Thyroid

Question 1

where is the thyroid gland?

Answer 1

at base of neck (butterfly shape)

Question 2

what are the two main classes of thyroid hormones?

Answer 2

1. T3 and T4 thyroid hormones

2. calcitonin

Question 3

is T3 or T4 more active on THR?

Answer 3

T3

Question 4

what are T3 vs T4 aka?

Answer 4

T3: triiodothryonine
T4: thyroxine

Question 5

what is the highest-circulating thyroid hormone?

Answer 5

T4T

Question 6

What is the HPT axis for thyroid hormones?

Answer 6

TRH released from hypothalamus stimulates ant pit to release TSH which stimulates thyroid (follicular cells) to release T3/T4 (neg feedback on hypo and ant pit)

Question 7

what are T3 and T4 collectively called?

Answer 7

thyroid hormone

Question 8

what are 3 physiological effects of thyroid hormone?

Answer 8

incr basal metabolic rate, sensitization to catecholamines (NA: incr HR, CO, breathing rate), growth and development

Question 9

are thyroid hormones synthesized from free tyrosine molecules?

Answer 9

No, synthesized from precursor protein (thyroglobulin)

Question 10

How many modified tyrosine molecules make up thyroid hormones?

Answer 10

2 (have iodine molecules)

Question 11

What is the process of thyroid hormone synthesis?

Answer 11

tyrosines undergo enzymatic iodination/iodide undergoes organification into MIT (1 I2) or DIT (2 I2), iodinated tyrosines are enzymatically coupled into T3 (MIT + DIT) or T4 (2 DIT)

Question 12

What position on the aromatic tyrosine ring are iodines added to?

Answer 12

3 and 5

Question 13

what stimulates T3 or T4 synthesis?

Answer 13

TSH stimulation causes thyroglobulin endocytosis and processing into T3 or T4 (> released)

Question 14

what is the basic unit of the thyroid gland? (3) and what occurs in each part?

Answer 14

apical side of follicle: iodination and coupling of thyroglobulin (lumen)
follicle cell: thyroglobulin processing
basolateral side: T3/4 released into bloodstream

Question 15

how does the thyroid gland concentrate iodide into follicle lumen?

Answer 15

from bloodstream via Na/I cotransporter (basolateral, Na down, I up)

Question 16

what is the thyroid hormone receptor?

Answer 16

intracellular (TF w/ TH binding)

Question 17

how is the THR an exception to most intracellular receptors?

Answer 17

T3/4 are not lipid-soluble and require a transport protein to reach THR

Question 18

what is THR bound to at rest (unactivated)?

Answer 18

thyroid response elements (TREs) on DNA and corepressors (homodimers)

Question 19

what occurs to T4 when it enters the cell?

Answer 19

de-iodinated to T3 (enzyme)

Question 20

what occurs when T3 binds to the THR?

Answer 20

recruitment of RXR (retinoic acid receptor) to form heterodimer (1 THR replaced) and coactivator binding (incr transcription)

Question 21

what are the 4 most common causes of hypothyroidism?

Answer 21

iodine deficiency, autoimmunity towards thyroid (Hashimoto’s thyroiditis), developmental defect, inappropriate hormonal regulation (decr TRH/TSH)

Question 22

what are 4 symptoms of hypothyroidism?

Answer 22

fatigue, weight gain (decr met rate), hypersensitivity to cold, bradycardia

Question 23

how are thyroid diseases diagnosed? (2)

Answer 23

measure TSH (THR circ never high-acts directly on ant pit) or anti-TSH antibodies for hyperthyroidism

Question 24

what is a cause and features of primary hypothyroidism?

Answer 24

cause: defect in thyroid function
feature: low T3/4, high TSH (low neg feedback)

Question 25

what is a cause and features of secondary hypothyroidism?

Answer 25

cause: central defect (hypo/ant pit) features: low TSH, low T3/4 (decr TSH)

Question 26

what is a treatment for hypothyroidism?

Answer 26

hormone replacement

Question 27

which hormone is used for hormone replacement in the treatment of hypothyroidism?

Answer 27

T4/thyroxine (main circ form)

Question 28

what is the name of the drug prescribed for hypothyroidism?

Answer 28

levothyroxine

Question 29

what are 2 most common causes of hyperthyroidism?

Answer 29

Grave's disease (autoimmune response to TSHR-activates) and hyperplasia (thyroid adenoma, goiter-excessive growth)

Question 30

what are 5 symptoms of hyperthyroidism?

Answer 30

sleep difficulty, heat intolerance, tachycardia, weight loss, tremor (incr met rate)

Question 31

what's the cause and features of Grave's disease?

Answer 31

cause: thyroid activation by anti-TSHR Abs features: high T3/4, low TSH (neg feedback)

Question 32

whats the cause and features of thyroid hyperplasia?

Answer 32

cause: benign tumour in/on thyroid features: high T3/4, low TSH (neg feedback)

Question 33

whats the cause and features of secondary hyperthyroidism?

Answer 33

cause: central defect (incr TSH from ant pit) features: incr TSH, high T3/4

Question 34

whats the difference btwn Grave's disease and Hashimoto's thyroiditis?

Answer 34

both autoimmune Grave's: Abs stimulate TSHR Hashimotos: Abs damage thyroid

Question 35

what are 2 special diagnostic features of Grave's disease?

Answer 35

exophthalmos (bulging eyes): autoimmune damgae to eye muscle/fibroblasts goiter (swelling of neck): overactive thyroid (stim Abs)

Question 36

t/f: goiter is only seen in Grave's disease

Answer 36

false, also seen in hypothyroidism (iodine deficiency) if TSH incr (stim thyroid)

Question 37

what is the surgical approach for hyperthyroidism and its drawbacks?

Answer 37

approach: part/all of thyroid is resected drawbacks: require hormones replacement (hypothyroidism), disruption to parathyroid (Ca disturbances/hypoparathyroidism)

Question 38

what is the radioactive iodine treatment approach for hyperthyroidism and its drawbacks?

Answer 38

approach: I^131 concentrates in thyroid, radiation destructs thyroid drawbacks: hormone replacement, not for pregnancy/nursing (damage to infant)

Question 39

what is the anti-thyroid drug (methimazole) approach for hyperthyroidism and its drawbacks?

Answer 39

approach: prevents synthesis of T3/4 drawbacks: diverse

Question 40

what is the symptomatic B-blocker approach for hyperthyroidism and its drawbacks?

Answer 40

approach: B-blockers help tachycardia drawbacks: doesn't treat underlying cause of disease

Question 41

how do thioamides (methimazole) treat hyperthyroidism?

Answer 41

inhibits thyroperoxidase enzyme (iodination/organification+coupling of thyroglobulin into colloid)