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parathyroid hormone - source

chief cells of parathyroid


PTH function

1. increased bone resorption of Ca2+ and PO43-
2. increased kidney reabsorption of Ca2+
3. decreased kidney reabsorption of


• Which cells normally produce parathyroid hormone?

Chief cells of the parathyroid glands


• A man presents with high parathyroid hormone (PTH). What serum, urinary findings do you see in a patient with primary hyperparathyroidism?

High serum Ca2+, low serum PO43-, and high urine PO43-


How does parathyroid hormone affect calcium absorption in the gut?

• Stimulates 1α-hydroxylase in renal proximal convoluted tubule; increased 1,25-(OH)2D3 (calcitriol) promotes calcium absorption from the gut


• A woman undergoing dialysis is found to have osteoporosis. Her parathyroid level is normal. What enzyme might she be deficient in?

1α-Hydroxylase (from renal proximal convoluted tubule) increases 1,25-(OH)2D3 and therefore Ca2+ absorption from the gut


• What electrolyte changes induce parathyroid hormone (PTH) secretion?

Decreased serum Ca2+ and mild-to-moderately decreased Mg2+ both increase PTH secretion


• An alcoholic, hypertensive man with diarrhea recently started gentamicin. How could this affect PTH secretion?

Alcohol abuse, diarrhea, aminoglycosides, and diuretics lower Mg2+: Mildly/moderately low Mg2+ increases PTH, severely low Mg2+ decreases it


• In lab rats, adding a RANK-L (receptor activator of NF-κB ligand) inhibitor lowers the serum Ca2+ level. Why might this be?

PTH stimulates RANK-L on osteoblasts/osteocytes, which then binds RANK on osteoclasts/osteoclast precursors, increasing the Ca2+ level


• A patient with advanced squamous cell lung cancer has a very low serum phosphate level. Why might this be?

Some cancers secrete PTH-related peptide (PTHrP), which mimics PTH; PTH causes reduced PO43– reabsorption (PTH = Phosphate Trashing Hormone)


• With which lab findings would a patient with parathyroid hyperplasia leading to excessive PTH secretion present?

Hypercalcemia, hypophosphatemia, increased vitamin D level


Almost counterintuitively, PTH can also be given to patient with osteoporosis to help form bone. In what fashion must PTH be given?

Intermittently (e.g., once-daily injection) administered PTH can stimulate bone formation


PTH works on three organ systems: bones, GI system, and kidneys. How does it affect Ca2+/PO43– (Ca/P) processing in each?

Bone: more Ca/P resorption; GI: more gut Ca/P uptake; kidney: more active vitamin D, more DCT Ca resorption, less PCT P resorption