Basic Science - Endocrine

Question 1

Functions of 1,25-dihydroxyvitamin D

Answer 1

↑ absorption of calcium and phosphate from the intestine
↑ bone resorption of Ca2+ and phosphate

Question 2

Describe the vitamin D pathway and functions

Answer 2

Question 3

Functions of PTH

Answer 3

↑ serum Ca2+ and ↓ serum phosphate in response to hypocalcemia/hypomagnesemia via

↑ bone resorption of calcium and phosphate (bone is destroyed)
- PTH receptor is on the osteoblasts which secretes IL-1 to activated osteoclasts

↑ kidney resorption of calcium in distal convoluted tubule
↓ kidney resorption of phosphate
↑ 1,25-(OH)2 vitamin D production

Question 4

osteomalacia labs

Answer 4

Hypocalcemia, hypophosphatemia, and a normal hemoglobin level

Question 5

labs in HYPOparathyroidism

Answer 5

decreased: PTH, calcium, 1,25 vit D, urinary Ca
increased: phosphate
normal: alk phos

Question 6

most common cause and treatment HYPOparathyroidsm

Answer 6

thyroidectomy

supplement Ca and Vit D

Question 7

intermittant PTH therapy

Answer 7

targets osteoblast

The biological activity in the clinically used recombinant PTH is in the 1-34 amino acid sequence at the N-terminus of the molecule

Question 8

Name 7 conditions causing Rickets syndrome

Answer 8

Vitamin D-Resistant Rickets (Familial hypophosphatemic rickets

Nutritional vitamin D deficient rickets

Type I and II vitamin D dependent

Hypophosphataisa

Renal osteodystrophy

Hyper PTH

Question 9

logic for vitamin D deficiency rickets (nutritional)

Answer 9

lack of vitamin D

leads to low-nl calcium → high PTH → low phos and high alk phos

Question 10

logic for vitamin D resistant rickets (familial x-linked hypophosphatemic)

Answer 10

defect in proximal renal tubules reabsorb phosphate

leads to elevated alk phos

So, Ca and PTH are normal

Presumed defect in 1,25 Vit D conversion because normally hypophosphemia would cause this to increase

Question 11

Which rickets condition is alk phos not elevated?

Answer 11

ONLY hypophosphatasia

Question 12

logic for Type 1 vitamin D dependent rickets

Answer 12

defect in conversion to 1,25 vit D

defect in renal 25-(OH)-vitamin D1 alpha-hydroxylase

→ low Ca/Phos → high PTH → high alk phos

Question 13

logic for Type 2 vitamin D dependent rickets

Answer 13

defect in 1,25 vit D RECEPTOR

→ very high 1,25 vit D levels

→ low Ca/Phos → high PTH → high alk phos

Question 14

logic for hypophosphatasia

Answer 14

defect in alk phos

→ alk phos activity is low

→ Ca and Phos are high (don’t know why)

Question 15

Renal osteodystrophy logic

Answer 15

defect is in phos excretion

→ PTH goes up to try to waste phos

→ high alk phos

defect is in conversion to 1,25 vit D

→ low Ca

Question 16

logic for hyperparathyoidism

Answer 16

90% adenoma

defect is in too much PTH

causes increased bone turnover, increased alk phos, increased Ca, phos wasting

Question 17

Genetics of Rickets

Answer 17

Type I/II vit d dependent and hypophosphatasia:AR

fam vit-D resistant rickets (hypophosphatemic): X-linked dominant