PENGANTAR METABOLISME ZAT GIZI MIKRO PERTEMUAN 3 DUDUNG
PENGANTAR METABOLISME ZAT GIZI MIKRO PERTEMUAN 3 DUDUNG ANGKASA PROGRAM STUDI ILMU GIZI-FIKES
VISI DAN MISI UNIVERSITAS ESA UNGGUL
Materi Sebelum UTS 01. Pengantar metabolisme mikro 02. Vitamin A 03. Vitamin D 04. Vitamin E dan K 05. Vitamin Larut Air- C 06. Vitamin Larut Air-B kompleks 07. Vitamins Interaction
Materi Setelah UTS 08. Mineral-Ca, Mg, Na, K, P, S 09. Mineral-Fe, Zn, I 10. Mineral-Mn, Cr, Cl 11. Mineral-Co, Mo, Cu, F 12. Mineral Interactions 13. Mineral-Vitamins Interactions 14. Review
KEMAMPUAN AKHIR YANG DIHARAPKAN • Mahasiswa dapat menjelaskan metabolisme vitamin D yang meliputi pencernaan, penyerapan, distribusi (sirkulasi), utilisasi, dan eksresinya serta tingkat kebutuhan dan resiko keracunannya.
METABOLISM OF VITAMIN D (“The Sunshine vitamin) Esa Unggul University
Chemical form of Vitamin D
Source of vitamin D
Source of vitamin D • • • The two most prominent members of this group are ergocalciferol (vitamin D 2) and cholecalciferol (vitamin D 3). Ergocalciferol is derived from a common plant steroid, ergosterol, Cholecalciferol is the form of vitamin D obtained when radiant energy from the sun strikes the skin and converts the precursor 7 dehydrocholesterol into vitamin D 3.
Absorption (Diet) • Vitamin D obtained from the diet is absorbed from the intestinal tract • Ingested vitamin D is solubilized within mixed micelles in the duodenum • Vitamin D is absorbed from the intestinal tract in association with fats, it requires the presence of bile salts for absorption. • The micelles dissociate in the acidic microclimate of the unstirred layer and the liberated vitamin D is absorbed in the jejunum by simple diffusion, along with other lipids • Duodenum most rapid absorption, the distal is the largest. • Vitamin D is incorporated into chylomicrons within the enterocytes and, when released, the chylomicrons convey the vitamin in the mesenteric lymph to the systemic circulation.
Absorption (Diet) • During the journey in the lymph, an appreciable amount of the vitamin D in the chylomicrons is transferred to the DBP • only 50% of a dose of vitamin D is absorbed. • The same with other fat soluble vitamin
Absorption (Skin) • Cholecalciferol, slowly diffuse from the skin to blood, picked up by DBP. • About 60% plasma cholecal– is bound to DBP • It will travels to muscle, adipose tissue, prior to liver
Transpor • In the plasma, 25(OH)D, and indeed all vitamin D metabolites, are mainly bound to a specifi c glycoprotein, known as the vitamin D-binding protein (DBP). • The binding affinities of the DBP for vitamin D and its metabolites are 25(OH)D 3 = 24 R, 25(OH)2 D 3 = 25, 26(OH)2 D 3 > 1α, 25(OH)2 D 3 > vitamin D 3.
In the Liver • Cholecal from DBP or CR is hydroxylated at carbon 25 25 -OH D 3 (calcidiol) by 25 hydroxylase (monoxygenase) • This enzym is NADPH-dependent, and more efficient during vitamin D deficiency • Most 25 -OH D 3 synthesized in the liver is secreted into blood by DBP • The blood is the largest single pool of 25 -OH D 3, which has a half-life of 3 weeks • When blood 25 -OH D 3 decrease, skin reservoir is activated
Wimalawansa, S. J. , 2016. Non-musculoskeletal benefits of vitamin D. The Journal of steroid biochemistry and molecular biology.
• Three key enzymes are involved in the conversion of vitamin D: – Vitamin D-25 -hydroxylase in the liver converts vitamin D to 25(OH)D; – a multicatalytic 1α-hydroxylase in the kidney converts 25(OH)D to 1α, 25(OH)2 D; and – 24 Rhydroxylase, another renal multicatalytic enzyme, converts 25(OH)D to 24 R, 25(OH)2 D
• DBP: Vitamin D binding protein
Excretion • Excretion of absorbed vitamin D and its metabolites occurs primarily in feces with the aid of bile salts. Very little vitamin D appears in urine.
Calcitriol and Intestine • Primary function is to increase absorption of calcium and phosporus • This vitamer is believed function as a steroid hormone as well as to function in signal transduction
Calcitriol and Calcium • Calcitriol, as a hormone, interact with high affinity receptors in the enterocyts and is carried to nucleus • It will interact with specific protein m. RNA • m. RNA endoplasmic reticulum into selected protein in brush border High calcium absorption
Calcitriol and P • Calcitriol, will increase the activity of brush border alkaline phospatase, which hydrolize phospate ester bond increase P abs • Calcitriol modulate the Na-dependent layer
Vitamin D-related diseases • Rickets Ricket (infant) failure of bone to mineralize Epiphyseal cartilage continues to grow and enlarge without replacement of bone matrix and mineral The spine becomes curved, pelvic and thoraic deformities occur
Toxicity • hypervitaminosis D results from the excessive consumption of vitamin D supplements, and not from the consumption of usual diets. • Toxic concentrations of vitamin D have not resulted from unlimited exposure to sunshine. • Vitamin D intoxication can be a concern in patients with specifi c diseases being treated with unusual amounts of vitamin D or analogues of the vitamin.
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