmos

62
Q

What is the name of the isotope used to scan the thyroid with a gamma camera?

A

Technetium-99m

63
Q

What is the name of an Antithyroid drug and what does it do?

A

Carbimazole

Blocks formation of thyroid hormone so treats Hyperthyroidism

MEH (33 decks)

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