Hormonal Control of Calcium and Phosphate Flashcards
Which Ca2+ is physiologically active? Bound or free
the free Ca2+ is physiolgically active
Describe alkalosis and acidosis effects on calcium concentration in the body?
alkalosis lowers free Ca2+ by increasing protein binding, while acidosis raises free Ca2+ by decreasing protein-bindng
What is OPG?
osteoprotegerin binds RANK-L, thereby preventing it from binding onto precursor or osteoclast cells
“acts as a decoy for RANK-L”
What are the 2 mechanisms by which estrogen is known for conserving bone integrity?
- induces the synthesis of OPG
- reduces the secretion of cytokines by T-lymphocytes; these cytokines stimulate differentiation of precursor cells into active osteoclasts and they stimulate activity of mature osteocytes
- by inhibiting cytokines and increasing OPG, estrogen reduces the activity of osteoclasts.
How can PTH be used as a treatment in treating osteoporosis?
it can actually stimulate osteoblastic activity resulting in bone deposition if given intermittent spikes in PTH
What is calcitonin?
a peptide hormone secreted by the parafollicular cells (C cells) of the thyroid gland; released in response to elevated free calcium
What is the MOA of calcitonin?
lowers plasma calcium be decreasing the activity of osteoclasts; thus decreasing bone resorption
What are conditions calcitonin in used to treat?
Paget disease, severe hypercalcemia, and osteoporosis
What is the other name for calcitriol?
Vitamin D
What are the sources of Vit. D?
Vit D2 (diet) (ergocalciferol)
Vita D3 (skin) (cholecalciferol)
What is the active form of vit. D?
1,25 di-OH vitamin D (calcitriol)
What is the enzyme in renal tubules that converts 25 OH vitamin D to the active form?
1 a-hydroxylase in renal proximal tubule
What stimulates 1 a-hydroxylase activity?
low phosphate and PTH
What are the actions of calcitriol on the body?
raises plasma Ca2+ and phosphate by
increasing absorption of Ca2+ and phosphate in intestinal mucosa by increasing the production of Ca2+ binding protein calbindin
Calcitriol enhances PTH action at what part of the kidney tubule?
renal distal tubule
Which type of hyperparathyroidism, primary or other, is associated with elevated plasma calcium and PTH normal or elevated?
primary hyperparathyroidsm
What is pseuodhypoparathyroidism? Signs and symptom?
rare familial disorder characterized by target tissue resistance to PTH
usually accompanied by developmental defects: mental retardation, short and stocky stature, one or more metacarpal or metatarsal bones missing
In cases of hypocalcemia. When plasma calcium and phosphate levels are changing in opposite direction that cause is primary or secondary?
primary disorder
Can hyperphosphatemia lead to hypocalcemia?
yes
When plasma calcium and phosphate are changing in the same direction, the origin is usually primary or secondary?
secondary disorder
secondary hyperparathyroidism: both decrease
secondary hypoparathyroidism: both increase
Bone mineral density range for osteoporosis?
2.5 standard deviations below the average
Bone mineral density range for osteopenia?
1-2.5 standard deviations below the avg. the equals osteopenia
Which is seen before plate closure? Rickets or osteomalacia?
rickets seen before plate closure
MOA denosumab?
inhibitor of RANKL (RANKL is a TNF family of cytokines that activates osteoclasts; thus, denosumab inhibits osteoclasts)
