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Clinical Pathology > Calcium, Phosphorus, Magnesium, and their Regulatory Hormones > Flashcards

Calcium, Phosphorus, Magnesium, and their Regulatory Hormones Flashcards

1
Q

Is Ca in body fluids ionized or not?

A

Ionized

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2
Q

What are the 3 major fractions of total calcium?

A

fCa
Anion bound: anionic protein
Anion bound: nonprotein anion

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3
Q

Describe fCa

A

About 50%
Free ions
Hormonally regulated and contributes to pathologic states

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4
Q

Describe anion bound: anionic protein

A

About 40-45%
Negatively charges sites on proteins
Changes in blood pH alter binding

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5
Q

Describe anion bound: nonprotein anion

A

5-10%

Citrates, PO4, lactate, and other small diffusible anions

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6
Q

What are major factors that determine serum [tCa]?

A

Age
Protein concentration
Intestinal absorption

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7
Q

What causes bone resorption/deposition of tCa?

A

PTH
Vitamin D
Calcitonin

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8
Q

What are the mechanisms of hypercalcemia?

A

Increased Ca mobilization from bone or absorption in intestine
Decreased urinary excretion
Increased protein-bound Ca
Other or unknown mechanisms

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9
Q

What are causes of increased bone mobilization or intestinal absorption associated with hypercalcemia?

A

Increased PTH (Primary hyperparathyroidism, Humoral hypercalcemia of malignancy)
Increased vitamin D activity
Neoplasia in bone

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10
Q

What are causes of decreased urinary excretion associated with hypercalcemia?

A

Renal insufficiency or failure (acute or chronic renal diseases)
Hypoadrenocorticism
Ruptured urinary bladder in foals
Thiazide diuretics

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11
Q

What are mechanisms of hypocalcemia?

A

Hypoalbuminic hypocalcemia
Decreased PTH activity
Inadequate Ca mobilization from bone or absorption from intestine
Excess urinary excretion
Ca binding with diffusible anions
Ca deposition during fraction healing
Other or unknown mechanisms (acute pancreatitis)

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12
Q

What are causes of decreased PTH activity associated with hypocalcemia?

A

Primary hypoparathyroidism
Pseudo-hypoparathyroidism
Hypomagnesemia

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13
Q

What are causes of inadequate Ca mobilization from bone or intestinal absorption associated with hypocalcemia?

A

Hypovitaminosis D (chronic renal disease and failure)
Vitamin D receptor defect rickets
Exocrine pancreatic insufficiency in dogs
Pregnancy, parturient, lactational
Hypercalcitonism
Nutritional
Oxalate toxicity

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14
Q

What are causes of excess renal glycol toxicity associated with hypocalcemia?

A

Ethylene glycol toxicity
Metabolic alkalosis
Furosemide treatment

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15
Q

What is [fCa] tightly controlled by?

A

Hormones

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16
Q

What are abnormal concentrations of fCa caused by?

A

Hypocalcemia caused by hypoproteinemia or hypoalbuminemia
Hypercalcemia in renal failure or multiple myeloma
Hypocalcemia in urinary obstruction in cats
Chronic renal failure in dogs
Hyperthyroidism in cats
Endurace sports in horses
Blood transfusion
Acidotic calves

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17
Q

How can acid-base status effect [fCa]?

A

Change in blood pH affects binding to proteins and other anions
Organic acidosis
Blood pH also affects [PTH]

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18
Q

What are the routine assays of [tCa]?

A

Free
Protein bound
Bound to anions other than proteins

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19
Q

How does the body regulate [fCa]?

A

Through actions of several hormones

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20
Q

What can make serum [fCa] values inaccurate?

A

When blood is not handled properly

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21
Q

What are protein/albumin like in hypocalcemia? Normal [fCa] regulation?

A

Decreased protein/albumin: decreased bound

WRI

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22
Q

What does it mean if protein concentrations are WRI with hypocalcemia?

A

Low [tCa] typically indicated decreased [fCa]
Inadequate PTH or vitamin D activities
Bound Ca is unchanged

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23
Q

Why may the severity of decreased [fCa] not be evident from [tCa]?

A

Bound Ca is increased

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24
Q

What can excess heparin in a sample cause?

A

Falsely decreased [fCa] because of binding to heparin

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25
Q

What does normocalcemia and hypoproteinemia suggest?

A

Increased [fCa]

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26
Q

What is [fCa] affected by?

A

Altered plasma pH and nonprotein anions

27
Q

What are the different forms of inorganic phosphorus that can be present?

A

pH 7.4: H2PO4 and HPO4 are in a 1:4 ratio
10% are bound to cationic proteins
35% are bound to nonprotein cations
55% is free

28
Q

What are the major factors that determine serum [Pi]?

A 
Renal clearance of PO4
Absorption of PO4 in intestines
Resorption from bone
Shifting of PO4 between ICF and ECF
Animal age
29
Q

What are mechanisms of hyperphosphatemia?

A 
Decreased urinary PO4 excretion
Increased PO4 absorption from intestine
Shift of PO4 from ICF to ECF
Other/unknown mechanisms
Pseud-hyperphosphatemia
30
Q

What is a cause of decreased urinary PO4 excretion associated with hyperphosphatemia?

A

Decreased GFR

31
Q

What are mechanisms of hypophosphatemia?

