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Calcium is distributed throughout the body, primarily extracellularly but also intracellularly. Intracellular calcium is maintained at very low levels (10,000 fold less than in serum); 99% of calcium is found in bone as Extracellular Matrix, in the form of hydroxyapatite.
Calcium is distributed throughout the body, primarily extracellularly but also intracellularly. Intracellular calcium is maintained at very low levels (10,000 fold less than in serum); 99% of calcium is found in bone as Extracellular Matrix, in the form of hydroxyapatite.
In the blood, calcium exists as 50% ionised, 40% protein-bound and 10% complexed with anions such as citrate and phosphate. Only ionised calcium is biologically active in bone formation, neuromuscular activity, cellular biochemical processes and blood coagulation. Factors governing the total plasma concentration are complex and include interaction with other chemical moieties, proteins and hormones. Calcium, phosphorus and albumin metabolism are interdependent. In the dog serum calcium values may be adjusted to take account of low albumin levels. References: [[NationWide Laboratories]]
Within the serum, 55% of the calcium is ionised - this is the biologically active form, and 10% of the calcium is in complexes such as citrate and phosphate. Together with the ionised form, this constitutes '''ultrafilterable calcium'''. 35% of the calcium is also bound to plasma proteins.
Within the serum, 55% of the calcium is ionised - this is the biologically active form, and 10% of the calcium is in complexes such as citrate and phosphate. Together with the ionised form, this constitutes '''ultrafilterable calcium'''. 35% of the calcium is also bound to plasma proteins.
There are also slight (insignificant) effects on the kidney and [[Alimentary System Overview - Anatomy & Physiology|gastrointestinal tract]].
There are also slight (insignificant) effects on the kidney and [[Alimentary System Overview - Anatomy & Physiology|gastrointestinal tract]].
== Small Animals ==
Small animals. Homeostatic mechanisms in small animals result in tight control of plasma calcium levels. Elevated and decreased levels are generally significant.
=== Causes of hypercalcaemia ===
* Primary hyperparathyroidism (primary parathyroid hyperplasia/neoplasia)
* Hypoadrenocorticism
* Cholecalciferol rodenticides
* Primary renal failure (CRF, ARF, familial)
* Hypercalcaemia of malignancy (malignant tumours including lymphoid tumours, myeloproliferative disease and some carcinomas) producing parathyroid like hormone
* Granulomatous disease
=== Causes of severe hypocalcaemia ===
* Eclampsia
* Primary hypoparathyroidism
* Ethylene glycol poisoning
=== Causes of mild to moderate hypocalcaemia ===
* Hypoalbuminaemia
* Acute pancreatitis
* Renal secondary hyperparathyroidism
* Nutritional secondary hyperparathyroidism
* Acute renal failure (especially post renal obstruction)
* Post thyroidectomy (cats)
=== Complementary tests ===
PTH assay, serum electrolytes and ACTH stimulation test, urea and creatinine, lipase, albumin and phosphorus. See section on calcium disorders.
References: [[NationWide Laboratories]]
== Equine ==
Homeostatic mechanisms are efficient in maintaining tight control of plasma calcium levels. Elevated and decreased levels are therefore significant. Slight increases may occur in hot weather and decreases following increased carbohydrate utilisation.
=== Causes of hypercalcaemia ===
* Renal failure (chronic)
* Intravenous calcium
* Hypervitaminosis D – supplementation
=== Causes of hypocalcaemia ===
* Hypoalbuminaemia
* Enterocolitis in adults
* Sepsis (foals)
* Lactation and transport tetany
* Acute renal failure
* Hypoparathyroidism
=== Consequences of hypocalcaemia ===
* Synchronous diaphragmatic flutter in performance horses
* Uterine inertia in full term pregnant mares
=== Complementary tests ===
Albumin and phosphorous determinations should always be included. Differentiation of diseases causing abnormal calcium levels can be facilitated by the determination of fractional clearance of calcium in blood and urine.
References: [[NationWide Laboratories]]
==Calcium Homeostasis in the Rabbit==
==Calcium Homeostasis in the Rabbit==
Cheeke, R. (2010) '''Comparative Animal Nutrition and Metabolism''' ''CABI''
Cheeke, R. (2010) '''Comparative Animal Nutrition and Metabolism''' ''CABI''
[[NationWide Laboratories]]