Human biology concepts and current issues 8th by johnson

Human biology concepts and current issues 8th by johnson Human biology concepts and current issues 8th by johnson Human biology concepts and current issues 8th by johnson Human biology concepts and current issues 8th by johnson Human biology concepts and current issues 8th by johnson Human biology concepts and current issues 8th by johnson Human biology concepts and current issues 8th by johnson Human biology concepts and current issues 8th by johnson

BRIEF CONTENTS Human Biology, Science, and Society 31 The Chemistry of Living Things 51 Structure and Function of Cells 77 From Cells to Organ Systems 107 The Skeletal System 129 The Muscular System 149 7 Blood 169 Heart and Blood Vessels 189 9 The Immune System and Mechanisms of Defense 217 10 The Respiratory System: Exchange of Gases 249 11 The Nervous System: Integration and Control 273 12 Sensory Mechanisms  304 13 The Endocrine System 328 14 The Digestive System and Nutrition 352 15 The Urinary System 381 16 Reproductive Systems 403 17 Cell Reproduction and Differentiation 429 18 Cancer: Uncontrolled Cell Division and Differentiation 449 19 Genetics and Inheritance 471 20 DNA Technology and Genetic Engineering 493 21 Development, Maturation, Aging, and Death 509 22 Evolution and the Origins of Life 533 23 Ecosystems and Populations 551 24 Human Impacts, Biodiversity, and Environmental Issues 571 Michael D Johnson Human Biology CONCEPTS AND CURRENT ISSUES Eighth Edition Global Edition Acquisitions Editor: Star MacKenzie Burruto Project Managers: Mae Lum and Brett Coker Program Manager: Anna Amato Developmental Editor: Susan Teahan Editorial Assistant: Maja Sidzinska Executive Editorial Manager: Ginnie Simione Jutson Editor-in-Chief: Beth Wilbur Program Management Team Lead: Michael Early Project Management Team Lead: David Zielonka Assistant Acquisitions Editor, Global Edition: Murchana Borthakur Assistant Project Editor, Global Edition: Shaoni Mukherjee Manager, Media Production, Global Edition: Vikram Kumar Senior Manufacturing Controller, Production, Global Edition: Trudy Kimber Production Management: Lumina Datamatics, Inc Copyeditor: Lumina Datamatics, Inc Design Manager: Derek Bacchus Interior Designer: tani hasegawa (TTEye) Cover Designer: Lumina Datamatics Ltd Illustrators: Imagineering Rights & Permissions Project Manager: Donna Kalal Rights & Permissions Management: Candice Velez (QBS Learning) Photo Researchers: Pat Holl (QBS Learning) and tani hasegawa (TTEye) Manufacturing Buyer: Stacey Weinberger Executive Marketing Manager: Lauren Harp Cover Photo Credit: Science Photo Library Acknowledgements of third-party content appear on pp 619–620, which constitutes an extension of this copyright page Pearson Education Limited Edinburgh Gate Harlow Essex CM20 2JE England and Associated Companies throughout the world Visit us on the World Wide Web at: www.pearsonglobaleditions.com © Pearson Education Limited 2017 The rights of Michael D Johnson to be identified as the author of this work have been asserted by him in accordance with the Copyright, Designs and Patents Act 1988 Authorized adaptation from the United States edition, entitled Human Biology: Concepts and Current Issues, 8th edition, ISBN 978-0-134-04243-5, by Michael D Johnson, published by Pearson Education © 2017 All rights reserved No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without either the prior written permission of the publisher or a license permitting restricted copying in the United Kingdom issued by the Copyright Licensing Agency Ltd, Saffron House, 6–10 Kirby Street, London EC 1N 8TS All trademarks used herein are the property of their respective owners The use of any trademark in this text does not vest in the author or publisher any trademark ownership rights in such trademarks, nor does the use of such trademarks imply any affiliation with or endorsement of this book by such owners MasteringBiology and BioFlix are trademarks, in the U.S and/or other countries, of Pearson Education, Inc or its affiliates Unless otherwise indicated herein, any third-party trademarks that may appear in this work are the property of their respective owners and any references to third-party trademarks, logos or other trade dress are for demonstrative or descriptive purposes only Such references are not intended to imply any sponsorship, endorsement, authorization, or promotion of Pearson’s products by the owners of such marks, or any relationship between the owner and Pearson Education, Inc or its affiliates, authors, licensees or distributors ISBN 10: 1-292-16627-4 ISBN 13: 978-1-292-16627-8 British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library 10 Typeset by Lumina Datamatics, Inc Printed and bound by Vivar in Malaysia ABOUT THE AUTHOR Dr Michael D Johnson spent most of his youth in the fields and forests of rural Washington, observing nature He earned his B.S degree in zoology from Washington State University and then moved east to earn a Ph.D in physiology from the University of Michigan After completing a Postdoctoral Research Fellowship at Harvard Medical School, he joined the faculty of West Virginia University, where he remained for most of his career In 2001, Dr Johnson moved to the Middle East, where he served first as the founding dean of Oman Medical College in the Sultanate of Oman and then as associate dean for premedical education at Weill Cornell Medical College in Qatar In both positions, he directed the premedical education of students from more than 25 countries He returned to the United States in 2011 to focus on his writing Dr Johnson received several teaching awards during his career, including the West Virginia University Foundation Outstanding Teacher award and the Distinguished Teacher Award of the School of Medicine He is a member of the American Physiological Society, the Human Anatomy and Physiology Society, the National Association of Biology Teachers, and the American Association for the Advancement of Science Whether teaching undergraduates or medical students, Dr Johnson has always had a keen interest in instilling in students an appreciation of science He seeks to show students how the advancement of scientific knowledge sometimes raises unforeseen ethical, political, economic, and social issues for all of us to discuss and solve Through this book, he encourages students to become scientifically literate so that they will feel comfortable making responsible choices as consumers of science CONTENTS The Chemistry of Living Things 51 Human Biology, Science, and Society 31 Current Issue Functional Foods and Dietary Supplements—Safe and Effective? 