Thyroid is a butterfly shaped, small gland resting at base of the front of your neck, below Adam’s apple. It produces triiodothyronine and thyroxine hormones which have a great impact on our health and our metabolism . they also control vital functions like body temperature and heart rate.
The thyroid hormones are synthesised by thyroid follicles and also stores them.
Synthesis
- Thyroid cells uptakes plasma iodides
- Iodide gets oxidised to iodinium ion by peroxidase enzyme with help of hydrogen peroxidase
- Combines with thyrogobuline’s tyrosine residues to form monoiodotyrosine and diiodotyrosine
- They both gets coupled to for T3 and T4
- Also catalysed by peroxidase enzyme
- Thyroglobuline containing iodinated tyrosine residues are stored in the follicles.
Secretion and releasing of the hormones is controlled by TSH which is secreted by anterior pituitary gland and TRH which is secreted by hypothalamus.T3 is a active hormone which is converted from T4 .the free hormones is metabolised in liver and excreted in the bile.
Actions
Hormones of thyroid is important for normal growth, development,function and maintenance of the all body tissues.they also increase metabolic rate, enhance carbohydrate and protein metabolism and also stimulate lipolysis.
Uses
- Non toxic goiter – TSH is suppressed by T4 and regression of gioter occurs
- Thyroid carcinoma – used after surgery, T4 induces temporary remission
- Miscellaneous – thyroxine is tried in refractory anemias, infertility and non-healing ulcers
- Replacement therapy
Hyperthyroidism
- Excessive circulating of thyroid hormones can cause hyperthyroidism
- Causes are grave’s diseases
Antithyroid drugs
Drugs used as antithyroid drugs in hyperthyroidism :
- Antithyroid drugs : thionamides, methimazole, carbimazole
- Iodines – iodine and radioactive iodine
Antithyroid drugs :
Antithyroid drugs may act by interfering with synthesis, release or action of hormones
- Thionamides and propylthiouracil inhibits the synthesis of thyroid hormones and inhibits the conversion of T4 to T3
- Carbimazole is commonly used because of long term action
Uses
- Grave’s diseases
- Toxic nodular goiter
- Preoperatively
Adverse effect
- Allergic reaction
- Headache
- Jaundice
- granulocytopenia
Iodines
Inhibited the release of gland
Uses :
- Antiseptic
- Expectorant : used in cough
- Prophylaxis : to prevent endemic goiter iodides is added to salt used in cooking
- Severe thyrotoxicosis
Adverse effect :
- Skin rashes
- Conjunctivitis
- Sore throat
- Cough
Radioactive iodides
- Concentrates by thyroid in follicles
- Rapidly absorbed
- Emits beta rays which only penetrates 0.5 to 2 mm of the tissues so that it only damages tissue
- Simple administration
- Risk can also be avoided
- Takes long time to response maximum
- Risk of hypothyroidism
- Can be used in thyroid carcinoma and hyperthyroidism
- Also used in TFT (thyroid function test)
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