11 Vit D and Calcium Flashcards
Vit D synthesized by?
skin
- needs sunlight
Forms of vitamin D?
D3 main form utilized by humans
- many forms exists
Active form of Vit D
-where is it converted
Calcitriol
1,25(OH)2 - D3
- converted in the kidney
D3 –> calcidiol –> calcitriol
Synthesis of vit D
cholestrol –> 7-dehydrocholesterol –> Vit D
occurs in the SKIN
Food sources of vit D
fatty fish
fish liver oils
mushrooms
fortified dairy products
Absorption of Vit D?
incorporation into chylomicrons (because its fat soluble vitamin)
- transported in plasma bound to DBP (vitD binding protein)
Vit D
- converted?
- storage?
converted in KIDNEY
stored in LIVER and ADIPOSE TISSUE (other tissues)
Overall metabolic role of Vit D?
maintains calcium and phosphorus homeostasis
- ensures availability in blood for bones/intestine
- steroid hormone (vitamin D endocrine system)
How vitamin D acts as a steroid hormone?
Targets vit D receptors (VDR)
- 1,25(OH)2-D3 travels to specific cell
- enters cell, binds VDR
- binds DNA
- alters transcription rate or mRNA, synthesis of specific proteins
Main target organs of Vit D?
- others?
*bones and intestine
brain and nervous system pancreas muscle cartilage reproductive organs cancer cells
Vitamin D effect on other micronutrients
tight regulation of calcium
- bone growth
- maintenance of bone density
- nervous system
- blood clotting (vit K)
keeps phosphorus in normal range
What hormone vitamin D works with?
Parathyroid Hormone (PTH)
What produces parathyroid hormone?
Where is it located?
Parathyroid Gland
- behind thyroid gland in neck
Role of parathyroid hormone in kidney?
- stimulates activation of vit D
- increases calcium “reabsorption”
- decrease urinary
- increase blood - decrease phosphate reabsorption
- prevents hyperphosphatemia (prevents D’s conversion to active form)
- calcium removed from bone also removes phosphate (keep P in check)
- increase urinary phosphate
Role of parathyroid hormone in Bone
Increases osteoclast activity
- bone resorption
- release calcium and phosphorus
- incr. blood calcium and phosphorus
Hyper vs Hypo parathyroidism
Hyper
- parathyroid gland tumor
- lower bone density
- high blood calcium (neg. feedback not working)
Hypo
- removal or thryoid/parathyroid glands
- low blood calcium (no sensor)
1,25 (OH)2 - D3 acts on?
intestine
- stims calcium and phosphorus absorption
- Increase blood levels
bone
- increase osteoclast activity
- bone resorption
- increase blood calcium and phosphorus
PTH vs calcitriol?
both calcium homeostasis (increase bl. levels) PTH - kidney and bone Calcitriol - intestine and bone
Most abundant mineral in the body?
Calcium
2 ways calcium is absorbed
Passive Absorption
- D independent
- concentration dependent
Active
- D dependent
- requires transporter and energy
- requires calbindin (calcium binding protein)
Calcium binding protein
- why needed?
Calbindin
- free calcium very toxic
- moves calcium across “intestinal” cell (shuttle)
How does vit C help calcium absorption ?
Increases calbindin synthesis
- calcium binding protein
Factors enhancing calcium absorption?
vit D calbindin synthesis stomach acid supplements (with meal) optimal ratio calcium-phosphorus
Factors inhibiting calcium absorption?
low vit D lack of stomach acid excess phosphorus high fiber diet phytic acid oxalate (metabolite of vit C)
Oxalate
inhibits calcium absorption
- metabolite of Vit C
- oxalate kidney stones
Metabolic Roles of calcium
Major
- bone health
Minor
- cellular processes
- muscle contration - blood clotting
- transmission of nerve impulses
- membrane excitiability
- second messenger
Calmodulin
- intracellular protein (calcium receptor) in all cells
- binds calcium
- activation of intracellular proteins and enzymes
- mechanism of action of many peptide hormones
Hormones involved in blood calcium homeostasis?
PTH
calcitriol
calcitonin
