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- It is a small round gland in the brain.
- It secretes melatonin that regulates the sexual cycle.
It is a butterfly-shaped, bilobed gland that is situated at the base of the larynx. The two lobes are joined by an isthmus. The hormone secreted is thyroxine.
Functions of Thyroxine
- Thermoregulation - it regulates the production of body heat by regulating respiration
- regulates metabolic rate
- regulates mental and physical development
- helps in absorption of glucose from intestine
Result of Undersecretion of Thyroxine
- Simple goitre in which there is enlargement of thyroid due to lack of iodine
- Cretinism which is dwarfism and mental retardation due to imperfect development of thyroid
- Myxoedema in which the thyroid does not function properly and the person becomes sluggish with swollen face and hands
Result of Oversecretion of Thyroxine
Oversecretion results in exophthalmic goitre in which the person shows a marked increase in metabolic rate, protrusion of eyes, rapid heart rate and shortness of breath.
They are present as two pairs at the back of the thyroid. They secrete parathormone which is important in calcium and phosphorus metabolism.
- Deficiency of parathormone causes brittle bones.
- Oversecretion of parathormone softens the teeth and bones.
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