16.2 Pumping Action of the Heart
3 min read•june 18, 2024
The is a complex dance of contractions and relaxations that keep our blood flowing. From to , each phase plays a crucial role in pumping oxygen-rich blood throughout our bodies and returning deoxygenated blood to the lungs.
Blood flow dynamics are governed by pressure gradients and resistance in our cardiovascular system. Factors like blood vessel diameter and tissue metabolic demands influence how blood moves through our bodies, ensuring that active tissues receive the oxygen and nutrients they need to function properly.
Cardiac Cycle and Hemodynamics
Phases of cardiac pumping action
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- : period of contraction
- Atrial systole: atria contract, forcefully pumping remaining blood into ventricles (80% of ventricular filling occurs passively during )
- : ventricles contract, pumping oxygen-poor blood into (right ventricle) and oxygen-rich blood into (left ventricle)
- : period of relaxation
- : atria relax and fill with blood from veins (superior and fill right atrium; fill left atrium)
- Ventricular : ventricles relax and fill with blood from atria, allowing for 80% of ventricular filling
Key events in cardiac cycle
- Atrial systole
- Atria contract, pumping remaining blood into ventricles (20% of ventricular filling)
- (tricuspid and mitral) open, allowing blood flow from atria to ventricles
- Ventricular systole
- Ventricles contract, pumping blood into pulmonary artery (right ventricle) and aorta (left ventricle)
- AV valves close, preventing backflow of blood into atria (first heart sound, , "lub")
- (pulmonary and aortic) open, allowing blood flow into arteries
- Ventricular diastole
- Ventricles relax and fill with blood from atria (80% of ventricular filling occurs passively)
- Semilunar valves close, preventing backflow of blood into ventricles (second heart sound, , "dub")
- AV valves open, allowing blood flow from atria to ventricles
- Atrial diastole
- Atria relax and fill with blood from veins (superior and inferior vena cava fill right atrium; pulmonary veins fill left atrium)
- Blood flows passively from atria to ventricles through open AV valves due to pressure gradient
Blood flow dynamics in cardiovascular system
- Blood flow () determined by relationship between pressure gradient () and resistance ()
- Increased pressure gradient leads to increased blood flow (e.g., during ventricular systole)
- Increased resistance leads to decreased blood flow (e.g., in narrowed or constricted blood vessels)
- Pressure gradient: difference in pressure between two points in cardiovascular system
- Pressure highest in aorta, decreases as blood flows through systemic circulation (arteries, arterioles, capillaries, venules, veins)
- Pressure lowest in vena cava, increases as blood returns to heart
- Resistance factors: blood vessel diameter, blood viscosity, total vessel length
- (narrowing of blood vessels) increases resistance, decreases blood flow
- (widening of blood vessels) decreases resistance, increases blood flow
- : local tissues adjust blood flow to meet metabolic demands
- Metabolically active tissues (e.g., exercising skeletal muscle) release vasodilators (e.g., ) to increase blood flow
- Less active tissues (e.g., resting skeletal muscle) experience vasoconstriction to decrease blood flow, conserving energy and redirecting blood to active tissues
Cardiac Performance Factors
- : the volume of blood in the ventricles at the end of diastole, influencing initial muscle fiber stretch
- : the pressure that the ventricles must overcome to eject blood, affected by arterial blood pressure
- : the amount of blood ejected from the ventricle during one contraction
- : the percentage of blood ejected from the ventricle during one contraction compared to its end-diastolic volume
- : describes how the heart naturally adapts to changes in blood volume, increasing stroke volume as preload increases
- : the volume of blood pumped by the heart in one minute, calculated by multiplying stroke volume by heart rate
Key Terms to Review (36)
Afterload: Afterload is the pressure the heart must work against to eject blood during systole. It is primarily determined by vascular resistance in the arteries.
Aorta: The aorta is the main and largest artery in the human body, responsible for carrying oxygenated blood from the left ventricle of the heart to the rest of the body. It is a crucial component in the pumping action of the heart, as it receives blood during ventricular systole and distributes it throughout the circulatory system.
