ü Location
§ In mammals, thyroid gland consists of two lobes present below the larynx.
ü Its hormones
§ Thyroxin
§ Tri-iodothyronine
§ Calcitonin
ü Function of thyroxin and tri-iodothyronine
§ They stimulate the breakdown of glucose, generate heat and ATP.
§ They work with somatotropin hormone and help in growth.
§ Act on brain cells and help them to differentiate.
§ In case of amphibians, they help in the process of metamorphosis.
ü Abnormalities due to excess secretion of thyroxin
· Grave disease
§ This disease causes exophthalmic goiter.
§ Increase metabolic rate.
§ It can cause cardiac failure if prolonged.
ü Abnormalities due to deficient secretion
§ The deficiency of thyroxin causes cretinism, which retards normal development.
§ People with cretinism have coarse scanty hair, thick yellowish scaly skin, mentally retarded.
§ They are small and sexual development fails in them.
§ Neck swells up due to shortage of iodine in case of thyroxin deficiency.
§ It may lead to deposition of excess fat due to which weight increases.
§ It causes puffiness of hands and skin and this condition called myxedema.
ü Excess /deficient secretion of calcitonin
§ Excess secretion of calcitonin causes excess release of calcium ion into blood from bones.
§ Low secretion of this hormone causes deficiency of calcium ion in blood.
§ Excess or deficiency causes disorders in metabolism of skeleton, muscles, blood and nervous system.
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