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EXAM 2 > Thyroid gland > Flashcards

Thyroid gland Flashcards

1
Q

What is T3 and where is it synthesized?

A

Tri-iodothyronine is the active thyroid hormone that is synthesized in the colloid space.

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2
Q

What is T4 and how is it converted to T3?

A

Thyroxine is the ‘inactive’ form of the thyroid hormone. It is converted into tri-iodotheyronine (T3) upon the entering of a target cell via de-iodinases

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3
Q

Thyroid hormone actions

A
  1. Increases basal metabolic rate
  2. Increases heat production
  3. Increases cells responsiveness to catecholamines
  4. Stimulates GH and IGF-1 secretion.
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4
Q

What are the carrier proteins that the thyroid hormone bind to?

A
  1. Thyroxine-binding globulin
  2. Transthyretin
  3. Albumin

Transthyretin = Thyroxine-binding prealbumin

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5
Q

Explain thyroid hormone synthesis

A
  1. Thyroperoxidase oxidises TWO iodide ions into ONE iodine.
  2. Thyroperoxidase iodinates the tyrosine residues on thyroglobulin.
  3. Thyroperoxidase conjugates the neighbouring tyrosine residues together.
  4. Proteases cleave the peptide bonds from the iodinated thyroglobulin resulting in stand-alone T3 molecules and T4 molecules.
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6
Q

What transports T3/T4 into the plasma and/or into cells?

A

Monocarboxylate transporter (MCT)

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7
Q

TRUE OR FALSE

T4 is cleaved via protease upon entering a target cell.

A

FALSE
T4 is de-iodinated [via de-iodinases]

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8
Q

What is the tri-iodothyronine mode of action ?

A

Genomic regulation
1. It binds to transcription factors {α1, α2, β1,β2} via high binding affinity.
2. Stimulation of the receptors causes a change in transcription of responsive genes.

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9
Q

Where is thyroxine-binding globulin (TBG) synthesized?

A

Liver

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10
Q

How does TSH regulate thyroid hormone synthesis ?

A
  1. TSH binds to cAMP-coupled receptors on epithelial cells.
  2. This stimulates iodine uptake by cells.
  3. Subsequently, increases thyroid hormone synthesis.
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11
Q

Thyroid cancer symptoms

A
  • Lump in your neck (Goitre)
  • Hoarse voice
  • Sore throat
  • Difficulty swallowing
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12
Q

Thyroid cancer risk factors

A
  • Radiation exposure
  • Genetics
  • Iodine intake
  • Gender ( 3x more likely in women)
  • Age (20-55)
  • Obesity
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13
Q

What is the most common form of thyroid cancer ?

A

Papillary cancer

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14
Q

What are the treatment options for thyroid cancer ?

A

All treatments depends on the stage and type of cancer.
1. Thyroidectomy (if possible)
2. Radiotherapy
3. Chemotherapy [Doxorubicin/cisplatin]
4. Targeted chemotherapy

Thyroidectomy is the removal of all or part of the thyroid gland.

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15
Q

When is targeted chemotherapy considered for the treatment of thyroid cancer ?

A

When Thyroidectomy, radiotherapy, chemotherapy have failed.

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16
Q

What are the most common drugs used during chemotherapy for thryroid cancer ?

A
  • Doxorubicin
  • Cisplatin
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17
Q

What are the common causes of hypothyroidism ?

A
  • Exposure to radiation (radiotherapy)
  • Iodine deficiency
  • Thyroidectomy (removal of the thyroid)
  • Amiodarone (used for cardiac arrhythmias)
  • Pituitary defect (secondary hypothyroidism)
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18
Q

What are the forms of primary hypothyroidism and what can cause them ?

A

A thyroid defect that is usually autoimmune related (which is called Hashimoto’s disease). Another form of primary hypo- is primary myxoedema.

