Exam 2 - Disorders of Mineral Metabolism

Question 1

_____ is the biologically active form of calcium

Answer 1

ionized calcium (Ca2+)

Question 2

___ is the form of calcium that is closely regulated in the body

Answer 2

Ca2+

Question 3

roles of Ca2+ in NMJ function

Answer 3

1. dampens effects of Na+ channels which decreases excitability of axon
2. promotes fusion of vesicle containing ACh to synaptic membrane to release ACh into NMJ
3. propagation of AP through muscles (initiates actin-myosin coupling in muscle)

Question 4

what does metabolic acidosis lead to?

Answer 4

signs of low [Ca2+] because acidosis renders bone mineral more soluble so Ca2+ is released more readily from bone increasing concentration in blood
- long term acidosis leads to demineralization of bone (osteoporosis)

Question 5

as pH _____ bone resorption (Ca2+ release) ______

Answer 5

decreases (acidic)
increases

Question 6

Calcitonin net effect

Answer 6

reduces [Ca+2] in ECF by promoting the deposition of calcium in bone & loss in urine

Question 7

PTH effects on kidney

Answer 7

1. increases Ca2+ reabsorption by nephrons (increase Ca)
2. PO4 in saliva/urine (less complexing with calcium)
3. conversion to vitamin D3 (the active form of vitamin D)

Question 8

vitamin D effect

Answer 8

increases calcium & PO4 by 1) promoting bone resorption and 2) increase absorption of Ca and P from gut

Question 9

purpose of a 2:1 Ca:P ratio

Answer 9

P inhibits Ca so need more Ca

Question 10

what can cause severe metabolic alkalosis?

Answer 10

repetitive vomiting (loss of HCl)

forms Ca-albumin complex = less ionized Ca2+ (unavailable)

Question 11

hypocalcemia in dogs/cats

Answer 11

during/after pregnancy; small breeds with big litters –>

1. Puerperal eclampsia (tetanic seizures)
2. Risus sardonicus (uncontrolled mm contractions of facial mm)

Question 12

hypocalcemia in horses

Answer 12

“lactational tetany” - eclampsia (similar to dogs,cats,humans); more common in draft breeds bc higher lactation rate

Question 13

hypocalcemia in ruminants

Answer 13

milk fever/periparturient hypocalcemia

Question 14

difference between stage I, II and III milk fever

Answer 14

stage I: Irritable, hyperesthetic, tongue protrusion with jaw open, trembling, jerking, motions, spasms, brief duration

stage II: S shape body (head to flank), reduced GI motility, bloat, constipation, urine retention, dilated pupils & rapid, weak pulse & decreased extremities temp*

stage III: coma, death

Question 15

treatment of milk fever/periparturient hypocalcemia

Answer 15

Ca2+ salts SLOWLY IV

Question 16

Mg function in neuromuscular transmission

Answer 16

key component for AChE –> reduces ACh in synaptic cleft
dampens Ca influx in axon terminal –> preventing ACh release –> relaxation of muscle

Question 17

what can cause hypermagnesemia

Answer 17

renal failure or poor renal function because Mg excreted by kidneys

Question 18

ruminantts grazing a lush grass pasture will cause _____________

Answer 18

hypomagnesemia “grass tetany” aka “wheat pasture poisoning”

Question 19

hypomagnesemia “grass tetany”

Answer 19

low Mg = ACh left in the synaptic cleft (no AChE) or Ca response not dampened = sustained muscle contractions = rigid tetany

Question 20

how can you prevent grass tetany

Answer 20

feed/soil influence Mg absorption so you can feed Mg supplement in springtime or soil with Mg

Question 21

nutritional secondary hyperparathyroidism “bran disease in horses”

Answer 21

high phosphorus in diet = competes with Ca for intestinal uptake = decrease Ca in the blood = chronic elevation of PTH to try to increase Ca = bone mineralization = lameness, bone remodeling with fibrous tissue (especially mandible)

Question 22

renal secondary hyperparathyroidism

Answer 22

kidney failure = hyperphosphatemia (reduced excretion of PO4) = Ca absorption inhibited = less Ca in the blood = chronic elevations in PTH to increase Ca levels = low grade metabolic acidosis = osteoporosis

Question 23

Describe the nutritional basis for struvite urolithiasis in ruminants fed high-grain diets.

Answer 23

feedlot cattle are often fed high grain diets (high P low Ca) which lead to phosphatic urinary calculi (PO4 containing urolith) –> urethral obstruction

Question 24

how can hypophosphatemia be caused

Answer 24

1) insulin treatment because insulin drives PO4 into cells
2) high PTH

Question 25

what does hypophosphatemia cause

Answer 25

1. rickets in camelids
2. pica activity in ruminants

Question 26

vitamin D poisoning

Answer 26

excess hypercalcemia & hyperphosphatemia –> soft tissue calcification and multiorgan failure