Calcium and Phosphate

Question 1

1,25-dihydroxycholecalciferol Regulation

Active and Inactive

Answer 1

Vit D increased by CYP1-alpha gene expression
Caused by PTH

Vit D decreased by CYP1-alpha suppression
Caused by Vit D and Calcium

Inactive Vit D increased by CYP24 expression
Caused by Vit D

Question 2

Vit D/PTH Bone Synergistic Activities

Answer 2

Increase M-CSF to increase osteoclast stem cells

Increase IL-6 and RANK Ligand to activate osteoclasts
Decrease OPG which blocks RANKL

Question 3

Calcitonin Actions

Bone and Kidney

Answer 3

Increases OPG which blocks RANK ligand to decrease resorption and increase formation

Decreases renal Calcium reabsorption

Question 4

Vitamin D Actions

Kidney, Intestine

Answer 4

Increases renal Calcium and Phosphate reabsorption

Increases TRPV6 and Calbindin protein synthesis in intestine
Increases absorption of Calcium and regulates IC Ca2+ levels

Question 5

Primary Hyperparathyroidism

Cause, Presentation and Lab Levels

Answer 5

Parathyroid adenoma

Hypercalciuria, Increased bone resorption and constipation
(Stones, Bones and Groans)

High PTH, Calcium and Vitamin D
Low Phosphate

Question 6

Secondary Hyperparathyroidism

Causes and Lab Levels

Answer 6

Increased PTH secondary to hypocalcemia
Caused by renal failure or Vit D deficiency

Renal: High PTH and Phosphate
Low Calcium and Vitamin D

Vit D: High PTH
Low Phosphate, Calcium and Vitamin D

Question 7

Total Calcium

Distribution and Bound State

Answer 7

Mostly stored in bones and teeth

Small amount is extracellular
40% protein bound, 10% anion complexed, 50% free ionized

Question 8

Hypocalcemia

Characteristics, Presentation, Diagnosis

Answer 8

Increases sodium conductance that increases excitability

Causes tetany, muscle spasms, tingling, numbness and hyperreflexivity

Diagnose with Chvostek and Trousseau signs

Question 9

Hypercalcemia

Presentation

Answer 9

Causes decreased excitability, constipation, polyuria, decreased QT interval, muscle weakness, lethargy

Question 10

Hormonal Regulation of Calcium

Answer 10

PTH: Increases bone resorption, renal reabsorption and calcitriol synthesis

Calcitonin: decreases bone resorption

Vitamin D: Increases bone resorption and intestinal absorption

Question 11

Total Phosphate

Distribution and Bound State

Answer 11

85% of Pi in bones, 15% in ICF and 1% in ECF

ECF is 84% ionized, 10% protein bound and 6% complexed

Question 12

Phosphate Hormonal Regulation

Answer 12

PTH: decreases renal Pi reabsorption

Vitamin D: Increases plasma Pi

Question 13

Parathyroid Hormone Regulation

Answer 13

Increased Ca2+ detected by CaSR
Uses Gq and Gi to decrease gene expression and block Ca2+ vesicle release

Vitamin D will decrease gene expression and upregulate CaSR

Question 14

Vitamin D Regulation

Answer 14

CYP1-alpha gene upregulates 1-alpha hydroxylase which increases 1,25 dihydroxycholecalciferol

PTH increases CYP1-alpha
Calcium and Vitamin D decrease CYP1-alpha

Vitamin D also increases CYP24 to increase inactive Vitamin D synthesis

Question 15

Parathyroid Hormone Bone Actions

Short and Long Term

Answer 15

Short Term PTH will increase osteoblast activity

Long Term PTH will increase osteoclast activity

Question 16

Hypoparathyroidism

Causes and Lab Values

Answer 16

Thyroid or Parathyroid Surgery, Autoimmune disease, Congenital defect

Low PTH, Calcium and Vitamin D
High Phosphate

Question 17

Pseudohypoparathyroidism Type 1a

Pathophysiology and Lab Values

Answer 17

Defective PTH Gs in bone and kidney
Causes hypocalcemia and hyperphosphatemia

High PTH and Phosphate
Low Calcium and Vitamin D

Question 18

Humoral Hypercalcemia of Malignancy

Pathophysiology and Lab Values

Answer 18

PTH-related peptide secreting tumor bind Type 1 PTH Receptor

High serum/urine Calcium, urine Phosphate
Low PTH, Vitamin D and serum Phosphate

Question 19

Familial Hypocalciuric Hypercalcemia

Pathophysiology and Lab Values

Answer 19

Inactive CaSR decreases Ca2+ regulation

High PTH, Serum Calcium
Low Urine Calcium
Phosphate and Vitamin D normal

Question 20

Rickets

Pathophysiology and Effects

Answer 20

Decreased 1-alpha hydroxylase and Vitamin D receptor

Growth failure and Skeletal Deformity (bow legs)

Question 21

Osteomalacia

Effects and Lab Values

Answer 21

No new bone mineralization, soft bones that bend

High PTH, Urine Phosphate ad bone resorption
Low Calcium, Serum Phosphate and Vitamin D

Question 22

Osteoporosis

Risk Factors and Treatment

Answer 22

Post-menopausal Women

Treat with intermittent PTH