Thyroid

Question 1

2 active thyroid hormones

Answer 1

1) T3 (synthetic is liothyronine)
2) T4 (synthetic is levothyroxine)

Question 2

What thyroid hormone is secreted most

Answer 2

T4

BUT must T4 is converted to T3

Question 3

How much T4 and T3 is available in the body

Answer 3

only a small amount… much is bound to plasma proteins

Question 4

thyroid hormones are eliminated via

Answer 4

hepatic metabolism

Question 5

half life of t3 and t4

Answer 5

t3 1 day
t4 7 days

Question 6

Thyroid hormone actions

Answer 6

1) Stimulation of energy use
2) Stimulation of heart
3) Promotion of growth and development

Question 7

How do thyroid hormones produce effect

Answer 7

by modulating specific genes (mostly via T3)

T3 penetrates cell
- binds to nuclear receptors
= production of proteins that mediate thyroid hormone effects

Question 8

Negative feedback of T3/4

Answer 8

as the levels increase
feedback to AP to stop TSH production

Question 9

Goiter

Answer 9

when iodine availability decreases
= increase TSH release
= increase thyroid gland to compensate
= GOITER

Question 10

T3/T4 pathway

Answer 10

Hypothalamus
TRH
Anterior Pit
TSH
Thyroid T3 and T 4 - neg feed back to AP
Effects

Question 11

Hypothyroidism

Answer 11

mild deficiency of T3

Question 12

Myxedema

Answer 12

severe deficiency of T3

Question 13

Symptoms of hypothyroidism in adults

Answer 13

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

Question 14

Cause hypothyroidism

Answer 14

t3 malfunction via chronic autoimmune thyroiditis (HASHIMOTO thyroiditis)

decreased iodine in diet
surgical removal of thyroid
destruction of thyroid by radioactove iodine

Question 15

treatment of hypothyroidism

Answer 15

thyroid hormones
T4 alone
T4 and T3
(research: no adv. to T4 and T3 over just T3)

Question 16

hypothyroidism and pregnancy

Answer 16

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

Question 17

hypothyroidism in infants

Answer 17

usually from failure of thyroid development
or exposure to radioactive iodine in utero

quick treatment development will be normal

Question 18

hyperthyroidism types

Answer 18

1) graves (exophthalamos)
2) toxic nodular goiter

Question 19

Graves disease

Answer 19

most common cause of excessive thyroid hormone
- women 20-40

Question 20

clinical presentation (thyrotoxicosis)

Answer 20

• raised metabolic rate, increase temp, increased appetite
• rapid HR, angina, dysrhythmia
  -CNS stimulated
• weak muscles, atrophy

Question 21

cause of graves disease

Answer 21

thyroid stimulating immunoglobulins (TSIs)
- mimic TSH effects on thyroid function

Question 22

Treatment of graves disease

Answer 22

1) surgical removal of thyroid tissue

2) radioactive iodine to destroy thyroid tissue (for adults)

3) antithyroid drug (methimazole or propylthiouracil)

Question 23

Toxic Nodular Goiter (Plummer disease) cause

Answer 23

thyroid adenoma (benign lesions of thyroid gland)
- enlarged thyroid gland contains small, rounded nodules which produce too much thyroid hormone

Question 24

Toxic Nodular Goiter treatment

Answer 24

antithyroid drug- symptoms occur when stopped

surgery, radiation- long term

Question 25

Thyrotoxic Crisis (Thyroid Storm)

Answer 25

Life threatening occurs with severe thyrotoixosis (excessive plasma levels of thyroid hormones)

Question 26

cause thyrotic crisis

Answer 26

surgery, infection, sepsis

Question 27

symptoms of thyrotoxic crisis

Answer 27

profound hyperthermia, tachycardia, tremor

Question 28

treatment for thyrotoxic crisis

Answer 28

high doses of potassium iodine to suppress thyroid hormone release

Question 29

Types of thyroid hormones available as

Answer 29

purse synthetic compounds - more stable, preferred Extracts of animal thyroid glands

Question 30

Levothyroxine T4

Answer 30

synthetic preparation - drug of choice for hormone replacement

Question 31

pharmacokinetics levothyroxine t4

Answer 31

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

Question 32

Therapeutic uses of Levothyroxine

Answer 32

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

Question 33

levothyroxine adverse effects

Answer 33

acute OD: thyrotoxicosis - tachycardia, angina, tremor

Question 34

levothyroxine drug interactions

Answer 34

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

Question 35

Levothyroxine dosage and administration

Answer 35

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

Question 36

Antithyroid drugs

Answer 36

Thioamides

Question 37

Methimazole

Answer 37

first line drug for hyperthyroidism

Question 38

methimazole mechanism

Answer 38

blocking thyroid hormone SYNTHESIS via 1) prevents oxidation of iodine 2) prevents iodinated tyrosine from coupling

Question 39

Pharmacokinetics

Answer 39

PO - binding is minimal - readily crosses membrane half life 10 hours

Question 40

methimazole therapeutic uses

Answer 40

- graves disease - adjunct to radiation therapy -prep for thyroid gland surgery -thyrotoxic crisis

Question 41

methimazole adverse effects

Answer 41

dont use pregnant/ breastfeeding - neonatal hypothyroidism agranulocytosis -neutrophil count less than 100. microlitre of blood) hypothyroidism

Question 42

Radioactive Iodine/ iodine- 131 half life

Answer 42

radioactive decay half-life 8 days = 56 days less than 1% of dose radioactivity remains

Question 43

Radioactive Iodine/ Iodine 131 Uses

Answer 43

Graves disease - destroy thyroid tissue -adv: cheaper than surgery -disadv: significant delayed hypothyroidism

Question 44

Non radioactive iodine: Lugol Solution

Answer 44

5% iodine and 10% potassium -iodine reduced to iodide in GIL

Question 45

Lugol solution mechanism

Answer 45

1) high iodide decreases iodine uptake 2) high iodide inhibit thyroid hormone synthesis iodide effects cannot be sustained indefinitely/ effects weaken

Question 46

Lugol solution therapeutic uses

Answer 46

thyroidectomy patients before surgery to suppress thyroid function