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- Herausgeber: John Wiley & Sons
- Kategorie: Fachliteratur
- Serie: Peate's Body Systems
- Sprache: Englisch
PEATE’S BODY SYSTEMS
THE CARDIOVASCULAR SYSTEM
A CONCISE, ILLUSTRATED, AND ACCESSIBLE GUIDE TO THE CARDIOVASCULAR SYSTEM
Each of the twelve volumes in Peate’s Body Systems series is rooted in the belief that a deep and thorough understanding of the human body is essential for providing the highest standard of care. Offering clear, accessible and up-to-date information on different body systems, this series bridges the gap between complex scientific concepts and practical, everyday applications in health and care settings. This series makes for an invaluable resource for those committed to understanding the intricacies of human biology, physiology and the various systems that sustain life.
The Cardiovascular System is the perfect companion for students and newly registered practitioners across nursing and allied health fields with an interest in cardiovascular care, providing a comprehensive yet easy-to-digest guide for both academic and clinical application.
- Equips healthcare students and practitioners with the necessary information to provide safe and competent care
- Features colourful illustrations to aid comprehension, clarify complicated concepts, and render content more engaging and accessible
- Empowers readers to adapt to a rapidly evolving healthcare landscape, preparing them for the future of healthcare delivery
- Contains information necessary for effective patient care of those with heart failure, hypertension, and other cardiovascular diseases and conditions
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Seitenzahl: 269
Veröffentlichungsjahr: 2024
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Table of Contents
Cover
Table of Contents
Title Page
Copyright
Preface
Acknowledgements
Chapter 1 Anatomy and Physiology: The Cardiovascular System
Blood
Blood Vessels
Heart
Conclusion
Glossary of Terms
Multiple Choice Questions
References
Chapter 2 Cardiovascular Assessment
The Importance of Cardiovascular Assessment
Assessing Needs
Chief Complaint and History of Present Condition
Family History
Lifestyle
Past Medical History
Physical Examination
Palpation
The Blood Pressure
Chest Examination
Electrocardiogram
Assessing Chest Pain
Conclusion
Glossary of Terms
Multiple Choice Questions
References
Chapter 3 Myocardial Infarction
Pathophysiological Changes Associated with Myocardial Infarction
Epidemiology
Risk Factors
Clinical Presentation
Clinical Investigations
Diagnosis
Management
Reperfusion
Health Teaching
Conclusion
Glossary of Terms
Multiple Choice Questions
References
Chapter 4 Heart Failure
Pathophysiological Changes Associated with Heart Failure
Epidemiology
Risk Factors
Clinical Presentation
Clinical Investigations and Diagnosis
Management
End of Life Care
Health Teaching
Conclusion
Glossary of Terms
Multiple Choice Questions
References
Chapter 5 Cardiogenic Shock
Cardiac Arrest
Epidemiology: Cardiac Arrest
Risk Factors Associated with Cardiac Arrest
Guidelines for Adult Basic Life Support
Shock
Shock: Signs and Symptoms
Pathophysiological Changes Associated with Cardiogenic Shock
Epidemiology
Risk Factors
Clinical Presentation
Clinical Investigations and Diagnosis
Potential Investigations
Management
Health Teaching
Conclusion
Glossary of Terms
Multiple Choice Questions
References
Chapter 6 Angina
Stable Angina
Silent Angina
Prinzmetal’s Angina
Microvascular Angina
Pathophysiological Changes Associated with Angina
Epidemiology
Risk Factors
Clinical Presentation
Clinical Investigations and Diagnosis
Management
Other Interventions
Health Teaching
Conclusion
Glossary of Terms
Multiple Choice Questions
References
Chapter 7 Hypertension
Primary and Secondary Hypertension
Blood Pressure
The Cardiac Cycle
