6: From Heart Anatomy to Cardiac Output
- Page ID
- 172845
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Chapter Overview
This chapter explains how the heart is built, how it generates and conducts electrical signals, how it pumps blood through the pulmonary and systemic circuits, and how its activity is regulated and changes over the lifespan. You will connect gross anatomy to microscopic structure, normal electrical activity to the electrocardiogram (ECG), and basic physiology to clinical concepts such as exercise responses and fetal heart development.
External and Internal Anatomy of the Heart
You will learn to identify and describe the external landmarks and internal chambers of the heart, including its position, size, and shape within the thoracic cavity. This section covers the major surfaces and borders of the heart, the great vessels attached to it, and the internal features of the atria and ventricles such as valves, chordae tendineae, and papillary muscles. You will also trace the coronary circulation that supplies blood to the myocardium itself.
Path of Blood Through the Heart and Circulatory Circuits
You will follow the flow of blood through the right and left sides of the heart and through the pulmonary and systemic circuits. Venous blood returns to the right atrium, passes to the right ventricle, and is pumped to the lungs through the pulmonary trunk and arteries. Oxygenated blood returns from the lungs via the pulmonary veins to the left atrium, flows into the left ventricle, and is ejected into the aorta and systemic arteries. Understanding this sequence will help you visualize how oxygen-poor and oxygen-rich blood are kept separate and how valves maintain one-way flow.
Cardiac Muscle and the Conduction System
You will compare cardiac muscle to skeletal and smooth muscle in terms of cell structure, junctions, and electrical properties. Cardiac muscle fibers are branched and interconnected by intercalated discs containing gap junctions and desmosomes, forming a functional syncytium. You will then explore the cardiac conduction system, including the sinoatrial node, atrioventricular node, atrioventricular bundle, bundle branches, and Purkinje fibers, and how these specialized structures generate and coordinate the electrical impulses that time atrial and ventricular contraction.
Electrical Activity and the Electrocardiogram
You will connect intrinsic electrical activity of cardiac cells to the surface electrocardiogram. This section explains how ion movements generate pacemaker and action potentials and how these electrical events appear as the P wave, QRS complex, and T wave on an ECG tracing. You will learn the basic process and purpose of recording an ECG and how it is used clinically to assess heart rhythm, conduction, and some types of ischemia or damage.
The Cardiac Cycle and Cardiac Output
You will examine the sequence of mechanical events in one heartbeat, known as the cardiac cycle. This includes ventricular filling, isovolumetric contraction, ventricular ejection, and isovolumetric relaxation, and how these phases relate to changes in chamber pressure, valve status, and heart sounds. You will learn how to define and calculate cardiac output as the product of heart rate and stroke volume, and how stroke volume is influenced by preload, contractility, and afterload.
Regulation of Heart Rate and the Effects of Exercise
You will study how heart rate and cardiac output are regulated by neural and hormonal mechanisms and by changing physiological demands. This section describes the autonomic centers in the medulla oblongata that control sympathetic and parasympathetic output to the heart, the roles of baroreceptors and chemoreceptors, and the influence of hormones, ions, body temperature, age, and fitness. You will also examine how acute exercise increases heart rate and cardiac output and how long-term training can enhance cardiac efficiency and alter resting heart rate.
Development of the Fetal and Neonatal Heart
You will trace the major stages of heart development, from formation of the primitive heart tube through looping and partitioning into four chambers, and the development of valves and great vessels. This section explains the special features of fetal circulation, including the foramen ovale and ductus arteriosus, which divert blood away from the nonfunctional fetal lungs. You will then learn how these shunts function before birth and what changes occur at and after birth as the lungs expand, pressures shift, and the fetal shunts close or remodel.
By the end of this chapter, you should be able to identify key structures of the heart, describe the path of blood through its chambers and circuits, explain how electrical and mechanical events are coordinated, calculate cardiac output, discuss how the heart responds to neural, hormonal, and exercise-related influences, and outline the basic steps of heart development.
