Hormones In Calcium And Bone Metabolism Flashcards
A normal adult body contains about
1kg of Ca
70kg indiv = 1,000g Ca
1% in soft tissues and extracellular fluids
Approx. 99% is present in the skeleton as
Hydroxyapatite (Ca10(PO4)6(OH)2)
A normal diet provides how much Ca per day
20-2000mg with an ave of 1000mg Ca per day
Approx. How much is absorbed, in majority in ileum bcs of its large absorptive surface
300g
Secreted into the intestinal tract in bile, pancreatic juice and intestinal secretions so that the net absorption of Ca equals about
175mg/day
The conc of Ca in plasma ave about
9.4mg/dL
Normally varying between 9 and 10 mg/dL
This is equivalent to about 2.4mmol of Ca per liter
The Ca present in plasma is present in 3 forms:
(1) 40% (1mmol/L) of Ca is combined w the plasma CHONs = nondiffusible form thru capillary mem
(2) 10% Ca (0.2 mmol/L) diffusible thru the cap mem but is combined w other subs of the plasma and interstitial fluids (citrate and phosphate) Not ionized
(3) 50% Ca is both diffusible and ionized (1.2 mmol/L or 2.4 mEq/L) divalent
The skeleton also serves as a storage depot for phosphorus and contains about how much of the total body phosphorus?
80%
The plasma conc of total Ca (ionized and non) is about
10mg/dL
Equivalent to 5mEq/L or 2.5mmol/L
Ca is present in plasma as
A. Ionized or free (45%)
B. Complexed w HPO4^2-, HCO3- or citrate ion (10%)
C. Bound to CHON (45%)
Sum of ionized and complexes Ca constitutes the diffusible fraction (55%) of Ca
The protein-bound form constitutes the nondiffusible fraction (45%)
Regulates the serum-ionized Ca conc
PTH, Calcitonin, Vit D
Distribution (mmol/L) of Ca in normal human plasma
Total diffusible
Ionized Ca
Complexed to HCO3, Citrate etc
Total diffusible = 1.34
Ionized Ca = 1.18
Complexed to HCO3, Citrate etc = 0.16
Total nondiffusible (protein bound)
Bound to albumin
Bound to globulin
Total nondiffusible (protein bound) = 1.16 Bound to albumin = 0.92 Bound to globulin = 0.24
Total plasma Ca
2.50mmol/L
This represents the Ca pool that is not readily exchangeable and it is not available for rapid mobilization
Larger Ca pool
This represents the Ca pool that is readily exchangeable bcs it’s in physiochemical equilibrium w the ECF
The pool consists of Ca phosphate salts and provides an immediate reserve for sudden decreases in bld Ca2+
Smaller Ca pool
When the pH of ECF becomes more acidic, there is a
Relative increase in H2PO4 and decrease in HPO4-
The ave total quantity of inorganic phosphorus represented by both phosphate ions is
4mg/dL
Varying between normal limits of 3-4mg/dL in adults and 4-5mg/dL in children
Total body phosphorus is
500-800g (16.1-25.8 mol), 85-90% of wc is in the skeleton
Total plasma phosphorus is abt
12 mg/dL
with 2/3 of total in organic compounds and remaining inorganic phosphorus mostly in PO4^3-, HPO4^2- and H2PO4-
When Ca intake is high, 1,25-dihydroxycholecalciferol levels fall bcs of
Increased plasma Ca
Relationship of Ca absorption and Ca intake
Inverse
Increase absorption
Increase CHON diet in adults