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GOATED BRS > Thyroid gland > Flashcards

Thyroid gland Flashcards

1
Q

How many lobes form the thyroid gland?

A

2

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2
Q

Which structure does the thyroid gland wrap?

A

Trachea

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3
Q

Which structure connected the two thyroid lobes?

A

Isthmus

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4
Q

Which hormone is predominantly secreted from the thyroid gland?

A

Thyroxine

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5
Q

Which two arteries supply the thyroid gland?

A

Superior & inferior thyroid arteries

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6
Q

Which nerve supplies the thyroid gland and what major nerve does it branch off of?

A

Recurrent laryngeal nerve

Branch of Vagus nerve

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7
Q

Which cells form the epithelia of the thyroid gland?

A

Follicular cells

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8
Q

What is the mucous extracellular fluid that fills the thyroid follicles?

A

Colloid

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9
Q

Which cells secrete calcitonin?

A

Parafollicular cells

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10
Q

Describe the anatomical position of the parathyroid glands?

A

Bilateral structures (superior and inferior), are embedded within the thyroid

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11
Q

What is the purpose of the parathyroid gland?

A

Secretion of parathyroid hormone. PTH elevates Ca2+ levels by degrading bone and stimulating calcium release

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12
Q

What are the associated risks with thyroidectomy?

A

Parathyroid glands can be impacted, inadvertently interfering with calcium levels.

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13
Q

Which growth factor is involved with the development of the thyroid gland?

A

Fibroblast growth factor signalling pathways

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14
Q

Where does the thyroid gland originate from embrylogically?

A

Base of the tongue

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15
Q

Which hormone is released by thyrotroph cells and how does it activate thyroid hormone production?

A

Thyroid-stimulating hormone binds to target TSH receptors on cell-surface membrane of follicular cells

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16
Q

What action occurs during TSH receptor activation?

A

Active transport of iodide into the follicular cell via the sodium-iodide symporter

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17
Q

How is the sodium gradient maintained?

A

Sodium potassium ATPase

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18
Q

Which surface are the Sodium/iodide pumps located on thyroid follicular cells?

A

Basal membrane

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19
Q

Which protein pump, pumps iodide from the follicle into the colloid, via the apical membrane?

A

Pendrin pumps

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20
Q

Where is thyroglobulin made?

A

Within follicular ribosomes and stored into secretory vesicles

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21
Q

Which amino-acid residues are associated with thyroglobulin molecules?

A

Tyrosine residues

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22
Q

Where is thyroglobulin secreted into?

A

Secreted into the colloid

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23
Q

What is thyroglobulin?

A

Prohormone for thyroid hormone

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24
Q

How is iodide activated in the production of thyroid hormones?

A

Thyroid peroxidase

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25
Q

What is the single iodinated form of thyroglobulin?

A

3-monoiodothyronine (3-MIT)

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26
Q

Where does iodination occur on thyroglobulin molecules?

A

Tyrosine residues

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27
Q

Which molecule is formed upon the secondary iodination of MIT?

A

3,5-Diiodotyrosine (DIT)

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28
Q

How is T3 formed?

A

Coupling of MIT and DIT

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29
Q

How is T4 formed?

A

Coupling of two DIT molecules (thyroxine)

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30
Q

What is the fate of iodinated thyroglobulin?

A

Endocytosis by the apical membrane into the follicular cell, subjected to proteolysis

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31
Q

What is the purpose of cleavage of T3 and T4?

A

Removes thyroglobulin from t3/t4 to produce the actual hormones

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32
Q

Which hormone is the active thyroid hormone?

A

T3

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33
Q

Which thyroid hormone is the major product?

A

T4

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34
Q

Which enzyme deiodinates T4 into t3?

A

Iodothyronine deiodinases

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35
Q

What is reverse T3?

A

Biologically inactive molecule formed by the removal of the wrong Iodine group

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36
Q

Under starvation circumstances, what is the fate of t4?

A

Convered into rT3, rather then T3

37
Q

What is the main thyroxine transportation hormone?

