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

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.