calcium and bone physiology

Question 1

how does Vitamin D effect the plasma calcium and phosphorus regulation

Answer 1

• Can increase uptake of Ca and phosphorus in small intestine

Question 2

how does PTH effect the plasma calcium and phosphorus regulation

Answer 2

• Increases plasma Ca and decreases plasma phosphorus
• decrease in Phosphorus is important because it prevents crystalization of calcium-phosphate
• Low plasma Ca casues the release of more PTH

Question 3

How does Calcitonin effect the plasma calcium and phosphorus regulation

Answer 3

• increased plasma Ca causes the release of calcitonin (CT)
• CT causes decrease in reabsorption of Ca and Phosphorus in the kidney
• may protect bones of mother from excess Ca loss during pregnancy

Question 4

Describe PTH role in the kidney

Answer 4

• PTH contols the amount of Ca reabsorbed in distal portion of nephron and thus the amount lost in urine

Question 5

describe PTH role in vitamin D

Answer 5

• PTH increases activity of enzyme 1alpha-hydroxylase which is involved in forming active Vit D
• Vit D inhibits PTH release (neg feedback)

Question 6

describe PTH role in Bone

Answer 6

• PTH increases bone resorption and delivery of Ca to plasma
• inhibits collage synth by osteoblasts
• Active vit D paired with PTH increases osteoclast bone resorption

Question 7

what are the forms of calcium that are filtered by the kidney

Answer 7

• free ionized Ca (50% of calcium)

- anion bound Ca (10% of calcium)

Question 8

Describe Hypocalcemia

Answer 8

• threshold closer to memb protential and neres/muscle mroe easily excitable
• Tetany, distal extremity numbness, larygospasm

Question 9

describe hypercalcemia

Answer 9

• voltage gated Na channels less likely to open

- fatigue, muscle weakness, constipation, polyuria, kidney stones, coma, cardiac arrest

Question 10

Define OPGL

Answer 10

• osteoproteigerin ligand (OPGL) or RANK ligand
• cytokine relased by osteoblast in response to PTH
• activates receptors on preosteoclasts cells that causes differentiation into osteoclasts to begin bone resorption

Question 11

define OPG

Answer 11

• Osteoprotegerin
• produced by osteoblasts to act as decoy for OPGL and INHIBITS bone resorption
• estrogen stimulates OPG production
• PTH decreases OPG production

Question 12

what effects of Low Vit D have on bone

Answer 12

• low vit D means little to no bone resoprtion caused by PTH

Question 13

describe the steps of vitamin D synthesis

Answer 13

1) 7-dehydrocholesterol is acted upon by sunlight and converted to pre-vit D and then into Vit D3
2) in the LIVER, 25-hydroxylase converts Vit D3 into 25-hydroxycholecalciferol
3) in KIDNEY, PTH and 1alpha-hydroxylase converts 25-hydroxy… into 1,25-dihydroxy…

Question 14

describe Hyperparathyroidism

Answer 14

• usually caused by tumors (benigh adenoma)
• leads to High secretion of PTH which results in increases in bone resoprtion, renal Ca Reabsorption and active Vit D production (which increaes intestinal Ca absorption)
• RESULTS = hypercalcemia = stones, weak bones, constipation, excessive urination

Question 15

describe Hypoparathyroidism

Answer 15

• caused by damaged or removed parathyroid
• Low to no PTH causes a decline in plasma Ca
• symptoms = neuromuscular excitability and hypocalemic tetany

Question 16

describe pseudohypoparathyroidism

Answer 16

• signs and symptoms of hypoparathyroidism, but NORMAL to ELEVATED levels of PTH
• problems with PTH receptors and decreased response to PTH

Question 17

How can renal disease cause Osteomalacia

Answer 17

• renal damage can mean insufficient production of active form Vit D
• this can lead to renal rickets (osteomalacia) which is softening of the bone due to deficient mineralization