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Bone and Calcium ofBiochemistry
dr. dwi arini
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SUSUNAN KIMIA TULANG
AIR 14 44 %
LEMAK 25 %ZAT ORGANIK 30 35 %
KOLAGEN GELATIN
GLIKOPROTEIN
OSTEOKALSIN GLA ( -karboksiglutamat)) ZAT ANORGANIK : PO 4, CaCO 3, Mg, Fl, OH, SO 4
SITRAT
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Physiologi of Ca & PO4
Homeostasis
Diet
Gut
Fecal
BLOOD
Vit D
absorptionBone
Resorption
Reabsorption
Kidney
Ca PO4
Reabsorption
UrineEkskresi
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KALSIUM (Ca 2+)
Diet
Gut
Fecal70-90 %
BLOOD
Vit D, laktosa &protein, PTH
absorptionBone
Resorptioncalcitonin
Reabsorption
Kidney
Ca : 10 g
Reabsorption 4,99 0,21 mg/mnt
Urine200 mg
Susu, Keju,Kacang, Kuning
Telur
Keringat 15mg/hr
calcitonin
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FOSFOR (PO 4 3-)
Diet
Gut
Fecal
BLOOD
Vit D, PTH &perbandingan Ca:P
absorptionBone
Resorption
Reabsorption
Kidney
Reabsorption
Urine
Hampir dalamsemua makanan
PTH
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Regulation of Ca & Po4
effected by
Gastrointestinal absortionKidney excretionBone resorption
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PTH, VIT D & VIT K work
together to promote
Absorption of calcium from intestinePromote bone resorption of caPTH deficiency impairs the synthesis of
vit D to its active form (1,25[OH] 2D3) Vit K is catalisator of carboxylationglutamic acid residu to Gla ( --carboxyglutamat)
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Calcitonin
Antagonistic action to PTH and vit D
Used in the treatment ofhyperparathyroidismInhibits bone reabsorption
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VITAMIN D
Ada 2 jenis : D2 (ergosterol) & D3 (kolekalsiferol)D2 plant
D3 animal, rantai samping kolesterol.ada 2 bentuk aktif : 1,25-[OH]2-D3 & 24,25-[OH]2-D3
Kerja vit D: Provit D (7-Dehidrokol) aktif (1,25-[OH]2-D3) ke
organ & liver Di membran usus : absorpsi Ca & Fosfat Di Ren : kendalikan ekskresi & klirens fosfat Di Tulang : mobilisasi bersama-sama dgn PTH.
UV/ PTH
Kulit / Ginjal
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VITAMIN D
If [Ca] & [PO] plasma rendah, so:GI Tract : intestinal absorptionBone : mobilization from bone (in concert withPTH.Kidney : excretion by kidneys
Mekanisme Kerja vit D di usus : Merangsang sintesa protein pengikat kalsium
(CaBP) melalui sistem reseptor sitosol inti (DNA-RNA).
Sumber : hati, ikan, mentega & telur.
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VITAMIN K
Peran vit K : sbg katalisator dalam karboksilasiresidu asam glutamat Gla ( --
carboxyglutamat) CaBP utk adsorpsiOsteokalsin CaBP utk demineralisasi tulang
Sumber : sayuran hijau tua, tomat, keju, kuningtelur dan hati.
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Parathyroid Hormon
Fungsi utama : mempertahankan [Ca 2+] dalam plasma tulang. mengatur ekskresi Ca & PO4 ginjal
Secara Fisiologis berperan : [Ca] serum & [PO4] serum. ekskresi PO4 but ekskresi Ca dalam urin. mengeluarkan Ca dari tulang bila intake kurang,
Ada 2 cara yaitu : asam laktat & asam sitrat.
Merangsang sintesa protein pd osteoklast. alkali fosfatase serum bila ada kelainan tulang. mengaktifkan vit D dalam ginjal.
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If [Ca] plasma turun PTH release, so: Bone : Ca & PO4 mobilization from bone.. Kidney :
Ca dan PO4 urinary ekskresi. 1,25-(OH)2-D3
GI tract : Ca absorption
Parathyroid Hormon
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CALCITONIN
Polypeptide produced in thyroidEfek utama : [Ca] & [PO4] serum, dg cara :
Bone : suppresses resorption of bone by inhibiting theactivity of osteoclast , a cell type that digest bone matrix,releasing calcium and phosphorus into blood.
Kidney : Ca & PO4 are prevented from being lost in urine byreabsorption in the kidney tubules . Calcitonin inhibits tubular
reabsorption of these two ions, leading to increased rates oftheir loss in urine.
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CALCITONIN
If : [Ca] & [PO4] serum meningkat : Bone : direct inhibition of osteoclast bone
resorption. May stimulate osteoblast formation. Kidney : Ca & PO4 (& other ions) excretion.
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Disease & disorders leading to
HypocalcemiaRickets & osteomalacia
Juvenile (rickets) & adult (osteomalcia) inadequate bonemineralization.
Due to : Vitamin D deficiency or Lack of activation of or resistence to vit D
Causes Ca malabsorption
Hypoparathyroidism (true or pseudo)Renal Failure (cant synthesize 1,25 -OH2-D3)
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Treatments for Hypocalcemia
Vitamin D (or active analogs)