Bone Vitamin and MInerals Flashcards
Calcium Store
Hydroxyapatite Ca(PO4)2.
Calcium function
Cofactor for alpha amylase and phospholipase
Calcium absorbed
Passive absorption through tight junctions
Active absorption TRPV6 Ca2+ channel along duodenum and upper jejunum
1,25(OH)2D stimulated production of Calbindin (CaBP) which transports calcum to basolateral membrane
Calcium reabsorption
In kidney at TRPV6 - Ca2+ channel
Calcium absorption efficiency
Children -75%
Adults - 30%
Short term deficiency of calcium
Not a measurement of dietary intake.
Means something is wrong hormonally
Low Plasma levels of Ca2+
Long term calcium deficiency
Chronic Ca deficiency/ not absorbing
Shown as reduced bone mass and osteoporosis
Excess Calcium
Hypercalcaemia – High blood Ca levels
Usually results from high vitamin D intake
If on supplements way more likely to go into excess compared with if consume that much in diet.
Increased risk of kidney stones
Vitamin D Overview
Fat soluble
Two forms
D2
Ergocalciferol
Plants
Less efficiency absorbed
D3
Cholecalciferol
Animals
Vitamin D Absorption
Fat soluble taken up by lipids in the gut Transported to liver Converted to 25(OH)D Carrier protein added DBP 25(OH)D-DBP filtered out of blood by kidney Reabsorbed by proximal convoluted tubule Separated from transporter Binds to mitochondria Hydroxylated by o 25(OH)D-1hydroxylase PTH released
1,24(OH)2D genomic action
Binds to CDR and forms heterodimer RXR
Binds to VDRE on DNA
Influences – mineral homeostasis, vitamin D metabolism, cell differentiation, DNA replication
1,24(OH)2D non-genomic action
Binds to Membrane bound receptors (MARRS)
Opens ion gated channels, increase intracellular Ca, activates protein kinase, adenylyl cyclase
1,25(OH)2D in intestine
Ca and P absorption Not known how Increase rapidly Increase activity of enzymes such as Ca-ATPase Increase synthesis of some proteins
1,25(OH)2D in bone
Normal bone growth
Effects osteoblasts directly
Effects osteoclasts indirect
Preosteoclast have a receptor called RANK
Which binds to ligand RABKL
Binds surface of osteoblast stimulating 1,25(OH)D
Deficiency of Vitamin D
Rickets
Phosphorus store
85% stored in bones Ca10(PO4)6(OH)2
rest in body
Phosphorus Absorption
55-70%
Small intestine has enzymes that hydrolyse phosphate
Passes epithelial boarder via Na dependent phosphate co-transporter (NPTs)
PTH decrease activity
1,25(OH)2D and
Low plasma concentration increases activity
Phosphorus deficiency
Rare Hypophosphatemia anorexia anaemia muscle weakness Bone pain Rickets and osteomalacia Increased risk of infection
Magnesium Overview
1/3 for metabolic activity
2/3 provide structure and support
Magnesium function
Muscle contraction
Enzyme activity that require ATP utilise Mg
Act as an allosteric activator
Transport ions such as potassium and calcium across membranes
Oxidative phosphorylate
Glycolysis
DNA and protein synthesis
Magnesium Absorption
Small intestine in jejunum and ileum
Active transport and paracellular absorption
50-60% absorbed
Inversely proportional to amount consumed
Vit D enhances absorption
Fibre and phosphorus decrease Mg absorption
Assessment of Magnesium
Serum not a good indicator due to homeostatic control. There is research as to whether an ion-specific electrode would be a good indicator but currently use intracellular Mg levels in red blood cells.
Sever magnesium deficiency
Hypomagnesemia Hypocalcemia Hypokalemia Resistance to Vit D Neuromuscular hyper excitability
Moderate Magnesium deficiency
Cardiovascular disease
Elevated blood pressure
Osteoporosis
Diabetes
Cardiovascular disease an magnesium link
anti-thrombotic
Coronary vasodilator
Anti-arrhythmic
Inhibits release of catecholamines
Osteoporosis
Reduce Mg in bones
Leads to abnormal crystal formation
