Quiz 3: PTH, Vit D, Calcitonin

Question 1

Terminology: Formation, Breakdown, Remodeling/Turnover

Answer 1

Osteogenesis: new bone formation
Resorption: absorption of old bone
Remodeling or Turnover: Reshaping –Depositing (formation) and absorbing (breakdown) bone to make new bone

Question 2

Parathyroid Hormone Metabolism

Answer 2

Metabolized to:
	N-terminal (1-34 aa) and several
	C-terminal and midmolecule fragments
Active forms: Intact and N-terminal
Free Ca++ controls secretion of PTH:
High free Ca++  =  Suppresses secretion 
Low  free Ca++  =	stimulates secretion

Question 3

Function of PTH

Answer 3

Acts on bone and kidneys to control Calcium (iCA)

1. Increase serum Calcium
2. Decrease serum Phosphorus
3. Increase active form of Vitamin D

Question 4

PTH Measurement and Reference Values

Answer 4

Immunoassay
Serum: 10-65 pg/mL
- May be age related 45/45 (45pg/mL at 45)

Question 5

PTH Effects: Kidney

Answer 5

INCREASES renal tubular resorption of Ca (Increase Ca)
INHIBITS proximal renal tubular resorption of inorganic phosphate (Decrease PO4)
Stimulates renal hydroxylation of 25-(OH)Vitamin D to 1,25-(OH)2 Vitamin D

Question 6

PTH Effects: Bone

Answer 6

Stimulates mobilization of Ca from bone, stimulating osteoclast formation and osteolysis, releasing CA and HPO4
Resulting in:
Increased Ca
Increased PO4

Question 7

PTH Effects: Gut

Answer 7

Increases CA absorption
Resulting in:
Increased Ca
Decreased PO4

Question 8

Hyperparathyroidism Statistics

Answer 8

U.S. statistics: around 100,000 new cases/year
Risk increases with age
Women/men: 2 to 1
Women >60 yr old have a frequency of: 2 out of 1000
Most frequent cause: benign parathyroid tumor
Treatment: surgery to remove glands (leave small amount of tissue—goal normal Calcium)

Question 9

Vitamin D/ Hormone D

Answer 9

Group of fat soluble prohormones, not vitamins

• vitamin D2 (ergocalciferol): Found in the diet from fish, plants and fungus, not made in body
• vitamin D3 (cholecalciferol): 90% produced by photosynthesis in the skin from exposure to sunlight, rest is from animal products in diet

Question 10

Decreased Vitamin D

Answer 10

Inadequate exposure to sunlight
Inadequate dietary Vitamin D
Liver and/or kidney disease
Disorders that limit absorption

Question 11

Increased Vitamin D

Answer 11

Vitamin D intoxication (milk fortification)

Question 12

Vitamin D Metabolism

Answer 12

Vitamin D metabolized in Liver to 25(OH)- Vitamin D which in the kidney is hydroxylated to 1,25 (OH)2 Vitamin D –the biologically active form

Question 13

1,25 Dihydroxy Vitamin D in Intestines, Bones, Kidneys, and Neuromuscular Effects

Answer 13

Increases blood Calcium and Phosphorus levels
Intestines: Increases CA and PO4 absorption, Decreases MG absorption
Bone: Facilitates action of PTH on osteoblasts, Increases Mineralization and formation
Kidney: Promotes CA and PO4 reabsorption
Neuromuscular: Better balance, may prevent falls

Question 14

Vitamin D Ranges

Answer 14

Vitamin D 25 OH metabolite 20 - 57 ng/mL
- Measured to assess Vitamin D stores
Vitamin D 1,25 OH metabolite 15-75 pg/mL

Question 15

Vitamin D Measurement

Answer 15

25-OH Methods:
Immunoassay (total of D2 and D3)
HPLC (fractionates D2 and D3)
LCMSMS (liquid chromotography tandem mass spectrometry)

Question 16

Effects of Vitamin D Deficiency

Answer 16

• Bone mineralization leading to bone softening causing Rickets and osteomalacia
• Hypertension
• Linked to colon cancer and breast cancer and possibly other forms of cancer

Question 17

Vitamin D Deficiency Treatment

Answer 17

• Nutritional deficiency (<20ng/mL) requires treatment with 50,000 units orally once per week for 6-8 weeks and 800-1000 IU daily thereafter
• Patients with liver disease should receive 25-hydroxyvitamin D supplementation
• Patients in renal failure should receive 1,25-dihydroxyvitamin D supplementation

Question 18

Excess Vitamin D Effects

Answer 18

Confusion, polyuria, polydipsia(thirst), anorexia, vomiting, muscle weakness, bone demineralization and calcium and phosphate deposits in the kidneys, blood vessels, lungs and heart

Question 19

Calcitonin

Answer 19

Hormone inhibits action of PTH and Vit D
Regulated by ionized Ca –> Elevated ionized Ca causes CT release, causing Calcium and Phosphorus levels to decline by decreases renal tubular reabsorption of Calcium, phosphorus, sodium, potassium and magnesium.

Question 20

Calcitonin Measurement and Ranges

Answer 20

Immunoassay
Normal: < 25 pg/mL
Post Calcium (and pentagastrin) infusion: < 350 pg/mL
Used to distinguish normal from medullary carcinoma

Question 21

Calcitonin Deficiencies

Answer 21

• Thyroid Disease
• Secondary to Thyroid removal
  Exogenous calcitonin helps control Ca levels

Question 22

Intra-operative PTH monitoring

Answer 22

Done to determine if the abnormal tissue has been removed
Obtain a baseline reading then check every 5-10 min to determine a 50% drop in PTH indicating the excision was successful