Calcium, Phosphate & Magnesium Homeostasis Flashcards by Imaani Goodier

what is the physiological importance of calcium?

important for

blood clotting
muscle contraction
neuronal excitation
enzyme activity (NA/K ATPase, hexokinase)

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what is the structural importance of calcium

Hydroxyapatite Ca₁₀(PO₄)₆(OH)₂ is the predominant mineral in bone

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what does the total Ca equal

Total Ca = Ionised Ca + Bound Ca + Complexed Ca

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what is the total body calcium split into?

Bone - 99%
intracellular - 1%
Extracellular - 0.1%

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At what values does lack or excess of calcium considered a medical emergency

calcium < 1.6 or >3.5 mmol/l

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What is the adjusted Calcium EQUAL

Adjusted Ca = Total Ca + [ (40 - Alb) x 0.025 ]

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what is the reference range for adjusted calcium

2.2 -2.6 mmol/l

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what is the physiological importance of phosphate

The P in ATP - our fuel
intracellular signalling
cellular metabolic processes e.g. glycolysis

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what is the structural importance of phosphate

backbone of DNA
component of hydroxyapatite Ca₁₀(PO₄)₆(OH)₂
membrane phospholipids

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what is the distribution of total body phosphorus - 700g?

bone - 85%
intracellular - 14%
extracellular -1%

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what is the distribution phosphorous in the blood?

Organic form (covalently bound) - 70%

inorganic form as phosphate - 30%

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what is the normal range for phosphate in adults

0.8 -1.5mmol/l

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what are the two key controlling factors of homeostasis of calcium?

parathyroid hormone (PTH)

2. Vitamin D and metabolites

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calcium homeostasis is the result of a balance of which processes?

GI uptake
Bone Storage
Renal Clearance

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what is the function of PTH?

PTH acts on bone to drive resorption of Ca and PO4
PTH acts on kidneys to increase reabsorption of Ca from the filtrate but increase excretion of PO4
PTH also acts on kidneys to increase conversion of vitamin D to its active form which increases Ca and PO4 absorption from the gut

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what is the net effect of PTH?

Increase Serum Calcium

- Decrease Serum Phosphate

what effect does calcium levels have on PTH?

High calcium inhibits release by negative feedback

low calcium stimulates PTH release

what factors affect your vitamin D level?

the season
latitude/climate
clothing
use of sunscreen
time spent indoors/outdoors
skin tone
Age
Diet
Body fat and BMI
Malabsorption

what are the other regulators of calcium and phosphate homeostasis

PTH
Vitamin D
FGF23
Calcitonin
Oestrogen

what is the role of FGS23 in the regulation of calcium and phosphate homeostasis?

Increases renal phosphate excretion

what is the role of calcitonin in regulating calcium and phosphate homeostasis?

Opposes the effect of PTH by acting on osteoclasts to inhibit bone resorption
function is usually insignificant in the regulation of normal calcium homeostasis

what are the common causes of hypocalcaemia?

Vitamin D deficiency
Inadequate dietary calcium intake
Hypoalbuminaemia
High phosphate
Hypoparathyroidism
EDTA contamination
Citrate Contamination

what are the signs and symptoms of hypocalcaemia?

Tetany
Paraesthesia in the extremities
Cramps
Convulsions
Psychosis

what are the signs and symptoms of hypercalcaemia?

Stones
- Renal stones due to hypercalciuria causing renal colic
Bone 
pain and osteoporosis 
Moans
- lethargy, fatigue, depression
Groans 
- Abdominal pain, constipation, nausea, vomitting

what are the causes of phosphate deficiency

Low intake - malnutrition - Malabsorption - Alcoholism Excess losses - Hyperparathyroidism - Renal tubular damage - Diarrhoea ECF/ICF Redistribution - Refeeding syndrome - Alkalosis

what are the signs/symptoms of phosphate deficiency

- Severe muscle weakness, respiratory muscle failure and rhabdomyolysis - Haemolysis, thrombocytopenia and poor granulocyte function - convulsions, coma, death - rickets/osteomalacia

what are the common causes of high phosphate?

Renal failure: acute kidney injury or chronic kidney disease Hypothyroidism Spurious - Haemolysis - Delayed separation of sample - Assay interference

what is the physiological importance of magnesium?

- Cofactor for ATP - our fuel - Neuromuscular excitability - Enzymatic function - regulates ion channels

what is the structural importance of magnesium?

comprises 0.5 - 1% of bone matrix

what is the total body distribution of magnesium (-1.1 mol)

Bone - 54% Intracellular (45%) Extracellular (1%)

what is the distribution of magnesium in the blood?

ionised free Mg2+ (60%) bound to plasma proteins (25%) complexed to anions (15%)

what predominantly controls homeostasis of magnesium

by the kidneys

what are the causes of magnesium depletion?

- Inadequate intake - malnutrition - malabsorption - total parenteral nutrition - Renal loss - Drugs - antibiotics - chemotherapy - diuretics - FK506 - GI Loss - Diarrhoea - PPIs - Redistribution into cells

signs and symptoms of magnesium depletion?

- Neuromuscular hyperexcitability, muscle weakness - CNS - depression, psychosis - Cardiovascular - ECG changes - GI - nausea and anorexia - Biochemical consequences

what are the causes of hypermagnesaemia?

usually Iatrogenic - cardiac surgery - Pre-eclampsia