CALCIUM
REABSORPTION
PHOSPHATE
EXCRETION
Ca2+
Ca2+
PLASMA Ca2+
PLASMA Ca2+
PARATHYROID
PO4
BONE
KIDNEY
CALCIUM
SENSOR
DECREASE
IN PLASMA
CALCIUM
STIMULATES
PARATHYROID
HORMONE
(PTH) SECRETION
GUT
PTH
PTH
25-(OH)-D3
CALCIUM IN DIET
CHOLESTEROL
URINE
VITAMIN D3
1,25-(OH)2-D3
INCREASE
IN PLASMA CALCIUM STIMULATES
CALCITONIN SECRETION
FROM THYROID PARAFOLLICULAR
CELLS
PO4