52 Current Issue Mandatory Childhood Vaccinations  32 1.1 The characteristics of life  34 1.2 How humans fit into the natural world  36 Living things are grouped according to their characteristics  36 The defining features of humans  37 MJ’s BlogInFocus  53 2.1 All matter consists of elements  54 Atoms are the smallest functional units of an element  54 Isotopes have a different number of neutrons  55 Free radicals have unpaired electrons  56 2.2 Atoms combine to form molecules  56 MJ’s BlogInFocus  37 Energy fuels life’s activities  56 Human biology can be studied on any level of biological organization  38 Chemical bonds link atoms to form molecules  57 1.3 Science is both a body of knowledge and a process  40 The scientific method is a process for testing ideas  40 Health & Wellness The Growing Threat of Antibiotic-Resistant Bacteria  41 Designing and conducting the experiment  42 Making the findings known  43 MJ’s BlogInFocus  43 A well-tested hypothesis becomes a theory  43 Living organisms contain only certain elements  59 2.3 Life depends on water  59 Water is the biological solvent  59 Water is a liquid at body temperature  60 Water helps regulate body temperature  60 Water participates in chemical reactions  61 2.4 The importance of hydrogen ions  61 Acids donate hydrogen ions, bases accept them  61 MJ’s BlogInFocus  61 1.4 Sources of scientific information vary in style and quality  44 1.5 Learning to be a critical thinker  44 Become a skeptic  44 Learn how to read graphs  45 Appreciate the value of statistics  46 Distinguish anecdotes from scientific evidence  46 Separate facts from conclusions  46 Understand the difference between correlation and causation  46 MJ’s BlogInFocus  46 1.6 The role of science in society  47 Science improves technology and the human physical condition  47 Science has limits  47 The importance of making informed choices  48 MJ’s BlogInFocus  50 The pH scale expresses hydrogen ion concentration  62 Buffers minimize changes in pH  62 2.5 The organic molecules of living organisms  63 Carbon is the common building block of organic molecules  63 Macromolecules are synthesized and broken down within the cell  63 2.6 Carbohydrates: used for energy and structural support  65 Monosaccharides are simple sugars  65 Oligosaccharides: more than one monosaccharide linked together  65 Polysaccharides store energy  65 2.7 Lipids: insoluble in water  66 Triglycerides are energy-storage molecules  66 Phospholipids are the primary component of cell membranes  66 Contents Health & Wellness Radon: A Known Cancer Risk 67 3.5 A plasma membrane surrounds the cell 88 Steroids are composed of four rings  68 2.8 Proteins: complex structures constructed of amino acids  68 The plasma membrane is a lipid bilayer 88 3.6 Molecules cross the plasma membrane in several ways 89 Protein function depends on structure  70 MJ’s BlogInFocus 89 Enzymes facilitate biochemical reactions  71 Passive transport: principles of diffusion and osmosis 89 Passive transport moves with the concentration gradient 91 2.9 Nucleic acids store genetic information  72 Active transport requires energy 92 Endocytosis and exocytosis move materials in bulk 92 2.10 ATP carries energy  73 Information can be transferred across the plasma membrane 93 MJ’s BlogInFocus 76 The sodium-potassium pump helps maintain cell volume 93 Health & Wellness Do Antioxidant Supplements Slow the Rate of Cellular Aging? 94 Structure and Function of Cells 77 Isotonic extracellular fluid also maintains cell volume 96 Current Issue The Use of Human Stem Cells 78 3.7 Cells use and transform matter and energy 96 Glucose provides the cell with energy 97 Glycolysis: glucose is split into two pyruvate molecules 97 Cellular respiration uses oxygen 99 3.1 Cells are classified according to their internal organization 79 Fats and proteins are additional energy sources 103 Eukaryotes have a nucleus, cytoplasm, and organelles 80 Anaerobic pathways make energy available without oxygen 104 MJ’s BlogInFocus 106 Prokaryotes lack a nucleus and organelles 80 3.2 Cell structure reflects cell function 80 From Cells to Organ Systems 107 Cells remain small to stay efficient 81 Current Issue Reshaping Your Body 108 Visualizing cells with microscopes 81 MJ’s BlogInFocus 82 3.3 Internal structures carry out specific functions 82 The nucleus controls the cell 82 Ribosomes are responsible for protein synthesis 84 The endoplasmic reticulum is the manufacturing center 84 The Golgi apparatus refines, packages, and ships 84 Vesicles: membrane-bound storage and shipping containers 85 Mitochondria provide energy 86 Fat and glycogen: sources of energy 86 3.4 Cells have structures for support and movement 87 4.1 Tissues are groups of cells with a common function 109 4.2 Epithelial tissues cover body surfaces and cavities 109 Epithelial tissues are classified according to cell shape 110 The basement membrane provides structural support 111 4.3 Connective tissue supports and connects body parts 112 The cytoskeleton supports the cell 87 Fibrous connective tissues provide strength and elasticity 112 Cilia and flagella are specialized for movement 87 Specialized connective tissues serve special functions 114 Centrioles are involved in cell division 88 Health & Wellness Suntans, Smoking, and Your Skin 115 MJ’s BlogInFocus 115 Contents 4.4 Muscle tissues contract to produce 5.4 Bones fit together to form the skeleton 136 movement 116 The axial skeleton forms the midline of the body 137 Skeletal muscles move body parts 116 The appendicular skeleton: pectoral girdle, pelvic girdle, and limbs 140 Cardiac muscle cells activate each other 116 Smooth muscle surrounds hollow structures 117 5.5 Joints form connections between bones 142 4.5 Nervous tissue transmits impulses 117 Joints vary from immovable to freely movable 142 4.6 Organs and organ systems perform complex Health & Wellness Treating a Sprained Ankle 143 functions 117 The human body is organized by organ systems 117 Tissue membranes line body cavities 120 Describing body position or direction 120 4.7 The skin as an organ system 121 Skin has many functions 121 MJ’s BlogInFocus 121 Skin consists of epidermis and dermis 122 MJ’s BlogInFocus  142 Ligaments, tendons, and muscles strengthen and stabilize joints 144 5.6 Diseases and disorders of the skeletal system 145 Osteoporosis is caused by excessive bone loss 145 MJ’s BlogInFocus 145 Sprains mean damage to ligaments 146 Bursitis and tendinitis are caused by inflammation 146 Arthritis is inflammation of joints 146 MJ’s BlogInFocus 148 4.8 Multicellular organisms must maintain homeostasis 124 Homeostasis is maintained by negative feedback 124 Negative feedback helps maintain core body temperature 125 The Muscular System 149 Current Issue Drug Abuse Among Athletes 150 Positive feedback amplifies events 126 MJ’s BlogInFocus 128 The Skeletal System 129 Current Issue A Black Market in Human Bones? 