Exam - Vitamin D Flashcards
supplement label for vitamin D
supports healthy immune system and bone health
what is the most prevalent micronutrient deficiency in the world
vitamin D
what does the bioactive form of vitamin d act as
a hormone - made in kidney and acts on other tissues
what does the bioactive form of Vit D work with
other hormones such as parathyroid and calcitonin
what is rickets
vitamin D deficiency
how long ago is there evidence of rickets
over 50,000 years ago
5 sources of vitamin D
natural plant
natural animal
sunlight
supplementation
fortification
plant form of vitamin D
ergocaliferol
animal form of vitamin D
cholecalciferol (Vit D3)
is the plant or animal form of vitamin D more bioactive
animal
where does provitamin D2 come from
plant
where does provitamin D3 come from
animals
what is an example of a plant with vitamin D
shiitake mushrooms
what is an example of an animal source with vitamin D
fish
fish liver oil
what happens with 7-dehydrocholesterol
it gets converted to cholecalciferol by sunlight in sebaceous glands of skin
is it easy to achieve good Vit D status by consuming plants/animals
no
what is Vit D3 made from in skin
7-D
how does Vit D3 circulate around body
by binding to the Vit D Binding protein
what absorbs UV rays
melanin in epidermis
why do people with more melanin have less vitamin D absorption in body
melanin absorbs UV rays which slows down Vit D3 production
who should consider supplementation of vitamin D3
someone who spends a lot of time indoors
what is fortification with Vit D
a government initiative - usually in milk or margarine
is Vit D fortification sufficient for health as the only source of Vit D
no
is there any risk of vit D toxicity from sun
no
how does Vit D3 enter blood
bound to DBP to go to liver or adipose
how is vitamin D3 absorbed from diet
in ileum - not very efficient
what does vitamin D3 get incorporated into from diet
chylomicrons - eventually ends up in liver
is there any difference between sun-derived and diet-derived Vit D3
no - same molecule
what carbon on Vit D3 gets hydroxylated and what does it form
25th carbon to form 25-OH D3
what enzyme hydroxylates the 25th carbon on Vit D3
25-hydroxylase
what is the KEY SIGN of Vit D deficiency
if 25-OH D3 levels are low in blood
what occurs in the body when calcium levels are low
25-OH D3 will be converted into an active molecule
what is VDR
type-2 steroid hormone receptor
does genomic or non-genomic calcitriol signalling depend on vitamin K
genomic
what are the 3 main organs relevant for the Vit D/Ca 2+ story
small intestine
kidney
bone
what occurs in the small intestine
absorption
what occurs in the kidney
reabsorption
what occurs in bone
resorption
small intestine - why do minerals need transporters
for absorption by intestinal cells and entry into portal circulation
what does the proper absorption of Ca2+ depend on
the expression of Ca2+ binding proteins in enterocytes
what happens to small molecules like Ca2+ in the kidney
they pass through a filter and can end up in the urine unless they are reabsorbed
what does reabsorption in kidney do
removes molecules from the filtrate and gets them back into blood
what resorption occurs in bone
dissolving bone structure to release Ca2+ into blood
what do osteoclasts do
resorb bone
what do osteoblasts do
build bone
what balance allows for bone maintenance, remodelling and repair
balance between breakdown and synthesis
what is the key point in the Ca2+ hormonal control system
maintaining blood Ca2+ is more important than maintaining Ca2+ reserves in bone
what does PTH serve to do for blood calcium
increase blood calcium
what does PTH promote
calcitriol production in kidney by activating 1-hydroxylase
what does PTH stimulate
bone resorption by activating osteoclasts
what does PTH maximize
tubular reabsorption of calcium in kidney
what does vitamin D serve to do to blood calcium
increase
what does Vit D stimulate
Ca2+ resorption from bone
what does vitamin D help to increase
absorption of Ca2+ from intestine
what does Vit D maximize
tubular reabsorption of Ca2+ in kidney
where is calcitonin secreted from
parafollicular cells in thyroid
what does calcitonin serve to do to blood Ca2+
decrease
what does calcitonin suppress
tubular reabsorption of Ca2+ in kidney
what does calcitonin inhibit
bone resorption
what does calcitonin facilitate
remineralization
what can be the result of too much calcitonin
kidney stones
what does Vit D deficiency in infants result in
rickets (poor mineralization)
what is rickets
bones don’t mineralize properly and cannot support weight when they start walking
what does Vit D deficiency in adolescents to adults result in
osteomalacia
what is osteomalacia
bones become demineralized and bone fractures can occur more easily
what does Vit D deficiency in middle-aged to elderly result in
osteoporosis
what is osteoporosis
normal part of aging - loss of mineral and organic parts of bones
how do you diagnose osteoporosis
bone density scan
is osteoporosis easy to reverse
no - erosion in bone (holes)
what is the healthy percentage of mineral vs organic solid bone composition
60% mineral
40% organic
can osteomalacia be reversed
yes with supplements
is there any risk of Vit D toxicity from sun exposure
no - production is limited by amounts of 7-D in skin
what can high dietary levels of D3 result in
hypercalcemia