Pathophysiological Changes Associated with Hypertension
Epidemiology
Risk Factors
Non-modifiable Risk Factors
Modifiable Risk Factors
Clinical Presentation
Blood Pressure Measurement
White Coat Syndrome
Clinical Investigations and Diagnosis
Management
Health Teaching
Conclusion
Glossary of Terms
Multiple Choice Questions
References
Chapter 8 Peripheral Arterial Disease
Pathophysiological Changes Associated with PAD
Epidemiology
Risk Factors
Clinical Presentation
Clinical Investigations and Diagnosis
Management
Pharmacological Interventions
Surgical and Radiological Interventions
Amputation
Prognosis
Health Teaching
Conclusion
Glossary of Terms
Multiple Choice Questions
References
Index
End User License Agreement
List of Illustrations
CHAPTER 1
Figure 1.1 Appearance of centrifuged blood
Figure 1.2 Three formed elements of blood
Figure 1.3 Components of blood
Figure 1.4 Haemopoiesis
Figure 1.5 ABO blood groups
Figure 1.6 Blood vessels
Figure 1.7 Layers of blood vessels
Figure 1.8 Comparison of a vein, artery and capillary
Figure 1.9 Capillary network
Figure 1.10 The location of the heart
Figure 1.11 The walls of the heart
Figure 1.12 Cells of the myocardium
Figure 1.13 The chambers of the heart
Figure 1.14 Blood flow through the heart
Figure 1.15 Blood vessels of the heart
Figure 1.16 Coronary veins
Figure 1.17 The conducting system of the heart
Figure 1.18 The cardiac cycle
CHAPTER 2
Figure 2.1 Usual sequence of events
Figure 2.2 Assessing the radial pulse
Figure 2.3 Palpating the dorsalis pedis pulse
Figure 2.4 Palpating the posterior tibial pulse
Figure 2.5 Palpating the popliteal pulse
Figure 2.6 Peripheral pulses
Figure 2.7 Cardiac auscultation points
Figure 2.8 Chest lead placement
Figure 2.9 Placement of limb leads
Figure 2.10 12‐lead normal electrocardiogram.
Figure 2.11 Areas associated with cardiac pain
CHAPTER 3
Figure 3.1 Atherosclerosis
Figure 3.2 Ruptured atherosclerotic plaque
Figure 3.3 Myocardial infarction
Figure 3.4 Areas of pain associated with myocardial infarction
Figure 3.5 Coronary stent insertion
CHAPTER 4
Figure 4.1 The structurally normal heart and the heart with an enlarged left ventricle
Figure 4.2 Atrial fibrillation
Figure 4.3 Red flags for heart failure
Figure 4.4 Some of the signs and symptoms associated with heart failure
CHAPTER 5
Figure 5.1 The sequence of basic adult life support.
Figure 5.2 Patient outcomes for people presenting with cardiogenic shock and the importan...
CHAPTER 6
Figure 6.1 Blockage of the coronary artery
Figure 6.2 Coronary artery disease depicting a healthy heart, angina pectoris and myocard...
Figure 6.3 Percutaneous coronary intervention
CHAPTER 7
Figure 7.1 The cardiac cycle
Figure 7.2 Complications of hypertension. Source: Adapted from Public Health England (2017...
Figure 7.3 Sphygmomanometer and stethoscope. Source: Clare (2021). With permission of Joh...
Figure 7.4 Correct positioning of cuff
CHAPTER 8
Figure 8.1 Lower limb arteries
List of Tables
CHAPTER 1
Table 1.1 The three types of blood cells
CHAPTER 2
Table 2.1 Areas where cardiovascular assessment is indicated
Table 2.2 Common manifestations of cardiovascular problems
Table 2.3 Peripheral pulses
Table 2.4 Possible causes of chest pain
Table 2.5 OLDCARTS chest pain assessment
Table 2.6 Inferences that may be made regarding cardiac pain
CHAPTER 3
Table 3.1 Modifiable and non-modifiable risk factors for developing cardiovascular disea...
Table 3.2 Medication and myocardial infarction (MI)
Table 3.3 Lifestyle discussion points following an myocardial infarction (MI)
CHAPTER 4
Table 4.1 Pathophysiological changes associated with heart failure
Table 4.2 Complications associated with heart failure
Table 4.3 Risk of heart failure increases if the person has one or more of the issues li...
Table 4.4 Classification of the severity of heart failure based on the New York Heart As...
