Vit D and Ca Flashcards
is Vit D a water soluble vitamin
no, it is fat soluble
where is Vit D synthesized
what is it synthesized from
what does it require
in the skin, from cholesterol…need sunlight
what is the main form of Vit D that is utilized by humans
D3
what is the active form of Vit D
calcitriol
Vit D food sources
found naturally in very few foods
…..fatty fish, fish liver oils
….mushrooms
….milk and a lot of dairy products are fortified
Vit D absorptions and transport
- absorbed involves incorporation into chylomicron
- transported in plasma BOUND to a PROTEIN (DBP-vitamin D Binding Protien)
- converted to active form (calcitriol) in kidney
where can Vit D be stored
in liver, other tissues, especially adipose (bc its fat soluble)
vit D produced in the skin in the spring summer and fall can be stored for winter
Overall metabolic role of Vit D
maintain calcium and phosphorus homeostasis
- ensure Ca and Phosphorus are available in the blood that “bathes” the bones
- acts as a STEROID hormone
- sometimes referred to as the Vit D Endocrine System
main thing it keep Ca in check…Phosphorus follows along
Vit D as steroid hormone
targets specific organs and their Vit D Receptor (VDR)
main target organs are INTESTINE and BONE
Also, brain and nervous system, pancreas, muscle, cartilage, repro organs, cancer cells
list the steps of Vit D acting as a steroid hormone
(1) 1,25(OH)2-D3 travels to specific cell
(2) enters cell and binds to nuclear VDR
(3) binds to the actual DNA
(4) alters transcription rate of mRNA which code for synthesis of specific proteins, which will alter metabolic function
Vit D and Ca homeostasis
tight regulation of Ca important for:
- bone growth
- maintenance of bone density
- nervous system
- blood clotting
also important to keep phosphorus in normal range
comple system..involved:
-vit D (steroid hormone)
-parathyroid hormone (PTH)
PTH
-peptie hormone
produced by parathyroid glands
- key role in Ca homeostasis….also regulates phosphorus
- parathyroid gland contains a protein that acts as a SENSOR of blood calcium
-dec blood Ca
(sensor PRO detects this, inc PTH synthesis)
PTH Effects…what is the goal
GOAL:
to restore normal blood Ca and maintain phosphorus homeostasis via negative feeedback loop
what are the primary target organs of PTH and what happens
KIDNEY (A) stimulates activation o fVit D (B) inc Ca reabsorption -dec urinary Ca - inc blood Ca (C) dec phosphate reabsorption -prevents hyperphosphatemia; whic can inhibit conversion of Vit D to its active form -when Ca removed from bone, P is as well -inc urinary phosphate
BONE (A) inc osteoclast activity -inc bone resorption (breakdown) -Ca and P are released -inc blood Ca and P
Hyperparathyroidism
- parathyroid gland tumour
- high blood Ca…bone will be broken down
hypoparathyroidism
- removal of parathyroid or thyroid glands
- Ca not being homeostatic
what is the goal of Calcitriol 1,25(OH)2-D3?
-to restore normal blood calcium
where is calcitriol produced and what is production stimulated by
kidney
PTH
where in the body does calcitriol act?
intestine and bone
what are the effects of calcitriol on the intestine?
