Lecture 23: Calcium Balance Flashcards
(85 cards)
In the human body, what type of cells are sensitive to changes in calcium ion concentrations?
Excitable cells, such as neurons.
What does an increase in calcium ion levels above normal cause?
Progressive depression of the nervous system.
- symptoms begin to appear when the blood calcium level rises above 12 mg/dl
- reflex activities of the nervous system are sluggish
- there is constipation and lack of appetite
What does a decrease in calcium ion levels below normal cause?
The nervous system to become more excited.
Is constipation and lack of appetite seen in patients with an increased or decreased calcium ion concentration?
Increased calcium ion concentration above normal - which causes depression of the nervous system.
Where is calcium stored in the body?
- 0.1% of total body calcium is in the extracellular fluid.
- 1% is in the cells and organelles.
- The rest is stored in the bones.
Where is phosphate stored in the body?
- 85% of total body phosphate stored in bones.
- 14-15% is in the cells.
- Less than 1% is in the extracellular fluid.
True or False:
Extracellular phosphate concentration is more regulated that that of calcium concentrations.
False - extracellular phosphate concentration is not nearly as well regulated as that of calcium.
Which two forms is inorganic phosphate in the plasma mainly found in?
- HPO4^2-
- H2PO4^-
Does large changes in the level of phosphate in the extracellular fluid cause major immediate effects on the body?
No - large changes in the level of phosphate in the extracellular fluid DO NOT cause major immediate effects on the body.
Large changes in the level of phosphate in the extracellular fluid do not cause major immediate effects on the body. What about changes in extracellular calcium levels?
Even slight changes in extracellular calcium can cause extreme immediate physiological effects.
What does hypocalcemia cause?
Nervous system excitement and tetany.
hypocalcemia may also cause seizures
How does hypocalcemia cause the nervous system to become progressively more excitable?
Due to increased neuronal membrane permeability to sodium ions.
Hypocalcemia causes nervous system excitement and tetany. Where does the fist sign of tetany typically occur in patients with hypocalcemia?
First sign of tetany typically occurs in the hand, resulting in carpopedal spasm.
Tetany ordinarily occurs when the blood concentration of calcium falls from its normal level of 9.5 mg/dl to about 6 mg/dl (35% below normal calcium concentration).
It is usually lethal at about 4 mg/dl.
What is the usual rates of intake for calcium and phosphorous each day?
about 1000 mg/day each for calcium and phosphorous
Normally, divalent ions are poorly absorbed, but what vitamin promotes calcium absorption by the intestines so that about 35% of ingested calcium is absorbed?
Vitamin D
What happens to calcium that is not absorbed in the body?
Excreted in the feces.
**about 250 mg/day of the absorbed calcium enters intestines via secreted GI juices and sloughed mucosal cells.
** Thus, about 90% of the daily intake of calcium is excreted.
How many mg/day of calcium is absorbed, which enters the intestines via secreted GI juices and sloughed mucosal cells?
250 mg/day
What percentage of daily intake of calcium is excreted?
90%
How many mg/day of ingested calcium is excreted in the urine?
100 mg/day (10%) of ingested calcium is excreted in the urine.
What percentage of calcium that is bound to plasma proteins is not filtered by glomerular capillaries?
41%
True or False:
Renal tubules reabsorb about 99% of the calcium in the filtrate.
True
What is the effect of the hormone, PTH, on phosphate excretion?
PTH can greatly increase phosphate excretion.
What is the function of pyrophosphate?
Hydroxyapatite crystals fail to precipitate in normal tissues (except in bone).
Inhibitors are present in almost all tissues and plasma, to prevent such precipitation.
Pyrophosphate is once of these inhibitors:
> bone may secrete a pyrophosphate inhibitor to allow hydroxyapatite precipitation.
What do osteoblasts secrete in the initial stage of bone production?
Collagen monomers - which polymerize rapidly to form collagen fibers.
the precipitation of calcium along the collagen fibers eventually forms hydroxyapatite crystals