Calcium Distribution in the Body

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Questions and Answers

What percentage of calcium in the body is primarily found in bone?

1%
99% (correct)
50%
75%

Which form accounts for the highest percentage of calcium in the blood?

Bound to anions
Bound to proteins
In bone tissue
Free Ca2+ ions (ionized Ca2+) (correct)

Why is the concentration of ionized Ca2+ in blood significantly higher than in the cytosol of muscle cells?

Calcium is mostly stored in the cytosol.
Calcium only plays a role in bone formation.
Muscle cells do not require calcium.
A large gradient is maintained for calcium flux. (correct)

Which of the following is NOT a form that calcium in blood is distributed among?

<p>Stored in bone (B)</p> Signup and view all the answers

What change can dramatically affect calcium concentrations during critical care?

<p>Concentrations of citrate, HCO3-, lactate, PO4-, and albumin (A)</p> Signup and view all the answers

Flashcards

Calcium Distribution in the Body

The majority of calcium in the body (99%) is found within bones, with the remaining 1% circulating in the blood and other bodily fluids.

Calcium Gradient between Blood and Muscle Cells

The concentration of ionized calcium (Ca2+) in the blood is significantly higher (5,000 to 10,000 times) than in the cytosol of muscle cells.

Distribution of Calcium in Blood

About 45% of calcium in the blood is free in the form of ionized calcium (Ca2+), 40% is bound to proteins, mostly albumin, and 15% is bound to anions like HCO3-, citrate, PO4-, and lactate.

Variations in Calcium Distribution during Illness

The relative amounts of calcium bound to proteins or anions can fluctuate, especially during surgical procedures or critical illness, affecting the accuracy of total calcium measurements.

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Reliability of Total Calcium Measurements during Illness

Because of fluctuations in calcium binding to various components, it can be difficult to accurately determine ionized calcium levels from total calcium measurements, particularly in acutely ill individuals.

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Study Notes

Calcium Distribution in the Body

Approximately 99% of body calcium is found in bone.
The remaining 1% is primarily in blood and other extracellular fluid (ECF).
Intracellular calcium (cytosol) is very low in most cells.
Blood ionized calcium concentration is significantly higher than in cardiac or smooth muscle cells (5,000-10,000 times greater).
This large gradient is crucial for rapid calcium influx.

Forms of Blood Calcium

45% of blood calcium is free ionized calcium.
40% is bound to protein, mainly albumin.
15% is bound to anions like bicarbonate, citrate, phosphate, and lactate.

Calcium Measurement Considerations

Blood calcium levels are affected by factors like citrate, bicarbonate, lactate, phosphate, and albumin concentrations.
These factors can significantly fluctuate in conditions like critical illness or surgery.
Consequently, total calcium levels are not a reliable predictor of ionized calcium, particularly in acutely ill patients.

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Description

This quiz explores the role and distribution of calcium in the human body, highlighting the significant presence in bones and its crucial role in blood. It also discusses the different forms of blood calcium and the factors affecting calcium measurement. Ideal for students studying physiology or health sciences.