Parathyroid Hormone
- functions
- regulation of expression
- consequences of overexpression
- consequences of underexpression
- signalling pathways
- structure
Function
PTH's primary function is to increase ionized Ca2+ levels in the plasma. If Ca2+ is low, PTH is elevated, while high Ca2+ results in a reduction in PTH.
PTH acts to increase calcium in a number of ways:
- increases release from bone by stimulating osteoclast number and activity
- stimulates reabsorption of Ca2+ and inhibits reabsorption of phosphate in the kidney's proximal and distal tubules
- stimulates renal synthesis of 1,25(OH2)D3 (through activity of 1α-hydroxylase), increasing intestinal Ca2+ and phosphate absorption (takes 24-48 hours)
Regulation of Expression
Decreased calcium
Consequences of Overexpression
Hyperparathyroidism causes an increase in serum calcium but is often asymptomatic.
Consequences of Underexpression
Signalling Pathways
Structure
PTH is an 84 aa peptide whose N-terminal portion interacts with the receptor.