Disorders of Calcium, Phosphate & Magnesium Flashcards
What is Ca used for in the body?
Muscle contraction Neuronal excitation Enzyme activity Blood clotting Bone mineral
What is phosphate used for in the body?
ATP intracellular signalling cellular metabolic processes e.g. glycolysis structural component of DNA Membrane phospholipids
What is magnesium used for in the body?
co factor for ATP neuromuscular excitability enzymatic function regulate ion channels structural component of bone matrix
What are the indications for a contaminated serum sample?
↑ K+ ↓ Ca ↓ P ↓ AKA ↓ Mg
What is the total plasma Ca made up of?
Ionised Ca
Bound Ca
Complexed Ca
What is ionised Ca?
Physiologically active part of Ca highest proportion in total Ca binds to negatively charged sites Cellular effects Regulates PTH
What is bound Ca?
Physiologically inactive part of Ca
main protein that binds to albumin
What is complex Ca?
salts
e.g. calcium phosphate
What is the adjusted calcium?
calcium values corrected for changes in albumin
total Ca + (40-Alb) x 0.025
How does pH affect Ca levels?
H+ and Ca compete for albumin binding sites
Acidosis = reduced Ca-Albumin and vice versa
More ionised Ca, less bound Ca
What is the consequence of a patient that is hypocalcaemic with alkalosis?
tetany - involuntary contraction of muscles
How is Vit D activated?
Precursor taken in via diet → converted into another precursor by UV light → kidney converts to active form of Vit D
What is measured in the lab when looking at levels of Vit D?
precursor 25(OH)D3 longer half life so easier to measure
What environmental factors affect Vit D absorption?
Endogenous: skin colour aging Exogenous: ozone sunscreen/clothes latitude/season/time of day diet/supplements
What are risk factors for low Vit D?
age
BMI
body fat
What are the causes of hypocalcaemia?
Hypoproteinaemia Vit D deficiency Hypoparathyroidism Low Ca Pseudohypoparathyroidism Artefactual cause
Low Ca and high PTH, is this hypoparathyroidism or Vit D deficiency?
Vit D deficiency
Low Ca, high P and low PTH, is this hypoparathyroidism or Vit D deficiency?
Hypoparathyroidism
What are the causes of hypercalcaemia?
Hyperparathyroidism
Malignancy - bone or PT
Drugs
Vit D excess
What are the symptoms of hypercalcaemia?
Bones - bone pain
Stones - crystallisation of Ca in the kidney
Moans - Abdo pain
Grones - low mood/depression
High calcium, high PTH and low phosphate, is this hyperparathyroidism or bone metastases?
Primary hyperparathyroidism
High calcium and low PTH, is this hyperparathyroidism or bone metastases?
bone metastases
What are the causes of phosphate deficiency?
Hyperparathyroidism
Excess losses - renal tubular damage, GI, diabetes
Poor intake
What are the symptoms of phosphate and magnesium deficiency?
Haemolysis Thrombocytopenia Poor granulocyte function Severe muscle weakness Respiratory muscle failure Rhabdomyolysis - the destruction of striated muscle cells Confusion Irritability Coma - due to a metabolic encephalopathy due to phosphate deficiency Renal dysfunction
Where is the main site of Mg handling?
Kidney - loop of Henle and distil convoluted tubule - important in drugs e.g. lithium
What are the causes of hypomagnesaemia?
Renal e.g. acute tubular necrosis, hypercalcaemic states
Drugs e.g. gentamicin, cisplatin
GI tract e.g. malnutrition
What effect does Mg have on cells?
Involved in mitochondrial respiration/phosphorylation
ATP activity - only activated when bound to a Mg
Required for DNA synthesis
What effect does low Mg have on the endocrine system?
impaired PTH release
PTH resistance in bone
What effect does low Mg have on the cardiovascular system?
Cardiac irritability/reduced contraction
What effect does low Mg have on the central nervous system?
Hyperreflexia Tetany - intermittent muscular spasms Ataxia - loss of control of full body movements Vetigo Psychosis/Deprssion
What effect does low Mg have on the muscles?
Weakness
Muscle fibrillation
Myopathic EMG
