Calcium/Phosphorus/Mg - Ex 4 Flashcards
Total calcium =
Protein bound (40%) + ionized (50%) + complexed (10%)
What does acidosis do to ionized Ca
increases ionized Ca++
What does alkalosis do to ionized Ca
decreased ionized Ca++
PTH effects
inc Ca and dec Pi
Vit D effects
inc Ca and inc Pi
Dairy cattle diet & Ca
Fed acidifying diet 3-5 weeks pre-partum –> acidosis promotes Ca release from bone, making Ca more available and increasing blood Ca levels at parturition and in the periparturient period
What is the most common cause of apparent hypocalcemia
Hypoalbuminemia
Hypocalcemia - Differentials (4)
- Hypoalbuminemia (most common)
- no CS
- iCa is normal - Chronic renal failure
- kidney can’t produce calcitriol –> reduced intestinal absorption of Ca and inc skeletal resistance to PTH
- iCa is below the reference interval more often than total Ca - Acute Pancreatitis
- release of lipase –> saponification - Periparturient hypocalcemia/Eclampsia
- Small animals: usually small dog breeds with large litter; loss of Ca into milk during lactation
- Lg animals: high lactating dairy cows
Hypocalcemia - Diffs (less common) (5)
- Nutritional hyperparathyroidism
- low Vit D, low Ca and/or high Pi diet, inc PTH secretion (Ca level normal, but PTH leaches Ca from bones –> osteopenia) - Renal 2nd’y hyperparathyroidism
- Primary hypoparathyroidism
- Hypercalcitonism
- Hypocalcemia in critical care pos
CS of hypocalcemia
(occur when iCa is low!)
Tetany/mm tremors in most spp
Paresis in ruminants (milk fever)
Tx of hypocalcemia
Usually only needed for cases of periparturient and acute hypocalcemia (following sx)
“True” Hypercalcemia - Differentials
- Paraneopastic (humoral hypercalcemia of malignancy) MOST COMMON
- inc PTHrp, dec PTH - Hypoadrenocorticism - 2nd most common
- Chronic renal failure
- Vit D toxicoses
- Primary hyperparathyroidism (rare)
Most affected tissues - hypercalcemia
CNS, GI, heart, kidneys
severity of CS related to iCa levels
*all dogs respond differently to hypercalcemia and two dogs with the same levels may have very different degrees of CS
Mineralization of soft tissue - hypercalcemia
most sever when the product of Ca and Pi is > 60 mg/dL
Hypophosphatemia - Differentials (3)
- Increased cellular uptake of phosphorus (maldistribution)
- Increased loss (reduced renal reabsorption)
- primary hyperparathyroidism: inc PTH –> dec Pi
- renal tubular disorders
- eclampsia (because PTH is high) - Dietary
- Vit D deficiency
Most common cause of hyperphosphatemia
Decreased excretion –> reduction in renal blood flow and dec GFR
Hypoparathyroidism
can lead to hyperphosphatemia
Hypomagnesemia - Diffs
- Excessive loss from gut, mostly from malabsorption syndromes or diarrhea
- Excessive loss from kidney, including fluid diuresis, diuretic therapy, or renal dz
Hypomagnesemia - Ruminants
Two causes & CS
- Milk tetany
- calves fed milk-only diets (low in Mg) - Grass tetany
- adults fed on lush, green pasture –> high K content in trash blocks normal Mg absorption from the rumen
Neuromuscular excitability, clonus, and contractors progressing to tetany may be observed
- acute death is possible
Sequelae of hypomagnesemia
can lead to hypocalcemia and hypokalemia
Hypermagnesemia
Clinically significant hypermagnesemia is most often seen when renal function and/or urinary elimination of excess Mg is compromised
CS rarely develop unless serum Mg exceeds approx 2 mmol/L, and are characterized by neuromuscular dysfunction (paresis or paralysis), cardiovascular depression, and Gi upset