It is also commonly caused by a lack of dietary iodine or hyperthyroidism drugs. This leads to the hyposecretion of thyroid hormone.

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19
Q

What is Hashimoto’s disease ?

A

Hashimoto’s disease is an autoimmune disease in that the body creates antibodies that attack part of the thyroid gland (thyroglobulin).

Subsequently, there is no TH synthesis or secretion without thyroglobulin therefore the TSH concentration remains HIGH.

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20
Q

What is secondary hypothyroidism ?

A

A pituitary defect that leads to a decreased secretion of TSH which leads to a decreased activity of the thyroid gland.

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21
Q

What is tertiary hypothyroidism ?

A

A hypothalamic defect that leads to a decreased secretion of TRH and therefore causes a cascade effect in which ultimately there is a decreased activity of the thyroid gland.

22
Q

What is peripheral hypothyroidism ?

A

When the target tissues are insensetive to the thyroid hormone and therefore has no effect.

23
Q

What are the hypothyroidism symptoms ?

A

Symptoms:
* Weakness/fatigue
* Constipation
* Dry skin
* Weight gain
* Hair loss
* Fluid retention

24
Q

What causes cretinism ?

A

Most commonly caused by maternal hypothyroidism that is due to iodine deficiency.

25
Q

What is primary myxoedema and its symptoms ?

A

A severe form of autoimmune-caused hypothyroidism indiciated by the thickening and swelling of the skin.

26
Q

How is hypothyroidism diagnosed ?

A

Hypothyroidism is confirmed via a thyroid function test (TFT) that measures the TSH level and the free T4 (FT4) levels in the body. This is ideally followed by another blood test to confirm the FT3 levels.

27
Q

Diagnosis criteria for hypothyroidism

A

Criteria:
* TSH: > 4.5 μIU/mL
* FT4: < 10 pmol/L
* FT3: < 4 pmol/L

28
Q

What is the treatment for hypothyroidism and what are its parameters ?

A

Levothyroxine

REPLACEMENT HORMONE THERAPY
Levothyroxine
* Starting dose: 50-100 μg OM|empty stomach
* Check TSH levels after 2-3 months
* TSH levels out of range ? -> INCREASE by 25-50 μg
* Maintenance dose: 100-150 μg

Liothyronine (synthetic T3)
* Rapid onset and used for emergencies.
* Short duration

Iodine
* Can only given if iodine deficiency is the cause.

29
Q

What are the common different forms of hyperthyroidism ?

A
  • Grave’s disease
  • Plummer’s disease (toxic multi-nodular goitre)
  • Toxic edenomas
30
Q

What is Grave’s disease ?

A

An autoimmune disease that produces thyroid-stimulating antibodies which mimic TSH and therefore stimulate the thyroid gland leading to hypersecretion of T3 and T4.

10x more likely in women

31
Q

What is most commonly presented in grave’s disease ?

A
  • Pretibial myxoedema (deposits of mucin under the skin on the leg)
32
Q

What is Plummer’s disease ?

A

The formation of new follicles resulting in more synthesis and secretion of thyroid hormone. These eventually grow into nodules hence its alternative name; toxic multi-nodular goitre.

33
Q

What are thyroid edenomas ?

A

The development of benign tumors that secrete thyroid hormone. This disease can lead to hyperthyroidism.

These are easy to surgically remove.

34
Q

What are the symptoms of hyperthyroidism ?

A

Symptoms:
Beta adrenergic symptoms
* Palpitations
* Excessive sweating
* Anxiety
* Tremor

Other
* Weight loss
* Goitre
* Bulging eyes = Exophthalmus
* Swelling of eyelids
* Diarrhoea

35
Q

How is hyperthyroidism diagnosed and what are the criteria?

A

Diagnosis requires a blood test that indicates LOW TSH levels and HIGH FT3 and FT4.
* TSH: < 0.4 μIU/mL
* FT4: > 24 pmol/L
* FT3: > 7.8 pmol/L

36
Q

What is thyroid storm ?