To achieve these chapter objectives, actively engage with the material. Learning tissues is not a passive process. Your understanding will grow as you interact with the content, peers, and your instructor. Regularly check your thinking against feedback. Revisit complex concepts until you can confidently explain and apply them on your own.
After completing this chapter, the student will be able to:
- After completing this chapter, the student will be able to:
- Identify the major external and internal structures of the heart and trace coronary circulation.
- Trace the path of blood through the heart and distinguish between pulmonary and systemic circuits.
- Compare cardiac muscle to other muscle types and outline the components and function of the cardiac conduction system.
- Relate cardiac electrical activity to the main waves of the electrocardiogram (P wave, QRS complex, T wave) and explain the basic clinical use of an ECG.
- Describe the phases of the cardiac cycle and define and calculate cardiac output, including key determinants (heart rate and stroke volume).
- Summarize how autonomic, hormonal, and physiological factors (including exercise) regulate heart rate and cardiac output.
- Outline the major steps of heart development, key features of fetal circulation, and the changes that occur at and after birth.
- 6.1: Heart Anatomy
- The vital importance of the heart is obvious. If one assumes an average rate of contraction of 75 contractions per minute, a human heart would contract approximately 108,000 times in one day, more than 39 million times in one year, and nearly 3 billion times during a 75-year lifespan. Each of the major pumping chambers of the heart ejects approximately 70 mL blood per contraction in a resting adult. This would be equal to 5.25 liters of fluid per minute and approximately 14,000 liters per day.
- 6.2: Cardiac Muscle and Electrical Activity
- Recall that cardiac muscle shares a few characteristics with both skeletal muscle and smooth muscle, but it has some unique properties of its own. Not the least of these exceptional properties is its ability to initiate an electrical potential at a fixed rate that spreads rapidly from cell to cell to trigger the contractile mechanism. This property is known as autorhythmicity. Neither smooth nor skeletal muscle can do this. Heart rate is modulated by the endocrine and nervous systems.
- 6.3: Cardiac Cycle
- The period of time that begins with contraction of the atria and ends with ventricular relaxation is known as the cardiac cycle. The period of contraction that the heart undergoes while it pumps blood into circulation is called systole. The period of relaxation that occurs as the chambers fill with blood is called diastole. Both the atria and ventricles undergo systole and diastole, and it is essential that these components be carefully regulated and coordinated.
- 6.4: Cardiac Physiology
- The autorhythmicity inherent in cardiac cells keeps the heart beating at a regular pace; however, the heart is regulated by and responds to outside influences as well. Neural and endocrine controls are vital to the regulation of cardiac function. In addition, the heart is sensitive to several environmental factors, including electrolytes.
- 6.5: Development of the Heart
- The human heart is the first functional organ to develop. It begins beating and pumping blood around day 21 or 22, a mere three weeks after fertilization. This emphasizes the critical nature of the heart in distributing blood through the vessels and the vital exchange of nutrients, oxygen, and wastes both to and from the developing baby. The critical early development of the heart is reflected by the prominent heart bulge that appears on the anterior surface of the embryo.
- 6.6: Terms and Definitions
- This page provides a comprehensive overview of the heart's structure and function, covering key terms related to cardiac anatomy, electrical conduction, and the cardiac cycle. It details important components like valves, arteries, and veins, as well as the roles of the septa and conducting system.
- 6.7: Chapter Review Questions
- This page provides a comprehensive overview of heart anatomy, function, and development. It discusses the roles of valves and chambers in blood flow, the heart's structural layers, and the cardiac cycle. The electrical conduction system, heart rate responses, and developmental aspects of the heart are examined. Additionally, it emphasizes the importance of ion influx in cardiac action potentials and explains blood dynamics, including preload and afterload, in relation to heart efficiency.
- 6.8: Critical Thinking Self-Assessment
- This page covers essential aspects of heart function, such as valve mechanisms for unidirectional blood flow, pressure differences in pulmonary vs. systemic circulation, and the plateau phase's significance in cardiac muscle. It elaborates on the atrioventricular node, gap junctions, intercalated disks, and autorhythmicity in cardiac cells.