Minerals Flashcards
What makes up the total calcium in the body?
- Free calcium makes up about 50%
- Calcium bound to an anionic protein makes up around 40-45%
- Calcium bound to non-protein anions makes up around 5%
Where is PTH secreted from?
It is secreted from chief cells in the parathyroid glands
What stimulates the synthesis of PTH release
It is stimulated by low levels of free calcium or low calcitriol (vitamin D)
What does PTH promote?
It promotoes increased Ca2+ absorption by the intestine and increased calcium mobilisation from bone
What causes increased production of parathyroid hormone?
- primary hyperparathyroidism
- endocrine neoplasia
What produces parathyroid hormone related protein?
a number of neoplasms e.g
* apopcrine anal sac adenocarcinomas
* lymphomas (but only a small proportion)
* squamous cell carcinomas (but only a small proportion)
What type of blood cell is thought to secrete parathyroid hormone related protein?
Macrophages
How is vitamin D formed?
Cholesterol becomes 7-dehydrocholesterol which then goes on to become cholecalciferol
In what kind of diseases is an increase in vitamin D expected?
- Granulomatous diseases
- primary hyperpararthyroidism
What cells synthesise calcitonin?
It is synthesised by thyroid C cells
What is the main function of calcitonin?
acts to reduce the levels of calcium in the blood
What are some ways calcitonin decreases blood calcium levels?
- It inhibits osteoclastic activity in the bone
- It inhibits renal tubular absorption of Ca2+ and PO4
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What is the function of fibroblast growth fcator?
To synthesise osteoblasts and osteocytes
What stimulates the synthesis of fibroblast growth factor?
Calcitriol (vitamin D) and increase PO4
What can cause hypercalcaemia?
Increased moblisation of calcium from bone
* Increased PTH or PTHrP
* Increased vitamin D activity
* Neoplasia in the bone
* Decreased urinary excretion
What can cause hypocalcaemia
- hypoalbuminaemia
- Decreased PTH activity
- Inadequate Calcium mobilisation from the bone
- Excess Urinary excretion of calcium
- Ca2+ binds with diffusable ions
What is hypocalcaemia known as in pregnant cows?
Milk fever
What is nutritional hypocalcaemia?
When they have a vitamin D deficient diet
The Ca2+/ PO4 ratio is therefore lower than desired
What is hyperphosphataemia?
Decreased Urinary PO4 excretion
Phosphate moves from the ICF to the ECF
What are three other mechanisms for Hyperphosphataemia?
- Hyperthyroidism in cats
- Lactic acidosis
- Hyperadrenocorticism in dogs
What can cause Hypophosphataemia?
- Increased Urinary Phosphate excretion
- Decreased Intestinal Phosphate absorption (prolonged anorexaia or a phosphate deficient diet)
- Shifting of phosphate from the ECF to the ICF
How commonly is magnesium measured?
less commonly measured in comparison to calcium and phosphorus
-serum is the preferred sample but heparinised plasma can also be used in some assays
haemolysis or delayed cell separation can also increase magnesium except in cattle
What disorder can result in a decreased total magnesium?
hyperproteinaemia
Where is magnesium absorbed and excreted?
- absorbed in the GI tract
- excreted in the faeces and the kidneys
What can control magnesium?
- 1, 25 DHCC administartion can reduce plasma magnesium
- thyroxine increases excretion of magnesium
- aldosterone promotes increased faecal and urinary excretion of magnesium
What can cause hypermagnesia?
- Decreased urinary excretion
- shift from the ICF to ECF
- Increased PTH (milk fever)
What can cause hypomagnesaemia?
- Hypoproteinaemia
- inadequate ruminal or intestinal resorption of Mg2+ (prolonged or poor feed intake) grass tetany
- excess urinary excretion of Mg2+ (osmotic diuresis)