Aortic Valve: The aortic valve is one of the four valves in the heart that regulates blood flow. It is responsible for controlling the flow of oxygenated blood from the left ventricle into the aorta, the main artery that distributes blood to the body's organs and tissues.
Atrial Diastole: Atrial diastole is the relaxation phase of the atria, the upper chambers of the heart. During this phase, the atria fill with blood returning from the body and lungs, preparing for the next contraction to pump blood into the ventricles below.
Atrial Systole: Atrial systole is the contraction of the atria, the upper chambers of the heart, which occurs during the cardiac cycle. This phase of the heart's pumping action is a crucial component in the overall functioning of the cardiovascular system.
Autoregulation: Autoregulation is the physiological process by which an organ or tissue can maintain relatively constant function despite changes in perfusion pressure. It is a crucial mechanism that helps maintain homeostasis and ensure adequate blood flow and oxygen delivery to vital organs.
AV Valves: The atrioventricular (AV) valves are one-way valves located between the atria and ventricles of the heart. They play a crucial role in the pumping action of the heart by ensuring the unidirectional flow of blood during the cardiac cycle.
Cardiac cycle: The cardiac cycle is the sequence of events that occur in the heart from the beginning of one heartbeat to the next. It includes both systole (contraction) and diastole (relaxation) phases.
Cardiac Cycle: The cardiac cycle refers to the coordinated series of events that occur during a single heartbeat, including the contraction and relaxation of the heart's chambers. This cyclical process is essential for the pumping action of the heart and the circulation of blood throughout the body.
Cardiac Output: Cardiac output is the volume of blood pumped by the heart per minute. It is a critical measure of the heart's pumping ability and a key determinant of tissue perfusion and oxygen delivery throughout the body. This term is essential in understanding the fundamental mechanics of the cardiovascular system and its role in various cardiovascular conditions and their management.
Contractility: Contractility is the intrinsic ability of cardiac muscle fibers to contract at a given fiber length. It is a crucial determinant of the heart's pumping efficiency.
Diastole: Diastole is the phase of the cardiac cycle when the heart muscles relax and allow the chambers to fill with blood. It occurs after systole, which is the contraction phase.
Diastole: Diastole is the period of the cardiac cycle when the heart's ventricles relax and fill with blood. It is an essential component of the pumping action of the heart, as it allows the ventricles to receive oxygenated blood from the atria before the next contraction.
Ejection Fraction: Ejection fraction is a measure of the percentage of blood that is pumped out of the heart's main pumping chamber, the left ventricle, with each contraction. It is a crucial indicator of the heart's overall pumping ability and is commonly used to assess cardiac function in various cardiovascular conditions.
Frank-Starling Law: The Frank-Starling law, also known as the law of the heart, describes the relationship between the stretch of the cardiac muscle and the force of contraction. It states that the greater the stretch of the ventricles prior to contraction, the greater the force of that contraction, up to an optimal point.
Hemodynamics: Hemodynamics refers to the study of the dynamics of blood flow and pressure within the cardiovascular system. It encompasses the principles that govern the movement and distribution of blood throughout the body, including the factors that influence cardiac output, blood pressure, and peripheral resistance.
Inferior Vena Cava: The inferior vena cava is the large vein that carries deoxygenated blood from the lower body back to the heart. It is a crucial component in the cardiovascular system, playing a vital role in the pumping action of the heart.
Mitral Valve: The mitral valve is one of the four heart valves responsible for regulating blood flow through the heart. It is located between the left atrium and the left ventricle, and its primary function is to ensure unidirectional flow of blood from the lungs into the left ventricle during the filling phase of the cardiac cycle.
National Heart, Lung, and Blood Institute: The National Heart, Lung, and Blood Institute (NHLBI) is a part of the U.S. National Institutes of Health (NIH). It provides global leadership for research, training, and education programs to promote the prevention and treatment of heart, lung, blood diseases, and sleep disorders.