CHAPTER 5
Table 5.1 Epidemiology of cardiac arrest
Table 5.2 Types of shock
Table 5.3 Mechanisms associated with cardiogenic shock
Table 5.4 Risk factors associated with cardiogenic shock
Table 5.5 Potential management options
CHAPTER 6
Table 6.1 Angina and myocardial infarction
Table 6.2 PQRST assessment of angina
Table 6.3 Tests and investigations
Table 6.4 Some pharmacological approaches to angina
Table 6.5 Pharmacological medication: prophylaxis
CHAPTER 7
Table 7.1 Blood pressure (BP) readings and what they might mean
Table 7.2 Modifiable and non-modifiable risk factors associated with hypertension (Publi...
CHAPTER 8
Table 8.1 Limb ischaemia
Table 8.2 Interpretation of ankle–brachial pressure index results (NICE 2023)
Table 8.3 Stages of peripheral arterial disease
Guide
Cover
Table of Contents
Title Page
Copyright
Preface
Acknowledgements
Begin Reading
Index
End User License Agreement
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Peate’s Body Systems
The Cardiovascular System
Ian Peate, OBE FRCN EN(G) RGN DipN(Lond) RNT BEd(Hons) MA(Lond) LLM
Editor in Chief, British Journal of Nursing;
Consultant Editor, Journal of Paramedic Practice;
Consultant Editor, International Journal for Advancing Practice;
Visiting Professor, Northumbria University;
Visiting Professor, Buckinghamshire New University;
Professorial Fellow, University of Roehampton;
Visiting Senior Clinical Fellow, University of Hertfordshire
This edition first published 2025.
©2025, John Wiley & Sons Ltd
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The contents of this work are intended to further general scientific research, understanding, and discussion only and are not intended and should not be relied upon as recommending or promoting scientific method, diagnosis, or treatment by physicians for any particular patient. In view of ongoing research, equipment modifications, changes in governmental regulations, and the constant flow of information relating to the use of medicines, equipment, and devices, the reader is urged to review and evaluate the information provided in the package insert or instructions for each medicine, equipment, or device for, among other things, any changes in the instructions or indication of usage and for added warnings and precautions. While the publisher and authors have used their best efforts in preparing this work, they make no representations or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties, including without limitation any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives, written sales materials or promotional statements for this work. This work is sold with the understanding that the publisher is not engaged in rendering professional services. The advice and strategies contained herein may not be suitable for your situation. You should consult with a specialist where appropriate. The fact that an organization, website, or product is referred to in this work as a citation and/or potential source of further information does not mean that the publisher and authors endorse the information or services the organization, website, or product may provide or recommendations it may make. Further, readers should be aware that websites listed in this work may have changed or disappeared between when this work was written and when it is read. Neither the publisher nor authors shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages.
Library of Congress Cataloging-in-Publication Data has been applied for.
ISBN: 978-1-394-252350
Cover Images: © marinashevchenko/Adobe Stock, © phototechno/Getty Images, © 4luck/Adobe Stock, © Oleksandr Pokusai/Adobe Stock
Cover Design: Wiley
Preface
Welcome to Peate’s Body Systems; there are 12 books in the series. This is a comprehensive collection of textbooks designed to support and enrich the knowledge of health and care workers across various fields. This series is intended to be a valuable resource for those who are dedicated to understanding the intricacies of human biology, physiology and the various systems that sustain life.
Peate’s Body Systems series is rooted in the belief that a deep and thorough understanding of the human body is essential for providing the highest standard of care. Each book in this series is thoroughly crafted to offer clear, accurate and up-to-date information on different body systems. The aim is to bridge the gap between complex scientific concepts and practical, everyday applications in healthcare settings.
