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322 > Lecture 22: Thyroid disorders > Flashcards

Lecture 22: Thyroid disorders Flashcards

1
Q

Where is the thyroid gland located?

A

Between the larynx and the trachea

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2
Q

What is the thyroid follicle?

A

The basic functional unit of the thyroid gland

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3
Q

What are the steps in the synthesis of thyroid hormones

A
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4
Q

What is the active thyroid hormone?

A

T3

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5
Q

Where is most T3 derived from?

A

T4 by deiodination

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6
Q

How are T3 and T4 found in the plasma?

A

Extensively protein bound

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7
Q

What are the thyroid hormones bound to?

A

Thyroxine-binding globulin (TBG) and transthyretin (TTR) thyroxine-binding prealbumin

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8
Q

How are thyroid hormones secreted?

A
  1. The Hypothalamus secretes thyrotrophin releasing
  2. TRH acts on the anterior pituitary to secrete thyroid stimulating hormone
  3. TSH acts on the thyroid hormone to secrete thyroid hormone
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9
Q

What is the euthyroid state?

A

Thyroid hormone secretion is normal

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10
Q

What is the Hypothyroid state?

A

Thyroid hormone secretion is subnormal (also referred to as myxoedema)

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11
Q

What is the hyperthyroid state?

A

Thyroid hormone secretion is excessive (also referred to as thyrotoxicosis)

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12
Q

What are the actions of the TSH?

A
  • TSH does more than just stimulate T3 and T4 production
  • TSH increases protein synthesis in follicular epithelial cells, increases DNA replication, and cell division
  • Increases rough endoplasmic reticulum and cell machinery required for protein synthesis
  • Thyroid will undergo hypertrophy if exposed to greater TSH concentration
  • Results in goitre
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13
Q

How much of the circulatng thyroid hormone is T3?

A

20%

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14
Q

How much of the circulatng thyroid hormone is T4?

A

80%

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15
Q

Are thyroid hormones lipohillic or hydrophillic?

A

Lipophillic and easily cross cell membranes

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16
Q

How does T3 act?

A

Acts by inducing gene transcription in protein synthesis

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17
Q

What is the primary action of thyroid hormones?

A

Increase the bodies metabolic rate - rate of oxygen consumption and energy expenditure at rest

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18
Q

What are the effects of thyroid hormones on tissues?

A
  • Increase basal metabolic rate
  • Increase heat production
  • Increase responsiveness to sympathetic input
  • Permits normal growth and development
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19
Q

What are the effects of thyroid hormone on the nervous system?

A
  • Permits normal growth and development
  • Permits maintenance of normal activity
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20
Q

What is iodine deficiency disease?

A

Cretinism is the most extreme version. It causes mental retardation, reduction in physical growth, deaf mutism.

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21
Q

What causes cretinism?

A
  • An inadequate dietary iodine intake
  • Meternal iodine deficiency during pregancnt
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22
Q

What is now fortified with iodine?

A

Salt

23
Q

What is the required iodine intake?

A

150mcg / day

24
Q

What are the thyroid function tests?

A
  • TSH
  • Free t4
  • Free t3
25
Q

What are the signs and symptoms of hypothyroidism?

A
  • Cold intolerance
  • Modest weight gain
  • Bradycardia
  • Tiredness for no apparent reason
  • Constipation
  • Forgetfulness and personality changes (depression)
  • Pale, dry coarse skin
  • Puffiness of face
26
Q

What is primary hypothyroidism?

A
  • T3 or T4 below normal
  • Increased TSH
27
Q

What causes most cases of hypothyroidism?

A

Damage or loss of thyroid tissue or due to inadquate iodine consumption

28
Q

What causes primary hypothyroidism?

A
  • Hashimotos thyroiditis
29
Q

What is hashimotos thyroiditis?

A

An autoimmune diseasse - antibodies to thyroid peroxidase. Its twice as common in woman. T4 decreases and TSH increases. Can result in a goitre

30
Q

What is the treatment for primary hypothyroidism?

A

Levothyroxine

31
Q

What is levothyroxine?

A

A synthetic hormone identical to thyroxine T4

32
Q

What are the adverse effects of levothyroxine?

A
  • Hair loss during the first few months of treatment
  • Headaches
  • Sleep problems (insomnia)
  • Nervousness
  • Fever, hot flashes and/or sweating
  • Pounding heart beat or fluttering in chest
  • Appetite changes, weight changes
33
Q

What is the treatment for primary hypothyroidism?

A

Liothyronine

34
Q

What is liothyronine?

A

Synthetic form of T3

35
Q

What are the risk of liothyronien?

A

Osteoporosis and arrythmia

36
Q

What is the half life of levothyroxine?

A
  • 7 days in euthyroid
  • 14 days in hypothyroidism
37
Q

What is the half life of liothyronine?

A

2 days in euthyroid

38
Q

What is secondary hypothyroidism?

A

Its uncommon. The pituitary doesnt produce TSH or the hypothalamus dosesnt produce TRH. T3 and T4 and TSH are below normal

39
Q

What is myxoedema coma?

A

It is the end result of untreated hypothyroidism. It is progressive weakness leading to a loss of consciousness. Extreme hypothermia

40
Q

What are the signs and symptoms of myxoedema coma?

A

Areflexia, seizures and respiratory depression

41
Q

What drugs affect throid function?

A

Corticosteroids, Lithium, Amiodarone, Cholestyramine

42
Q

How do corticosteroids affect thyroid function?

A

Can decrease basal production of TRH and TSH, consequently decreasing thyroid hormone levels

43
Q

How does lithium affect thyroid function?

A

Inhibits the release of thyroid hormones and interferes with their peripheral deiodination

44
Q

How does Amiodarone affect thyroid function?

A

Contains iodine and can cause both hypothyroidism and hyperthyroidism

45
Q

How does Cholestyramine affect thyroid function?

A

Reduces the absorption of thyroxine

46
Q

what are the Signs and symptoms of Hyperthyroidism?

A
  • Heat intolerance
  • Palpitations
  • Weight loss (despite increased appetite)
  • Restlessness and nervousness
  • Fatigue
  • Increased sweating
  • Frequent bowel movements
  • Goitre may be present
47
Q

What is hyperthyroidism?

A

Thyroid produces an excess of T4. Reduction in TSH due to negative feedback loop. T3 is usually elevated as well

48
Q

What are the signs of graves disease?

A

Goiter and exopthalmos

49
Q

What is the most common cause of hyperthyroidism?

A

Graves disease

50
Q

What is graves disease?

A

An autoimmune disease caused by thyroid stimulating immunoglobulin. It activates TSH receptor on thyroid follicular cells and increases secretion of thyroid hormones.

51
Q

What is the treatment for hyperthyroidism?

A
  • Surgery
  • Radioactive iodine
52
Q

What are the antithyroid drugs?

A
  • Thioamides eg carbimazole, propylthiouracil
53
Q

How do antithyroid drugs work?

A

They are accumulated by the thyroid, inhibit thyroid peroxidase - the enzyme responsivle for iodiniation of tyrosine and prevent hormone synthesis. Propylthiouracil also inhibits peripheral deiodination. Its effect is slow in onset 4-6 weeks.

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