Endocrine

Question 1

Vit D Metabolism

Answer 1

7-dehydrocholesterol -> cholecalciferol in skin by UV light
Cholecalciferol -> 25-hydroxycholecalciferol in liver
25-hydroxycholecalciferol -> 1a,25-dihydroxy vit D in kidney
Calcitriol facilitates absorption of calcium and phos in SI

PTH tightly regulates vit D 1a hydroxylase

Question 2

Normocalcemic hyperparathyroidism

Answer 2

Subtype primary hyperparathyroidism
normal Ca, elevated PTH
Low bone density
Distinguish from secondary hyperparathyroidism by checking: creat, urinary Ca, vit D levels
Low Vit D, High creat, High urine Ca -> secondary Hyper PTH

Question 3

Differential diagnosis of secondary hyperparathyroidism

Answer 3

Insufficient dietary calcium intake
Vit D deficiency
GI malabsorption (gastric bypass, pancreatic disease, cystic fibrosis)
CKD

Question 4

Indications for parathyroidectomy

Answer 4

symptomatic pts w/ medically refractory hyperparathyroidism and PTH > 800

asymptomatic patients with PTH > 1000

Question 5

Locations of ectopic parathyroid glands

Answer 5

inferior parathyroid glands derived from 3rd pharyngeal pouch - descend with thymus

MC location of ectopic inferior parathyroid glands: thyrothymic ligament

MC location of ectopic superior parathyroid glands: tracheoesophageal groove