Thyroid Flashcards
2 active thyroid hormones
1) T3 (synthetic is liothyronine)
2) T4 (synthetic is levothyroxine)
What thyroid hormone is secreted most
T4
BUT must T4 is converted to T3
How much T4 and T3 is available in the body
only a small amount… much is bound to plasma proteins
thyroid hormones are eliminated via
hepatic metabolism
half life of t3 and t4
t3 1 day
t4 7 days
Thyroid hormone actions
1) Stimulation of energy use
2) Stimulation of heart
3) Promotion of growth and development
How do thyroid hormones produce effect
by modulating specific genes (mostly via T3)
T3 penetrates cell
- binds to nuclear receptors
= production of proteins that mediate thyroid hormone effects
Negative feedback of T3/4
as the levels increase
feedback to AP to stop TSH production
Goiter
when iodine availability decreases
= increase TSH release
= increase thyroid gland to compensate
= GOITER
T3/T4 pathway
Hypothalamus
TRH
Anterior Pit
TSH
Thyroid T3 and T 4 - neg feed back to AP
Effects
Hypothyroidism
mild deficiency of T3
Myxedema
severe deficiency of T3
Symptoms of hypothyroidism in adults
mild- subtle and go unrecognized
sever: face= pale, skin = cold dry, hair = brittle, loss of hair, HR and temp are lowered, fatigue, intolerance to cold
Cause hypothyroidism
t3 malfunction via chronic autoimmune thyroiditis (HASHIMOTO thyroiditis)
decreased iodine in diet
surgical removal of thyroid
destruction of thyroid by radioactove iodine
treatment of hypothyroidism
thyroid hormones
T4 alone
T4 and T3
(research: no adv. to T4 and T3 over just T3)
hypothyroidism and pregnancy
can result in neuro-psychologic deficits in child
limited to first trimester when fetus unable to produce its own thyroid hormones
if taking supplements before pregnancy usually requires increased dosage during pregnancy
hypothyroidism in infants
usually from failure of thyroid development
or exposure to radioactive iodine in utero
quick treatment development will be normal
hyperthyroidism types
1) graves (exophthalamos)
2) toxic nodular goiter
Graves disease
most common cause of excessive thyroid hormone
- women 20-40
clinical presentation (thyrotoxicosis)
- raised metabolic rate, increase temp, increased appetite
- rapid HR, angina, dysrhythmia
-CNS stimulated - weak muscles, atrophy
cause of graves disease
thyroid stimulating immunoglobulins (TSIs)
- mimic TSH effects on thyroid function
Treatment of graves disease
1) surgical removal of thyroid tissue
2) radioactive iodine to destroy thyroid tissue (for adults)
3) antithyroid drug (methimazole or propylthiouracil)
Toxic Nodular Goiter (Plummer disease) cause
thyroid adenoma (benign lesions of thyroid gland)
- enlarged thyroid gland contains small, rounded nodules which produce too much thyroid hormone
Toxic Nodular Goiter treatment
antithyroid drug- symptoms occur when stopped
surgery, radiation- long term
Thyrotoxic Crisis (Thyroid Storm)
Life threatening
occurs with severe thyrotoixosis (excessive plasma levels of thyroid hormones)
cause thyrotic crisis
surgery, infection, sepsis
symptoms of thyrotoxic crisis
profound hyperthermia, tachycardia, tremor
treatment for thyrotoxic crisis
high doses of potassium iodine to suppress thyroid hormone release
Types of thyroid hormones available as
purse synthetic compounds
- more stable, preferred
Extracts of animal thyroid glands
Levothyroxine T4
synthetic preparation
- drug of choice for hormone replacement
pharmacokinetics levothyroxine t4
absorption: reduced by food
take 30-60min before breakfast
converted to T3
Half-life: 7 days
- highly protein bound (99.97%)
good: remains stable
bad: requires 1 month to reach steady state (full effect is delayed
Therapeutic uses of Levothyroxine
all forms hypothyroidism
used to maintain proper thyroid levels post surgery, irradiation, treatment with antithyroid drugs
note: not for weight loss
- dosage required will establish pathological state
levothyroxine adverse effects
acute OD: thyrotoxicosis
- tachycardia, angina, tremor
levothyroxine drug interactions
reduce absorption: lots CHECK LIST WHEN NEEDED
- separate by 4 hours
accelerate drugs metabolism: SEVERAL
Warfarin: accelerates degradation of vit K
- enhances warfarin effects
Catecholamines: increase cardiac effects effects–> dysrhythmias
Levothyroxine dosage and administration
PO mostly x1 day before breakfast
IV: for myxedema coma and pt that cant PO
or 50po/50iv
Measure TSH
duration: for life is best
Antithyroid drugs
Thioamides
Methimazole
first line drug for hyperthyroidism
methimazole mechanism
blocking thyroid hormone SYNTHESIS via
1) prevents oxidation of iodine
2) prevents iodinated tyrosine from coupling
Pharmacokinetics
PO
- binding is minimal
- readily crosses membrane
half life 10 hours
methimazole therapeutic uses
- graves disease
- adjunct to radiation therapy
-prep for thyroid gland surgery
-thyrotoxic crisis
methimazole adverse effects
dont use pregnant/ breastfeeding
- neonatal hypothyroidism
agranulocytosis
-neutrophil count less than 100. microlitre of blood)
hypothyroidism
Radioactive Iodine/ iodine- 131
half life
radioactive decay half-life 8 days
= 56 days less than 1% of dose radioactivity remains
Radioactive Iodine/ Iodine 131 Uses
Graves disease
- destroy thyroid tissue
-adv: cheaper than surgery
-disadv: significant delayed hypothyroidism
Non radioactive iodine: Lugol Solution
5% iodine and 10% potassium
-iodine reduced to iodide in GIL
Lugol solution mechanism
1) high iodide decreases iodine uptake
2) high iodide inhibit thyroid hormone synthesis
iodide effects cannot be sustained indefinitely/ effects weaken
Lugol solution therapeutic uses
thyroidectomy patients before surgery to suppress thyroid function
