calcium phosphate and magnesium Flashcards
what is the biochemistry of calcium?
it is a divalent cation Ca2+ unless in EDTA that is physiologically important and structurally important. A patient who has low albumin will have the same ionised and complexed calcium but low protein bound calcium
why is calcium structurally important?
it is a component of hydroxyapatite - Ca10(PO4)6(OH)2 which is the main mineral in bones
why is calcium physiologically important?
neuronal excitation, muscle contraction, enzymatic activity such as the Na/K ATPase and hexokinase and for blood clotting
what are the three areas that calcium is distributed?
99% of it is in the bone, 1% intracellular and 0.1% extracellular
what is a normal range of plasma calcium and how is this comprised?
2.2-2.6mmol/L
it is arranged into complexed anions for 9%, 41% bound to plasma proteins and 50% ionised free calcium ions
the ionised free calcium ions can be made by the bound and complexed and in turn can make these
what is considered a medical emergency with calcium?
when the calcium is <1.6 or >3.5mmol/L and requires treatment
what is the total calcium?
ionised calcium+complexed calcium+ bound calcium
what is the adjusted calcium?
calcium values can be adjusted and corrected for changes in albumin - the adjusted calcium is the total calcium + ((40-alb)x0.025)
the reference range is 2.2-2.6mmol/L
and the equation is not valid if the albumin is less than 20g/L
what is the recommended measure of calcium?
a point of care blood gas analyser to measure the calcium ions
what will happen if the albumin or other protein binders drop?
the protein bound calcium will drop but the ionised or complexed will remain the same and therefore the total calcium will drop
total calcium increases as albumin increases
what is the biochemistry of phosphate?
it is PO43- and is physiologically and structurally important. A deficiency can be fatal. It is predominantly intracellular
why is phosphate physiologically important?
ATP fuel, intracellular signalling and cellular metabolic processes such as glycolysis
why is phosphate structurally important?
for membrane phospholipids, component of hydroxyapatite and forms the backbone of DNA
what is the structure of phosphate?
it is a central P with a double bond to one O, and three single bonds
what is the distribution of phosphate in the body?
the total body phosphorus is 23mol or around 700g and this is distributed in 85% bone, 14% intracellular and 1% extracellular
what do the distributed forms of phosphorus make?
they make phosphorus in the blood of which 70% in organic and covalently bound such as in phospholipids and 30% in in the inorganic form as phosphate with a ratio of 4:1 of HPO4 2-: H2PO4-
what is the reference range for phosphate?
0.8-1.5mmol/L
in terms of these ions, what is homeostasis?
it is balancing the internal environment and responding to changes in stimuli - this involves intake, excretion and loss and tissue redistribution and storage
how is calcium levels maintained?
it is tightly regulated in the reference range and there are two key controlling factors - these are parathyroid hormones and Vit D and metabolites. The calcium homeostasis is a direct result of the balance of GI uptake, bone storage and renal clearance
what is the main function of PTH?
to increase serum calcium and to decrease serum phosphate
how does the role of PTH relate to the process?
high calcium will inhibit PTH released by negative feedback via the CaSR and high phosphate to a lesser ectent will stimulate PTH along with low calcium
how does PTH work?
parathyroid glands (where magnesium also works) secretes PTH in states of low calcium. This PTH acts on the bone and drives resorption of Ca and PO4. It also acts on the kidneys to increase resabsorption of Ca from the filtrate but increase excretion of PO4. It also acts on the kidney to increase the conversion of Vit D to its active form which increases Ca and PO4 absorption from the gut
what is vitamin D for?
it is for providing enough energy. It is for bone health and therefore recently there has been a recent resurgence in rickets due to around 30% of children in the UK being insufficient in Vit D
what are the reference ranges for vit D?
25-OH Vit D :
<75nmol/L is insufficient
>75nmol/L is normal
>500nmol/L is toxicity