Calcium Review

Calcium Review

Bone density ~ ca supplements
Ca on its own can exacerbate inflammation
Also involved in muscle and nerve function, clotting
cofactors in many reaction

DIGESTION AND ABSORPTION

• Absorption requires soluble free Ca2+
• Adequate stomach acid (watch acid inhibitors)
• Enhancing factors
• Minimal binding factors
• Interactions between Ca
• Enhancing:
• Vit D
• Sugars and sugar alcohols
• Protein
• Inhibiting
• Fiber
• Phytic acid
• Oxalic acid
• Excessive divalent cations (Zn Mg)
• Unabsorbed fatty acids
• Primary system is vitamin D-dependent
• Brush border transporter (TRPV6)
• Cytosolic binding protein (Calbindin D9k)
• Basolateral membrane pumps (ATP-ase pumps)
• Paracellular diffusion between cells -also vit D dependent
• More important when calcium amount is large

CALCIUM TRANSPORT, STORAGE, EXCRETION

Circulates 50% ionized, 50% bound or complexed

Regulated by PTH, calcitriol, calcitonin

Stored in bone, excreted in urine feces sweat

EXCRETION

• Urinary Excretion of Ca
• Enhancers
• Sodium
• Protein
• Caffeine
• Inhibitors
• Phosphorous
• Iron
• Fatty acids

CALCIUM FUNCTIONS AND MECHANISMS

Bone mineralization

• 99% of body Ca found in bone
• Mainly as crystalline compounds such as hydroxyapatite
• Bound to bone proteins such as collagen and to ground substance
• Non-collagen proteins facilitate calcium deposition
• including vit K dependent proteins (osteocalcin)
• Young adult hood = peak bone mass
• Osteoporosis can be due to inflammation not just Ca levels; also vit D, protein decrease

Blood clotting

Nerve transmission

• For NMDA receptors - need Mg in channel -- Ca can rush in unchecked without doorman, Mg. Can cause irritability. 

Muscle contraction

• Ca stored in sarcoplasmic reticulum
• Binds myosin head to contract, requires Ca

Other signaling / regulating functions

• Smooth muscle contraction
• glycogenolysis 
• fatty acid
• glucosenoid formation