Nitric Oxide: Nitric oxide (NO) is a colorless gas that acts as a signaling molecule in the body, playing a crucial role in various physiological processes, including the regulation of blood pressure, cardiac function, and neurotransmission. This versatile molecule has implications in several topics related to cardiovascular and respiratory health.
Preload: Preload is the degree of stretch of the cardiac muscle fibers at the end of diastole, just before contraction. It is influenced by the volume of blood returning to the heart.
Pulmonary Artery: The pulmonary artery is a large blood vessel that carries deoxygenated blood from the right ventricle of the heart to the lungs. It plays a crucial role in the pumping action of the heart, facilitating the exchange of gases between the blood and the lungs.
Pulmonary Valve: The pulmonary valve is one of the four valves in the human heart that controls the flow of blood. It is located between the right ventricle and the pulmonary artery, ensuring that blood flows in the correct direction from the heart to the lungs for oxygenation.
Pulmonary Veins: The pulmonary veins are a set of four veins that carry oxygenated blood from the lungs to the left atrium of the heart. They play a crucial role in the pumping action of the heart by delivering this oxygen-rich blood to be pumped out to the body's tissues.
S1: S1 refers to the first heart sound, which is produced by the closing of the atrioventricular (AV) valves during ventricular systole. This sound is an important indicator of the pumping action of the heart and is a crucial component in understanding the overall functioning of the cardiovascular system.
S2: S2 refers to the second heart sound, which is produced by the closure of the atrioventricular (AV) valves, specifically the mitral and tricuspid valves, during ventricular systole. This heart sound is an important indicator of the proper functioning of the heart's pumping mechanism.
Semilunar Valves: The semilunar valves are one-way valves located at the base of the aorta and pulmonary artery that ensure blood flow in the heart occurs in the correct direction during the pumping action of the heart.
Stroke Volume: Stroke volume is the amount of blood pumped from the ventricles of the heart with each contraction. It is a critical component of cardiac output, which is the measure of the heart's ability to pump blood throughout the body.
Superior Vena Cava: The superior vena cava is a large vein that carries deoxygenated blood from the upper body to the right atrium of the heart, playing a crucial role in the pumping action of the heart.
Systole: Systole is the contraction phase of the cardiac cycle, during which the heart's ventricles contract to pump blood out of the heart and into the circulatory system. This phase is a critical component of the pumping action of the heart.
Tricuspid Valve: The tricuspid valve is one of the four major valves in the heart, located between the right atrium and the right ventricle. It is responsible for regulating the flow of blood from the right atrium to the right ventricle during the cardiac cycle.
Vasoconstriction: Vasoconstriction is the narrowing or constriction of blood vessels, specifically the arteries and arterioles, which leads to a decrease in blood flow and blood pressure. This physiological process is an important mechanism in the regulation of blood flow and blood pressure throughout the body.
Vasodilation: Vasodilation refers to the widening or dilation of blood vessels, particularly the arteries and arterioles. This process leads to increased blood flow and reduced vascular resistance, which can have significant implications in various physiological and pharmacological contexts.
Ventricular diastole: Ventricular diastole is the phase of the cardiac cycle when the ventricles relax and fill with blood from the atria. This phase is crucial for proper cardiac function and occurs between contractions.
Ventricular Diastole: Ventricular diastole is the relaxation phase of the cardiac cycle, during which the ventricles of the heart fill with blood in preparation for the next contraction. This phase is a crucial component of the pumping action of the heart, as it allows the ventricles to refill with oxygenated blood from the atria, ensuring an adequate supply of blood to be pumped throughout the body.
Ventricular Systole: Ventricular systole is the contraction phase of the ventricles in the cardiac cycle, during which oxygenated blood is pumped from the ventricles to the lungs and body. This crucial phase of the heart's pumping action is essential for maintaining blood flow and circulation throughout the body.