Ca + Ph + vit D

Question 1

what are the characteristics of Ca?

Answer 1

• Ca2+ is preferred valence state + tight configuration
• signalling molecule, interacts with other ions/proteins within the cell

Question 2

what are the characteristics of P?

Answer 2

• found in bone as hydroxyapatite
• preferred ionic state is orthophosphate as HPO4 2- + H2PO4 -

Question 3

what are the functions of Ca?

Answer 3

• tool/carrier/messenger, can initiate a series of processes
• major component of bone (99%)/teeth mineralization
• 1% as Ca2+ regulates processes (blood clotting / nerve conduction / muscle contraction / enzyme regulation / membrane permeability)

Question 4

what are the functions of P?

Answer 4

• major component of bone mineralization (80-90%)
• second messenger (phosphorylation/dephosphorylation are essential for molecular regulation)
• electrolyte homeostasis / acid-base balance
• structural role (backbone of DNA/RNA)
• energy storage + transfer (ATP)

Question 5

how is Ca absorbed?

Answer 5

• only 20-30% effective
• major route: transcellular (saturable + requires energy + channel + binding protein/calbindin + stimulated by [low]/calcitriol + in duodenum)
• paracellular (nonsaturable + passive/[dependent] + in ileum/jejunum)
• colonic fermentation may release some

Question 6

how is P absorbed?

Answer 6

• 60-70% effective
• absorbed linearly to intake, preference as HPO4 2-
• twice as efficient as Ca
• responds to calcitriol but less so than C

Question 7

what hormones control Ca + P metabolism + where are they from ?

Answer 7

calcitonin = thyroid glands
PTH = parathyroid glands

Question 8

when is PTH released + what does it do

Answer 8

when blood [Ca] is low
- increased vit D activation
- increased Ca reabsorption in kidney + release from bone + absorption in intestines
- increased blood [Ca]

Question 9

when is calcitonin released + what does it do

Answer 9

when blood [Ca] is high
- inhibits vit D action
- decreased Ca reabsorption in kidney + release from bone + absorption in intestines
- decreased blood [Ca]

Question 10

what is the bone remodelling cycle?

Answer 10

replacement/turnover of bone mass that occurs every year in adults
activation phase / 40 days: pre-osteoclasts > active osteoclasts > mononuclear cells
reversal phase / 145 days: mononuclear cells > pre-osteoblasts > osteoblasts > osteocytes

Question 11

what are osteoclasts vs osteoblasts

Answer 11

osteoclasts = destroy + resorb old bone
osteoblasts = cells that deposit new bone in its place

Question 12

what increases Ca absorption / decrease excretion

Answer 12

increase absorption: calcitriol, sugars, protein

decrease excretion: high plasma [P] = low ionic [Ca] = increased PTH synthesis = increased Ca reabsorption

Question 13

what decreases Ca absorption / increases excretion

Answer 13

decrease absorption: fiber/phytate binding, oxalate chelating, excess divalent cations, excess unabsorbed fatty acids

increase excretion: sodium, protein/sulfur AAs, caffeine

Question 14

what increases P absorption / decrease excretion

Answer 14

increase absorption: calcitriol

decrease excretion: P depletion, parathyroidectomy, calcitriol

Question 15

what decreases P absorption / increases excretion

Answer 15

decrease absorption: phytate, excess Ca/Mg/Al

increase excretion: high plasma [P or Ca or PTH], estrogen, thyroid hormones, phosphatonins

Question 16

what are food sources of Ca

Answer 16

skim milk, spinach, sesame seeds

Question 17

what is the RDA for Ca

Answer 17

adults: 1000mg/day UL 2500mg/day
increase with adolescence + elderly

Question 18

what are food sources of P

Answer 18

pork, salmon, sardines, additives in processed foods

Question 19

what is the RDA for P

Answer 19

adults: 700mg/day
increase with adolescence + elderly

Question 20

what are symptoms of Ca deficiency?

Answer 20

fatigue, neuromuscular irritability/spasms, altered CNS function, cardiomyopathy

Question 21

what are symptoms of P deficiency?

