Lyrics · 完整歌詞
The thyroid secretes predominantly thyroxine, or T4,
much of
whose physiological activity depends on its conversion to the more potent hormone T3.
Peripheral deiodinase removes one iodine to make T3,
roughly three to four times more potent.
In starvation or critical illness the enzyme instead produces inactive reverse T3,
so T3 falls while reverse T3 rises.
This sick euthyroid pattern needs no thyroid replacement.
Hormone excess accelerates every system, bringing weight loss, heat intolerance,
tremor and atrial fibrillation.
Deficiency slows everything, producing weight gain, bradycardia,
delayed reflex relaxation and non-pitting myxoedema.
Two axes sort almost every thyroid result.
In primary disease TSH and free T4 move in opposite directions.
In central disease they move together,
or TSH sits inappropriately within the normal range
while free T4 is low.
Consequently, a lone TSH cannot exclude pituitary failure,
and central replacement is titrated to free T4.
Hashimoto thyroiditis carries anti-thyroid peroxidase antibodies that grind the gland down towards hypothyroidism.
Graves' disease carries TSH receptor antibodies that stimulate the gland,
and the same antibodies inflame orbital fibroblasts.
Orbitopathy therefore runs independently of hormone levels,
and smoking is its strongest modifiable risk.
The thyroid secretes predominantly thyroxine, or T4,
much of
whose physiological activity depends on its conversion to the more potent hormone T3.
Carbimazole is the first-line thionamide, usually continued for twelve to eighteen months.
Propylthiouracil is reserved for the first trimester and for thyroid storm,
because it also blocks peripheral conversion of T4 to T3.
Fever or sore throat on either drug means stopping it
and checking the neutrophil count the same day.
Agranulocytosis affects roughly two to five patients per thousand,
mostly within the first three months.
Radioiodine is definitive but contraindicated in pregnancy and breastfeeding;
conception must wait six months, and active orbitopathy may worsen.
Surgery suits a compressive goitre,
suspected malignancy or a pregnant patient intolerant of drugs.
Established hypothyroidism in pregnancy needs a dose increase of about 25 to 30 per
cent.
Thyroid storm is treated with every lever at once.
Propylthiouracil is given first, and iodine follows about an hour later.
Iodine given earlier would become substrate for new hormone.
Propranolol controls the rate and blocks conversion,
while hydrocortisone covers relative adrenal insufficiency.
Amiodarone is avoided because each tablet carries a heavy iodine load.
At the opposite extreme, myxoedema coma receives intravenous levothyroxine only after hydrocortisone,
to avoid precipitating an adrenal crisis.
A nodule is assessed with TSH and ultrasound.
A low TSH prompts a radionuclide scan for a hot nodule;
otherwise suspicious features lead to fine-needle aspiration, the gold standard before surgery.
Papillary carcinoma accounts for 80 to 85 per cent of cancers,
shows psammoma bodies, spreads by lymphatics and has the best prognosis.
Follicular carcinoma spreads by blood and cannot be diagnosed by aspiration,
because malignancy depends on capsular invasion.
Medullary carcinoma arises from C cells, secretes calcitonin,
and belongs to MEN2 through the RET gene.
Differentiated cancers are followed with thyroglobulin, medullary cancer with calcitonin and CEA.
The thyroid secretes predominantly thyroxine, or T4,
much of
whose physiological activity depends on its conversion to the more potent hormone T3.
The thyroid secretes predominantly thyroxine, or T4,
much of