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MSK I > Lecture 6 + DLA 40 > Flashcards

Lecture 6 + DLA 40 Flashcards

1
Q

What type of vitamin D is found in plants?

A

Ergocalciferol (D2)

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2
Q

What type of vitamin D is found in animal sources?

A

Cholecalciferol (D3)

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3
Q

How is the active form of vitamin D produced in the body?

A

7-dehydrocholesterol is converted to cholecalciferol by sunlight (skin)

cholecalciferol is converted to 25-hydroxycholecalciferol (in the liver) by 25-hydroxylase

25-hydroxycholecalciferol is converted to 1,25-dihydroxycholecalciferol (in the kidney) by 1-hydroxylase

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4
Q

What factors affect the formation of Vit.D in the skin?

A
  1. increased melanin pigment
  2. time of exposure and latitude
  3. amount of exposed skin
  4. winter months and latitude
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5
Q

How is the active form of Vit.D inactivated?

A

1,25-dihydroxycholecalciferol can be converted to 1,24,25 hydroxycholecalciferol by 24-hydroxylase

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6
Q

What is the mechanism of Calcitriol (active form)?

A
  1. binds to intracellular receptor proteins in target cells in the intestine.
  2. 1,25 DHCC receptor complex interacts with DNA (hormone response element) in the nucleus of intestinal cells.
  3. can increase or decrease the synthesis of calbindins
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7
Q

What does the protein calbidnin do?

A

stimulates the absorption of calcium and phosphate in the intestine

stimulates the mobilization of calcium and phosphate from the bone

inhibits calcium excretion in the kidneys

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8
Q

What is seen in those with low Vit. D levels?

A

low serum calcium levels and low serum phosphate levels

decreased bone mineralization

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9
Q

What are the risk factors for Vit.D deficiency?

A
  1. inadequate exposure to sunlight
  2. nutritional deficiency
  3. chronic renal disease or chronic liver disease
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10
Q

What causes rickets?

A

Vit.D deficiency in children

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11
Q

What are the symptoms of rickets?

A
  1. demineralization of the bone
  2. bow-leg deformity
  3. rachitic rosary
  4. pigeon chest deformity
  5. frontal bossing
  6. delayed teeth
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12
Q

lab findings in those who have rickets?

A
  1. elevated ALP levels
  2. low calcium
  3. low phosphate
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13
Q

What is osteomalacia?

A

Vitamin D deficiency in adults

similar symptoms and lab findings as seen in children

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14
Q

what happens if the calcitriol receptor is mutated?

A
  1. seen to have high levels of calcitriol (loss of feedback inhibition)
  2. calcium and phosphate levels are low
  3. 1,25 hydroxyvitamin D levels are high
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15
Q

What is hypervitaminosis D?

A

characterized by hypercalcemia due to increased calcium absorption from the diet

Increase in serum calcium and phosphate results in an
increased tendency for ectopic (soft tissues) mineralization

Prolonged hypervitaminosis D (prescription medications) can lead to calcification in soft tissues like kidney

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16
Q

What are the intrinsic factors that impact bone mass?

A

gender

family history/ genetics

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17
Q

What are the extrinsic factors that impact bone mass?

A

diet, body mass, hormones, illnesses, exercise, and lifestyle

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18
Q

What are the three forms of calcium found in the body?

A
  1. protein-bound calcium
  2. ionized calcium
  3. calcium bound to anions
19
Q

What are some functions of calcium?

A
  1. required for bone formation and remodeling
  2. import cofactor for many enzymes (blood clotting and muscle contraction)
  3. neurotransmitter for some neuron signals
20
Q

Food with calcium and how much calcium is needed daily?

A

foods:

dairy, green leafy veggies, soya beans, nuts, sardines

how much?

1000-1200mg daily

21
Q

What is calcium absorption via the intestine dependent on?

A

vitamin D

22
Q

What is bone deposition and resorption dependent on?

A

Vitamin D and PTH

23
Q

What is the excretion of calcium via the kidneys dependent on?

A

PTH

24
Q

What effect does PTH have on the concentration of calcium and phosphate in the blood?

A

PTH will increase the level of calcium in the blood, thus preventing hypocalcemia

involved in the homeostasis of phosphate

25
Q

How does PTH effect bones?

A

PTH promotes the demineralization of bone and the resorption of calcium into the plasma

also leads to increased phosphate into the plasma

26
Q

How does PTH effect the kidneys?

A

Will increase the excretion of phosphate, thus allowing more free calcium to be in the blood

decrease the excretion of free calcium

27
Q

how does Vitamin D impact the intestine?

A

stimulates the absorption of calcium and phosphate by the increased synthesis of calbindin

may also stimulate the ATP dependent calcium pump

28
Q

How does vitamin D impact the bone?

A

stimulates the mobilization of calcium and phosphate from the bone

in smaller quantities, may promote bone calcification

29
Q

How does vitamin D impact the kidney’s?

A

stimulates the reabsorption of calcium back into the blood

30
Q

What does calcitonin do?

A

reduces blood calcium levels

inhibits osteoclast activity

31
Q

What is the treatment for Vitamin D resistance?

A

nocturnal calcium infusions

improve growth, but will not restore hair growth

32
Q

What leads to hypocalcemia?

A
  1. low PTH (hypoparathyriodism)
  2. high PTH (secondary hyperparathyriodism)
    Vitamin D deficiency or resistance
33
Q

What are the lab findings in those with hypocalcemia?

A
  1. low vitamin D levels
  2. Low PTH after parathyriodectomy
  3. Low 1,25 dihydroxyvitamin D levels - low if renal insufficiency
34
Q

What is seen in those with hypocalcemia?

A
  1. hypocalcemic tetany
  2. stridor
  3. possibly cardiac arrhythmias
35
Q

How to treat hypocalcemia?

A

Ca and vitamin D supplementation

emergency: calcium gluconate IV

36
Q

What would lead to hypercalcemia?

A
  1. Excessive PTH production
  2. Hypervitaminosis
  3. Excessive 1,25 (OH)2D production
  4. Excessive Calcium intake
37
Q

How to diagnose hypercalcemia?

A

PTH immunometric assay with blood calcium levels

38
Q

what are some manifestations of hypercalcemia?

A
  1. polyuria and polydipsia
  2. renal calculi
  3. lethargy
  4. anorexia and nausea
  5. peptic ulcers
  6. depression
  7. drowsiness
  8. impaired cognition
39
Q

what are the causes of hypophosphatemia?

A
  1. inadequate intestinal phosphate absorption- vitamin D deficiency
  2. excessive renal excretion- PTH excess
40
Q

What are some symptoms of hypophosphatemia?

A

nerve, bone, red and white blood cells, membrane, and muscle functional issues

41
Q

What are some causes of hyperphosphatemia?

A
  1. decreased renal excretion- impaired kidney function
  2. hypoparathyriodism
  3. Excessive release of phosphate into the ECM
  4. A combination of all above
42
Q

clinical effects of hyperphosphatemia?

A

calcification of soft-tissue
tetany
seizures

43
Q

lab findings in those with hyperphosphatemia?

A

concentration greater than 1.8mmol/L

MSK I (23 decks)

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