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Ch. 20 The Heart
Martini - Fundamentals of Anatomy & Physiology 12th Edition
Martini, Nath, Bartholomew12th EditionFundamentals of Anatomy & PhysiologyISBN: 9780137854011Non è quello che usi tu?Cambia libro di testo
Tutti i libri di testoMartini, Nath, Bartholomew 12th EditionCh. 20 The HeartProblema 31
Capitolo 20, Problema 31

Karen is taking the medication verapamil, a drug that blocks the calcium channels in cardiac muscle cells. What effect should this medication have on Karen's stroke volume?

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1
Step 1: Understand the role of calcium in cardiac muscle contraction. Calcium ions enter cardiac muscle cells through calcium channels during the plateau phase of the action potential, which triggers further calcium release from the sarcoplasmic reticulum, leading to muscle contraction.
Step 2: Recognize that verapamil blocks these calcium channels, reducing the influx of calcium into cardiac muscle cells during each heartbeat.
Step 3: Connect the reduction in calcium influx to a decrease in the strength of cardiac muscle contraction, since less calcium means less activation of the contractile proteins (actin and myosin).
Step 4: Recall that stroke volume is the amount of blood ejected by the left ventricle with each contraction, and it depends on the force of contraction (contractility) among other factors.
Step 5: Conclude that by blocking calcium channels and reducing contractility, verapamil should decrease stroke volume because the heart pumps less forcefully.

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Calcium Channels in Cardiac Muscle Cells

Calcium channels in cardiac muscle cells allow calcium ions to enter during an action potential, triggering muscle contraction. Blocking these channels reduces calcium influx, which weakens the contraction strength of the heart muscle.
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Stroke Volume

Stroke volume is the amount of blood ejected by the left ventricle with each heartbeat. It depends on the force of cardiac muscle contraction, preload, and afterload. Stronger contractions generally increase stroke volume.
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Effect of Calcium Channel Blockers on Cardiac Function

Calcium channel blockers like verapamil decrease the force of cardiac contractions by limiting calcium entry. This leads to reduced contractility, which typically lowers stroke volume and can affect overall cardiac output.
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The following measurements were made on two individuals (the values recorded remained stable for 1 hour):

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Which person has the longer ventricular filling time?

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Harvey has a heart murmur in his left ventricle that produces a loud 'gurgling' sound at the beginning of systole. Which valve is probably faulty?

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