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Year 2 - Endocrinology > Thyroid Hormones And Thyroid Diseas > Flashcards

Thyroid Hormones And Thyroid Diseas Flashcards

1
Q

What is the essential component of thyroid hormones?

A

Iodine

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2
Q

What is contained in the lumen of thyroid follicles?

A

Colloid - mainly made up of thyroglobulin

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3
Q

What happens to follicular cells of the follicle, when stimulated?

A

They become columnar and the lumen is depleted of colloid

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4
Q

What happens to the follicular cells of the follicle when suppressed?

A

They become flat (cuboidal) and colloid accumulates in the lumen

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5
Q

What food is iodine found in, and how much is needed per day?

A

Found in seawater, fruit and vegetables

- 150-300micrograms are required every day

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6
Q

How is iodine absorbed?

A

Iodine is reduced to iodide in the GI tract and absorbed

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7
Q

How is iodide transported into the follicular cell?

A

By a sodium iodide transporter on the basolateral membrane

  • against the concentration gradient
  • active transport
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8
Q

How does iodide enter the colloid from the follicular cell?

A

It diffuses to the apex of the cell, and is then transported by prendrin into vesicles attached to the apical membrane

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9
Q

Where does oxidation of iodide to iodine occur?

A

In the vesicles, in the colloid

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10
Q

What happens to iodine in the vesicles?

A

It binds to tyrosine residues on thyroglobulin, forming either diiodotyronine or monoiodotyronine. This is called organification

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11
Q

What enzymes catalysts organification?

A

Thyroid peroxidase

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12
Q

How is T3 and T4 created from MIT and DIT?

A

Two DITs bind together to form T4

A DIT and an MIT bind together to form T3

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13
Q

How do the thyroid hormones re-enter the follicle cell?

A

Endocytosis of thyroglobulin

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14
Q

How does T3 and T4 get released into the blood?

A

The thyroglobulin vesicles fuse with lysosomes

Lysosomes degrade the thyroglobulin and the hormones are released into the circulation

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15
Q

Which thyroid hormone is released in largest quantities by the thyroid gland?

A

T4

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16
Q

Which thyroid hormone is the active form of the hormone?

A

T3 - released in low quantities by the gland

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17
Q

How does T3 have any effect when released in such low quantities by the thyroid gland?

A

It’s formed by 5’iodination of T4 in the peripheral tissues, shortly before it is needed

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18
Q

How do most thyroid hormones circulate?

A
  1. 5% - freely

99. 5% - bound to a protein

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19
Q

Which compartment (free or bound) is the active and regulated component?

A

The free component

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20
Q

Which proteins do thyroid hormones bind to in circulation?

A

Thyroid binding globulin, transthyretin and albumin

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21
Q

Describe thyroid hormone binding in tissues?

A

T3 travels freely into the cytoplasm of the target cell

It’s if then transported into the nucleus, where it binds to its receptor

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22
Q

Name the two types of T3 nuclear receptors, and what is the difference?

A

Alpha and beta

- varies depending on which tissue is being acted upon

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23
Q

Which tissues have the most T3 receptors?

A

Sensitive tissues - like the pituitary and liver

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24
Q

What is the effect of T3 on devlopemnt?

A

Affects brain and somatic development

25
Q

What effects does T3 have on the skeletal and CV and systems?

A

Skeletal - bone turnover - high levels of T3 cause osteoporosis
CV - regulates heart rate

26
Q

What effects does T3 have on metabolism?

A

Increases metabolic rate of many tissues (so increases BMR)
Increases gluconeogensis and glycogenolysis
- glucose produced is used for fuel for thermogenesis
Stimulates lipolysis (cAMP dependant activation of HSL)
- fatty acids produced are oxidised to create ATP and used for thermogenesis

27
Q

Which hormone from the anterior pituitary stimulates synthesis and secretion of T3 and T4, and describe the molecular binding.

A

Thyroid stimulating hormone (TSH)
Acts on G-protein couple receptor
- coupled to adenylyl cyclase, leading to increased PKA production
- affects iodide transport, MIT/DIT formation and thyroglobulin proteolysis

28
Q

What inhibits TSH secretion?

A

Increased levels of T3 and T4 (negative feedback)

- decreases TRH receptors on the cell membranes

29
Q

What is the action of thyrotropin releasing hormone (TRH)?

A

It stimulates the release of TSH from the anterior pituitary
- binds to a G-protein couple receptor on the cell surface
- phosphlipase C produced
- calcium release from intracellularly storage = TSH release
It’s also stimulates TSH biosynthesis

30
Q

Describe TSH and T4 levels in primary hypothyroid disease?

A

TSH levels are high

T4 levels are low

31
Q

Describe TSH and T4 levels in secondary hypothyroid disease?

A

TSH is low

T4 is low

32
Q

Describe TSH and T4 levels in primary hyperthyroid disease?

A

TSH is low

T4 is high

33
Q

Describe TSH and T4 levels in sick euthyroid disease?

A

TSH is low

T4 is low

34
Q

What are the causes of hyperthyroidism?

A 
Autoimmune - Graves' disease
Toxic adenoma 
Multinodular goitre 
Thyroiditis 
Excess administration of thyroxine
35
Q

Clinical manifestations of thyrotoxicosis?

