Thyroid Hormone

Question 1

H-P-Thyroid axis activated by (3)

Answer 1

circadian rhythm
cold exposure
acute psychosis

Question 2

H-P-Thyroid axis suppressed by

Answer 2

Severe stress

Question 3

Thyroid hormone release chain

Answer 3

TRH (hypothalamus) –> TSH (pituitary –> TH (thyroid)

Question 4

Thyroid Stimulating Hormone inhibited by

Answer 4

somatostatin, dopamine, glucocorticoids

Question 5

Biosynthesis of TH (4 steps), regulated by TSH

Answer 5

(Regulated step) Uptake of iodide into gland.
Iodide placed onto thyroglobulin molecules via thyroid peroxidase (MIT and DIT).
Coupling of precursors, via thyroid peroxidase, MIT+DIT=T3, DIT+DIT=T4.
Released from gland by pinocytosis.

Question 6

TRH (synthetic) MOA

Answer 6

activates phospholipase C –> increases IP3 —> increases intracellular calcium. Stimulates production of TSH

Question 7

Synthetic TRH Uses

Answer 7

test for pituitary reserve of TSH in suspected hypothyroidism and hyperthyroidism

Question 8

Synthetic TSH Use

Answer 8

Therapy for thyroid carcinoma – increases the uptake of radioactive I- into thyroid

Question 9

Synthetic TSH MOA

Answer 9

stimulates cAMP production via adenylyl cyclase–> increased uptake of iodine and production of TH

Question 10

Thyroid hormone MOA

Answer 10

Enters cell via active transport. T4 converted to T3, which enters nucleus and binds to receptor. Ultimately increases RNA and protein synthesis

Question 11

Thyroid Hormone effects

Answer 11

Growth via protein synthesis, development, function of all tissues.
Myelination of the NS, ossification of epiphyses, reproductive system development.
Influences secretion and degradation of all other hormones.
SNS activity is increased in response - especially cardiovascular

Question 12

Hypothyroidism presents as

Answer 12

a multisystem disorder of reduced metabolism

Question 13

Hypothyroidism replacement therapy

Answer 13

Levothyroxine (T4)

adults: 1.6-1.8 mcg/kg/day. May need higher doses when treating pregnant women
children: need more… 10mcg/kg

Question 14

Myxedema Coma is an acute medical emergency occurs in untreated hypothyroidism. Presents with:

Answer 14

Hyponatremia, hypoglycemia, hypothermia, shock

Question 15

Levothyroxine (t4) and Triiodothyronine (T3) ABS

Answer 15

Ileum and colon. Should be taken alone on an empty stomach with water
Imparied by metal ions, ciprofloxacin, bile acid sequesterants, raloxifene, soy, dietary fiber

Question 16

Levothyroxine (t4) and Triiodothyronine (T3) transport

Answer 16

Bound to thyroid-binding-globulin. ONLY unbound has metabolic effects.
Pituitary only responds to FREE hormone

Question 17

T3 and T4 binding increased by

Answer 17

Estrogens/ SERMs/ Tamoxifen

Question 18

T3 and T4 binding decreased by

Answer 18

Salicylates/ antiseizures

Question 19

T3 is the active hormone

Answer 19

:)

Question 20

Levothyroxine is synthetic T4

Answer 20

treatment of choice

many formulations - none are superior but you should use the SAME one once started

Question 21

Liothyronine is synthetic T3

Answer 21

not recommended in routine replacement

Question 22

Liotrix 4:1 ratio of T4 and T3

Answer 22

Not recommended in routine replcement

Question 23

T4 toxicity presents like acute hyperthyroid crisis

Answer 23

:)

Question 24

Grave’s DIsease (hyperthyroidism) is the most common cause. Etiology:

Answer 24

Thyroid stimulating antibody that mimics TSH

Question 25

SSx of Hyperthyroidism

Answer 25

Metabolic and CVS hyperactivity

Question 26

Symptomatic treatment of Grave’s DZ

Answer 26

beta blockers and corticosteroids

Question 27

Tx of Grave’s DZ with hormone production interference and glandular destruction with:

Answer 27

Thionimide, iodide, surgery, radioactive iodide

Question 28

Methimazole (Tapazole) is a thionimide MOA

Answer 28

Leaves gland intact, is a large chance of relapse. Control symptoms until resolved (synthesis, not release, is blocked)
Blocks TH synthesis by not allowing precursor coupling

Question 29

Thionamides are treatment of choice in hyperthyroidism of pregnancy

Answer 29

:)

Question 30

Iodide therapy in high doses can inhibit hormone synthesis, but variable effects

Answer 30

Should not be used alone

Question 31

Radioactive iodine PO concentrated in thyroid and slowly destroys parenchyma. Complication:

Answer 31

Hypothyroidism.

NOT for use in pregnant women

Question 32

Thyroidectomy is treatment of choice if large gland, but radioactive iodine works best

Answer 32

most patients will need TH supplements after surgery

Question 33

Thyroid storm treatment

Answer 33

Propranolol for cardiovascular manifestations
Hydrocortisone to protect against shock
Sodium iodide to block release of TH
Thionamide to block TH synthesis