thyroid disorders

Question 1

thyroid follicle

Answer 1

epithelial cells arranged in spheres

Question 2

colloid

Answer 2

proteinaceous depot of thyroid hormone precursors

Question 3

thyroid hormones

Answer 3

• 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

Question 4

euthyroid state

Answer 4

thyroid hormone secretion is normal

Question 5

hypothyroid state

Answer 5

thyroid hormone secretion is subnormal
also referred to as myxoedema

Question 6

hyperthyroid state

Answer 6

thyroid hormone secretion is excessive
also referred to as thyrotoxicosis

Question 7

actions of thyroid stimulating hormone (TSH)

Answer 7

• 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

Question 8

goitre

Answer 8

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

Question 9

actions of thyroid hormones T3/T4

Answer 9

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

Question 10

signs and symptoms of hypothyroidism

Answer 10

• 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

Question 11

primary hypothyroidism

Answer 11

• 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

Question 12

aetiology of primary hypothyroidism

Answer 12

• 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

Question 13

levothyroxine

Answer 13

• 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

Question 14

adverse effects of levothyroxine

Answer 14

• 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

Question 15

liothyronine

Answer 15

• 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

Question 16

secondary hypothyroidism

Answer 16

• 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

Question 17

myxoedema coma

Answer 17

• 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

Question 18

drugs that affect thyroid function

Answer 18

• 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

Question 19

signs and symptoms of hyperthyroidism

Answer 19

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

Question 20

hyperthyroidism

Answer 20

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

Question 21

grave’s disease

Answer 21

• 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)

Question 22

treatment of hyperthyroidism

Answer 22

• 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

Question 23

antithyroid drugs

Answer 23

• 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

Question 24

peroxidase

Answer 24

enzyme responsible for iodination of tyrosine