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Biochem Final > 11/14: Calcium and Phosphorus I > Flashcards

11/14: Calcium and Phosphorus I Flashcards

1
Q

What are the 3 main pools within the body that calcium is stored in?

A
  1. Bone
  2. Blood/ECF
  3. Intracellular calcium
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2
Q

What is the normal range for total serum calcium?

A

8.5-10.5 mg/dL

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3
Q

What is the 45% of calcium that is actually biologically active called?

A

Ionized calcium

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4
Q

What is the normal range for ionized calcium?

A

4.4-5.4 mg/dL

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5
Q

Does calcium intake needed increase as you age?

A

Yes

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6
Q

What is the molarity of calcium normally in the interstitial fluid in the extracellular space?

A

1-2 mM

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7
Q

What is the calcium molarity intracellular?

A

.0001 mM

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8
Q
  1. Why is this steep gradient needed?
A

a. It is needed to regulate cell function

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9
Q
  1. What is phosphorous found as within the body?
A

a. Inorganic phosphate (Pi)

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10
Q
  1. Where is the majority of phosphorus found?
A

In hydroxyapatite of bone and teeth

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11
Q

Is the majority of phosphorous absorbed in the gut unlike calcium?

A

Yes

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12
Q

What is the normal adult phosphorosus concentration?

A

2.5-4.5

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13
Q

What are the 4 main organ systems that deal with calcium regulation?

A
  1. Gut
  2. Bone
  3. Kidney
  4. Parathyroid
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14
Q

What 3 areas involving these 4 organs deal with the regulation of calcium and phosphorus?

A
  1. Gut absorption
  2. Bone turnover
  3. Kidney filtration
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15
Q

What is net zero Ca and Phosphate balance?

A

When Ca/Pi ingestion is equal to loss by peeing and pooping

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16
Q

What are the 3 key steps involving calcium uptake?

A
  1. Uptake
  2. Transcellular transport
  3. Extrusion
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17
Q

What occurs in uptake of calcium?

A

Calcium is taking from the apical side of the cell through TRP ion channels

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18
Q

What occurs in transcellular transport of calcium?

A

Calcium once ingested in taken through the cell by calbindin proteins

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19
Q

What occurs in extrusion?

A

Calcium is removed by CaATPase pumps on the basal surface of the cell

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20
Q

What transporter takes Pi into the cells within the gut?

A

NaPi-IIb co-transporter

21
Q
  1. Where is this co-transporter located?
A

a. On the brush border within the ileum

22
Q
  1. Why is reabsorption of the kidney so important?
A

a. Because it gets back up to 90% of Ca and Pi within body

23
Q
  1. Are the 3 steps used in gut absorption of Ca the same in the kidney?
A

Yes

24
Q
  1. What differs for Pi absorption in the kidney?
A

a. A different isoform is used

25
Q

Since the majority of Ca and Pi absorption is similar across organs, how are they altered?

A

They are altered through hormones that change the expression of the key transporters

26
Q

What are the 3 hormones which regulate calcium?

A

PTH
1,25-OH2 D3
Calcitonin

27
Q

What are the 3 hormones which regulate phosphate?

A

PTH
1,25-OH2 D3
Fibroblast growth factor 23 (FGF23)

28
Q
  1. Can calcium and phosphate be regulated independently?
A

Yes

29
Q
  1. If calcium is too LOW what happens?
A
  1. Serum Ca decreased
  2. PT releases PTH
  3. PTH causes
    i. Bone release of Ca
    ii. Gut Ca absorption increase
    iii. Kidney Ca absorption increase
  4. Serum Ca restored
30
Q

What occurs if calcium is too HIGH?

A
  1. Serum Ca elevated
  2. PT stops releasing PTH 3. PTH decrease causes
    i. Bone to decrease Ca release
    ii. Gut to decrease Ca absorption
    iii. Kidney to decrease Ca reabsorption
  3. Serum Ca decreased, homeostasis achieved
31
Q

What protein is expressed by the parathyroid glands to monitor serum calcium?

A

Calcium sensing receptor (CaSR)
i. If calcium to high, CaSR expression increased causing decreased PTH
ii. If calcium to low, CaSR expression decreased causing increased PTH

32
Q

What receptor does PTH bind to?

A

PTH1R

33
Q
  1. How does PTH1R and PTH regulate its action?
A

a. Through the production of cyclic AMP

34
Q
  1. What does PTH hormone do to the gut, bone, and kidney?
A

a. Gut
i. Increases Ca resorption
b. Bone
i. Increases Ca resorption
c. Kidney
i. Increases Ca reabsorption

35
Q
  1. Does PTH have the same effect on the kidney regarding Pi?
A

No
i. PTH causes a reduction in phosphate reabsorption

36
Q

What does PTH do to the active form of Vit. D3?

A

Cause the conversion of 25 OH D3 to active 1-25 OH2 D3

37
Q

What does 1-25 OH2 D3 do to calcium?

A

Increases uptake in intestine
Increase reabsorption in kidney
Increase Ca secretion from bone

38
Q

What does 1-25 OH2 D3 do to Pi?

A

Increases Pi uptake in intestine
Increases Pi resorption in kidney
Increases Pi into blood from bone

39
Q

What occurs when calcium is HIGH?

A

The opposite
i. CaSR is activated, resulting in decreased PTH and decreased 1-25 OH2 D3

40
Q

Does calcitonin also help?

A

Yes, it opposed PTH

41
Q
  1. When is calcitonin released?
A

a. During elevated Ca levels

42
Q
  1. How does it do this?
A

a. Through inhibiting osteoclast resportion through the ruffled border

43
Q
  1. Is phosphate regulation as well understood as calcium?
A

No

44
Q
  1. When is FGF23 expressed?
A

When serum phosphate levels are too high (which occurs when serum calcium
levels are too high)

45
Q

What cell expresses it?

A

Osteocytes

46
Q

What two molecules inhibit the expression of FGF23?

A

DMP1
PHEX

47
Q

What does FGF23 do in the kidney?

A

Decrease reabsorption of phosphate by decreasing Na Pi transport expression
and decreased 1-25 OH2 D3

48
Q
  1. Which are the organ systems is the main regulator of phosphate regulation?
A

Kidney

49
Q
  1. What are the two Na Pi transporters expressed in the kidneys?
A

NaPiIIa and c

Biochem Final (7 decks)

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