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Old 08-11-2012
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Heart Beginning of irreversible damage to the cardiac muscle

A 62-year-old man was admitted to the hospital with severe retrosternal chest pain that radiated down the left arm. Three days later, he developed a ventricular arrhythmia and died. In the hours shortly after the patient first experienced chest pain, which of the following biochemical changes would have marked the beginning of irreversible damage to the cardiac muscle?

A. Decreased intracellular pH
B. Decreased Na+, K+-ATPase activity
C. Increased activity of phosphofructokinase
D. Increased concentration of cytosolic Ca2+
E. Increased conversion of pyruvate to lactate
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Old 08-11-2012
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Dd.....cell membrane damage
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Old 08-11-2012
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Answer is D
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D. Increased concentration of cytosolic Ca2+
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Old 08-11-2012
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Will go with D!
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Old 08-12-2012
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@koolkiller88- what's the answer?
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Option D (Increased concentration of cytosolic Ca2+) is correct. An increase in cytosolic Ca2+ concentration marks the beginning of irreversible damage to the cardiac muscle. Normally, a Ca2+ ATPase pump pumps Ca2+ out of the cytosol into the interstitial fluid. Calcium within the cytosol activates phospholipase in the cell membrane, proteases in the cytosol, and endonucleases in the nucleus, which produces irreversible injury and death of the cell.

Option A (Decreased intracellular pH) is incorrect. Decreased intracellular pH marks hypoxic change that is still reversible if O2 becomes available to hypoxic tissue, in this case, cardiac muscle. The nicotinamide adenine dinucleotide plus hydrogen (NADH) that is normally shuttled into the mitochondria for adenosine-5'-triphosphate (ATP) synthesis is used in anaerobic glycolysis to convert pyruvate to lactate, which reduces the intracellular pH.

Option B (Decreased Na+, K+-ATPase activity) is incorrect. Decreased Na+, K+-ATPase activity marks hypoxic change that is reversible if O2 becomes available to hypoxic tissue. During the early stages of an myocardial infarction (MI), lack of O2 in the muscle leads to reduced synthesis of ATP, which normally drives the ATPase pump. A dysfunctional Na+, K+ ATPase pump causes Na+ and H2O to move into cells, causing cellular swelling.

Option C (Increased activity of phosphofructokinase) is incorrect. Increased phosphofructokinase activity marks hypoxic changes that are reversible if O2 becomes available to hypoxic tissue. In the early stages of an MI, lack of O2 in cardiac muscle causes ATP synthesis to shift to anaerobic glycolysis in the cytosol. This triggers increased activity of phosphofructokinase, the rate-limiting reaction of glycolysis.

Option E (Increased conversion of pyruvate to lactate) is incorrect. Increased conversion of pyruvate to lactate occurs in anaerobic glycolysis, which is a reversible finding if O2 becomes available to the hypoxic tissue.
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Cardiovascular-, Cell-Biology-, Pathology-, Step-1-Questions

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