130 6.1 Muscles produce movement or generate tension 152 The fundamental activity of muscle is contraction 153 Skeletal muscles cause bones to move 153 A muscle is composed of many muscle cells 154 The contractile unit is a sarcomere 155 MJ’s BlogInFocus 156 5.1 The skeletal system consists of connective tissue 131 6.2 Individual muscle cells contract and relax 156 Bones are the hard elements of the skeleton 131 Nerves activate skeletal muscles 156 Bone contains living cells 132 Activation releases calcium 157 Ligaments hold bones together 133 Calcium initiates the sliding filament mechanism 157 Cartilage lends support 133 When nerve activation ends, contraction ends 158 Muscles require energy to contract and to relax 158 5.2 Bones develop from cartilage 133 5.3 Mature bone undergoes remodeling and repair 134 Bones can change in shape, size, and strength 134 Producing and storing energy within muscle 159 Health & Wellness Delayed Onset Muscle Soreness 160 6.3 Muscles vary in movement, force, and MJ’s BlogInFocus 135 endurance 160 Bone cells are regulated by hormones 135 Isotonic versus isometric contractions: movement versus static position 160 Bones undergo repair 136 Contents The degree of nerve activation influences force 161 Slow-twitch versus fast-twitch fibers: endurance versus strength 162 Exercise training improves muscle mass, strength, and endurance 163 MJ’s BlogInFocus 164 6.4 Cardiac and smooth muscles have special features 164 How cardiac and smooth muscles are activated 164 Arrangement of myosin and actin filaments 165 Speed and sustainability of contraction 165 6.5 Diseases and disorders of the muscular system 166 Muscular dystrophy 166 Tetanus 166 Muscle cramps 166 7.3 Human blood types 180 ABO blood typing is based on A and B antigens 180 Rh blood typing is based on Rh factor 181 Blood typing and cross-matching ensure blood compatibility 182 New tests make transfused blood safer 183 7.4 Blood substitutes 183 Health & Wellness Donating Blood 184 7.5 Blood disorders 184 Mononucleosis: contagious viral infection of lymphocytes 184 Blood poisoning: bacterial infection of blood 185 Anemia: reduction in blood’s oxygen-carrying capacity 185 Leukemia: uncontrolled production of white blood cells 185 Pulled muscles 166 Multiple myeloma: uncontrolled production of plasma cells 186 Fasciitis 166 Thrombocytopenia: reduction in platelet number 186 MJ’s BlogInFocus 168 MJ’s BlogInFocus 188 Blood 169 Current Issue Should You Bank Your Baby’s Cord Blood? 170 7.1 The composition and functions of blood 172 Plasma consists of water and dissolved solutes 172 Red blood cells transport oxygen and carbon dioxide 173 Hematocrit and hemoglobin reflect oxygen-carrying capacity 174 All blood cells and platelets originate from stem cells 175 Heart and Blood Vessels 189 Current Issue How Should Comparative Effectiveness Research Be Used? 190 8.1 Blood vessels transport blood 191 Arteries transport blood away from the heart 192 Arterioles and precapillary sphincters regulate blood flow 193 Capillaries: where blood exchanges substances with tissues 194 The lymphatic system helps maintain blood volume 195 Veins return blood to the heart 195 RBCs have a short life span 175 RBC production is regulated by a hormone 176 8.2 The heart pumps blood through the vessels 196 White blood cells defend the body 176 The heart is mostly muscle 196 Platelets are essential for blood clotting 178 The heart has four chambers and four valves 197 7.2 Hemostasis: stopping blood loss 178 Vascular spasms constrict blood vessels to reduce blood flow 178 The pattern of blood flow through the cardiovascular system 198 Arteries and veins of the human body 199 MJ’s BlogInFocus 200 Platelets stick together to seal a ruptured vessel 179 The cardiac cycle: the heart contracts and relaxes 200 MJ’s BlogInFocus 179 A blood clot forms around the platelet plug 179 Heart sounds reflect closing heart valves 202 MJ’s BlogInFocus 179 Electrocardiogram records the heart’s electrical activity 203 The cardiac conduction system coordinates contraction 202 MJ’s BlogInFocus 204 Contents 8.3 Blood exerts pressure against vessel walls 204 9.3 Keeping pathogens out: the first line Measuring blood pressure 204 of defense 225 Hypertension: high blood pressure can be dangerous 205 Skin: an effective deterrent 225 Impeding pathogen entry in areas not covered by skin 225 Health & Wellness Cholesterol and Atherosclerosis 206 Hypotension: when blood pressure is too low 207 9.4 Nonspecific defenses: the second line of defense 226 8.4 How the cardiovascular system is regulated 207 Baroreceptors maintain arterial blood pressure 208 Local requirements dictate local blood flows 208 Exercise: increased blood flow and cardiac output 209 8.5 Cardiovascular disorders: a major health issue 209 Angina: chest pain warns of impaired blood flow 210 Heart attack: permanent damage to heart tissue 210 Heart failure: the heart becomes less efficient 211 Embolism: blockage of a blood vessel 211 Stroke: damage to blood vessels in the brain 211 8.6 Replacing a failing heart 212 MJ’s BlogInFocus 213 8.7 Reducing your risk of cardiovascular disease 213 The complement system assists other defense mechanisms 226 Phagocytes engulf foreign cells 227 Inflammation: redness, warmth, swelling, and pain 228 Natural killer cells target tumors and virus-infected cells 229 Interferons interfere with viral reproduction 229 Fever raises body temperature 229 9.5 Specific defense mechanisms: the third line of defense 229 The immune system targets antigens 230 Lymphocytes are central to specific defenses 230 B cells: antibody-mediated immunity 230 The five classes of antibodies 232 An antibody’s structure enables it to bind to a specific antigen 232 T cells: cell-mediated immunity 232 MJ’s BlogInFocus 216 9.6 Immune memory creates immunity 235 The Immune System and Mechanisms of Defense 217 Current Issue An Outbreak of Ebola 218 Health & Wellness The Case for Breast Milk 236 MJ’s BlogInFocus 236 9.7 Medical assistance in the war against pathogens 237 Active immunization: an effective weapon against pathogens 237 9.1 Pathogens cause disease 220 Passive immunization can help against existing or anticipated infections 237 Viruses: tiny infectious agents 221 Monoclonal antibodies: laboratory-created for commercial use 237 Antibiotics combat bacteria 239 Prions: infectious proteins 221 MJ’s BlogInFocus 239 Bacteria: single-celled living organisms 220 Transmissibility, mode of transmission, and virulence determine health risk 222 9.2 The lymphatic system defends the body 222 Lymphatic vessels transport lymph 222 Lymph nodes cleanse the lymph 222 The spleen cleanses blood 224 Thymus gland hormones cause T lymphocytes to mature 224 Tonsils protect the throat 224 9.8 Tissue rejection: a medical challenge 239 9.9 Inappropriate immune system activity causes health problems 239 Allergies: a hypersensitive immune system 240 Autoimmune disorders: defective recognition of self 241 184 C HA P TE R Blood HEALTH & WELLNESS Donating Blood A rapid loss of 30% or more of blood volume strains the body’s ability to maintain blood pressure and deliver oxygen to cells throughout the body When this happens, survival may depend on receiving a gift of donated blood In addition, blood is often needed for certain planned surgical procedures Approximately 15 million units of blood are donated every year, and almost million people receive donated blood Most