Veterinary Physiology-III

HYPERTHYROIDISM

• Hyperthyroidism: The entire thyroid gland is hyperplastic, increase in size to two to three times normal; cell number is also increased with increase in secretion rate.
• These changes are brought about by antibodies (thyroid stimulating antibodies -TSI) that bind with thyroid cell membrane receptors similar to TSH and induce continual activation of the cells. The antibodies develop as autoimmunity against TSH receptors. This condition is called as toxic goitre or thyrotoxicosis or Grave’s Disease in human beings. Plasma TSH level is usually low.
• Hyperthyroidism occurs in toxic goitre and thyroid tumours of older cats.
• Symptoms: Intolerance to heat, increased sweating, weight-loss, diarrhoea, muscle weakness, psychic disorders etc. In hyperthyroidism protrusion of eyeball occurs - called as exophthalmous.
• Treatment for hyperthyroidism is surgical removal of the thyroid gland; injection of radioactive iodine (I2 taken by the gland and radioactivity destroys the gland cells).