Lecture 4/12/16 Flashcards
Vitamin D in Recent Years
Increased RDA; increased fortification; a lot of deficiency
What are some of the deficiency syndromes associated with Vitamin D?
Children: Ricketts Adults: Osteomalacia
Ways to obtain Vitamin D
From sun exposure (UV) ; fortified foods;
DBP
Vitamin D binding protein; transports Vitamin D synthesized by the skin w/ chylomicron
How are injested
Absorption of Vit D associated with chylomicrons
What modification does vitamin D undergo in the liver?
vitamin D has a hydroxyl group added to carbon 25 forming a diol
In the kidney, what modification does vitamin D undergo?
Kidney adds OH group to carbon 1, forming 1, 25 (OH)2 D (cholecalciferol or calcitrol) the active form of vitamin D
Vitamin D is quite unstable and will easily degrade during cooking, storage or food processing (T/F)
False; Vitamin D is stable; also, foods fortified with vitamin D typically do not need heating before consumption
Why is serum 25-OH D and not serum 1,25-(OH)2 D the form of vitamin D that best represents the vitamin D status of an individual?
Because 25-OH D concentrations change as a function of dietary intake.
Non- genomic action
mediated by vit. D binding to cell membrane receptor (MARRS) leads to cell signaling, which leads to CA2+ metabolism
Genomic action
mediated by vit. D binding to nuclear receptor (VDR); VDR-RXR complex goes to VDRE goes to gene expression (genes relate to bone synthesis and healing system)
VDRE
Vitamin D response element
Functions of calcitriol
Calcium homeostasis
Parathyroid hormone
released by the parathyroid gland in response to low calcium levels
Function of PTH
Acts on the kidneys and bones to increase Ca2+ concentration
