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Metabolic disease

METABOLIC.doc  (Word format document)

-  Includes additional charts.

bone metabolism

bone metabolism

CALCIUM 99% in bone. Main functions- muscle /nerve function, clotting. Plasma calcium- 50% free, 50% bound to albumin.

Dietary needs-kids- 600mg/day, adolesc.-1300mg/day, adult-750mg/day, pregnancy-1500mg/day, breastfeeding-2g/day, Fractures- 1500mg/day

Absorbed in duodenum (active transport) and jejunum (diffusion), 98% reabsorbed in kidney prox. tubule, may be excreted in stool.

Calcium balance- positive first 3 decades then neg.

PHOSPHATE 85% in bone. Functions-metabolite and buffer in enzyme systems.

Plasma phosphate mainly unbound. Daily requ. 1-1.5g/day

REGULATION OF CALCIUM AND PHOSPHATE METABOLISM

In all conditions except osteoporosis there is coupling of calcium metabolism

Origin

Factors causing incr.

Factors  causing decr.

Effects on intestine

Effects on kidney

Effects on bone

Effects on [calcium]

Effects on [phosphate]

PTH peptide

chief cells parathyroid gland

decr. [Ca2+]

incr. [Ca2+]

incr. 1,25...

No direct affect,

incr. absorption of Ca indirectly via incr. 1,25

incr. prodn of 1,25(OH)D

incr. reabsorption of calcium,

incr. excretion of phosphate

Stimulates osteoclasts to absorb bone,

stimulates recruitment of preosteoclasts

incr.

decr.

1,25(OH)2D steroid

prox tubule of kidney

decr. [Ca2+]

decr. [phos]

incr. PTH

incr. [Ca2+]

incr. [phos]

decr. PTH

incr. absorption of Ca

incr. absorption of phos

 

stimulates reabsorption of bone (osteoclastic)

incr.

incr.

Calcitonin

para follic. cells of thyroid

incr. [ca2+]

decr. [ca2+]

   

inhibits osteoclastic reabsorption of bone

transient decr.

 

Regulation of Calcium & Phosphate Metabolism:

Calcium & Phosphate Metabolism

Oestrogen Prevents bone loss

Prevents bone loss

Corticosteroids Increased bone loss (reduced gut absorption, decreased bone formation ( via collagen)

Increased bone loss (reduced gut absorption, decreased bone formation ( via collagen)

Growth Hormone Causes positive calcium balance

Causes positive calcium balance

Growth factors

  • Insulin like growth factor; produced by osteoblasts, recruits osteoblasts
  • Transforming Growth factors; produced during bone resorption, stimulate osteoblasts
  • IL1 and osteoclast activating factor; activate bone resorption
  • Transforming Growth factors; produced during bone resorption, stimulate osteoblasts
  • IL1 and osteoclast activating factor; activate bone resorption
  • IL1 and osteoclast activating factor; activate bone resorption
  • Prostaglandins; regulate both osteoblasts and osteoclasts
Insulin like growth factor; produced by osteoblasts, recruits osteoblasts
  • Transforming Growth factors; produced during bone resorption, stimulate osteoblasts
    • IL1 and osteoclast activating factor; activate bone resorption ; produced during bone resorption, stimulate osteoblasts
    • IL1 and osteoclast activating factor; activate bone resorption IL1 and osteoclast activating factor; activate bone resorption
    • Prostaglandins; regulate both osteoblasts and osteoclasts


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