Purpose and Scope
The purpose of this series is to provide health and care workers with:
Foundational knowledge, with explanations of the anatomical structures and physiological functions of the body systems
Insights into how these systems interact with each other and how they are impacted by various diseases and conditions, highlighting clinical relevance and encouraging practical application
Structure of the Series
Each book in Peate’s Body Systems focuses on a specific body system:
The Cardiovascular System
The Respiratory System
The Digestive System
The Renal System
The Nervous System
The Endocrine System
The Female Reproductive System
The Male Reproductive System
The Musculoskeletal System
The Skin
The Ear, Nose and Throat
The Eyes
Every chapter is designed to be comprehensive yet accessible, making complex information easier to digest and apply. Figures, tables, boxes, illustrations and flowcharts have been extensively used to support visual learning and reinforce key concepts.
This series is tailored for:
Healthcare students: those in nursing and allied health programmes
Practicing professionals: nurses, therapists and other care workers seeking to deepen their understanding and stay current with the latest developments in health and care
Educators and trainers: Educators who require reliable and comprehensive teaching materials to advise and instruct the next generation of healthcare providers.
Commitment to Excellence.
The series is committed to providing quality educational resources that not only inform but also inspire and empower health and care workers. By equipping you with a robust understanding of the systems of life, you will be better prepared to make informed decisions, deliver compassionate care and ultimately improve patient outcomes.
Thank you for choosing Peate’s Body Systems as your trusted resource. I hope these textbooks serve as a valuable tool in your ongoing journey of learning and professional development.
Ian Peate
London
Acknowledgements
I would like to acknowledge the help and support of my partner Jussi Lahtinen. Acknowledgements also go to staff at the RCN Library in London. My thanks go to Tom Marriott, Christabel Daniel Raj, Bhavya Boopathi and all those at Wiley.
Chapter 1Anatomy and Physiology: The Cardiovascular System
The cardiovascular system, also known as the circulatory system, is a complex network of organs and vessels responsible for circulating blood throughout the body. It consists of:
Blood: the fluid in which materials are transported to and from tissues.
Blood vessels: the system by which the blood moves to and through tissues and back to the heart.
Heart: the pump driving blood throughout the body.
Blood provides the fluid environment for the cells of the body with blood vessels transporting the blood. Blood vessels are the network carrying the blood. The heart performs its work as a pump, maintaining blood circulation. The cardiovascular system is essential for maintaining overall health and homeostasis, ensuring all cells receive the necessary oxygen and nutrients whilst removing waste products.
Circulation is key to maintaining organs and tissues. This chapter discusses the anatomy and physiology of the cardiovascular system, the system maintaining blood volume and perfusion of tissues and organs. Understanding how circulation is fundamental to maintaining organs and tissues can help enhance patient care and safety across all spheres of practice.
Blood
Through the blood (and lymph) substances are transported around the body; it is the main transportation system of the body, playing a critical role in maintaining homeostasis and supporting the functioning of various body systems. Blood performs three general functions:
Transport: transportation of substances around the body, delivering oxygen to every cell.
Regulation: blood regulates fluid and electrolyte balance, acid−base balance (pH) and temperature.
Protection: clotting factors are present in the blood (thrombocytes), helping protect the body from haemorrhage; blood also contains leucocytes; they help fight infection.
Composition of Blood
A red sticky fluid, blood is classified as a connective tissue despite its fluid nature. Connective tissues connect, support and bind together various structures and organs in the body. Blood has several different components and can vary slightly from person to person; it can change in response to factors such as hydration, diet and overall health.
Blood consists of formed elements, for example, red blood cells (erythrocytes), white blood cells (leucocytes) and platelets (thrombocytes) (see Table 1.1).
Table 1.1 The three types of blood cells
Blood cell
Description
Role
Erythrocytes
Make up 90% of the formed elements of blood.
Disc shaped (bi-concave).
Young red blood cells contain a nucleus (nucleated), while this is absent in mature red blood cells, thereby increasing the oxygen‐carrying capacity of the cell.
Red in colour due to the presence of the protein haemoglobin (Hb).
Formed in the red bone marrow.
Life span of approximately 120 days.
Old and worn-out erythrocytes are destroyed in the liver and spleen.
Transportation of gases (take oxygen to cells and carry carbon dioxide away from cells).
Leucocytes
These are the largest of all blood cells.
They lack Hb and, as such, are white in colour.
Two categories:
Granulocytes: Accounting for 75% of white blood cells, further divided into neutrophils, eosinophils and basophils.
