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Questions and Answers
What is the primary factor that determines the sinus rhythm of the heart?
What is the effect of increased Ca2+ levels on heart rate?
What is the term for a heart rate greater than 100bpm?
What is the formula to calculate cardiac output?
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What is the normal cardiac output at rest?
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Which of the following is a factor that decreases heart rate?
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What is the formula to calculate stroke volume?
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What is the term for the amount of stretch of the ventricles at the end of diastole?
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Study Notes
Cardiac Output
- Cardiac output is the amount of blood pumped from the right or left ventricles per minute, calculated by multiplying heart rate and stroke volume.
- At rest, cardiac output is approximately 5L/minute, increasing to around 25L/minute during exercise.
- The cardiac output should meet the body's demand for oxygen and nutrients.
Heart Rate
- The average heart rate in a healthy adult is 60-80 beats per minute (bpm).
- The sinoatrial (SA) node sets the sinus rhythm, which can be influenced by various factors.
- Factors that increase heart rate (positive chronotropic): • Sympathetic nervous system (adrenaline/noradrenaline) signals • Hormones (T3, T4) increasing metabolism • Body temperature • Increased Ca2+ levels • Hypoxia and hypercapnia (low oxygen and high carbon dioxide)
- Tachycardia is a heart rate above 100bpm, while bradycardia is a heart rate below 60bpm.
- Factors that decrease heart rate (negative chronotropic): • Parasympathetic nervous system (acetylcholine) signals • Hyperkalaemia (increased K+ levels) • Decreased Ca2+ levels
Stroke Volume
- Stroke volume is the amount of blood pumped from the left or right ventricles per beat, calculated by subtracting end-systolic volume (ESV) from end-diastolic volume (EDV).
- The stroke volume is influenced by three factors: • Preload: • Amount of stretch of the ventricles at the end of diastole (EDV) • Factors that alter preload: - Venous return - Skeletal muscle pump - Respiratory pump - Venous tone - Gravity • Contractility: • The Frank-Starling Law, which states that the more the heart stretches, the more it contracts.
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Description
Learn about cardiac output, heart rate, and factors that influence them, including the role of the sympathetic nervous system.
