Quiz 3: PTH, Vit D, Calcitonin Flashcards Preview

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Terminology: Formation, Breakdown, Remodeling/Turnover

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


Parathyroid Hormone Metabolism

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


Function of PTH

Acts on bone and kidneys to control Calcium (iCA)
1. Increase serum Calcium
2. Decrease serum Phosphorus
3. Increase active form of Vitamin D


PTH Measurement and Reference Values

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


PTH Effects: Kidney

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


PTH Effects: Bone

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


PTH Effects: Gut

Increases CA absorption
Resulting in:
Increased Ca
Decreased PO4


Hyperparathyroidism Statistics

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)


Vitamin D/ Hormone D

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


Decreased Vitamin D

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


Increased Vitamin D

Vitamin D intoxication (milk fortification)


Vitamin D Metabolism

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


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

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


Vitamin D Ranges

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


Vitamin D Measurement

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


Effects of Vitamin D Deficiency

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


Vitamin D Deficiency Treatment

- 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


Excess Vitamin D Effects

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



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.


Calcitonin Measurement and Ranges

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


Calcitonin Deficiencies

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


Intra-operative PTH monitoring

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