Thyroid hormone
Thyroid gland secretes three hormones – T4 (thyroxine), T3 (triiodothyronine) (both produced by thyroid follicle) and calcitonin ( produced by inter follicular “c” cells.
Regulation of secretion- Secretion from thyroid is controlled by anterior pituitary, by elaboration of thyrotropin, while TSH ( thyroid stimulating hormone) itself is regulated by TRH ( Thyroid releasing hormone) produced in hypothalamus.
Somatostatin from hypothalamus inhibit TSH secretion from pituitary.
Symptoms of hypo and hyper thyroidism
Actions or work of T3 and T4
- Effects growth and development
- Effects lipids, carbohydrates and protein metabolism.
- Increases BMR by stimulating cellular metabolism and resetting of energy state called Caloriogenesis process.
This process uncoupled oxidative phosphorylation, excess energy released as heat.
Dinitrophenol uncouples oxidative phosphorylation but has no effect on Thyroid activities.
- Effects nervous system- CNS, mental retardation, behaviour features, tremor etc.
- GIT (gastrointestinal tract)- hypothyroidism play role in causing constipation while hyperthyroidism cause diarrhoea.
- Muscles gets weak
- Hypothyroid patient suffer from degree of anemia
- Fertility affected in hypothyroidism
- Women suffer from Oligomenorrhea
(Oligomenorrhea is a condition in which you have infrequent menstrual periods.)
CAUTION– So normal Thyroid function required for suitable pregnancy and lactation.
Thyroid inhibitors
Drugs used to lower the function capacity of thyroid gland called thyroid inhibitors.
Thyrotoxicosis cause is due to hyper secretion of thyroidism hormones.
The two main causes are- Grave’s disease and toxic noduler goiter.
- Grave’s disease= A autoimmune disorder, IgG class of antibiodies to TSH receptors are detected in blood.
- Toxic noduler goitre= produces thyroid hormone independently especially in elder age.
Anti thyroid drugs
Also called thioamides.
hormone synthesis inhibitors are called anti thyroid drugs, applied in all thyroid inhibitors.
Work =
These drugs bind to thyroid peroxidase and prevent oxidation of iodine.
Anti thyroid medications inhibit the formation and coupling of iodo tyrosine in thyroglobulin.
Because these two processes are necessary for thyroid hormone synthesis, this inhibition induces a gradual reduction in thyroid hormone levels over 2-8 weeks or longer.
propylthiouracil– 50-150 mg
Carbimazole– 5-15 mg
Methimazole– 5-10 mg
pharmacokinetics
All Anti thyroid drugs are quickly absorbed orally, in pregnant lady enter in milk and cross placenta metabolized in liver excrete from urine.
Side Effects of anti thyroid drugs
- Maculopapular rash (4-6% of patients); the most common side effect, sometimes associated with fever.
- Cholestatic hepatitis
- Nausea, GI distress, altered taste or smell.
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