A

Thyroxine-binding globulin (TBG)

38
Q

What are the other thyroxine transportation hormones(Apart from TBG)?

A

Albumin

Prealbumin

39
Q

Describe the binding of albumin with T3/4?

A

Weak/loose

40
Q

Which thyroxine hormone predominantly is associated with prealbumin?

A

T4

41
Q

What is the circulating period for T3?

A

12 hours

42
Q

What is the circulating time for t4?

A

72 hours

43
Q

What are the sources of T3?

A

80% deiodination of T4
20% MIT+DIT coupling in thyroid

44
Q

Why can iodothyronine enter cells?

A

Lipid soluble, thus can interact with intracellular receptors

45
Q

Which thyroid hormone receptors bind onto iodothyronines?

A

T3 response elements (TREs)

46
Q

Which receptors do heterodimer thyroid hormones receptors bind to?

A

Retinoid X receptor

47
Q

What effect does iodotyronines have on cells?

A

Genomic action

48
Q

What is the main action of iodothyronines?

A

Increases basal metabolic rate
Important in calorigeneis,
Temperature regulation
Increased protein, fat & carbohydrate metabolism.

49
Q

How are thyroid levels measured?

A

Using a heel-prick test

50
Q

What are the main actions of iodothyronines?

A

Enhances the effects of catecholamines,leading to tachycardia, glycogenolysis, and lipolysis
Interaction with endocrine systems
Have effects on the CNS
Increase Vitamin C synthesis

51
Q

What effect does hypothyroidism have on retinal?

A

Retinal accumulation, leads to yellow skin

52
Q

Which hormones increase iodothyronine production?

A

Thyroid releasing/stimulating hormones and oestrogen

53
Q

What effect does elevated levels of T3/T4 have?

A

Negative feedback effect, directly acting on the adenohypophysis to inhibit the secretion of TRH, and indirectly on the hypothalamus

54
Q

What effect does somatostatin have on the anterior pituitary?

A

Inhibits the release of growth hormone

55
Q

What effects do glucocorticoids have on thyrotrophs?

A

Inhibitory effect-Decrease blood TSH conc

56
Q

What is the Wolff-Chaikoff effect?

A

Inhibits the production of iodothyronines, through inhibition of TPO.

Due to increases inorganic iodide

57
Q

What is primary hypothyroidism?

A

Autoimmune stimulated damage to the thyroid gland subsequently reduced iodothyronine productions, hence thyroxine levels decline.

58
Q

Why are TSH levels elevated due to hypothyroidism?

A

TSH levels elevate due to reduced inhibitory effect from T3/T4 (Negative feedback loop is disrupted); eventually TSH levels decline as resources are exhausted.

59
Q

Which autoimmune thyroid disease is associated with hypothyroidism?

A

Hashimoto’s thyroiditis

60
Q

What are the symptoms of primary hypothyroidism? (6)

A

Deepening voice, depression and tiredness
Cold intolerance (Calorigenesis effects of secondary heat production is reduced)
Weight gain
Constipation
Bradycardia
Eventual myxoedema coma

61
Q

Why is there weight gain with primary hypothyroidism?

A

Reduced basal metabolic rate of tissues and reduced lipolysis

62
Q

what effects does T3 and T4 have on cells (genomic action)?

A

T4 and T3 bind to thyroid receptor proteins (TREs, and RXRs) in the cell nucleus and cause metabolic effects through transcription activation Levothyroxine is a chiral molecule in the L-form. Thyroxine supplements primarily replace the reduced level of iodothyronines.

63
Q

Which therapy is the most effective for hypothyroidism?

A

T4/T3 therapy

64
Q

What are the implications of thyroxine supplements?

A

Tachycardia, potential heart attack; weight loss; headaches and hyperthyroidism.

65
Q

What is hyperthyroidism?

A

An overactivity of the thyroid gland, resulting in an elevated production of thyroxine, and subsequently reducing TSH levels.

66
Q

What are the main features of hyperthyroidism?

A

Overproduction of thyroxine; raised basal metabolic rate; raised temperature; burn up calories and weight loss; tachycardia.

