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Reproductive and Endocrine > Thyroid > Flashcards

Thyroid Flashcards

1
Q

Levels of which hormone in the blood are most likely to confirm hyperthyroidism?

A

Low TSH levels (due to negative feedback effect of thyroid hormones)

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2
Q

Antibodies to which enzyme can cause hypothyroidism?

A

Thyroid peroxidase

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3
Q

Level of what is raised by most thyroid cancers?

A

Thyroglobulin

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4
Q

What is atosiban?

A

Inhibits release of vasopressin and oxytocin, so used intravenously to halt premature labour.

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5
Q

What is bromocriptine?

A

Dopamine receptor agonist

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6
Q

What is buserelin?

A

A gonadorelin analogue which desensitises GnRH receptors on the anterior pituitary gland.

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7
Q

What is tamoxifen?

A

Selective Estrogen Receptor Modulator, used in the treatment of breast cancer.

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8
Q

What proportion of the thyroid hormone secreted by the thyroid is T4 and what proportion is T3?

A

93% T4

7% T3

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9
Q

What is the cascade that controls thyroid hormone secretion?

A

The hypothalamus is stimulated by higher cortical centres (e.g by a decrease in temperature) and releases Thyrotropin Releasing Hormone (TRH).
TRH stimulates the anterior pituitary to release Thyroid Stimulating Hormone (TSH).
Thyroid Stimulating Hormone increases the activity of TPO and so stimulates the thyroid to release more T4 and T3.

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10
Q

What are the thyroid hormones?

A

Thyroxine (T4)

Triiodothyronine (T3)

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11
Q

How is T3 different to T4?

A

T3 is much more potent and has a much shorter half life

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12
Q

What are the effects of calcitonin?

A

Stimulates osteoblastic activity
Inhibits osteoclasts
Decreases renal calcium resorption

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13
Q

What is the term used to describe iodide ions being actively transported into follicular cells from the blood?

A

Iodine trapping

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14
Q

How is thyroglobulin produced?

A

Thyroglobulin is a glycoprotein which is synthesised in the Rough Endoplasmic Reticulum, modified in the Golgi Body, then packaged into secretory vesicles and released into the lumen of the follicle.

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15
Q

What is the role of Thyroid Peroxidase?

A

Oxidises iodide to iodine as it moves from the follicular cell to the lumen of the follicle, so that it can iodinate the tyrosine residues on thyroglobulin.

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16
Q

What is formed by the iodination of tyrosine?

A

Monoiodotyrosine

Diiodotyrosine

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17
Q

How are the thyroid hormones secreted from the follicle?

A

Droplets of colloid re-enter the follicular cell by pinocytosis. They fuse with a lysosome and proteases break down the colloid to cleave off T3 and T4. T3 and T4 then diffuse out of the cell and are carried in the blood bound to transport proteins like Thyroxine Binding Globulin.

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18
Q

What is the biologically inactive isomer that can be formed and is thought to cause conditions such as euthyroid sick syndrome?

A

Reverse T3

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19
Q

What are some of the effects of thyroid hormones?

A

Increase basal metabolic rate
Increase heat production (calorigenic effect)
Increase the number and size of mitochondria
Positive chronotropic and inotropic effects on the heart
Increase depth and rate of respiration
Increase oxygen delivery and consumption by metabolically active tissue
Increase appetite and digestive motility
Regulate substrate metabolism
Promotes erythropoiesis
Influences lung development and is necessary for producing surfactant
Crucial for development of nervous and skeletal systems

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20
Q

By how much does excess thyroid hormones increase the basal metabolic rate?

A

100%

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21
Q

By how much does deficiency of thyroid hormones decrease basal metabolic rate?

A

50%

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22
Q

Why does hypothyroidism lead to atherosclerosis and ischaemic heart disease?

A

The level of thyroid hormones in the blood is inversely proportional to the level of NEFA in the blood.

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23
Q

What is the effect of thyroid hormones on release of growth hormone from somatotrophs in the anterior pituitary?

A

Thyroid hormone stimulates release of growth hormone. But excess thyroid hormone does not cause excess growth (acromegaly), like excess growth hormone does.

24
Q

What happens to development of the brain during foetal and postnatal life if there is a deficiency of thyroid hormones?

A

There is mental retardation, which becomes irreversible unless treatment is administeres days or weeks after birth.

25
Q

What are four ways thyroid hormones can be transported in the blood?

A

As free T4 and free T3
Bound to Thyroxine-Binding Globulin
Bound to Thyroxine-Binding Prealbumin
Bound to Albumin

26
Q

What happens to T4 after it diffuses across the plasma membrane into the cell?

A

It is deiodinated to T3.
T3 binds to the nuclear receptor, which migrates into the nucleus and binds to a Thyroid Hormone Response Element on the gene. This can then influence gene transcription.

27
Q

What do you call the molecules that bind to the thyroid hormone receptor and cause a conformational change to either enable or inhibit binding of T3 to the receptor?