people who donate blood get nothing more (and nothing less) than the satisfaction of knowing they have helped someone in need To donate blood, you must be at least 17 years old (16 in some states) and weigh at least 110 pounds You’ll be given a physical examination and asked for your health history, including a confidential questionnaire about your sexual history and recent international travel This is not done to embarrass you but to ensure that it is safe for you to give blood and that your blood will be safe for others You will not be allowed to donate if you are pregnant, for example, and you may not be allowed to donate if you have traveled recently to a malaria-infected area or if you have ever received a blood transfusion in (or Donating blood The procedure is relatively painless, takes only a short time, and can save lives were born in) certain countries For more specific information, your blood volume) This is not enough to consult the American Red Cross affect you adversely Usually the donated The blood withdrawal procedure itself is blood volume is replaced within several relatively painless (a needle is inserted into hours by any fluids that you drink The liver an arm vein) and takes about 10–20 minreplaces the lost plasma proteins within utes All needles used are brand-new and two days, and stem cells in bone marrow sterile—you cannot catch AIDS or any other replace the lost RBCs in about a month bloodborne disease by donating blood What happens to the blood you give? Afterward, you’ll be advised to drink and Sometimes, it is stored as whole blood, eat something and avoid rigorous physical but more often it is separated into three exercise for the rest of the day This is not components: packed cells, platelets, and the best day to go mountain climbing, but plasma Each component may be given just about anything less strenuous is OK to different recipients, meaning that your Most donors are allowed to give only single “gift of life” can benefit several one unit of blood (1 pint, about 10% of people The other type of oxygen-carrying blood substitute seeks to take advantage of the high oxygen-carrying capacity of perfluorocarbons (PFCs), a group of colorless liquids containing only carbon and fluorine PFCs are not soluble in water, so they must be dispersed (emulsified) as small droplets in water Each droplet is about 1/40th the size of a red blood cell, making them small enough to travel through the smallest blood vessels An aqueous solution containing PFC can carry several times more oxygen than whole blood, and because PFCs are completely man-made and can be heat-sterilized, they carry virtually no risk of transmitting disease They could also be manufactured in unlimited quantities and stored for prolonged periods without refrigeration However, a distinct disadvantage of the PFCs is that they are removed from the bloodstream within two days by exhalation and evaporation via the lungs PFCs currently are used only as a temporary substitute for blood Several commercial hemoglobin-based and PFC-based products have been developed and tested in clinical trials, only to be withdrawn due to safety concerns The bottom line is that there is still no ideal substitute for whole blood Research into blood substitutes continues, however, so don’t be surprised if there is a viable blood substitute in commercial use in your lifetime Recap Blood substitutes currently under investigation include modified hemoglobin products and perfluorocarbons 7.5 Blood disorders Blood disorders include infections, several types of cancers, and disorders that affect the ability of the blood to deliver oxygen to the tissues or to clot properly when injury occurs The effects of blood disorders are often widespread because blood passes through every organ in the body Mononucleosis: contagious viral infection of lymphocytes Mononucleosis is a contagious infection of lymphocytes in blood and lymph tissues caused by the Epstein–Barr virus, a relative of the virus that causes herpes Most common CHAPTER during adolescence, “mono” is nicknamed the “kissing disease” because it’s frequently spread through physical contact Symptoms of mononucleosis can mimic those of the flu: fever, headache, sore throat, fatigue, and swollen tonsils and lymph nodes A blood test reveals increased numbers of monocytes and lymphocytes The disease is called mononucleosis because many of the lymphocytes enlarge and begin to resemble monocytes There is no known cure for mononucleosis, but almost all patients recover on their own within four to six weeks Extra rest and good nutrition help the body overcome the virus Anemia: reduction in blood’s oxygen-carrying capacity Anemia is a general term for reduction in the oxygencarrying capacity of blood All causes of anemia produce similar symptoms: pale skin, headaches, fatigue, dizziness, difficulty breathing, and heart palpitations—the uncomfortable feeling that one’s heart is beating too fast as 185 it tries to compensate for the lack of oxygen delivery Major types of anemia include the following: ●● Blood poisoning: bacterial infection of blood Although blood normally is well defended by the immune system, occasionally bacteria may invade the blood, overwhelm its defenses, and multiply rapidly in blood plasma The bacteria may be toxic themselves, or they may secrete toxic chemicals as by-products of their metabolism A bacterial infection of blood is called blood poisoning, or septicemia Blood poisoning may develop from infected wounds (especially deep puncture wounds), severe burns, urinary system infections, or major dental procedures To help prevent it, wash wounds and burns thoroughly with soap and water Consult your doctor immediately when an infection is accompanied by flushed skin, chills and fever, rapid heartbeat, or shallow breathing An early sign of some blood poisonings is the sudden appearance of red streaks on healthy skin near the site of an infection (Figure 7.14) The red streaks are due to inflammation of veins or lymph vessels in the area, indicating that the infection is spreading toward the systemic circulation Although blood poisonings can be very dangerous (even fatal) if left untreated, in most cases they can be treated effectively with antibiotics Blood ●● ●● ●● ●● Iron-deficiency anemia Recall that every hemoglobin molecule contains four molecules of iron When the body is deficient in iron, hemoglobin cannot be synthesized properly The result is fewer hemoglobin molecules per red blood cell, and thus a decreased ability to transport oxygen Iron-deficiency anemia is the most common form of anemia worldwide Usually, it is due to too little iron in the diet, but it can also be caused by an inability of the digestive tract to absorb iron properly Generally, it can be treated by taking pills that contain iron or by eating foods rich in iron such as leafy green vegetables and meat Hemorrhagic anemia Anemia due to blood loss (hemorrhage) may be caused by injuries, bleeding ulcers, excessive