Thyroid gland

Question 1

Anatomy of Thyroid gland?

Answer 1

2 lobes: Left and Right, Isthmus (sometimes pyramid)

Question 2

thyroid gland surrounding structures?

Answer 2

thyroid wrapped around trachea and is inferior to the thyroid and cricoid cartilage. Left recurrent laryngeal nerve runs close to left lobe. Also close to carotid and jugular veins bilaterally

Question 3

microanatomy?

Answer 3

follicular cells surround colloid (mucus/ECF) + parafollicular cells

Question 4

Thyroid hormone production?

Answer 4

1 - Iodide enters follicular cell and TSH binds to TSHR on cell membrane
2 - Iodide passes through into colloid and TSH stimulates production of TPO which oxidises Iodide to Iodine
3 - TSH stimulates synthesis of TG -> iodine binds to TG tyrosine residues form MIT/DIT
4 - MIT/DIT bound to TG undergo coupling reaction to form T3/T4 which is released into circulation once unbound from TG in lysosome.

Question 5

Coupling reactions?

Answer 5

MIT + MIT = T3; DIT + DIT = T4 (thyroxine)

Question 6

Thyroid Hormone function?

Answer 6

Thyroxine (T4=80%) converted to T3 (20%) in tissues by DEIODINASE enzyme; transported by TBG, Albumin, transthyretin (prealbumin)

Question 7

Thyroid Hormone effects?

Answer 7

acts via nuclear receptor to alter gene expression; essential for foetal/CNS development, ↑basal metabolic rate, ↑glucose promotion, protein synthesis and lipolysis, potentiates catecholamines

Question 8

importance of thyroid hormone for foetus?

Answer 8

untreated congenital hypothyroidism -> cretinism

Question 9

thyroid hormone regulation?

Answer 9

TRH produced in hypothalamus stimulates TSH secretion from AP -> TSH acts on thyroid, stimulating T4/T3 synthesis; T3+T4 -tive feedback loop on AP, hypothalamus, SS inhibits TRH+TSH

Question 10

Wolff Chaikoff effect?

Answer 10

high [Iodide] inhibits T3+T4 production

Question 11

↑TSH, ↓T4?

Answer 11

Primary Hypothyroidism: autoimmune dammage to thyroid eg. Hashimoto’s Thyroiditis

Question 12

Hypothyroidism S&S?

Answer 12

CNS: fatigue, depression, impaired memory
Goitre, deeper voice; shaggy hair, hair loss, dry/rough skin
GI: weight gain with loss of appetite, constipation
CV: bradycardia, facial oedema
eventual myxoedema coma

Question 13

Levothyroxine? indications, dosage

Answer 13

synthetic T4 -> indications: hypothyroidism, hyperthyroidism (blocking & replacing regime)
dosage: PO starting dose 50-100 micrograms, titrate to TSH levels aiming for normal range

Question 14

Potential complications?

Answer 14

weight loss, headache, heart attack, tachycardia

combination T3/T4 potential for thyrotoxicity

Question 15

↓TSH, ↑T4 ?

Answer 15

Hyperthyroidism -> Graves’ disease, toxic multi nodular goitre, solitary toxic nodule

Question 16

Graves’ disease? S&S?

Answer 16

Abs bind to TSH receptor -> -tive feedback loop disrupted.
diffuse smooth goitre, exophthalmos due to Abs binding to eye muscles, pretibial myxoedema due to Abs stimulating soft tissue growth

Question 17

Hyperthyroidism S&S?

Answer 17

GI: weight loss with ↑appetite, diarrhoea, myopathy: tachycardia, arrhythmia, hand tremors
CNS: mood swings, heat intolerance, depression
goitre, sore eyes