Agranulocytes: Divided into lymphocytes, 20% of all white blood cells and monocytes account for 5% of white blood cells.
Leucocytes often only survive for a few hours but may live for months or years.
Provides the body with protection against infection and disease through the process of phagocytosis (engulfing and ingesting microbes, dead cells and tissues).
Thrombocytes
Also known as platelets.
Granular, disc shaped with no nucleus.
Small fragments of cells.
The smallest cellular elements of blood.
Formed in bone marrow.
Life span of a thrombocyte is short – five to nine days.
Responsible for initiating the blood clotting process leading to the development of blood clots. These blood cells prevent blood loss from a blood vessel by:
Gathering where a blood vessel is injured.
Forming a plug at the injured site and releasing fibrinogen (a chemical) and converting this to fibrin (the net that holds the clot together).
The fluid portion of blood, plasma, contains different types of proteins and other soluble molecules. When a blood sample is separated, the formed elements account for 45% of blood and plasma makes up 55% of the total blood volume. Normally, more than 99% of the formed elements are cells named for their red colour (red blood cells). White blood cells and platelets comprise less than 1% of the formed elements (Figure 1.1). Between the plasma and erythrocytes is the buffy coat, consisting of white blood cells and platelets. See Figure 1.2 for the three formed elements of blood.
Figure 1.1 Appearance of centrifuged blood
Figure 1.2 Three formed elements of blood
The volume of blood is constant unless a person has physiological problems, for example, haemorrhage.
Properties of Blood
The average adult has a blood volume of approximately 5 L, accounting for 7–9% of the body’s weight. Men have 5–6 L and women 4–5 L of blood. Blood is thicker, denser and flows slower than water due to the red blood cells and plasma proteins. Plasma proteins, including albumin, fibrinogen, prothrombin and gamma globulins, make up around 8% of blood plasma in the body (Tortora and Derrickson 2017). These proteins help maintain water balance, affecting osmotic pressure, increasing blood viscosity and helping to maintain blood pressure. The plasma proteins, apart from the gamma globulins, are synthesised in the liver.
Blood has a high viscosity, resisting blood flow. Red blood cells and proteins contribute to the viscosity of blood, which ranges from 3.5 to 5.5 compared with 1.000 for water. Viscosity relates to stickiness of blood; normal viscosity of blood is low, allowing it to flow smoothly. However, the more red blood cells and plasma proteins in blood, the higher the viscosity and the slower the flow of blood. Normal blood varies in viscosity as it flows through the blood vessels; the viscosity decreases as it reaches the capillaries.
Plasma
Plasma is a straw-coloured aqueous solution containing plasma proteins, i.e. albumin, globulins and fibrinogen. It also contains inorganic ions regulating cell function, blood pH and osmotic pressure; these include sodium, potassium, chloride, phosphate, magnesium and calcium. Small amounts of nutrients, waste products, drugs, hormones and gases are also found in plasma. Figure 1.3 shows the composition of blood plasma along with the different types of formed elements in the blood.
Figure 1.3 Components of blood
Plasma is around 91.5% water with 8.5% solutes and most are proteins. Some of the proteins in blood plasma are found elsewhere in the body; those confined to blood are known as plasma proteins. Specific blood cells develop into cells producing gamma globulins, an important type of globulin; these are called antibodies or immunoglobulins, produced during specific immune responses. Other solutes in plasma include electrolytes, nutrients, regulatory substances, such as enzymes and hormones, gases as well as waste products such as urea, uric acid, creatinine, ammonia and bilirubin.
Formation of Blood Cells
Red bone marrow is the primary centre for haemopoiesis. Bone marrow is the soft fatty substance found in bone cavities. Within the bone marrow, all blood cells originate from a single type of unspecialised cell, a stem cell. When a stem cell divides, it first becomes an immature red blood cell, white blood cell or platelet‐producing cell. The immature cell divides, matures further and eventually becomes a mature red blood cell, white cell or platelet. Haemopoiesis describes the process by which the formed elements of blood develop (Figure 1.4).
