Changes

#*'''Fast Phase''' - This phase begins in minutes and progressively increases for hours. PTH acts on existing osteoblasts and osteocytes to increase calcium uptake from the ''bone fluid''. Nearby calcium phosphate crystals will then replace the calcium which has been removed.

#*'''Fast Phase''' - This phase begins in minutes and progressively increases for hours. PTH acts on existing osteoblasts and osteocytes to increase calcium uptake from the ''bone fluid''. Nearby calcium phosphate crystals will then replace the calcium which has been removed.

#*'''Slow Phase''' - This phase involves the activation of osteoclasts and the creation of new osteoclasts, and takes ~48 hours to activate. There are no receptors for PTH on osteoclasts, so the signal comes from existing osteoblasts and osteocytes. This results in a progressive depletion of bone mineral.

#*'''Slow Phase''' - This phase involves the activation of osteoclasts and the creation of new osteoclasts, and takes ~48 hours to activate. There are no receptors for PTH on osteoclasts, so the signal comes from existing osteoblasts and osteocytes. This results in a progressive depletion of bone mineral.

#Kidneys - PTH increases the calcium reabsorption at the level of the late distal tubules and collecting ducts. It also increases [[Magnesium|magnesium]] reabsorption. This occurs at the expense of [[Phosphorus Homeostasis - Anatomy & Physiology|phosphorus]] in the proximal tubule. Thus Mg and Ca are reabsorbed and Potassium is excreted in the urine.  

#Kidneys - PTH increases the calcium reabsorption at the level of the late distal tubules and collecting ducts. It also increases [[Magnesium|magnesium]] reabsorption. This occurs at the expense of [[Phosphorus|phosphorus]] in the proximal tubule. Thus Mg and Ca are reabsorbed and Potassium is excreted in the urine.  

#GI tract - indirect effects occur via activation of Vitamin D3.

#GI tract - indirect effects occur via activation of Vitamin D3.