menstrual flow, and even certain parasites Treatment includes finding and treating the underlying cause of blood loss, if possible, and making sure one has enough iron in the diet to replenish the lost red blood cells Pernicious anemia Pernicious anemia is caused by a deficiency of vitamin B12 absorption by the digestive tract Vitamin B12 is important for the production of normal red blood cells Pernicious anemia can be treated by injections of B12 Hemolytic anemia Hemolytic anemia is the result of rupture (lysis) or early destruction of red blood cells One cause is sickle-cell disease, an inherited disorder in which the red blood cells take on an abnormal sickle shape when the oxygen concentration is low Because of their abnormal shape, sickled red blood cells become damaged as they travel through small blood vessels Once damaged, they are destroyed by the body Sicklecell anemia is most prevalent in Africans who live near the equator and in African Americans Another common cause of hemolytic anemia is the parasite that causes malaria Anemia due to renal failure When the kidneys fail, they not produce enough erythropoietin to maintain normal red blood cell production In this case, the anemia is secondary to the renal failure and the attendant decline in erythropoietin, not the primary problem This type of anemia is easily corrected by treatment with exogenous erythropoietin, called EPO, which maintains red blood cell production within normal limits Why does exogenous erythropoietin (EPO) effectively treat anemia due to renal failure but is ineffective in treating the other four types? Leukemia: uncontrolled production of white blood cells Figure 7.14  Blood poisoning Leukemia refers to any of several types of blood cancer Their common characteristic is uncontrolled proliferation of abnormal or immature white blood cells in the bone 186 C HA P TE R Blood marrow Overproduction of abnormal WBCs crowds out the production of normal white blood cells, red cells, and platelets Huge numbers of leukemia cells enter and circulate in the blood, interfering with normal organ function There are two major categories of leukemia: acute, which develops rapidly; and chronic, which develops slowly Both are thought to originate in the mutation of a white blood cell (a change in genetic structure) that results in uncontrolled cell division, producing billions of copies of the abnormal cell Possible causes for the original mutation include viral infection or exposure to radiation or harmful chemicals Genetic factors may also play a role Leukemia can produce a wide range of symptoms Tissues may bruise easily because of insufficient production of platelets Anemia may develop if the blood does not contain enough red blood cells Bones may feel tender because the marrow is packed with immature white blood cells Some people experience headaches or enlarged lymph nodes Treatment can cure leukemia in some cases and prolong life in others Treatment generally involves radiation therapy and chemotherapy to destroy the rapidly proliferating cancer cells This kills the normal stem cells as well, so transplants of bone marrow tissue are required to provide new stem cells Cord blood transplants may be another option (see Current Issue, Should You Bank Your Baby’s Cord Blood?) As with blood transfusions, all tissue must undergo testing to make sure the donor’s antigens are compatible with those of the patient uncontrolled division Plasma cells are a type of lymphocyte responsible for making a specific antibody The proliferating plasma cells manufacture too much of an abnormal, frequently incomplete antibody, impairing production of other antibodies and leaving the body vulnerable to infections Bones become tender as healthy bone marrow is crowded out by malignant plasma cells Levels of calcium in the blood soar as bone tissue is destroyed Treatment includes anticancer drugs and radiation therapy Thrombocytopenia: reduction in platelet number Thrombocytopenia is a reduction in the number of platelets in the blood Thrombocytopenia can occur for a number of reasons, such as viral infection, anemia, leukemia, other blood disorders, exposure to X-rays or radiation, and even as a reaction to certain drugs Sometimes platelet levels decline for no apparent reason, in which case, they often rise again after several weeks Symptoms include easy bruising or bleeding, nosebleeds, bleeding in the mouth, blood in urine, and heavy menstrual periods Treatment of the underlying cause generally improves the condition If it persists, surgical removal of the spleen often helps Recap Blood poisoning and mononucleosis are types of blood infection Several factors, including iron deficiency or hemorrhage, can lead to a reduction in oxygen-carrying capacity of blood Leukemia and multiple myeloma are blood cell cancers that arise when abnormal cells in the bone marrow divide uncontrollably Thrombocytopenia, a disease of too few platelets, is characterized by easy bleeding or bruising Multiple myeloma: uncontrolled production of plasma cells Like leukemia, multiple myeloma is a type of cancer In this case, abnormal plasma cells in the bone marrow undergo Chapter Summary 7.2  Hemostasis: stopping blood loss p 178 ●● 7.1  The composition and functions of blood p 172 ●● ●● ●● ●● ●● ●● ●● ●● Blood consists of formed elements and plasma Blood has transport, regulatory, and protective functions Plasma contains numerous plasma proteins involved in transport, regulation of water balance, and protection It also contains ions, hormones, nutrients, wastes, and gases Erythrocytes (RBCs) are highly specialized for the transport of oxygen, but they also transport some carbon dioxide Hemoglobin is the primary protein in red blood cells and gives blood its oxygen-carrying capacity The formed elements of blood all originate from stem cells in red bone marrow Leukocytes (WBCs) defend the body against disease and the effects of injury RBCs and WBCs have short life spans and must continually be replaced RBC production is stimulated when the body detects low oxygen levels in the blood Platelets are cell products that participate in blood hemostasis ●● Hemostasis is a three-phase process that prevents blood loss through damaged vessels The phases are (1) vascular spasm, (2) the formation of a platelet plug, and (3) blood clotting During the formation of a blood clot, substances released by damaged blood vessels cause soluble proteins called fibrinogen to become insoluble protein threads called fibrin The threads form an interlocking mesh of fibers, trapping blood cells and sealing ruptured vessels 7.3  Human blood types p 180 ●● ●● ●● Successful transfusion of blood from one person into another depends on compatibility of their blood types, which is determined by antibodies in plasma and surface antigens on red blood cells Blood types are classified primarily on the basis of the ABO system and the presence or absence of the Rh factor Rh factor in particular can affect certain