Micronutrients Part 1 B Flashcards
Is 25-OH D3 the active form of vitamin D? How is it formed and where? What is it’s significance?
- No, it is inactive.
- 25-hydroxylase adds and OH group to Vit D3 to form 25-OH D3
- Occurs in the liver
- 25-OH D3 is bound to DBP (vit D binding protein) and released into the blood
- If 25-OF D3 levels are low in the blood, this corresponds to a VIT D DEFICIENCY!!
What causes the conversion of 25-OH D3 to the active form of vitamin D (calcitriol)? What enzyme is involved? Where does this occur?
- Low levels of blood Ca2+ is recognized by the parathyroid
- Parathyroid releases PTH (parathyroid hormones)
- PTH promotes the uptake and conversion of 25-OH D3 to the calcitriol (1,25-(OH)2 D3)
- enzyme –> 1-hydroxylase
- uptake and conversion of inactive vitamin D occur in the kidneys!
What is the genomic significance of calcitriol signaling?
- once calcitriol enters the nucleus, it interacts with vit D receptors
- causes gene expression that promotes the synthesis of calcium-binding protein
What molecule activates the calcium-binding protein via which post-translational modification?
Vit K; gamma-carboxylation
What is the non-genomic function of calcitriol signaling at the levels of the bone (in the case of low blood calcium levels)? What bone cell is involved?
- resorption of bone
- parathyroid hormones and calcitriol stimulate the degradation of bones to supply calcium
- osteoclasts resorb bone (breakdown)
Where do ABSORPTION, REABSORPTION, and RESORPTION of calcium occur in the body?
- intestine (absorption)
- kidney (takes calcium from the filtrate back into the blood; reabsorption)
- bone (breaking down bone to resupply calcium to blood; resorption)
True or False: calcium reserves in the bone are the most important levels of calcium that needs to be maintained.
False: blood calcium must be diligently controlled. bone will be sacrificed to replenish blood calcium.
Do these following molecules increase or decrease calcium blood levels?
- PTH
- Calcitriol
- Calcitonin
- increase
- increase
- decreases
True or false: pregnant or lactating women observe a greater RDA for vitamin D.
False: pregnant or lactating women need the same amount of vit d as regular adults. Pregnant women undergo hormonal changes that increase the absorption and reabsorption of calcium.
True or false: vitamin d deficiency in teenagers is considered osteoporosis
False: deficiency in teenagers would be considered osteomalacia (bones become demineralized)
Who is most susceptible to vit K deficiency ? Why?
- infants
- they do not consume leafy greens ( phylloquinone)
- they also do not have a fully developed colon/ gut microbiome (menaquinone)
Describe the main role of vitamin K and how it asks as a cofactor?
- quinone (vit K) is reduced to hydroquinone (active form)
- hydroquinone acts as a cofactor to gamma-glutamyl carboxylase
- gamma-glutamyl carboxylase mediates the carboxylation of glutamic acid to gamma-carboxyglutamic acid
- in this process, hydroquinone is oxidized to epoxide(inactive form)
SUMMARY
–> the main role of vit k is to act as a cofactor for the gamma-carboxylation of glutamic acid, which promotes blood clotting
Why is gamma-carboxylation of glutamic acid residues specific to blood clotting?
- it is a post-translational modification (known as “Gla” residues)
- allows to the protein to bind to calcium ions
- calcium promotes coagulation
Describe the difference in the upper limit for calcium intake in children vs. elderly people
Children:
- bones are developing, therefore require more calcium
Elderly:
- greater susceptibility to forming kidney stones
TRUE OR FALSE:
Fluoride is absorbed via the facilitated diffusion in the intestines.
- false, fluoride ion is absorbed in the stomach via passive diffusion.