67
Q

What are the main causes of hyperthyroidism?

A

Graves’ disease – whole gland smoothly enlarged and whole gland overactive
Toxic multinodular goitre
Solitary toxic nodule

68
Q

Describe the pathophysiology of Graves disease:

A

Whole gland smoothly enlarged and the entirely of the gland is overactive. Autoimmune condition attributed towards increased thyroid-stimulating immunoglobulin (TSIs) levels that encourages the thyroid gland to hypertrophy, and synthesising increased amounts of thyroid hormone than required.
TSIs bind to thyroid cell receptors, ’docking stations’ for thyroid-stimulating hormone. The TSI behaves as an agonist, stimulating follicular cells and thyroid follicles to synthesis iodothyronines.
(Type 2 hypersensitivity)

69
Q

What is a toxic multinodular goitre?

A

Excess production of thyroid hormones from functionally autonomous thyroid nodules which do not require stimulation from TSH.

70
Q

What is a solitary toxic nodule?

A

A toxic adenoma, whereby a single nodule undergoes hypertrophy and produces excess thyroid hormones.

71
Q

What is an exophthalmos?

A

Immunoglobulins bind to muscles behind the eye, which project the eye forwards and cause proptosis.

72
Q

What are the clinical features of hyperthyroidism?

A

Myopathy; mood swings; feeling hot; diarrhoea; increased appetite despite weight loss; tremor of hands; palpitations; sore eyes and goitre.

73
Q

What are the symptoms of hyperthryroidism?

A

Neuro: Insomnia, nervousness, depression
CV:Tach, +BP
Hair:Broken hair/hair loss
Endo: Goitre
Gastro:Weight loss,
Fragile fingernails, shaking hands

74
Q

What are the symptoms of hypothyroidism?

A

Neuro:Fatigue, Memory impairment
Gastro:Weight gain, constipation
Repro:Low libido, diminished fertility and potency
Skin: Dry and rough
Endo: Goitre
Swelling of face, eye socket and deep, rough voice

75
Q

What molecule is produced when thyroid peroxidase activates iodine

A

H2O2(Hydrogen peroxide)

76
Q

What are the functions of thyroid peroxidase?

A

Activation of iodine
Stimulation of coupling reactions

77
Q

What are the half lives of T3 and T4?

A

T4: 7-9 days
T3: ~2 days

78
Q

What duct forms alongside the thyroid gland and what foramen does it leave

A

The thyroglossal duct
leaving the foramen caecum in the mouth

79
Q

By what time has the thyroid gland finished development

A

Week 7

80
Q

What 5 congenital abnormalities can the thyroid develop?

A

Thyroid agenesis
Lingular thyroid
Retrosternal goitre
Thyroglossal cyst
Thyroglossal fistula

81
Q
A

In thyroid:
Top>Bottom
Follicular cells
Colloid

82
Q

How are iodothyronines transported in the blood and in what percentages?

A

Mostly bound to plasma proteins
a) thyroxine-binding globulin: TBG (70-80%)
b) albumin (10-15%)
c) prealbumin (aka transthyretin)

83
Q

What is released by the follicular nucleus after TSH receptor activation and why does said molecule do?

A

Thyroglobulin, binds to activated iodine as well as assists in coupling reactions

84
Q
A

Parafollicular cells

85
Q

How are t3/t4 levels controlled?

A

Negative feedback into the anterior pituitary releasing TSH and hypothalamus releasing TRH

86
Q

What are the effects of thyroid hormone?

A

**Effects on growth, CNS, GI, Reproductive systems

↑Basal metabolic rate

Protein, carbohydrate & fat metabolism

Potentiate actions of catecholamines (e.g. tachycardia, lipolysis)**

87
Q

What occurs to T3 and T4 when entering a cell

A

T4 deiodinated into T3, T3 binds to receptor in nucleus causing altered gene expression

88
Q

Whole thyroid T4/T3 production

A
89
Q

Where are the Na+/I- pumps found on follicular cells?

A

Basolateral membrane

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