pregnancies adversely CHAPTER 7.4  Blood substitutes p 183 ●● ●● Hemoglobin-based blood substitutes are made from modified hemoglobin derived from animals or genetically engineered bacteria Perfluorocarbon-based blood substitutes are emulsions of colorless liquids with a high oxygen-carrying capacity, called perfluorocarbons (PFCs) 7.5  Blood disorders p 184 ●● ●● ●● ●● Mononucleosis is a contagious viral disease of lymphocytes and lymphatic tissue Blood poisoning is a general term for infection of blood plasma by various microorganisms Anemia is a reduction in blood oxygen-carrying capacity for any number of reasons, including insufficient red blood cell or hemoglobin production and excessive blood loss Leukemia is a cancer characterized by uncontrolled production of abnormal leukocytes (white blood cells) Terms You Should Know anemia, 185 blood type, 180 erythrocyte (RBC), 173 erythropoietin, 176 fibrin, 179 hematocrit, 174 hemoglobin, 174 hemostasis, 178 leukocytes (WBC), 176 phagocytosis, 176 plasma, 172 plasma proteins, 172 platelet, 178 Rh factor, 181 stem cell, 175 Concept Review Answers can be found in the Study Area in MasteringBiology Describe the functions of blood Describe the role of hemoglobin in the transport of oxygen and carbon dioxide Explain how the production of red blood cells is regulated to maintain homeostasis of the oxygen-carrying capacity of blood Define hematocrit, and explain why it is important Describe how damaged or dead RBCs and the hemoglobin they contain are removed from the blood Describe the difference between the actions of neutrophils and eosinophils Describe the mechanism of hemostasis List the four ABO blood types For each one, list its red blood cell surface antigen(s) and plasma antibody (antibodies) Describe the Rh factor and its implications for pregnancy 10 Compare and contrast the various causes of anemia Blood 187 Test Yourself Answers can be found in the Appendix All of the following proteins are associated with blood Which of these is found specifically inside red blood cells? a prothrombin c albumin b fibrinogen d hemoglobin Which of the following blood components protects the individual from a variety of infectious agents such as bacteria and viruses? a white blood cells c albumin b platelets d red blood cells Which of the following make(s) up the greatest volume of whole blood? a platelets c plasma b red blood cells d white blood cells Which of the following influence(s) the bonding of oxygen to hemoglobin? a pH c temperature b oxygen concentration d all of the above Jason has just spent four weeks in Rocky Mountain National Park, studying plants that grow above 10,000 feet elevation Which of the following would be a likely change in his blood because of time spent at high elevation? c increased number of a increased number of red platelets blood cells d increased amount of b increased number of globulins in the plasma white blood cells A person with Type O− (O-negative) blood will have: c Rh antigens on the red a type A and B plasma blood cells antibodies d none of the above b type A and B antigens on the red blood cells A deficiency of red blood cells would result in: a fatigue and dizziness c increased susceptibility to b bleeding and bruising infections d all of the above Which donor blood type would be most appropriate for ­transfusing an AB+ recipient? a A− c O− b B− d all of the above What myeloblasts, lymphoblasts, and monoblasts have in common? a They are immature cells that develop into white blood cells b They are immature cells that develop into red blood cells c They are found in the circulating blood d They are immature cells that develop into platelets 10 Jaundice is caused by the presence of in the blood plasma, which is a breakdown product of a hemoglobin red c albumin white blood blood cells cells b bilirubin hemoglobin d prothrombin platelets 188 C HA P TE R Blood 11 Which white blood cells are present in the greatest number in the blood and are the body’s first responders to infection? a neutrophils c platelets b lymphocytes d monocytes 12 The steps in the hemostasis process are (1) platelets become sticky and form a platelet plug, (2) walls of a damaged blood vessel undergo spasms, (3) a clot forms from fibrin, platelets, and trapped red blood cells Which of the following choices represents the correct order of these steps? a 1-3-2 c 2-3-1 b 3-1-2 d 2-1-3 13 Hemophilia results from a(n): c lack of one or more a insufficient number of plasma proteins involved red blood cells in blood clotting b insufficient number of d abnormal type of platelets hemoglobin 14 Which of the following can lead to anemia? a insufficient iron in the c spending several weeks at diet a high altitude b insufficient Vitamin B12 d both (a) and (b) absorption from the ­digestive tract 15 Which property granular and agranular leukocytes have in common? a Both lack a nucleus b Both contain granules or vesicles c Both are found in approximately equal numbers in the circulating blood d Both are derived from myeloblasts Apply What You Know Answers can be found in the Study Area in MasteringBiology A heavily menstruating 25-year-old female is sent by her gynecologist for a blood test The lab results indicate her platelet count (PC) is 90,000 per cubic millimeter The typical platelet count for a woman her age is 150,000– 450,000, meaning her PC is lower than normal What may this mean? One year after their first son was born, a couple gave birth to twins, a boy and a girl At the age of three, one of the twins was diagnosed with leukemia, and he needed a bone marrow transplant Who is most likely to be a good donor? What if the parents had banked the twins’ cord blood? Explain In the not too distant past, people with type O-negative blood were considered to be universal blood donors, and their blood was sought out during times of need Explain what was meant by the term universal donor, why O-negative persons were considered to be universal donors, and why universal donor is now considered an outdated term The text states that when red blood cells reach actively metabolizing tissues, they release their cargo of oxygen because both the oxygen concentration and the pH are lower in metabolically active tissues than in the general circulation The oxygen concentration is lower because actively metabolizing tissues are using oxygen at a rapid rate But what causes the pH to fall? And how might a fall in pH cause the hemoglobin to release oxygen? Can you think of any other variables that might also lead to the release of oxygen by hemoglobin? You find your vegan neighbor with her one-year-old daughter at the hospital where you are training as a medical student She tells you that her daughter is not doing well after switching from breast milk to a solid diet, and has started to grow pale and is sleeping all the time You find that her height and weight are way below normal A blood test reveals the hyper segmentation of neutrophil cells, an indicator of bone marrow malfunction You deduce that she has pernicious anemia, and refer her to an experienced doctor Explain the development of anemia in this case, and propose a long term treatment Coumadin is an anticoagulant drug that is sometimes given to patients who have just suffered a deep vein thrombosis, a pulmonary embolism, a heart attack, or to patients with artificial heart valves It helps reduce the chance of future clots and the further risk of embolism The active ingredient in Coumadin is warfarin, a rat poison How you think the same compound can be used for these two very different purposes? MJ’s BlogInFocus Answers can be found in the Study Area in MasteringBiology A drug has been discovered that prevents newly formed blood clots from breaking down What sorts of patients or medical conditions might be helped with such a drug? Visit MJ’s blog in the Study Area in MasteringBiology and look under “Drug Reduces Bleeding.”  