Figure 1.4 Haemopoiesis
Blood Groups
Red blood cells define which blood group an individual belongs to. On the surface of red cells are markers called antigens. Apart from identical twins, each person has different antigens and these antigens are the key to identifying blood types and must be matched in transfusions to avoid serious complications. The structure for defining blood groups is known as the ABO system. If an individual has blood group A, then they have A antigens covering their red cells. Group B has B antigens on their red blood cells, while group O has neither antigens and group AB has both antigens (see Figure 1.5).
Figure 1.5 ABO blood groups
The ABO system also covers antibodies in the plasma, the body’s natural defence against foreign antigens, for example, blood group A has anti‐B in their plasma, B has anti‐A and so on. However, group AB has no antibodies and group O has both. If these antibodies find the wrong red blood cells, they attack them and destroy them. Transfusing the wrong blood to a patient can be fatal.
Blood Vessels
Blood vessels are part of the circulatory system transporting blood throughout the body. There are three major types of blood vessels (see Figure 1.6):
Arteries carry blood away from the heart.
Capillaries enable the actual exchange of water, nutrients and chemicals between blood and tissues.
Veins carry blood from capillaries back towards the heart.
Figure 1.6 Blood vessels
The different types of blood vessels are specialised, playing a specific role in circulating the blood around the body.
All arteries, except pulmonary and umbilical arteries, carry oxygenated blood; most veins carry deoxygenated blood from tissues back to the heart; exceptions are the pulmonary and umbilical veins, which carry oxygenated blood. The capillaries form the microcirculatory system; at this point, nutrients, gases, water and electrolytes are exchanged between blood and tissue fluid. Capillaries are tiny, extremely thin‐walled vessels acting as a bridge between arteries and veins. The thin walls of capillaries allow oxygen and nutrients to pass from the blood into the tissue fluid and allow waste products to pass from tissue fluid into blood.
Structure and Function of Arteries and Veins
In most blood vessels, the walls consist of three layers:
Tunica interna (a thin layer of endothelial cells. The epithelial lining is only one cell thick. Therefore, this layer is always very thin.)
Tunica media (consists of smooth muscle and elastic fibres).
Tunica externa (an outer layer, consisting of fibroblasts, nerves and collagenous tissue).
See Figure 1.7, layers of blood vessels.
Figure 1.7 Layers of blood vessels
Arteries
Arteries receive blood under high pressure from the ventricles. They must stretch each time the heart beats, without collapsing under the increased pressure. The walls of arteries have three layers.
Outer layer
Thick middle layer
Inner layer
The outer layer consists of white fibrous connective tissue, merging into the outside with the loose connective tissue. This helps anchor the arteries as the heart pumps the blood through arteries at great pressure (Blanchflower and Peate 2021). The thick middle layer consists of elastic connective tissue and involuntary muscle tissue. This layer is supplied with two sets of nerves: one that stimulates muscles to relax, so the artery is permitted to widen and the other stimulates circular muscles to contract, causing the artery to become narrower. The inner layer of endothelium is made up of flat epithelial cells packed closely together, continuous with the endocardium of the heart. The flat cells make the inside of the arteries smooth to limit friction between blood flowing within the artery and the lining of the vessel.
Veins
The veins are the major vessels of the venous system. As veins carry blood back to the heart, the pressure exerted by the heartbeat on them is much less than in the arteries. The middle muscular wall of a vein is much thinner than an artery and generally the diameter is larger. Veins also differ from arteries in that they have semilunar valves helping prevent blood from flowing backwards. Figure 1.8 shows a comparison of a vein, artery and capillary.
Figure 1.8 Comparison of a vein, artery and capillary
The vein’s valves are necessary to keep blood flowing towards the heart; they are also required to allow blood to flow against the force of gravity; for example, blood returning to the heart from the foot must be able to flow up the leg. Generally, the force of gravity would discourage that from happening. The vein’s valves, however, provide ‘footholds’ for blood as it flows its way up. The valves are like gates, only allowing traffic to move in one direction. They also act with muscle contraction, squeezing the veins and propelling blood towards the heart.
