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Bone Response to Damage (view source)

Revision as of 14:23, 28 September 2007

222 bytes removed ,  14:23, 28 September 2007
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**'''Parathyroid hormone (PTH)'''
 
**'''Parathyroid hormone (PTH)'''
 
***Produced by <u>chief cells in the parathyroid glands</u> in response to <u>decreased</u> serum calcium
 
***Produced by <u>chief cells in the parathyroid glands</u> in response to <u>decreased</u> serum calcium
 +
***In response, osteoclasts increase in number and resorb mineralised matrix - increase Ca in blood
 
**'''Calcitonin'''
 
**'''Calcitonin'''
 
***Produced by <u>C-cells in the thyroid glands</u> in response to <u>increased</u> serum calcium
 
***Produced by <u>C-cells in the thyroid glands</u> in response to <u>increased</u> serum calcium
 +
***Inhibits osteoclasts
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   −
    PTH
+
===Bone dynamics===
−
↓
  −
Osteoclasts increase in number
  −
↓
  −
Osteoclasts attach to bone and resorb mineralised matrix
     −
Osteoclasts do not have receptors for PTH so how do they do this?
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*Bone growth and maintenance of normal structure are directly related to mechanical forces
−
Answer:
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*Mechanical forces generate bioelectrical potentials (piezoelectricity)
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**These potentials strengthen bone
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**Inactivity reduces the potentials -> bone loss
   −
LOW CALCIUM → INDUCES PTH SECRETION →
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*In neonates:
−
BONE RESORPTION → CALCIUM 
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**Bone growth predominates
 +
**Modelling is important
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*In adults:
 +
**Formation of bone is balanced by resorption - remodelling
 +
**Continues 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
   −
CALCITONIN HAS THE OPPOSITE EFFECT - IT INHIBITS OSTEOCLASTS
  −
  −
Bone dynamics
  −
  −
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.
         
<big><center>[[Bones|'''BACK TO BONES''']]</center></big>
 
<big><center>[[Bones|'''BACK TO BONES''']]</center></big>
Bara
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