Metabolism/Nutrition

Question 1

How much calcium does a normal vs a pregnant or growing horse need per day?

Answer 1

Normal: 40 mg/kg/d
Pregnant: 50-60 mg/kg/d
Growing: 50-75 mg/kg/d

Question 2

What effect have the following substances/circumstances on Ca homeostasis?

Answer 2

Acidic diet: increase absorption
Oxalates/Phytates: decrease absorption
Corticosteroids: decrease absorption/bone resorption/increase urinary excretion

Question 3

Where in the kidney does calcium get reabsorbed?

Answer 3

60 % proximal convoluted renal tubule

20 % thick ascending loop

20 % distal convoluted - major site for PTH stimulation

Question 4

Where and by which cells does calcitonin get secreted?

Answer 4

C cells of the thyroid gland

Question 5

Which factors are responsible for signaling for formation for mature osteoclasts? (calcium metabolism)

Answer 5

RANKL
macrohpage colony-stimulating factor

Question 6

Which factor inhibits RANKL form binding to its receptor (therefore inhibiting preosteoclast maturation)

Answer 6

OPG (osteoprotegerin)

estrogen stimulates OPG
corticosteroids stimulate RANKL

Question 7

How does vitamin D increase intestinal Ca absorption?

Answer 7

Increases calbindin in the intestinal epithelial cells (calcium binding protein)- transports Ca into cytoplasm

Question 8

Where does PTH mainly affect renal calcium absorption?

Answer 8

Late distal tubules
Collecting tubules
Early collecting ducts
Ascending loop of Henle (lesser extent)