A 
Increased urinary PO4 excretion
Decreased intestinal PO4 absorption
Shift of PO4 from ECF to ICF
Defective mobilization of PO4 from bone
Other/unknown
Pseud-hypophosphatemia
32
Q

What is a cause of decreased intestinal PO4 absorption?

A

Prolonged anorexia or PO4 deficient diet

33
Q

What is an unknown mechanism of hypophosphatemia?

A

Equine renal disease

34
Q

What are the 3 major fractions of total magnesium?

A

Free fMg: 55%
Bound to negatively charged sites in proteins: 30%
Bound to anions (citrate and PO4): 15%

35
Q

Where is magnesium located?

A

Bones (60%), soft tissues (38%), and ECF (1-2%)

36
Q

In what species are erythrocytes not rich in magnesium?

A

Cattle

37
Q

What are the major factors that determine [tMg]?

A

Hypoproteinemia (decreases bound Mg)
Absorption in GI tract
Excretion

38
Q

What hormones regulate [tMg]?

A

ADH, PTH, Glucagon, Calcitonin, and B-adrenergic agonists increase renal absorption
PTH increases intestinal absorption and tubular resorption
Administration of 1,25 DHCC decreases PTH activity which decreases [tMg]
Thyroxin and aldosterone increase urine and fecal excretion–> decreased [tMg]

39
Q

What are causes of increased [tMg]?

A

Decreased urinary excretion
Shift of Mg from ICF to ECF
Increased intestinal absorption
Other mechanisms (milk fever, postpartum cattle, IV infusion)

40
Q

What are causes of decreased [tMg]?

A

Hypoproteinemia
Inadequate ruminal or intestinal absorption
Excess urinary excretion
Other/unknown mechanisms

41
Q

What are causes of inadequate ruminal or intestinal absorption associated with decreased [tMg]?

A

Prolonged anorexia/poor feed intake

Grass tetany in cattle

42
Q

What are causes of excess urinary excretion associated with decreased [tMg]?

A

Osmotic diuresis

Ketonuria

43
Q

What are disorders of tMg homesostasis disorders of?

A

May be disorders of fMg homeostasis or disorders affecting anions that bind fMg

44
Q

What is PTH?

A

Polypeptide hormone produced by parathyroid glands in response to decreased [fCa]

45
Q

What inhibits the synthesis of PTH?

A

Vitamin D and increased [fCa]

46
Q

What are the primary target organs of PTH?

A

Increased Ca absorption by intestine and increased Ca resorption in renal tubules
Promotes mobilization of Ca and PO4 from bine
Promotes renal excretion of PO4

47
Q

What is the net effect of PTH?

A

Increase plasma [fCa] and decrease [Pi]

48
Q

What is the assay for [iPTH]?

A

React with preproparathyroid hormone, protparathyroid hormone, intact PTH, or PTH fragment

49
Q

What are causes of increased [iPTH]?

A

Neoplastic parathyroid gland

Increased PTH production by hyperplastic parathyroid glands

50
Q

What are causes of decreased [iPTH]?

A

Decreased PTH production due to damaged or removed parathyroid glands
Decreased PTH production to inhibition

51
Q

What are the physiologic processes of PTHrp?

A

Produced by many cells in fetuses and adults, but plasma [PTHrp] is very low in healthy adults
Promotes Ca balance and modulates cartilage bone and development in fetus

52
Q

What are causes of increased PTHrp?

A

Neoplasms, especially lymphomas and carcinomas

Can result in hypercalcemia

53
Q

What is the formation of vitamin D?

A

Cholesterol –> 7-dehydrocholesterol –> UV light –> cholecaliferol (vitamine D3)

54
Q

What do hepatocytes do to cholecaliferol?

A

Turn it into 25-HCC

55
Q

What do renal tubular cells do to 25-HCC?

A

Turn it into 1,25-DHCC (calcitriol)

56
Q

What is the most potent biologic activity of vitamin D?

A

Calcitriol > 25-HCC > cholecalcifirol

57
Q

What is the major factor controlling 1,25-DHCC?

A

[Ca]

58
Q

What are the actions of vitamin D in dogs, cats, and cattle?

A

Intestinal uptake of Ca
Ca and PO4 liberation from bone by stimulating osteoclastic activity
Resorption of fCa by proximal renal tubules
Inhibits PTH synthesis

59
Q

What is the net effect of vitamin D?

A

Promotes hypercalcemia

60
Q

What are causes of increased Vitamin D?

A 
Granulomatous disease
Primary hyperparathyroidism
Lymphoma and other neoplasma
Vitamin D intoxication
Vitamin D receptor rickets
Bovine parturient paresis
61
Q

What are causes of decreased vitamin D?

A 
Renal failure
Hyperphosphatemia
Hypomagnesemia
Hypoparathyroidism
Pseudo-hypoparathyroidism
Hypecalcemia neoplasms
Protein-losing enteropathies
Vitamin D deficient diet
62
Q

What is calcitonin produced by?

A

Thyroid C cells

63
Q

What are the actions of calcitonin?

A

Inhibits osteoclastic activity
Inhibits renal tubular resorption of Ca and PO4
Net effect: decrease [fCa] and [Pi]

64
Q

What are causes of increased calcitonin?

A

Medullary thyroid carcinoma

Nonthyroid cancer

Clinical Pathology (16 decks)

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