Calcium Physiology Overview

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Questions and Answers

What did Ringer demonstrate about Ca2+ in 1883?

Ca2+ is essential for myocardial contraction. (correct)

Ca2+ has no effect on heart function.

Ca2+ is non-essential for muscle contraction.

Ca2+ only affects skeletal muscle contraction.

What aspect of Ca2+ did McLean and Hastings find to be proportional to frog heart contraction amplitude?

Citrate-bound calcium concentration.

Protein-bound calcium concentration.

Ionized/free calcium concentration. (correct)

Total calcium concentration in the blood.

What was the mean concentration of blood-ionized Ca2+ in humans, as identified in the studies?

0.50 mmol/L

1.18 mmol/L (correct)

2.50 mmol/L

3.00 mmol/L

Why is it important to maintain ionized Ca2+ levels during surgery?

To ensure normal myocardial function. (B) Signup and view all the answers

What clinical symptom may result from decreased ionized Ca2+ concentrations in blood?

Irregular muscle spasms, called tetany. (B) Signup and view all the answers

Which of the following forms of Ca2+ was shown to have no effect on frog heart contraction?

Protein-bound Ca2+ (A), Citrate-bound Ca2+ (B) Signup and view all the answers

Flashcards

Calcium's Role in Heart Contraction

Calcium (Ca2+) is essential for muscle contraction, specifically the heart's ability to beat.

Free vs. Bound Calcium in Heart Function

Experimenters discovered that the free, or ionized, form of calcium is what directly affects heart muscle contraction, not calcium bound to proteins or other molecules.

Early Calcium Measurement

The first measurement of free calcium in the blood relied on observing the contraction of frog hearts.

Blood Calcium Regulation

The amount of free calcium in the blood is carefully regulated, typically around 1.18 mmol/L in humans.

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Low Blood Calcium and Tetany

Low levels of free calcium in the blood can disrupt muscle function, leading to spasms or twitches, a condition called tetany.

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Calcium Importance in Critical Care

Maintaining normal levels of free calcium is crucial during surgery and for critically ill patients, as low calcium can impair heart function.

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Study Notes

Calcium Physiology

Ringer demonstrated in 1883 that calcium is essential for myocardial contraction.
McLean and Hastings investigated the impact of bound and free calcium on frog heart contraction.
They found a direct correlation between ionized calcium concentration and the amplitude of frog heart contraction.
Protein-bound and citrate-bound calcium had no effect on contraction.
This discovery led to the development of the first assay for ionized calcium using frog hearts.
This early method, although not precise by modern standards, revealed the tight regulation of blood-ionized calcium.
The average ionized calcium concentration in humans is approximately 1.18 mmol/L.
Maintaining near-normal ionized calcium levels is crucial during surgery and in critically ill patients due to its impact on myocardial function.
Low ionized calcium can cause neuromuscular irritability, manifested as irregular muscle spasms (tetany).

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Description

This quiz explores the essential role of calcium in myocardial contraction as demonstrated through historical research, including key findings on ionized calcium's effects on frog hearts. It highlights the importance of maintaining normal ionized calcium levels in surgical and critical care settings, as well as the consequences of low calcium levels in muscle function.