Hypothyroidism & Hyperthyroidism
Hypothyroidism is the reduced working of thyroid gland that cause endemic goiter and Hyperthyroidism is the increased functioning of the thyroid gland.
Hypothyroidism
Insufficient I2 intake in animals and man leads to goiter known as endemic goiter. Goiter means enlarged thyroid gland.
Lack of I2 reduces thyroid hormone synthesis and the reduced blood TH enhances TSH from adenohypophysis. The TSH stimulates the thyroid gland to secrete excess thyroglobulins into the follicles and the gland grows very large. But the thyroid hormone secretion cannot be increased due to lack of I2 leading to further increase in TSH secretion. Hence this condition is called as endemic colloid goitre.
Mild thyroiditis causes slight hypothyroidism which leads to increased TSH secretion and the gland enlarges producingnon-toxic or colloid goiter.
Hypothyroidism is common in dogs. Ingestion of goitrogenic substances also causes goiter.
Symptoms of Hypothyroidism
Fatigue, somnolence, muscular sluggishness, reduced heart rate, decreased blood volume, increased weight, constipation, mental sluggishness, hair falling and edematous appearance of whole body, bagginess of eyes, and swelling of face. Increased quantities of mucoplysaccharides accumulate in the interstitial spaces leading to myxedema.
When hypothyroidism is severe during foetal life, infancy and in young age especially in humans, there is failure of body growth and CNS development is impaired with brain hypoplasia and this condition is called as cretinism – physical and mental growth are retarded; skeletal growth is inhibited, soft tissues enlarge greatly and the cretin appears obese and stocky.
Treatment of Hypothyroidism
Oral ingestion of thyroid hormone. Hypothyroidism results in retarded growth while in hyperthyroidism, excessive skeletal growth in young animals.
Hyperthyroidism
Hyperthyroidism is 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 of Hyperthyroidism
Intolerance to heat, increased sweating, weight-loss, diarrhea, muscle weakness, psychic disorders etc. In hyperthyroidism protrusion of eyeball occurs – called as exophthalmous.
Treatment of Hyperthyroidism
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).