Thyroid Flashcards
Pituitary gland
Synthesize and release thyroid stimulating hormone to stimulate thyroid
Hypothalamus
Releases thyrotropin releasing hormone to stimulate the pituitary gland
TRH suppressed by dopamine, corticosteroids, somatostatin
Thyroid stimulating hormone
Causes iodine uptake for synthesis
T3/T4 release into circulation
Stimulates synthesis of iodine transporter, thyroid peroxidase, thyroglobulin
Low T4, high TSH
Iodine metabolism
Oxidize iodide by thyroid peroxidase
Able to iodinate tyrosines
Ether linkage between iodotyrosine to form T3/T4
Goiter
Can present in both iodine deficiency and iodine excess
T4
Most abundantly produced
Thyroxine
2 Tyrosine + 4 iodines
T3
Most active metabolite
Greater affinity to thyroid receptor
Triiodothyronine
Not a good indicator of hypothyroidism
Synthesized in peripheral tissues
Deiodinase Activity
Type 1: plasma membrane of liver kidney thyroid, T3 enter bloodstream
Type 2: ER of pituitary, brain cells
T3 greedy and intercellular
Type 3: inactivator, T4-RT3, T3-T2
Thyroid hormone actions
Necessary for normal growth and metabolic stability in bone & CNS
Heart beta sensitivity and inotrope
Lipolysis of adipocytes
CHO absorption, O2 consumption
Grave’s disease
TSH receptor stimulating antibodies (TSI Ab) Grave receptor Ab
Can lead to TNT to fetus
CD8+ cells mediate toxicity
Increases with increased iodine
Hashimoto’s disease
Hypothyroid
Anti thyroid peroxidase antibody
Antibody against Na-I symporter
Can’t produce thyroid hormone
Lymphocyte infiltration and WBC damage thyroid cells
Prevalent in Japanese
Primary hypothyroidism
Iodine deficiency
Autoimmune:Hashimoto’s
Secondary hypothyroidism
Hypopituitarism
TSH deficient or inactive
Hypothyroid signs
Dry skin (diminished sweating)
Edema (puffy face, hands, feet)
Weight gain
Myxedema
Pale, Yellow tinge
Sexual dysfunction
Cardio dysfunction, diastolic HTN
Dry brittle hair
Thyrotoxicosis signs
Weight loss (increased metabolism) Increased appetite
Tremor
Tachycardia, high cardiac output
Warm moist skin
Dermopathy
Decreased male sexual function
Bone resorption and osteoporosis
Enlarged, firm thyroid with bruit
Lid retraction, stare
Solitary toxic nodule
Mild hyperthyroid
Palpable nodule
Hot on scan
HCG & TSH induced thyrotoxicosis
hCG binds to TSH receptor
Or
TSH secreting pituitary tumor
Diffuse (simple goiter)
Iodine deficiency
Compensatory hypertrophy
Goitrogens: Brussels sprouts, cabbage
PTU, MMI, lithium
Thyroid nodules
90% benign
Increase with age
Hashimoto’s is benign
Malignant: papillary carcinoma
Thyroid secretes
T4
Calcitonin
Thyroglobulin
Provides tyrosine for T4 synthesis
Hashimoto’s and Grave’s have antibodies against thyroglobulin
Pendrin
Defect results in iodination malfunction
Goiter, hypothyroidism
Exchange iodine to the colloid
To be utilized with tyrosine on thyroglobulin
Target tissue uptake
MCT8 in liver, kidney, thyroid, brain for T3 uptake (X chromosome gene) defect in men
OATP for T4 uptake in tissues
Thyroid hormone metabolism
Conjugation by
Glucuronidation
Sulfation
Hyperthyroidism treatment
1) thioamides inhibit thyroid peroxidase and deiodinase T4 conversion to T3
Methimazole - preferred less AE
Propylthiouracil
2) cholecystographic inhibit D1, D2
Iospanoic acid
amiodarone - block T3 binding to THR
Iodine, radioioidine
Propranolol for beta symptoms
Iodine MOA
Large amounts of iodine - auto regulation - inhibit TH formation
Wolff chaikoff
Small iodine - fail autoregulation - increase thyroid hormone formation
Jod-basedow
Hypothyroidism treatment
Give T4 in general, body has choice to utilize it
Give T3 if you know specific T3 defect in OATP uptake
Thyroid TSH T4 screening
For women > 50 years old
TSH range
0.5-4.7 mIU/L
T4 levels
Free T4 0.8-2.7ng/dL
Drugs that increase T4
Amphetamines
Propranolol
Nadolol
Drugs that decrease T4
Glucocorticoids
Lithium
Phenobarbital
Phenytoin
If hypothyroid
Need to lower dose of digoxin, insulin
Avoid opioids and respiratory depression
Levothyroxine counseling
AE: CHF, angina, MI, osteoporosis
Take on empty stomach
Separate from dairy Mg
Myxedema
Longstanding hypothyroidism
Stupor, coma
Hypothermia 74F
Decrease Na, glucose
Give IV levothyroxine bolus 500mcg, followed by 50-100 mcg
Hydrocortisone IV
Vasopressors, fluids, warm blanket
Can give liotrix T4-T3 combo
Hyperthyroidism treatment
Surgery (give thionamide, potassium iodide, propranolol before)
Give propranolol also 7 days post-op
Radioactive iodine
Antithyroid drugs: 4-8 weeks, taper monthly based on T4
Propylthiouracil
Initial: 300mg divided TID PO
Maintenance: 100mg divided TID PO
AE: hepatotoxicity
Inhibits D1
Methimazole
15 mild - 60 severe mg/ divided TID
Maintenance: 10mg
AE: myopathy
Hyperthyroidism relapse
Give radioactive iodine
Concentrated in thyroid
Disrupt T4 synthesis ~ Wolff chaikoff
Propranolol for adrenergic symptoms
Can give potassium iodide as adjunct
Thyroid storm
Fever, Tachycardia
Dyspbea, Dehydration, Coma
Maybe due to infection, T4 OD
Treat precipitating cause
Give PTU 1000mg/day divided
Potassium iodide TID 1 hour after PTU
Esmolol IV
Propranolol PO
APAP fever, cool blanket, fluids
Euthyroid sick syndrome
Normal T4
Low T3
Low TSH
Impaired T4-T3 conversion
Treat underlying condition not thyroidism
T3 levels
Total: 100-200 ng/dL