A

Costimulators and corepressers.

28
Q

What two things have negative feedback effects on the secretion of TRH and TSH?

A

Thyroid hormones directly

Effects of thyroid hormones (calorigenic, increased metabolic rate) indirectly

29
Q

What are the three effects of TSH?

A

Increased active uptake of iodide
Stimulates uptake of colloid
Induces growth of thyroid (which is why hyperthyroidism causes goitre)

30
Q

How many times its original size can the thyroid gland enlarge to due to hyperthyroidism?

A

3x

31
Q

What are the two types are primary hypothyroidism?

A

Congenital (genetic defect e.g athyreosis)

Acquired (e.g autoimmunity, iodide deficiency, iatrogenic)

32
Q

What is secondary hypothyroidism?

A

A problem in the pituitary gland leading to decreased TSH (e.g a pituitary tumour)

33
Q

What is tertiary hypothyroidism?

A

A problem in the hypothalamus e.g sarcoidosis

34
Q

What is the test used to screen neonates for congenital hypothyroidism?

A

Guthrie blood spot test

35
Q

Why is iodine deficiency no longer the most common cause worldwide of goitre and borderline hypothyroidism?

A

Table salt is supplemented by iodine

36
Q

What will the levels of thyroid hormones and TSH be like in primary hypothyroidism compared to secondary hypothyroidism?

A

Primary hypothyroidism = Low T4 and T3, higher than normal TSH
Secondary hypothyroidism = Low T4 and T3, low TSH

37
Q

What are the signs of hypothyroidism?

A 
Goitre
Myxoedema 
Fatigue
Cold intolerance
Dry, scaly skin
Dry hair and hair loss
Anaemia
Puffy eyes
38
Q

What is myxoedema?

A

Swelling due to water retention due to altered carbohydrate metabolism

39
Q

What is the most common non-iatrogenic cause of hypothyroidism in the UK?

A

Hashimoto’s disease (antibodies reduce the activity of TPO enzyme)

40
Q

Why might it be hard to diagnose Hashimoto’s disease?

A

It has slow progress over many years causing chronic thyroid damage and a drop in blood hormones - so the changes may be harder to spot because they are gradual.

41
Q

What is the test used to diagnose secondary hypothyroidism?

A

Administer protirelin to increase TRH levels and record if there is a subsequent rise in TSH.

42
Q

What is cellular hypothyroidism?

A

Excessive production of reverse T3, so normal T3 and T4 and TSH levels in the blood.

43
Q

What is the treatment of hypothyroidism?

A

Levothyroxine

44
Q

Which supplements interfere with levothyroxine treatment, so need to be taken at the right time so they don’t interfere?

A

Calcium and iron supplements.

45
Q

What is a major cause of relapse of hypothyroidism even after regaining euthyroid?

A

Poor compliance to treatment.

46
Q

What are three common causes of hyperthyroidism?

A

Grave’s disease (autoimmune), thyroiditis (inflammation), toxic nodular goitre (tumour).

47
Q

Which autoantibody causes Grave’s disease?

A

Thyroid Stimulating Immunoglobulin (TSI)

48
Q

What are the blood levels of T4, T3, TSH in primary hyperthyroidism?

A

Primary hyperthyroidism = High T3 and T4, low/absent TSH

49
Q

What are the signs of hyperthyroidism?

A 
Fine tremor
Intolerance to heat
Sweating
Anxiety/Irritability
Weight loss
Exophthalmos
Increased appetite
Palpitations/Tachycardia
Diarrhoea
Goitre
50
Q

What are the three parts of thyroid eye disease?

A

Proptosis/Exophthalmos
Lid retraction/Lid lag
Opthalmoplegia (paralysis of muscles within or surrounding eye)

51
Q

What is the first, second and third line of treatment in Grave’s disease?

A

1st line - drugs (thionmides and beta blockers)
2nd line - radioiodine treatment
3rd line - partial or full thyroidectomy

52
Q

What are the thionamides used to treat Grave’s disease?

A

Carbimazole - inhibits TPO

Propylthiouracil - inhibits TPO and deiodination of T4 to T3

53
Q

How long is hyperthyroidism treated with drugs, and what percentage of people relapse after stopping the drugs?

A

Drugs for 12 months

50% relapse on stopping drugs

54
Q

What are the effects of parathyroid hormone?

A

Decrease renal excretion of Ca2+
Increased renal synthesis of 1,25-(OH)2 vitamin D3
Stimulates osteoclastic activity

55
Q

What is the most common cause of primary hyperthyroidism?

A

Single benign parathyroid adenoma

56
Q

What are the symptoms of primary hyperthyroidism?

A 
Nausea and vomiting
Kidney stones
Diffuse bone pain
Fragility fractures
Weakness and fatigue
Depression and cognitive dysfunction
57
Q

What is secondary hyperparathyroidism?

A

The physiological response to hypocalcaemia, with symptoms similar to primary hyperparathyroidism.

Reproductive and Endocrine (11 decks)

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