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20 Cards in this Set
- Front
- Back
Ca2+/Pi balance refers to the exchange of Ca and Pi between blood and three major target organs:
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Bone
Kidney small Intestine |
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This form of calcium is active and can cross the membrane.
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Ionized (free)
Bound forms do not cross membranes! |
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Alkalosis (increases|decreases) protein-binding Ca and (increases|decreases) ionized Ca in the blood.
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Increases
Decreases (thus decreases plasma Ca) (normally ECF Ca should be higher than ICF) |
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Form that Ca is stored in the bone.
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hydroxyapatite
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Effect on Ca and Pi by calcitrol (Vit D), PTH, & Calcitonin
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calcitrol (vit D) - Increases Ca & Pi
PTH- Increases Ca & Decreases Pi Calcitonin- Decreases Ca & Pi |
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PTH secretion is regulated by what two plasma particles?
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Ca2+ and VitD
(inverse relationship, if Ca 2+ and/or Vit D are high, PTH secretion will be low) |
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Two locations of PTH receptors
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Bone (osteoblasts):
(PTH activates osteoblasts--> convert to osteoclasts for reabsorptiion) Kidney (proximal tubule): (PTH decreases Pi reabsorption & increases Ca reabsorption) |
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PTH effect on intestine
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NO DIRECT EFFECT
(only Vit D acts on small intestine) |
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Enzyme responsible for activating vit D
Where is vit D activated? |
1a-hydroxylase
(PTH activates this enzyme) activated in kidney (taken in via skin (sun) & liver) |
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What stimulates and inhibits calcitriol synthesis
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Stimuates:
PTH Low Ca Low Pi Inhibits: High VitD (Neg feedback) High Ca |
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Calcitriol effect on intestine
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Increases Ca absorption
Increases Pi absorption Stimulates synthesis of calbindin (shuttle protein) |
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Calcitriol (vit D) effect on bone
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INDIRECTLY promotes bone calcification by increasing available substrates (Ca2+ & Pi)
DIRECTLY by stimulating osteoblasts (extreme quantities cause resportion by converting osteoblasts to osteoclasts) |
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Indirect effect on kidneys by Vitamin D
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Stimulates re-absorption of Pi by inhibiting PTH
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Calcitonin effect on kidney & bone
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kidney- Induces 1a-hydroxylase transcription (vit D synthesis)
bone- inhibits osteoclast activity |
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____________ leads to tetany
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hypocalcemia
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What does Vit D deficiency result in?
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rickets (children) & osteomalacia (adults)
= failure of osteoid to calcify (soft bones) |
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What does primary hyperparathyroidism lead to?
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hypercalcemia (muscle weakness, bradycardia)
bone loss (weak, pain, too much resorption) kidney stones (too much resorption |
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Effects of GH on bone growth.
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Increases Ca absorption in the intestine
Increases renal Pi reabsorption (increases substrates needed for bone formation) |
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Effect of low TH levels in children
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Delayed ossification of cartilaginous bone = more cartilage
(*if TH is too high, bone resporption will increase= less bone) |
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Effects of excess glucocorticoid
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Decrease renal Ca reabsorption
Decrease intestinal Ca absorption Stimulates bone resorption Inhibits bone formation (decreases Ca) |