Answer 21

CNS irritability, decreased GFR, electrolyte imbalance, abnormal metabolism

Question 22

what are symptoms of Ca toxicity?

Answer 22

abnormal ECG, nausea/vomiting, constipation, kidney stones

Question 23

what are symptoms of P toxicity?

Answer 23

hypocalcemia, tetany, soft tissue calcification
- if secondary to renal diseases: hyperparathyroidism + renal osteodystrophy

Question 24

what are causes of Ca deficiency?

Answer 24

intestinal disorders, osteoporosis, abnormal metabolism/decreased turnover
- inadequate vit D production
- PTH + vit D resistance

Question 25

what are causes of P deficiency?

Answer 25

- vit D resistance/deficiency - increased urinary loss (due to rickets) - intracellular shift (respiratory alkalosis)

Question 26

what are causes of Ca toxicity?

Answer 26

- high PTH = Ca hyperabsorption + increase bone resorption

Question 27

what are causes of P toxicity?

Answer 27

- decreased urinary excretion (due to hypoparathyroidism) - altered extracellular space/acidosis

Question 28

how is Ca status assessed

Answer 28

difficult to do, many confounding factors + tight regulation - bone density to observe mineralization over time

Question 29

what is osteoporosis

Answer 29

lack of close coupling of bone formation + resorption - more common in elderly

Question 30

what are the 2 types of osteoporosis?

Answer 30

type I: postmenopausal, 50-70 years old, rapid estrogen loss + testosterone loss type II: senile, 70+, reduced Ca absorption

Question 31

what are some risk factors + protective factors for osteoporosis?

Answer 31

risk: old age, low BMI, smoking, alcohol, sedentary, lifetime low Ca/vit D intake, female protective: younger, high BMI, weight-bearing exercise, diuretic use, estrogen therapy

Question 32

what are the functions of vit D

Answer 32

- Ca balance - immunomodulator - regulates cell growth - reduces hypertension

Question 33

what is the major role of vit D? (form + where)

Answer 33

1,25(OH)2D major role is maintaining normal plasma [Ca] - intestine: increase absorption efficiency - bone/kidney: induces formation + activation of osteoclasts + renal reabsorption

Question 34

where is vit D stored in the body + why?

Answer 34

in the skin as DHC, isomerization to D3 then hydroxylation to 25(OH)D in liver then activation to 1,25(OH)2D in kidney - tightly regulated - stored in skin because high enzyme presence in kidney = high degradation rate

Question 35

what is the process of vit D conversion from sun exposure

Answer 35

7DHC converted to pre vit D via UVB/radiation rays pre vit D converted to D3 via time + body temp or from dietary intake transferred to blood/circulation + binds to vit D binding proteins for conversion to liver/kidney

Question 36

what factors impact/promote vit D conversion in the kidney

Answer 36

low Ca, PTH, calcitonin, low P

Question 37

what enzyme converts vit D to the active form in the kidney + what inhibits it

Answer 37

1-OHase, inhibited by high levels of 1,25(OH)2D

Question 38

what is the RDA for vit D

Answer 38

adults: 600IU UL 1000-4000IU increases with age

Question 39

what are food sources of vit D

Answer 39

fatty fish, egg yolks, fortified drinks/cereals

Question 40

symptoms of vit D deficiency

Answer 40

kids: rickets - bone softening/deformities, short stature, things can't form/mineralize at same rate of growth adults: osteomalacia - increased fracture risk, bone pain, osteopenia/decreased skeleton opacity, poor collagen matric mineralization

Question 41

symptoms of vit D toxicity

Answer 41

toxicity in skin is impossible - excessive intake can lead to hypervitaminosis D = leads to hypercalcemia + soft tissue calcification = renal/cardiovascular damage

Question 42

what are causes of vit D deficency

Answer 42

- inadequate sun exposure (clothes, spf, melanin, latitude) - malabsorption (GI diseases, liver disease, cystic fibrosis) - medications/supplements (glucocorticoids, st johns wart, antiseizure)