Pathophysiology of Calcium Metabolism & Bone Disease Flashcards
Excess vitamin D can lead to what endocrine disorder?
Hypoparathyroidism - excess vitamin D elevates Ca2+ and suppressed PTH
What is the most common cause of secondary hyperparathyroidism?
Chronic renal failure - low calcium leads to increased PTH secretion
What laboratory findings would be likely in a patient with primary hyperparathyroidism?
Elevated PTH, elevated Ca2+, elevated cAMP, decreased phosphate
This is a less severe form of osteoporosis characterized by decreased bone mass, without increased feature risk.
Osteopenia
What is generally the first clinical sign of osteoporosis?
Decreased height
What is the normal plasma calcium levels?
8.5-10.5 mg/dL
What laboratory results would be expected in a patient with secondary hyperparathyroidism?
Decreased Ca2+, elevated phosphate, elevated PTH
Vitamin D may also be decreased in severe cases
Increased levels of alkaline phosphatase are indicative of what bone process?
Osteoblast activity (bone formation)
What is the inciting factor in cases of tertiary hyperparathyroidism?
Prolonged secondary hyperparathyroidism causing hyperplasia of the parathyroid
What molecule is excreted in higher levels in the urine during periods of bone resorption?
Hydroxyproline
These cytokines are produced by osteoblasts and promote development of mature osteoclasts.
Macrophage-colony stimulating factor (M-CSF) & IL-6
Patients with this disorder require higher than normal Ca2+ levels to suppress PTH secretion by the parathyroid. What mutation is associated with the disorder?
Familial Hypocalciuric Hypercalcemia (FHH) - loss of function mutation in CaSR gene
Bisphosphonates treat hypercalcemia, but take a few days to reach maximum effect. What rapid-acting drug is given as a bridge therapy?
Cinacalcet
What is the most widely used test for osteoporosis?
Fracture Risk Assessment Tool (FRAX)
What is the most common cause of primary hypoparathyroidism?
Surgical excision of the gland
What are the stages of Paget Disease?
Lytic phase - increased osteoclast activity
Sclerotic phase - increased osteoblast activity
Quiescent phase - reduced activity
How are osteocytes activated by osteoblasts?
Osteoblasts secrete RANK-L, which binds to RANK receptors on osteocytes and activates them
Estrogen protects against bone resorption. How?
Estrogen promotes secretion of osteoprotegerin (OPG), which is a decoy receptor for RANK-L, thus preventing osteocyte activation
This is the pediatric form of osteomalacia due to vitamin D deficiency.
Rickets
These are mature bone cells that regulate bone resorption and formation.
Osteocytes
This bone disorder is characterized by increased bone density due to failure of bone resorption.
Osteopetrosis
What are the most common causes of primary osteoporosis?
Postmenopausal & senile
What disorder is associated with a gain of function mutation in the CaSR gene?
Hypoparathyroidism - lower levels of Ca2+ suppress PTH leading to hypocalcemia
What is the most common clinical presentation of patients with primary hyperparathyroidism?
Asymptomatic - symptoms that do present are due to the associated hypercalcemia