Veins receive blood from capillaries after the exchange of oxygen and carbon dioxide has occurred. Veins transport carbon dioxide–rich blood back to the lungs and heart. It is important that carbon dioxide–rich blood keeps moving in the right direction and is not allowed to flow backward; this is accomplished by the semilunar valves present in the veins.
Capillaries
Capillaries are tiny blood vessels of approximately 5–20 μm in diameter. There are networks of capillaries (Figure 1.9) in most organs and tissues. Capillary walls are composed of a single layer of cells, the endothelium. This layer is so thin that molecules such as oxygen, water and lipids can pass through it by diffusion and enter tissues. Waste products such as carbon dioxide and urea can diffuse back into the blood to be carried away for removal from the body. Capillaries are so small, red blood cells must change their shape to pass through them in single file.
Figure 1.9 Capillary network
The flow of blood in the capillaries is controlled by structures known as precapillary sphincters. These are located between arterioles and capillaries and contain muscle fibres, allowing them to contract. When the sphincters are open, blood flows freely to the capillary beds of body tissue. When the sphincters are closed, blood cannot flow through the capillary beds. Fluid exchange between the capillaries and the body tissues takes place in the capillary bed.
Heart
This is the hollow muscular pump that forces the movement of blood around the body.
It weighs approximately 250–390 g in men and 200–275 g in women and is about 12 cm long and 9 cm wide. It is in the thoracic cavity (chest) in the mediastinum (between the lungs), behind and to the left of the sternum (breastbone) (Figure 1.10). The heart rests on the diaphragm in the thoracic cavity.
Figure 1.10 The location of the heart
Walls of the Heart
Pericardium
A membrane, the pericardium surrounds the heart. This is referred to as a single sac surrounding the heart but is in fact made up of two sacs (fibrous pericardium and serous pericardium) closely connected to each other. These sacs have different structures (Figure 1.11).
Figure 1.11 The walls of the heart
Fibrous Pericardium
It is a tough, inelastic layer made up of dense, irregular, connective tissue. Its purpose is to prevent overstretching of the heart. It also provides protection to the heart and anchors it in place.
Serous Pericardium
It is a thinner, more delicate structure forming a double layer around the heart. The outer layer is fused to the fibrous pericardium. The visceral pericardium (otherwise known as the epicardium) adheres tightly to the surface of the heart.
Myocardium
The myocardium makes up most of the bulk of the heart. It is a muscle only found within the heart, specialised in structure and function. The work of the myocardium can be divided into two parts: much of the myocardium is specialised to undertake mechanical work (contraction); the remainder is specialised to undertake the task of initiating and conducting electrical impulses. The cardiac muscle cells (myocytes) are held together in interlacing bundles of fibres arranged in a spiral or in circular bundles (Figure 1.12).
Figure 1.12 Cells of the myocardium
Myocardial thickness varies between all chambers of the heart. Ventricles have thicker walls than atria; however, the left ventricle has the thickest myocardial wall. This is because the left ventricle must pump blood great distances to parts of the body at a higher pressure and the resistance to blood flow is greater.
Endocardium
The innermost layer is made up of endothelium overlying a thin layer of connective tissue. The endothelium is continuous with the endothelial lining of the large vessels of the heart. It also provides a lining allowing blood to flow through the chambers smoothly.
Chambers of the Heart
The heart has four chambers: two atria (left and right; singular is atrium) and two ventricles (left and right). On the anterior surface of each of the atria is a wrinkled pouch‐like structure called an auricle; the main function is to increase the volume of blood in the atrium. Between the ventricles is a dividing wall, the intraventricular septum (Figure 1.13). With the septum between the atria and the septum between the ventricles, there is no mixing of blood between the two sides.
Figure 1.13 The chambers of the heart
Valves of the Heart
Between the atria and ventricles are two valves (atrioventricular [AV] valves).
Tricuspid valve – made up of three cusps (leaflets) lying between the right atrium and the right ventricle.
Bicuspid (mitral) valve – made up of two cusps lying between the left atrium and the left ventricle.
The AV valves prevent the backward flow of blood from the ventricles into the atria.
