Mrs reeds Flashcards
Explain how the autonomic nervous system regulates heart rate during exercise.
The autonomic nervous system consists of the sympathetic and parasympathetic branches. During exercise, the sympathetic nervous system increases heart rate by releasing noradrenaline, stimulating the sinoatrial node (SAN). The parasympathetic nervous system slows heart rate during rest or recovery via the vagus nerve, which reduces SAN activity.
Describe the role of baroreceptors and chemoreceptors in the control of heart rate.
Baroreceptors, located in the carotid arteries and aorta, detect changes in blood pressure. When blood pressure drops (e.g., during exercise), they send signals to the brain to increase heart rate. Chemoreceptors, sensitive to carbon dioxide (CO₂) and pH changes in the blood, trigger an increase in heart rate when CO₂ levels rise (indicating higher metabolism during exercise).
How does adrenaline affect heart rate before and during physical activity?
Adrenaline, released from the adrenal glands before and during exercise (anticipatory rise), increases heart rate by stimulating the SAN and enhancing blood flow to muscles.
Outline the sequence of events in the heart’s conduction system that results in a heartbeat.
The conduction system starts at the sinoatrial node (SAN), which initiates the heartbeat, sending an impulse across the atria, causing them to contract. The signal reaches the atrioventricular node (AVN), where there’s a brief delay to allow ventricular filling. The impulse then travels through the bundle of His and down the Purkinje fibers, causing ventricular contraction.
Describe the role of the sinoatrial node (SAN) and atrioventricular node (AVN) in the heart’s electrical activity.
The SAN is the heart’s natural pacemaker, setting the pace of the heart rate. The AVN ensures the impulse is delayed, allowing the atria to fully contract before the ventricles do, preventing simultaneous contractions.
Explain the importance of the bundle of His and Purkinje fibers in the coordination of the heart’s contraction.
The bundle of His and Purkinje fibers ensure rapid transmission of electrical impulses to the ventricles, resulting in a coordinated and efficient contraction that pumps blood out of the heart.
What causes anticipatory rise in heart rate before exercise begins?
Anticipatory rise occurs due to the release of adrenaline and noradrenaline from the adrenal glands in response to the brain’s preparation for exercise. This increase happens before physical activity begins.
How does heart rate change during different intensities of exercise, and what mechanisms are responsible for these changes?
During low-intensity exercise, heart rate increases gradually as more oxygen is needed. In high-intensity exercise, heart rate rises sharply to meet the increased oxygen demand. This is controlled by the sympathetic nervous system and the increased release of adrenaline.
Compare the heart rate response during steady-state and intermittent forms of exercise.
In steady-state exercise, heart rate increases initially and then plateaus when a balance between oxygen supply and demand is reached. In intermittent exercise, such as interval training, heart rate fluctuates with alternating periods of high and low intensity.
Define stroke volume, end-diastolic volume, and end-systolic volume, and explain how they are related.
Stroke volume is the amount of blood pumped out of the left ventricle with each beat. End-diastolic volume (EDV) is the volume of blood in the ventricles at the end of filling (diastole). End-systolic volume (ESV) is the volume remaining after contraction (systole).
How does stroke volume change with increasing exercise intensity, and what physiological factors contribute to this?
Stroke volume increases as exercise intensity rises due to venous return (Frank-Starling mechanism), increased contractility, and decreased afterload. It plateaus at around 40-60% of maximal intensity.
Explain how training affects cardiac volumes in elite endurance athletes.
Endurance training increases stroke volume and EDV due to cardiac hypertrophy (especially of the left ventricle), improved venous return, and increased blood volume. This leads to a more efficient heart and a lower resting heart rate.
Define A-VO2 difference and explain its significance during exercise.
A-VO2 difference is the difference in the oxygen content of the blood between the arteries and the veins. It shows how much oxygen is extracted by the muscles during exercise. A larger A-VO2 difference indicates more oxygen is being used by the working muscles.
How does the A-VO2 difference change during exercise compared to rest, and what factors contribute to this change?
During exercise, A-VO2 difference increases because muscles demand more oxygen, and the body extracts more oxygen from the blood. This is facilitated by increased capillary density, mitochondrial activity, and improved blood flow.
Explain the role of increased capillarization in enhancing A-VO2 difference during aerobic training.
Increased capillarization (more capillaries per muscle fiber) enhances oxygen delivery to muscles, increasing the A-VO2 difference during exercise. This is a long-term adaptation to aerobic training.
