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MP322 > thyroid disorders > Flashcards

thyroid disorders Flashcards

1
Q

thyroid follicle

A

epithelial cells arranged in spheres

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2
Q

colloid

A

proteinaceous depot of thyroid hormone precursors

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3
Q

thyroid hormones

A
  • T3 is active hormone
  • most circulating T3 is derived from T4
  • both T3 and T4 are extensively protein bound in the plasma
  • bound to thyroxine-binding globulin (TBG) and transthyretin (TTR) thyroxine-binding prealbumin
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4
Q

euthyroid state

A

thyroid hormone secretion is normal

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5
Q

hypothyroid state

A

thyroid hormone secretion is subnormal
also referred to as myxoedema

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6
Q

hyperthyroid state

A

thyroid hormone secretion is excessive
also referred to as thyrotoxicosis

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7
Q

actions of thyroid stimulating hormone (TSH)

A
  • TSH does more than stimulating T3 and T4 production
  • it 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 resulting in goitre
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8
Q

goitre

A
  • a lump or swelling at the front of the neck caused by a swollen thyroid
  • can occur in hypothyroidism, hyperthyroidism and euthyroidism
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9
Q

actions of thyroid hormones T3/T4

A

in tissues:
- increases metabolic rate
- increases heat production
- increases responsiveness to sympathetic input
- permits normal growth/development
in nervous system:
- permits maintenance of normal activity

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10
Q

signs and symptoms of hypothyroidism

A
  • cold intolerance
  • modest weight gain
  • bradycardia (slow heart rate)
  • tiredness for no apparent reason
  • constipation
  • forgetfulness and personality changes (depression)
  • pale/dry coarse skin
  • puffiness of face
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11
Q

primary hypothyroidism

A
  • any condition characterised by plasma T3 or T4 below normal and increased TSH
  • most cases are due to damage or loss of thyroid tissue
  • can also be due to inadequate iodine consumption
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12
Q

aetiology of primary hypothyroidism

A
  • hashimoto’s thyroiditis is most common cause of primary hypothyroidism
  • autoimmune disease, antibodies to thyroid peroxidase
  • twice as prevalent in women
  • T4 decreases and TSH increases
  • can result in goitre
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13
Q

levothyroxine

A
  • treatment for primary hypothyroidism
  • synthetic thyroid hormone that is identical to thyroxine T4
  • single dose reaches its maximum effect in 10 days and passes off in 2-3 weeks
  • half-life is 7 days in euthyroid; 14 days in hypothyroidism
  • dose adjusted until TSH levels are in mid-range
  • patients should be monitored at annual intervals
  • pregnant women require monthly monitoring and require 50-100% increase in normal dose
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14
Q

adverse effects of levothyroxine

A
  • hair loss during first few months of treatment
  • headaches
  • sleep problems (insomnia)
  • nervousness
  • fever, hot flashes/sweating
  • pounding heart beat/fluttering chest
  • appetite changes/weight changes
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15
Q

liothyronine

A
  • treatment for primary hypothyroidism
  • not supported as treatment
  • risks from T3 therapy on bone (osteoporosis) and heart (arrhythmia)
  • 5x as biologically potent as T4
  • single dose reaches maximum effect in 24 hours and passes off in 1 week
  • half-life is 2 days in euthyroid
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16
Q

secondary hypothyroidism

A
  • uncommon
  • pituitary doesn’t produce TSH or hypothalamus doesn’t produce sufficient TRH (tertiary)
  • both T3 and T4 as well ass TSH are below normal
  • symptoms are very similar to primary hypothyroidism and treated in same manner
17
Q

myxoedema coma

A
  • end result of untreated hypothyroidism
  • progressive weakness leading to loss of consciousness
  • extreme hypothermia (24-32)
  • areflexia, seizures, and respiratory depression
  • participating factors: illness, infection, trauma, drugs that suppress the CNS, exposure to cold
18
Q

drugs that affect thyroid function

A
  • corticosteroids: decrease basal production of TRH and TSH
  • lithium: inhibits the release of thyroid hormones and interferes with their peripheral deiodination
  • amiodarone: contains iodine and can cause both hypo/hyperthyroidism
  • cholestyramine: reduces the absorption of thyroxine
19
Q

signs and symptoms of hyperthyroidism

A
  • heat intolerance
  • palpitations
  • weight loss
  • restlessness/nervousness
  • fatigue
  • increased sweating
  • frequent bowel movements
  • goitre may be present
20
Q

hyperthyroidism

A
  • thyroid produces excess of T4
  • reduction in TSH due to negative feedback loop
  • T3 is usually elevated as well
21
Q

grave’s disease

A
  • most common cause of hyperthyroidism
  • autoimmune disease
  • caused by thyroid stimulating immunoglobulin (TSI)
  • activates TSH receptor on thyroid follicular cells
  • increased secretion of thyroid hormones
  • causes goitre and exophthalmos (protruding eyeballs)
22
Q

treatment of hyperthyroidism

A
  • surgery
  • radioactive iodine
  • administered orally (solution or capsule)
  • taken up by thyroid gland
  • emits gamma and beta radiation (half-life 8.1 days)
  • treatment usually has its maximum effect around 3 months but can last as long as 6 months
23
Q

antithyroid drugs

A
  • thioamides (carbimazole/propylthiouracil)
  • accumulated by the thyroid
  • inhibit thyroid peroxidase and prevent hormone synthesis
  • propylthiouracil also inhibits peripheral deiodination
  • effect is slow in onset 4-6 weeks
  • generally safe but may cause agranulocytosis thereby increasing the risk of infection
24
Q

peroxidase

A

enzyme responsible for iodination of tyrosine

MP322 (18 decks)

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