Calcium Regulation Flashcards
1
Q
Role of VITAMIN D
&
Vitamin D action on GI TRACT
A
- Calcium homeostasis: increase plasma Ca
- Synthesized sequentially in skin, liver, and kidneys
- Exerts effects directly on gastrointestinal tract
- increases calcium absorption and to a lesser extent, phosphate
2
Q
Vitamin D synthesis in skin depends on: (3)
A
- age (skin ineffecient >70yrs)
- Length of sun exposure
- UV strength exposure; latitude & season
- Ethnicity
3
Q
Dietary sources of Vitamin D (4)
A
- Fatty fish
- Fish oils
- Dairy products, eggs
- Fortified milk, cereals, grains
4
Q
25 hydroxyvitamin D
A
- storage form
- substrate dependent; not regulated
5
Q
1-alpha hydroxylase
A
- Produces activated: 1,25 Vitamin D
- Stimulated by low calcium levels and low 25 hydroxyvitamin D
- increased PTH
- low phosphate
6
Q
Vitamin D action on BONE
A
- Indirect action; improves bone health
-
Deficiency causes decreased:
- bone density
- osteomalacia (soft bones)
7
Q
Vitamin D action on KIDNEY
A
- Indrect action
- Deficiency: renal phosphate wasting due to increased PTH levels
8
Q
Role of PARATHYROID HORMONE (PTH)
A
- Increase plasma calcium
- Synthesized in the parathyroid glands located in the neck
- Exerts effects directly on skeleton and kidneys
- Secreted by exocytosis in response to hypocalcemia
- Calcium sensint receptor on cell membrane
- As vitamin D decreases, only a small decrease in Ca is seen b/c of an increase in PTH to maintain levels
9
Q
Parathyroid hormone action on BONE
A
Increases bone resorption by stimulating activity of osteoclasts (break down)
10
Q
Parathyroid hormone action on KIDNEYS
A
- Increases renal calcium reabsorption
- Decreases renal phosphate reabsorption/increases secretion
- Promotes conversion of 25-hydroxyvitamin D –>
1,25-dihydroxyvitamin D
11
Q
Parathyroid hormone actions on GI TRACT
A
- Indirect action
- Stimulates produciton of active form of Vit D —> increases absorption of calcium and to a lesser extend phosphate
12
Q
Hyperparathyroidism
4 hormone levels
4 effects
A
- High calcium
- low phosphate
- normal 25; high 1,25
- HIGH PTH
Effects:
- Hypercalcemia
- hypophosphatemia
- osteoporosis
- nephrolithiasis (kidney stones)
13
Q
Vitamin D toxicity
4 hormone levels
4 effects
A
- High calcium
- High phosphate
- HIGH 25; normal-high 1,25
- Low PTH
Effects:
- Hypercalcemia
- Hypercalciuria (nephrolithiasis, renal calcinosis, renal insufficiency)
- Hyperphosphatemia
- Inhibition of PTH secretion (reason why 1,25 vit D levels aren’t extremely high)
14
Q
Hypoparathyroidism
4 hormone levels
2 effects
A
- Low calcium
- high phosphate
- normal 25; low 1,25
- LOW PTH
Effects:
- Hypocalcemia
- paresthesias
- muscle spasm
- tetany
- laryngospasm
- seizures - Hyperphosphatemia (due to lack of stimulation of secretion in kidneys)
15
Q
Vitamin D deficiency
4 hormone levels
5 Effects
A
- Low calcium
- Low phosphate
- LOW 25; normal 1, 25
- High PTH
Effects:
Due to malabsorption
- Hypocalcemia
- Hypophosphatemia
- Myopathy: weakness, muscle pain
- Secondary hyperparathyroidism
- Inadequate bone mineralization
- osteomalacia: not enough Ca to form correclty; excess osteoid
- osteoporosis
- Rickets: bowing of lower extremeties