http://goo.gl/hHvbo2 Students  Go to MasteringBiology for assignments, the eText, and the Study Area with animations, practice tests, and activities Professors  Go to MasteringBiology for automatically graded tutorials and questions that you can assign to your students, plus Instructor Resources Answers to   questions are available in the Appendix CHAPTER Heart and Blood Vessels 8.1 Blood vessels transport blood  191 8.2 The heart pumps blood through the vessels  196 8.3 Blood exerts pressure against vessel walls  204 8.4 How the cardiovascular system is regulated  207 8.5 Cardiovascular disorders: a major health issue  209 8.6 8.7 Replacing a failing heart  212 Reducing your risk of cardiovascular disease  213 A human heart, showing the blood vessels that lie just beneath the surface Key Concepts ●● ●● ●● ●● ●● The structure of blood vessels reflects their function Thick-walled arteries and ­arterioles transport blood to the tissues under high pressure; capillaries allow fluid exchange between blood and interstitial fluid; large thin-walled veins store most of the blood and return it to the heart The heart is a pump composed primarily of muscle Its ability to pump blood ­depends on one-way valves and coordination of muscle ­contraction Arterial blood pressure is held fairly constant by homeostatic control mechanisms With arterial blood pressure held ­constant, blood flow to each tissue can be regulated by local control mechanisms Cardiovascular disorders are the number one cause of death in the United States Cardiovascular disorders include heart ­attack, heart failure, stroke, and cardiac ­arrhythmias Your risk of developing cardiovascular disease is affected by your lifestyle choices Risk factors include smoking, a lack of exercise, obesity, and chronic stress 189 CURRENT ISSUE How Should Comparative Effectiveness Research Be Used? Mr Reynolds has a heart problem An angiogram shows that a short section of one of the main arteries supplying the left ventricle of his heart is narrowed, restricting blood flow to his heart muscle His doctor tells him that he is at serious risk of a heart attack The doctor explains that there are at least three techniques that could be used to restore blood flow to his heart: (1) balloon angioplasty, (2) a coronary artery stent, or (3) a coronary artery bypass graft (CABG) Which technique would be best for Mr Reynolds? The doctor and Mr Reynolds go over the options together, but the differences between the techniques are difficult for Mr Reynolds to understand He leaves the decision to his physician, whom he has known for 25 years The physician chooses a coronary artery stent because it has worked best for his previous patients with heart disease The body of medical literature is now so vast and expanding so rapidly that even the best physicians can’t know it all This is where a relatively new field of medical science called Comparative Effectiveness Research (CER) comes in CER focuses on analysis of the medical literature available to date, in order to reach scientifically sound judgments about the value (or lack thereof) Questions to Consider 1  Who you want to help you decide which treatment options would be best for you? If not a specific professional (doctor, patient representative, health insurance specialist), what other information would you like to have available to you? 2  Do you think cost-effectiveness should be a part of any comparative effectiveness analysis of treatment or diagnostic options? Why or why not? Doctoring, 1948 of specific medical tests, treatments, and disease prevention strategies In essence, CER seeks to determine the best practices in medicine based on our current knowledge Changing How Medicine Is Practiced Consider how CER might benefit Mr Reynolds’s physician (and Mr Reynolds, of course) By reviewing CER data, Mr Reynolds’s physician learns that a stent tends to be most effective for middle-­aged white males with heart disease However, the research shows that there’s an agerelated tipping point on the effectiveness of the technique and that the best treatment option depends on the severity of the narrowing: If the patient is over 55, the data indicates that balloon angioplasty is the best option (Hmmm, how old is Mr Reynolds this year?) If the degree of narrowing of a coronary artery is greater than 80%, for example, then the best option (again, for a middle-aged white male) would be a coronary artery bypass graft (What is the degree of narrowing in Mr Reynolds, anyway?) Toss in other factors like gender, race, physical condition, body weight, smoker-versusnonsmoker, and you can begin to see the full power of CER In theory, CER could analyze multiple factors at once to arrive at the best treatment option for patients who are described by a particular combination of factors Even the most experienced physicians can’t carry that much information around in their heads! Some politicians believe that the federal government should invest in CER, because any money spent on the research now would be offset by reduced health care expenditures in the future To jump-start a national CER program, Congress passed the Comparative Effectiveness Research Act of 2009 and funded it with $1.1 billion as part of the economic stimulus package To keep the program free of bias, the prestigious Institute of Medicine of the National Academies of Science was asked to come up with a list of 100 top priority topics for CER funding Among the topics are comparisons of the most effective practices to treat or prevent a number of cardiovascular diseases and risk factors, including high blood pressure, coronary artery disease, heart failure, ➔ Doctoring in the twenty-first century 190 CH APTER and abnormalities of heart electrical rhythm This is not surprising because cardiovascular diseases are the number one cause of death in the United States (cancer is second) Who Will Make Health Care Decisions? CER could become a powerful tool for improving health care quality and lowering costs Nevertheless, the CER Act of 2009 has stirred strong feelings among