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44 Cards in this Set

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When is parathyroid hormone released?
In response to hypocalcemia and to some extent hypomagnesemia
What are the overall results of parathyroid hormone?
Increases calcium
Decreases phosphorus
What are the 4 ways the parathyroid hormone acts to increase serum calcium and decrease serum phosphorus?
1) Increased calcium release from bone
2) Decreases phosphorus resorption by kidneys, thus excreting more phosphorus
3) Increases activity of Vit D by accelerating formation of active form
4) Increased calcium absorption from gut and distal renal tubules
What produces parathyroid-related protein (PTH-rP)? What does it do?
Similar actions as PTH and is abnormally produced by some neoplastic cells
What produces calcitonin and when is it produced?
Thyroid parafollicular cells (C cells) in response to hypercalcemia
What is the function of calcitonin?
Acts to decrease calcium and phosphorus by inhibiting PTH-stimulated bone resorption and renal tubular resorption of calcium and phosphorus
What are the 2 locations where Vitamin D is hydroxylated?
Hydroxylation to the active form occurs first in the liver, then in the kidney under PTH influence
What is the overall effect of metabolically active vitamin D? What are 2 ways vitamin D accomplishes this?
Acts to increase serum calcium and phosphorus
1) Increases GI calcium and phosphorus absorption from the gut
2) May facilitate PTH action on bone
How much of the total calcium is free ionized calcium? Protein bound?
50%-free ionized calcium
45%-protein bound calcium
What is the biologically active form of calcium?
Free ionized calcium
What are the 3 different fractions of calcium?
1) Free ionized calcium
2) Protein bound calcium
3) Complexed calcium
What fraction of calcium is hormonally regulated?
Free ionized calcium
What are the effects of hypercalcemia on free ionized calcium? Severe hypocalcemia?
Hypercalcemia almost always increases free ionized calcium
Severe hypocalcemia (<6.5) almost always decreases free ionized calcium
How does acidosis affect calcium levels?
Acidosis increases free ionized calcium, alkalosis decreases it
What are protein bound calcium bound to?
Anionic proteins (primarily albumin)
True or false. Decrease in albumin can decreases total protein.
True
What is the general cause of hypercalcemia?
Results from imbalance of calcium release from bones, excreted by the kidney and absorbed from the GI tract.
What is primary hyperparathyroidism?
Increased PTH due to neoplasia or idiopathic
How can you diagnose primary hyperparathyroidism?
Measure PTH levels they will be increased
Increased calcium
Decreased phosphorus
What lesions may develop from primary hyperparathyroidism?
Soft-tissue mineralization
Bone lesions
Renal failure
What is the most common cause of hypercalcemia?
Hypercalcemia of malignancy
What are 3 tumors that hypercalcemia of malignancy is usually associated with?
1) Lymphoma
2) Apocrine adenocarcinomas of the anal sac
3) Multiple myeloma
What will you see in blood work in a dog with hypercalcemia of malignancy?
Low PTH
High PTHrp (can be measured in dogs)
High calcium levels
Phosphorus=low to normal (can become increased w/ renal disease)
What are 5 common causes of hypercalcemia?
1) Primary hyperparathyroidism
2) Pseudohyperparathyroidism
3) Renal failure (most common in horses)
4) Hypoadrenocorticism
5) Vitamin D toxicity
What is the only cause of hypercalcemia that will have high PTH?
Primary hyperparathyroidism
What is one of the most common causes of hypercalcemia in equine?
Renal failure
True or false. Hypercalcemia is common in dogs and cats with renal failure.
False, hypocalcemia is more common and hyperphosphatemia
What is the most common cause of hypocalcemia?
Hypoalbuminemia
-Ionized calcium will be in normal range
What are 10 causes of hypocalcemia?
1) Hypoalbuminemia
2) Chronic/acute renal failure and renal secondary hyperparathyroidism
3) Pregnancy, parturient, or lactational hypocalcemia
4) rimary hypoparathyroidism
5) Hypomagnesemic tetany
6) Nutritional secondary hyperparathyroidism
7) Uptake of calcium into tissues
8) Precipitation of calcium into calcium oxalate crystals w/ ethylene glycol toxicity
9) Decreased intake
10) Blister beetle toxicity
Why does chronic/acute renal failure cause hypocalcemia?
Because decreased GFR increases phosphorus resulting in decreased calcium bc of inverse relationship and decreased Vit D activation
What is the pathogenesis of secondary renal hyperparathyroidism?
Decreased GFR--> increased phosphorus---> decreasd calcium---> increased PTH but there's decreased Vit D activation and decreased responsiveness to PTH so calcium can't increase
What is milk fever in cattle?
Parturient hypocalcemia in cattle- demand is greater than intake/ability to respond
May also be hypophosphatemic
How does hypomagnesemic tetany cause hypocalcemia?
Results in decreased PTH activity leading to hypocalcemia
What is the pathogenesis of nutritional secondary hyperparathyroidism?
Dietary excess of phosphorus (all meat diets) and/or relative or absolute calcium deficiency leads to a low dietary calcium: phosphorus ratio---> increased PTH
What are 2 causes of uptake of calcium in to tissues?
1) Massive tissue degeneration/ acute tumor lysis
2) Acute pancreatitis
What causes blister beetle toxicity?
Blister beetles are bailed with hay and ingested by horses
-Also called cantharidiasis in horses
How does insulin affect phosphorus levels?
Insulin causes phosphorus to shift into the cells
What is the most common cause of hyperphosphatemia?
Decreased urinary excretion with decreased GFR (except in horses!!!)
What are 6 causes of hyperphosphatemia?
1) Decreased excretion
2) Hypoparathyroidism
3) Increased intestinal absorption
4) Phosphate release from cells
5) Osteolytic bone lesion
6) Young, growing animal if using ranges for adults
What are 5 causes of hypophosphatemia (not that common)?
1) Increased urinary loss
2) Decreased intestinal absorption
3) Intracellular phosphate shift
4) Postparturient paresis or eclampsia
5) Equine renal failure w/ hypercalcemia
What is grass tetany?
Cattle on lush, green pasture with high potassium and low magnesium content-K+ blocks normal magnesium absorption in rumen
Why are calves commonly magnesium deficient?
Milk is low in magnesium
What are 3 causes of hypomagnesemia?
1) Decreased intake (most common)
2) Increased loss
3) Hypoproteinemia
What are 4 causes of hypermagnesemia?
1) Decreased renal excretion
2) Hemolysis
3) Excess oral drugs (such as antacids) w/ Mg2+
4) Milk fever
-Increased PTH may lead to increased renal resorption of Mg2+