Changes

===Bone resorption===

===Bone resorption===

• Mediated by two hormones

*Mediated by two hormones:

o Parathyroid hormone (PTH) which is produced by chief cells in the parathyroid glands in response to decreased serum calcium

**'''Parathyroid hormone (PTH)'''

 

***Produced by <u>chief cells in the parathyroid glands</u> in response to <u>decreased</u> serum calcium

o Calcitonin which is produced by C-cells in the thyroid glands in response to increased serum calcium

***Produced by <u>C-cells in the thyroid glands</u> in response to <u>increased</u> serum calcium

     PTH

     PTH

Bone growth and maintenance of normal structure are directly related to mechanical forces which generate bioelectrical potentials (piezoelectricity).  These potentials strengthen bone and inactivity reduces them, thereby leading to bone loss.  In neonates, bone growth predominates and modelling is important.  In adults, formation of bone is balanced by resorption;  this is known as remodelling.  It continues in a subtle but active way throughout life under the influence of hormones and mechanical pressure.  Bone resorption may exceed formation in pathological states (hormonal, trauma, nutritional) or in old age and disuse.

Bone growth and maintenance of normal structure are directly related to mechanical forces which generate bioelectrical potentials (piezoelectricity).  These potentials strengthen bone and inactivity reduces them, thereby leading to bone loss.  In neonates, bone growth predominates and modelling is important.  In adults, formation of bone is balanced by resorption;  this is known as remodelling.  It continues in a subtle but active way throughout life under the influence of hormones and mechanical pressure.  Bone resorption may exceed formation in pathological states (hormonal, trauma, nutritional) or in old age and disuse.