A

An acute, life-threatening state induced by extreme hypersecretion of thyroid hormone. This is a medical emergency and requires admission and close monitoring.

37
Q

What are the symptoms of thyroid storm ?

A

Symptoms:
* Pyrexia (fever)
* Tachycardia
* Delerium

38
Q

What are the treatment options for hyperthyroidism ?

A
  • Management of beta adrenergic symptoms
  • Pharmaceutical therapy
  • Thyrodectomy (would require lifelong hormone replacement)
  • Radiotherapy
  • Lugol’s iodine
39
Q

What is the antithyroid drug first-line treatment of hyperthyroidism ?

A

Carbimazole
1. Successful after 4-8 weeks -> Normal thyroid function
2a. Once reached… titrate down to maintanance dose [5-15mg daily] for 12-18 months
OR
2b. HIGH DOSE|Block all thyroid hormone secretion and replace with Levothyroxine (life-long) Block and replace

40
Q

What is the pharmaceutical second-line treatment for hyperthyroidism ?

A

Propylthiouracil
(only used for patients unable to tolerate carbimazole)
* Small risk of severe hepatic reactions that can be fatal (hence second-line)
* Initial dose: 200-400mg daily
* Successful after 4-8 weeks.
* Once reached…titrate it down to maintance dose [50-150mg]

41
Q

What is the management therapy for hyperthyroidism ?

A

This is the treating of the beta adrenergic reactions that come with hyperthyroidism. First-line drug for this is Propanolol as it is non-selective at all beta receptors and therefore treats all…
* Palpitations
* Tremors
* Sweating
* Anxiety

42
Q

How do Thioureylenes work ?

A

They work by inhibiting thyroperoxidase; the enzyme responsible for T3 and T4 synthesis. They also inhibit the T4 to T3 conversion in target tissues.

43
Q

What are the cautions with Thioureylenes ?

A

Thioureylenes can cause…
* Rashes
* Agranulocytosis (complete depletion of neutrophils)
Therefore a higher susceptibility to bacterial infections.

44
Q

What should a patient report immediately upon development regarding Thioureylenes issues ?

A
  • Mouth ulcers
  • Sore throat
  • Fever
  • Malaise
  • Bruising
  • Bleeding
45
Q

What is Lugol’s iodine ?

A

Lugol’s iodine is the administration of HIGH iodine/iodide dose for the temporary inhibition of thyroid hormone synthesis. Usually consdered in thyroid storm patients.

46
Q

What medication can also induce either hypothyroidism or hyperthyroidism ?

A

Amiodarone (used for cardiac arrhythmias). They contain a HIGH dose of iodine.

Patients taking this medication should…
* Measure baseline TFTs at the start of treatment
* TFT test every 6 months.

47
Q

What is the first-line treatment option for toxic single nodule ?

A

1) Hemithyroidectomy
2) Radioactive iodine (if surgery unsuitable)

48
Q

What is the first-line treatment for grave’s disease ?

A

1) Radioactive iodine therapy unless…
* Pregnant
* Fathering < 6month old child
* Thyroid eye disease
* Compression or thyroid malignancy

2) Measure TSH, FT4 and FT3 every 6 weeks for 6 months (until TSH is normal)

49
Q

What is the first-line treatment for toxic multiple nodules ?

A

1) Radioactive iodine therapy unless…
* Pregnant
* Fathering < 6 month child
* Thyroid eye disease

2) Measure TSH, FT4 and FT3 every 6 weeks for 6 months (until TSH normal)
3) Total thyroidectomy (if radioactive iodine unistable)

50
Q

How does carbimazole work and what is it used for ?

A

Carbimazole blocks the way your body processes iodine thereby reducing iodination of tyrosine residues on thyroglobulin and reducing the synthesis of T3 and T4.

EXAM 2 (8 decks)

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