To review:
Effects of sympathoadrenal and parasympathetic nerve activities on the cardiac rate and stroke volume.
Introduction:
Sympathoaderanal is the connection between the sympathetic nervous system and adrenal medulla. Sympathetic nervous system affects various regions of the heart. Parasympathetic nerve system is a part of the autonomic nervous system which slows down the heart rate by conserving energy.
Explanation of Solution
Sympathoadrenal system stimulates the cyclic AMP (adenosine monophosphate) production. Norepinephrine secreted from the sympathetic axons and epinephrine released from the adrenal medulla attach to the β1 adrenergic receptors. The action of cyclic AMP, on the calcium channels located on the pacemaker cells, results in the production of a pacemaker potential which, in turn, raises the rate of diastolic depolarization. This results in a faster cardiac rate. The effects of sympathoadrenal system include elevated conduction rate in the AV (atrio-ventricular) node, and the strength of both atrial and ventricular muscle contractions increases.
Norepinephrine and epinephrine increase contraction in the fibers which cause the amount of blood being released to increase. Hence, the stroke volume also rises. Parasympathetic nerve releases acetylcholine (Ach) which reduces the rate of diastolic depolarization by binding to the Ach receptors and causes diffusion of potassium outside. The cardiac rate also declines. Conduction rate decreases in the AV node, and the stroke volume also declines.
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Chapter 14 Solutions
Human Physiology
- Describe the factors that influence preload and afterload, and explain how they affect cardiac output?arrow_forwardDescribe the redistribution of cardiac output during exercise to the CNS, coronary, splanchnic, cutaneous, and skeletal muscle vascular beds during sustained exercise (distance running).arrow_forwardExplain why afterload is critical in cardiac function and maintaining long-term heart health (i.e. heart failure). Hint: Decreased output, by itself, not lead to heart failure.arrow_forward
- Define cardiac output, describe the factors that influence heart rate and stroke volume, and explain how adjustments in stroke volume and cardiac output are coordinated at different levels of physical activity.arrow_forwardDescribe the Flank-Starling law in the heart. Describe how the heart alters stroke volume under sympathetic stimulation.arrow_forwardWrite the word formula relating cardiac output, heart rate, and stroke volume. Give normal values for a resting adult.arrow_forward
- Human Physiology: From Cells to Systems (MindTap ...BiologyISBN:9781285866932Author:Lauralee SherwoodPublisher:Cengage Learning