(A) stimulates Ca absorption
- also need Mg
- inc blood Ca
(B)stimulates phosphorus absorption
-inc blood phosphorus
what are the effects of calcitriol on bones
increased osteoclast activity (same as PTH)
- inc bone resorption (breakdown)
- Ca and P are released
- inc blood calcium and P
what is the most abundant mineral in the body
calcium
outline the two types of Ca absorption
PASSIVE
- does not depend on Vit D
- concentration dependent
- we can absorb Ca without vit D, but we dont always get enough, or sources are being inhibited
ACTIVE TRANSPORT absorption
- Depends on Vit D
- requires a transporter and energy
- requires calbindin (Ca binding protein)
- Vit D increases synthesis of calbindin therefore increases Ca absorption
what is the purpose of Calbindin
free Ca is very toxic to inside of cells so the Ca needs to move across cell. The Ca needs to be BOUND in order to shuttle it across the cell
CALBINDIN binds Ca and acts as a shuttle for Ca through the cell
Calbindin facilitates Ca absorption across the intestinal cell
VIT D INCREASES CALBINDIN SYNTHESIS
Factors enhancing Ca absorption
Vit D presence of calbindin stomach acid supplements best absorbed with a meal optimal ratio of Ca to Phosphorus
factors inhibiting Ca absorption
Vit D deficiency
- lack of stomach acid
- excess phosphorus
- high fiber diet
- phytic acid
- oxalate
metabolic role of Ca
bone health
- Ca’s major role
- bone is dynamic….losing and gaining minerals all the time
- goal is balance
regulator of cellular processes (minor role)
- muscle contraction, blood clotting
- transmission of nerve impulses
- membrane excitability
- second messenger
Ca as a second messenger
- signal transduction
- intracellular messenger of hormone action
- peptide hormone action
- calmodulin is an intracellular protein (Ca receptor) that binds Ca allowing for activation of intracellular proteins and enzymes
Calmodulin
- intracellular protein/Ca receptor
- also called Ca-dependent regulatory protein
- found in all cells
- binds intracellular Ca
- allows for signal transduction to occur
- activated proteins and enzymes
- key in the mechanism of action of numerous peptide hormones
calcitonin acts in the opposite of _____
PTH
what are the hormones involved in the regulation of Ca homeostasis
PTH
calcitriol
calcitonin
Calcitonin
- peptide hormone
- produced in thyroid gland
- acts in OPPOSITION to PTH
- production stimulated by INC in blood calcium
- production inhibited by derease in blood calcium
overall hypocalcemic effect
where in the body does calcitonin act
kidney and bone
what are the effects of calcitonin in kidney
inhibits activation of Vit D
-inhibits 1-hydroxylase
stimulates Ca excretion OR decreases Ca reabsorption
-inc urinary Ca
what are the effects of Calcitonin on bone
inhibits activity of osteoclasts
- inhibits bone resorption
- hypocalcemic effect
what hormone is used to treat diseases with high rates of bone resorption
calcitonin
in a vit D deficiency,
production of _____, and _____ absorption is decreased
calbindin
Ca
list 3 syndromes related to Vit D and Ca deficiencies
Rickets(children)
osteomalacia
osteoporosis
rickets
vit D deficiency
low blood Ca
impaired mineralization of growing bones
muscle weakness and nervousness
factors contributing to development of rickets
poor diet
low UV light exposure
Osteomalacia
Vit D deficiency
low blood Ca
looking at composition and quality of bone
(remember bone is in constant state of turnover)
new bone matrix is laid down but NOT mineralized properly (amount not affected, COMPOSITION affected)
RARE
softening of bones
defect in mineralization of the bone matrix
osteoporosis
Ca deficiency
looks at AMOUNT of bone
reduced bone density
what are the 2 compartments of bone
cortical
- 80% of skeleton
- dense bone tissue, shafts of long bone, outer hard shell of flat bones
- Ca loss is slow
trabecular
- inner structural matric
- at ends of long bones, inside the cortical shell of flat bones
- loses Ca readily (faster)
Type I osteoporosis
rapid bone loss
50-70y/o
due to rapid loss of estrogen in women following menopause
due to dec in testosterone in men with advancing age
more common in women
primarily TRABECULAR BONE
wrist and spine fractures
Type II osteoporosis
slower bone loss >70y/o due to aging factors -reduced Ca absorption -inc risk of falling -increased bone mineral loss
BOTH trabecular and cortical bone
hip fractures
what is used as an indicator of Vit D and Ca status?
bone health
what is Vit D and Ca toxicity called
hypervitaminosis D
Vit D and Calcium- toxicity
results in Ca absorption
Symptoms:
-hypercalcemia**
-Calcinosis
-not due to excess sun (this is self limiting)
what is calcinosis
results from Vit D and Ca- toxicity
- deposition of Ca in soft tissues
- blood vessels
- heart kidney lungs
- kidney stones
- tissues around joints
Ca and disease prevention
osteoporosis
colon cancer
hypertension
-inverse relationship between Ca and blood pressure
obesity
