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Human Body
The effects of thyroid gland on other functions are widespread :
-aids in normal mental and physical development; -secretes the iodine-containing hormones
combats the poison of the body;
-gives nerve stability;
-helps to control the amount of fat stored in the body and the basal metabolic rate; -prevents and cures goitre.
(iv) The Parathyroid Glands
Parathyroids are four minute yellowish brown ovoid bodies about 6 mm long and 3 mm wide, embedded in the lobes of the thyroid gland (two in each lobe). Sometimes the lower two are found much further down and in the chest. The hormone secreted by these glands is called parathormone (PTH). Its action sets the long term calcium levels in the body.
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The overall effects of parathyroid hormone are to increase the calcium levels in the extra-cellular fluids and decrease the phosphate concentration. The hormone is secreted in a self-regulating feedback system, independent of pituitary control. In exerts its effects in three major sites:
which
(i) In the bones, where it promotes reabsorption of calcium and phosphate into the extra-cellular fluid by increasing the number and activity of the osteoclasts.
(ii) In the intestine, where it enhances the absorption of calcium and phosphate, and
(iii) In the kidneys, where it increases the reabsorption of calcium but enhances excretion of phosphate with the urine.
Jain Education International
The functioning of the hormone PTH is dependent on adequate supply of Vitamin-D.
(v) The Thymus Gland
Unlike other glands, the thymus gland is not universally
*Osteoclasts (lit. bone-breakers) are cells which dissolve away inner bony tissue adjacent to the marrow-cavity, thus enlarging it to keep pace with the overall growth of the bone.
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