23.3 Calcium Balance Flashcards
What happens if Ca levels rise too high above normal?
- nervous system becomes progressively damaged.
- constipation, and sluggish reflexes
- above 12mg/dl
What happens if Ca levels fall too low below normal?
- nervous sytem become overexcited
Where is the majority of Ca stored in teh body?
bones. 1% in the cells/organells. 0.1% in ECF
Where is the majority of phosphate stored in the body?
bones. 15% in cells. 1% in ECF
Which system is much more tolerant to varying levels of concentration?
phosphate, allows multiple changes without having large effect. Ca has large effect with minor changes
What are the effects of hypocalcemia?
- increased excitability of nervous system
2. seizures, seen in the hand with carpopedal spasm
When can tetany become lethal?
at 4mg/dl, onset at
how much of Ca intake from diet is absorbed?
only 10%. the rest is excreted. Poor absorption rate in the GI, is improved with Vitamin D
What hormone can increase the excretion of phosphate through renal system?
parathyroid hormone. required for survival
How much calcium is reabsorbed from the filtrate?
99%, minimal amount is secreted in urine
What is present that inhibits the precipitation of hydroxyapatite crytsals, and prevents formation of bone?
pyrophosphate
WHat is the benefit of keeping hydroxyapatite in an amorphous (noncrystalline form)?
this allows for faster reabsorption into ECF for migration to different tissues when needed
When will calcium salts precipitate to other tissues?
normal conditions, but calcium salt deposition inhibitor factors disappear
How rapidly can [Ca] return to normal after large amounts are removed from body fluids?
return to normal in 30 minutes
How rapidly can [Ca] return to normla after large amounts are injected IV?
return to normal in 30-60 minutes
What is responsible for providing the body the ability to rapidly alter [Ca] levels in circulating fluids?
exchangeable calcium present in all cell types
What is the active form of Vitamin D?
1,25-dihydroxycholecalciferol
What does the active form of Vitamin D do?
- increase Ca and phosphate absorption into ECF from the intestine, kidneys, and bones
Vit D binds its receptor as what type?
binds as hormone that activates a DNA region
What complex does Vit D form in order to activate trasncription?
binds with retinoid X-factor to initiate transcription. is possible to inhibit trasnscirption
The absence of Vit D can severely (negatively) affect what other hormone?
PTH, becasue there is reduced calcium transport through cellular membranes.
What is the difference of super high Ca presence versus small amount of Ca presence?
- high amount= absorption into bone
2. low amounts= bone calcification
Excess activity of the parathyroid hormone causes what condition?
- secretion of calcium salts from bones, leading to hypercalcemia
Under activity of the parathyroid hormone causes what condition?
- reduced secretion of calcium salt from bone, leading to hypocalcemia
Where is PTH synthesized?
ER and golgi
What occurs during the rapid phase of PTH stimulation?
- results form activation of osteocytes that promote calcium and phosphate absorption
- begins in minutes and progressively increases for hours
WHat occurs during the slow phase of PTH stimulation?
- over days and weeks
2. osteroclasts proliferate and reabsorb bone
How can PTH induce the absorption of Ca and phosphate from bone?
- PTH binds directly with osteoblasts and osteocytes to activate Ca pumps, causing removal of calcium phosphate salts
What effect does PTH have on osteoclasts?
- no PM PTH receptor
- two stage activation
- immediate activation of formed osteoclasts, and stimulate new osteoclast production. - causes break down of bone
How does PTH affect absorption in the proximal tublar system?
- phosphate is secreted, not absorbed
2. calcium is rapidly reabsorbed
Which ions are reabsorbed with presence of PTH?
- Mg and H ions
Which ions are rapidly secreted with presence of PTH?
- Na, K, amino acids ions are highly secreted
What would happen if the parathyroid were surgically removed?
- loss of PTH
2. urine would deplete ECF and calcium of the bones
What conditions/diseases will contribute to decreased ca ion concentration?
- rickets
- pregnancy
- lactation
What conditions can increase Ca ions above the normal value range?
- excessive Ca intake
- increased Vit D
- Bone absorption secondary to disease
How are decreased ca ion levels detected and corrected?
- low Ca ion detected by parathyroid. which releases PTH
- PTH acts to increase bone resoprtion;releasing Ca
- PTH acts on kidneys to secrete phosphate, absorb Ca, and vitamin D to help with absorption of Ca in the intestine
What organs can help increase Ca levels int he body?
bone, kidneys, and intestine
Where is calcitonin secreted from?
- thyroid gland
What is the common effect of calcitonin?
- decrease plasma calcium concentration
Were is calcitonin formed?
- parafollicular cells
Does calcitonin have a strong or weak effect on Ca ion concentration in the human body?
weak effect, that ‘s followed by powerful effect of PTH
In what specific case can calcitonin have a strong effec int reducing calcium reabsorption?
paget’s disease, wher osteoclast activity is severely high
What happens in hypoparathyroidism?
- reduced PTH, inactivates osteoclasts
- this reduces blood Ca levels
- this can lead to tetany. start with laryngeal muscles
What is primary hyperparathyroidism?
- abnormality of parathyroid glands secrete excess PTH
2. prevalent in women bc of lactation and pregnancy
What is secondary hyperparathyroidism?
- high PTH levels to compensate for hypocalcemia
2. Vit D deficiency leading to osteomalacia
