Calcium, Phosphorus, Magnesium, and their Regulatory Hormones Flashcards by Anika Eidson

Is Ca in body fluids ionized or not?

Ionized

How well did you know this?

Not at all

Perfectly

What are the 3 major fractions of total calcium?

fCa
Anion bound: anionic protein
Anion bound: nonprotein anion

How well did you know this?

Not at all

Perfectly

Describe fCa

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

How well did you know this?

Not at all

Perfectly

Describe anion bound: anionic protein

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

How well did you know this?

Not at all

Perfectly

Describe anion bound: nonprotein anion

5-10%

Citrates, PO4, lactate, and other small diffusible anions

How well did you know this?

Not at all

Perfectly

What are major factors that determine serum [tCa]?

Age
Protein concentration
Intestinal absorption

How well did you know this?

Not at all

Perfectly

What causes bone resorption/deposition of tCa?

PTH
Vitamin D
Calcitonin

How well did you know this?

Not at all

Perfectly

What are the mechanisms of hypercalcemia?

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

How well did you know this?

Not at all

Perfectly

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

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

How well did you know this?

Not at all

Perfectly

What are causes of decreased urinary excretion associated with hypercalcemia?

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

How well did you know this?

Not at all

Perfectly

What are mechanisms of hypocalcemia?

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)

How well did you know this?

Not at all

Perfectly

What are causes of decreased PTH activity associated with hypocalcemia?

Primary hypoparathyroidism
Pseudo-hypoparathyroidism
Hypomagnesemia

How well did you know this?

Not at all

Perfectly

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

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

How well did you know this?

Not at all

Perfectly

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

Ethylene glycol toxicity
Metabolic alkalosis
Furosemide treatment

How well did you know this?

Not at all

Perfectly

What is [fCa] tightly controlled by?

Hormones

How well did you know this?

Not at all

Perfectly

What are abnormal concentrations of fCa caused by?

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

How well did you know this?

Not at all

Perfectly

How can acid-base status effect [fCa]?

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

How well did you know this?

Not at all

Perfectly

What are the routine assays of [tCa]?

Free
Protein bound
Bound to anions other than proteins

How well did you know this?

Not at all

Perfectly

How does the body regulate [fCa]?

Through actions of several hormones

How well did you know this?

Not at all

Perfectly

What can make serum [fCa] values inaccurate?

When blood is not handled properly

How well did you know this?

Not at all

Perfectly

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

Decreased protein/albumin: decreased bound

WRI

How well did you know this?

Not at all

Perfectly

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

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

How well did you know this?

Not at all

Perfectly

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

Bound Ca is increased

How well did you know this?

Not at all

Perfectly

What can excess heparin in a sample cause?

Falsely decreased [fCa] because of binding to heparin

How well did you know this?

Not at all

Perfectly

What does normocalcemia and hypoproteinemia suggest?

Increased [fCa]

What is [fCa] affected by?

Altered plasma pH and nonprotein anions

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

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

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

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

What are mechanisms of hyperphosphatemia?

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

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

Decreased GFR

What are mechanisms of hypophosphatemia?

``` 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 ```

What is a cause of decreased intestinal PO4 absorption?

Prolonged anorexia or PO4 deficient diet

What is an unknown mechanism of hypophosphatemia?

Equine renal disease

What are the 3 major fractions of total magnesium?

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

Where is magnesium located?

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

In what species are erythrocytes not rich in magnesium?

Cattle

What are the major factors that determine [tMg]?

Hypoproteinemia (decreases bound Mg) Absorption in GI tract Excretion

What hormones regulate [tMg]?

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]

What are causes of increased [tMg]?

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

What are causes of decreased [tMg]?

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

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

Prolonged anorexia/poor feed intake | Grass tetany in cattle

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

Osmotic diuresis | Ketonuria

What are disorders of tMg homesostasis disorders of?

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

What is PTH?

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

What inhibits the synthesis of PTH?

Vitamin D and increased [fCa]

What are the primary target organs of PTH?

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

What is the net effect of PTH?

Increase plasma [fCa] and decrease [Pi]

What is the assay for [iPTH]?

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

What are causes of increased [iPTH]?

Neoplastic parathyroid gland | Increased PTH production by hyperplastic parathyroid glands

What are causes of decreased [iPTH]?

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

What are the physiologic processes of PTHrp?

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

What are causes of increased PTHrp?

Neoplasms, especially lymphomas and carcinomas | Can result in hypercalcemia

What is the formation of vitamin D?

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

What do hepatocytes do to cholecaliferol?

Turn it into 25-HCC

What do renal tubular cells do to 25-HCC?

Turn it into 1,25-DHCC (calcitriol)

What is the most potent biologic activity of vitamin D?

Calcitriol > 25-HCC > cholecalcifirol

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

[Ca]

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

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

What is the net effect of vitamin D?

Promotes hypercalcemia

What are causes of increased Vitamin D?

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

What are causes of decreased vitamin D?

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

What is calcitonin produced by?

Thyroid C cells

What are the actions of calcitonin?

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

What are causes of increased calcitonin?

Medullary thyroid carcinoma | Nonthyroid cancer