A 
Weight loss
Tremor 
Heat intolerance
Sweating
Diarrhoea 
Tachycardia 
Hypertension
Palpitations
36
Q

What are some signs an symptoms specific to Graves’ disease?

A 
Dysthymia eye disease
Thyroid dermopathy 
- localised lesions on the skin
- deposition of hyaluronic acid 
Thyroid acropachy (another skin problem)
- soft-tissue swelling of the hands
- clubbing of the fingers
37
Q

Describe Graves ophthalmology.

A 
Found in 50% of patients 
Lid retraction/ lag
Peri orbital oedema 
Proptosis - protrusion of the eyeball 
Diplopia - seeing two images instead of one
Nerve compression is rare
38
Q

What is the treatment of Graves’ disease?

A

Anti thyroid drugs (thionamines)
Surgery
Radio-iodine

39
Q

Name the thionamides

A

Carbimazole - most used

Propylthiouracil

40
Q

What is the mechanism of action of the thionamines?

A

They inhibit the enzyme thyroid peroxidase
- so the tyrosine residues can’t become iodinated and form MIT/DIT
- prevents oxidation of iodide to iodine
Propylthiouracil also blocks conversion of T3 to T4 in peripheral tissues

41
Q

What are the risk factors to thionamided drugs?

A

Agranulocytosis

Rashes

42
Q

Describe radioiodine therapy and associated problems.

A

Uses beta-emission to destroy thyroid tissues
May worsen eye disease
Can cause hypothyroidism
- may be transient for the first 6 months
- easier to manage

43
Q

What are the risks of thyroid surgery?

A

Heamorrhage
Recurrent laryngeal palsy
Permanent hypocalcaemia
Hypothyroidism

44
Q

Briefly describe Graves’ disease.

A

An autoimmune disorder that abnormally stimulates the thyroid gland with thyroid stimulating antibodies (TSH-receptor antibodies)
Associated with HLA-DR3 and B8

45
Q

List how hyperthyroidism can be tested for.

A

T4, TSH level measurement
- T4 levels will be high
- TSH levels will be high in secondary and low in primary
Assesment of thyroid antibodies to diagnoses Graves
Thyroid scans can detects nodules
Fine needle aspiration can tell whether any tumours are benign or malignant

46
Q

List some causes of hypothyroidism.

A 
Hashimotos - autoimmune thyroid disease
Thyroiditis - viral and painful
Thyroidectomy 
Drug-indicted 
Pituitary disease - secondary 
Severe iodine deficiency
47
Q

Describe hashimotios pathophysiology.

A

Destruction of the thyroid gland with anti-TPO antibodies
- these target thyroid peroxidase
May be a family history and is common in females

48
Q

Name some of the signs and symptoms of hypothyroidism.

A 
Weight gain
Cold intolerance 
Amenorrhoea 
Depression 
Bradycardia lethargy 
Constipation 
Hoarseness 
Dry skin
Thin, coarse hair
Anaemia 
May have goitre
49
Q

In which thyroid problem can you see goitre?

A

Can be in both hypo and hyperthyroidism

- can even be seen in euthyroid with modular disease

50
Q

Describe the investigations you would perform if you suspected hypothyroidism.

A

T4 and TSH level measurement
- low T4
- TSH would be high in primary, and low in secondary
Assessment of thyroid antibodies to asses for Hashimotos’
- anti-TOP antibodies

51
Q

What is the treatment for hypothyroidism?

A

Levothyroxine
- need 1.7-2micrograms/kg/day
- taken on an empty stomach
- avoid use with PPIs, ferrous sulphate or calcium
Start low in the elderly or those with cardiac disease

52
Q

What is full suppression of TSH associated with?

A

Osteoporosis and atrial fibrillation

53
Q

Name the types of undifferentiated thyroid cancer.

A

Papillary
Follicular
Mixed
Medullary carcinoma of the thyroid

54
Q

Name the types of undifferentiated thyroid cancer.

A

Anaplastic

Small cell

55
Q

What are other types of cancer that can affect the thyroid?

A

Lymphoma
Sarcoma
Metastatic

56
Q

What is the difference between thyrotoxicosis and hyperthyroidism?

A

Thyrotoxicosis is the clinical effect of high thyroid hormone in the blood, not the actual secretion of the hormones
- e.g. Tachycardia, heat intolerance, weight loss, diarrhoea, tremor, sweating, palpitations, etc

57
Q

What are the causes of thyrotoxicosis?

A 
Hyperthyroidism 
Excessive intake of levothyroxine
Ectopic thyroid tissue
Trophoblastic tumour
Subacute thyroiditis
58
Q

What are the symptoms of a thyroid storm (severe form of thyrotoxicosis)

A

High fever
Extreme CV effects - tachycardia, angina
Severe CNS effects -agitation, restlessness, delirium

59
Q

What is there treatment for a thyroid storm?

A

Peripheral cooling - shivering response must be prevented
Replace fluid, electrolytes, and glucose
Beta-adrenergic blockers - reduce CV effects
Glucocorticoids can treat relative adrenal insufficiency resulting from stress of hyperthyroid state

Year 2 - Endocrinology (14 decks)

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