11/14: Calcium and Phosphorus I Flashcards
What are the 3 main pools within the body that calcium is stored in?
- Bone
- Blood/ECF
- Intracellular calcium
What is the normal range for total serum calcium?
8.5-10.5 mg/dL
What is the 45% of calcium that is actually biologically active called?
Ionized calcium
What is the normal range for ionized calcium?
4.4-5.4 mg/dL
Does calcium intake needed increase as you age?
Yes
What is the molarity of calcium normally in the interstitial fluid in the extracellular space?
1-2 mM
What is the calcium molarity intracellular?
.0001 mM
- Why is this steep gradient needed?
a. It is needed to regulate cell function
- What is phosphorous found as within the body?
a. Inorganic phosphate (Pi)
- Where is the majority of phosphorus found?
In hydroxyapatite of bone and teeth
Is the majority of phosphorous absorbed in the gut unlike calcium?
Yes
What is the normal adult phosphorosus concentration?
2.5-4.5
What are the 4 main organ systems that deal with calcium regulation?
- Gut
- Bone
- Kidney
- Parathyroid
What 3 areas involving these 4 organs deal with the regulation of calcium and phosphorus?
- Gut absorption
- Bone turnover
- Kidney filtration
What is net zero Ca and Phosphate balance?
When Ca/Pi ingestion is equal to loss by peeing and pooping
What are the 3 key steps involving calcium uptake?
- Uptake
- Transcellular transport
- Extrusion
What occurs in uptake of calcium?
Calcium is taking from the apical side of the cell through TRP ion channels
What occurs in transcellular transport of calcium?
Calcium once ingested in taken through the cell by calbindin proteins
What occurs in extrusion?
Calcium is removed by CaATPase pumps on the basal surface of the cell
What transporter takes Pi into the cells within the gut?
NaPi-IIb co-transporter
- Where is this co-transporter located?
a. On the brush border within the ileum
- Why is reabsorption of the kidney so important?
a. Because it gets back up to 90% of Ca and Pi within body
- Are the 3 steps used in gut absorption of Ca the same in the kidney?
Yes
- What differs for Pi absorption in the kidney?
a. A different isoform is used
Since the majority of Ca and Pi absorption is similar across organs, how are they altered?
They are altered through hormones that change the expression of the key transporters
What are the 3 hormones which regulate calcium?
PTH
1,25-OH2 D3
Calcitonin
What are the 3 hormones which regulate phosphate?
PTH
1,25-OH2 D3
Fibroblast growth factor 23 (FGF23)
- Can calcium and phosphate be regulated independently?
Yes
- If calcium is too LOW what happens?
- Serum Ca decreased
- PT releases PTH
- PTH causes
i. Bone release of Ca
ii. Gut Ca absorption increase
iii. Kidney Ca absorption increase - Serum Ca restored
What occurs if calcium is too HIGH?
- Serum Ca elevated
- 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 - Serum Ca decreased, homeostasis achieved
What protein is expressed by the parathyroid glands to monitor serum calcium?
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
What receptor does PTH bind to?
PTH1R
- How does PTH1R and PTH regulate its action?
a. Through the production of cyclic AMP
- What does PTH hormone do to the gut, bone, and kidney?
a. Gut
i. Increases Ca resorption
b. Bone
i. Increases Ca resorption
c. Kidney
i. Increases Ca reabsorption
- Does PTH have the same effect on the kidney regarding Pi?
No
i. PTH causes a reduction in phosphate reabsorption
What does PTH do to the active form of Vit. D3?
Cause the conversion of 25 OH D3 to active 1-25 OH2 D3
What does 1-25 OH2 D3 do to calcium?
Increases uptake in intestine
Increase reabsorption in kidney
Increase Ca secretion from bone
What does 1-25 OH2 D3 do to Pi?
Increases Pi uptake in intestine
Increases Pi resorption in kidney
Increases Pi into blood from bone
What occurs when calcium is HIGH?
The opposite
i. CaSR is activated, resulting in decreased PTH and decreased 1-25 OH2 D3
Does calcitonin also help?
Yes, it opposed PTH
- When is calcitonin released?
a. During elevated Ca levels
- How does it do this?
a. Through inhibiting osteoclast resportion through the ruffled border
- Is phosphate regulation as well understood as calcium?
No
- When is FGF23 expressed?
When serum phosphate levels are too high (which occurs when serum calcium
levels are too high)
What cell expresses it?
Osteocytes
What two molecules inhibit the expression of FGF23?
DMP1
PHEX
What does FGF23 do in the kidney?
Decrease reabsorption of phosphate by decreasing Na Pi transport expression
and decreased 1-25 OH2 D3
- Which are the organ systems is the main regulator of phosphate regulation?
Kidney
- What are the two Na Pi transporters expressed in the kidneys?
NaPiIIa and c
