Calcium Balance (Lec 18) Flashcards
Increases in calcium ions above normal cause progressive depression of what?
nervous system
symptoms of hypercalemia tend to appear when the blood calcium level rises above ___ mg/dl
12
Decreases in calcium storage cause the nervous system to become more ___
excited
___ % of the total body calcium is in the extracellular fluid
0.1
___ % of the calcium in the body is in the cells and organelles, the rest is stored in ___
1; bones
Breakdown the store of phosphate in bones, cells and ECF
bones: 85 %
cells: 14-15%
ECF: less than 1%
What are the two forms of inorganic phosphate in the plasma?
HPO4; H2PO-4
True or false?
large changes in the level of phosphate in the extracellular fluid cause major immediate effects on the body
false, do not cause
True or false?
slight changes in extracellular calcium can cause extreme immediate physiological effects
true
In regards to hypocalcemia causing the nervous system to become more excitable, this is mainly a result of what?
increased neuronal membrane permeability to sodium ions
Hypocalcemia may cause seizures. Where is the first sign of this?
tetany in the hand causing carpopedal spasm
Tetany ordinarily occurs when the blood concentration of calcium falls form its normal level of ___ mg/dl to about ___ mg/dl
- 5; 6
note: it is usually lethal at about 4 mg/dl
Usual rates of intake are about ___ mg/day each for calcium and phosphorous
1000
Normally, divalent ions are poorly absorbed, but vitamin D promotes calcium absorption by the intestines so that about ___% of ingested calcium is absorbed
35
Calcium not absorbed is excreted where?
feces
note: about 90% of daily intake is excreted
In regards to renal excretion of calcium and phosphate, __% of the plasma calcium bound to plasma protein is not filtered by glomerular capillaries
41
The renal tubules absorb about ___% of the calcium in the filtrate
99
PTH can greatly increase __ excretion
phosphate
____ crystals fail to precipitate in normal tissues
Hydroxyapatite
note: pyrophosphate is an inhibitor
In the initial stage of bone production, osteoblasts secrete ___ monomers which polymerize rapidly to form fibers
collagen
The precipitation of calcium along the collagen fibers eventually forms what?
hydroxyapatite crystals
If calcium is injected intravaneously it takes ___ to __ minutes for the concentration to return to normal
30; 60
note: same for if calcium is removed from body
Exchangeable calcium provides a rapid ___ mechanism
buffering
what are the 3 hormones that control calcium balance?
vitamin D, PTH, calcitonin
what is the active form of vitamin D?
1,25-dihydroxycholecalciferol
What does the active form of vitamin D cause?
kidneys and bones to increase absorption of calcium and phosphate into the extracellular fluid
The vitamin D receptor forms a complex with another intracellular receptor the _____ receptor, and this complex binds to DNA and activates transription
retinoid-X
formation of ___ a calcium-binding protein, functions in the brush border of epithelial cells to transport calcium to the cytoplasm
calbindin
calbindin remains in the cell for how long after the 1,25-dihydroxycholecalciferol has been removed?
weeks
A calcium stimulated ATPase in the brush border of epithelial cells and an alkaline phosphatase are two ways that 1,25-dihydroxycholecalciferol promotes what?
absorption of calcium
In the absence of vitamin D, the effect of PTH in causing bone absorption is greatly ____
reduced
Vitamin D in small quantities ___ bone calcification
promotes
note: increases calcium and phosphate absorption from intestines
Excess activity of PTH causes what?
rapid absorption of calcium salts from bone
note: results in hypercalemia in ECF
Synthesis of PTH occurs where?
ER and golgi
Effects on bone in causing absorption of calcium and phosphate include?
a rapid phase that begins in minutes and increases progressively for hours; a much slower phase that results in increased osteoclastic reabsorption of the bone itself
true or false?
the cell membranes of both the osteoblasts and the osteoclasts have receptor proteins for binding PTH
true
The osteoclasts do not have ___ receptor proteins for PTH
membrane
A major secondary signal used between osteoblasts and osteoclasts is ___ ligand, which activates receptors on preosteoclast cells and transforms them into mature osteoclasts
osteoprotegerin
What are the two stages of the osteoclastic system?
immediate activation of osteoclasts that are already formed, formation of new ones
Administration of PTH causes rapid loss of ___ in the urine
phosphate
PTH increases renal tubular reabsorption of ___ and diminishes reabsorption of ___
calcium; phosphate
Without the effect of PTH on the kidneys to increase calcium reabsorption, the urine would eventually do what?
deplete both ECF and bones of calcium
A large share of the effect of PTH on its target organs is mediated by ___
cAMP
Rickets, pregnancy, and lactation, are all conditions that?
decrease calcium ion concentration
Calcitonin is secreted by what gland?
thyroid
Calcitonin tends to decrease plasma ___ concentration
calcium
Calcitonin is synthesized in and secreted by ___ cells
parafollicular (C cells)
Any initial reduction of the calcium ion concentration caused by calcitonin leads within hours to a powerful stimulation of ___ secretion
PTH
In certain bone diseases such as ___ disease, osteoclastic activity is greatly accelerated and calcitonin has a more potent effect on reducing calcium absorption
Paget
____ occurs when the parathyroid glands do not secrete sufficient PTH
hypoparathyroidism
What is the usual cause of death from hypoparathyroidism?
spasms of laryngeal muscles
Primary or secondary hyperthyroidism?
An abnormality of the parathyroid glands causes inappropriate, excess PTH secretions, more prevalent in women.
primary
Primary or secondary hyperthyroidism?
high levels of PTH occur as a compensation for hypocalcemia, can be caused by vitamin D deficiency which can lead to osteomalacia
secondary
characteristics of rickets
softening and poor mineralization of bones leading to skeletal deformities - severely deficient in vitamin D
characteristics of osteoperosis
weak bones, loss of bone density - causes fractures