physicians, patients, politicians, and the health care industry because of the ways it could change how medicine is practiced Physicians and patient advocacy groups worry that if “best practices” become defined by CER, doctors and patients could begin to lose the right to make decisions regarding treatment options They fear that health care decisions may be dictated primarily by bureaucrats and insurance companies In recognition of this concern, the CER Act includes language to the effect that the findings of CER research shall “not be construed as mandates for practice guidelines, coverage recommendations, payment, or policy recommendations.” In other words, physicians and patients can still use their judgment in deciding the appropriate treatment option But by the same token, neither private insurers nor our primary public health care system (Medicare) are required by law to pay for it Therein lie the big questions: Will physicians and patients continue to be the decision makers in medical treatment decisions? Or is it inevitable that the old way of practicing medicine is going to change? Do we really believe that health insurance companies, group health plans, and even Medicare/Medicaid will not find a way to use CER data to influence reimbursement policies and hence treatment decisions? Would it be a good thing or a bad thing if they did? Flash forward 25 years You’re in the doctor’s office, and the doctor is telling you that a scan of your heart shows a 63% narrowing of a section of your left-anterior Heart and Blood Vessels 191 descending coronary artery She swings around to her computer, taps a few keys, and turns back to you to report that according to the latest data from the Comparative Effectiveness Research Institute, the most effective method for repair of your coronary artery is Robotic Artificial Vessel Extension (RAVE) A few more taps on her computer keyboard informs her that your government-supported health insurance will pay for the procedure and that there is an opening on the hospital’s surgical schedule on Tuesday Data further reveals that 99.7% of Dr Sloan’s RAVE surgeries have been successful and that 94% of all patients with your condition who undergo RAVE are discharged from the hospital on the same day as their surgery You go ahead and book that vacation to London next month SUMMARY ●● ●● ●● ●● The medical literature is expanding so rapidly that even the best physicians can no longer keep up with it Recognizing this, the government will spend $1.1 billion on Comparative Effective Research (CER) to determine the best practices in medicine based on our current knowledge and make that information available to everyone CER could slow down rising health-care costs A concern is that CER recommendations will eventually influence third-party payer reimbursement policies, so that patients and doctors will lose the ability to make treatment choices The heart and blood vessels play a critical role in the maintenance of homeostasis Collectively known as the cardiovascular system (from the Greek kardia, heart, and the Latin vasculum, small vessel), the heart and blood vessels function as a centrally controlled blood distribution network The heart provides the power to move the blood, and the vascular system represents the network of branching conduit vessels through which the blood flows Central control (oversight and management, if you will) is provided by the nervous system By controlling the rate at which the heart pumps and the resistance to flow through blood vessels, the nervous system apportions blood flow to the various tissues and organs according to need Homeostasis is not maintained by just the cardiovascular and nervous systems, however; other organ systems are also involved The digestive system delivers nutrients to the blood passing through its blood vessels The kidneys of the urinary system remove excess salt, water, and the waste products of cellular metabolism Glands of the endocrine system secrete hormones into the blood The respiratory system provides life-sustaining oxygen and removes the waste by-product carbon dioxide Even the skin is involved in homeostasis, by adjusting the amount of heat lost from the body We’ll start the chapter by considering the blood vessels and the structure and function of the heart Then we’ll describe how the cardiovascular system is regulated Finally, we’ll take a look at some major cardiovascular disorders 8.1 Blood vessels transport blood A branching network of blood vessels transports blood to all parts of the body The network is so extensive that if our blood vessels were laid end to end, they would stretch 60,000 miles! We classify the body’s blood vessels into three major types: arteries, capillaries, and veins Thick-walled arteries transport blood to body tissues under high pressure Microscopic capillaries exchange solutes and water with the 192 C HA P TE R Heart and Blood Vessels cells of the body Thin-walled veins store blood and return it to the heart Figure 8.1 illustrates the structures of each type of blood vessel, described in more detail below Arteries transport blood away from the heart As blood leaves the heart, it is pumped into large, muscular, thick-walled arteries Arteries transport blood away from the heart The larger arteries have a thick layer of muscle because they must be able to withstand the high pressures generated by the heart Arteries branch again and again, so the farther blood moves from the heart, the smaller in diameter the arteries become Large- and medium-sized arteries are like thick garden hoses, stiff yet somewhat elastic (distensible) Arteries stretch a little in response to high pressure but are strong enough to withstand high pressures year after year The ability to stretch under pressure is important because a function of arteries is to store the blood that is pumped into them with each beat of the heart and then provide it to the capillaries (at high pressure) even between heartbeats The elastic recoil of arteries is the force that maintains the blood pressure between beats Think of the arteries as analogous to a city’s water system of branching, iron or steel pipes that provide nearly constant water pressure to nearly every building in the vicinity Direction of blood flow Outer layer: Connective tissue Middle layer: Smooth muscle with elastic fibers Inner layer: Endothelium Hollow interior: Lumen Vein Artery Connective tissue Smooth muscle Endothelium Venule Arteriole Capillary Tissue cells Figure 8.1  The structures of blood vessels in the human body Epithelial cells of capillary endothelium CH APTER The structure of the walls of large and medium-sized arteries is ideally suited to their functions The vessel wall is a sandwich of three distinct layers surrounding the lumen, or hollow interior of the vessel: The thin inner layer, the endothelium, is a layer of flattened, ­squamous epithelial cells It is a continuation of the lining of the heart The flattened cells fit closely together, creating a slick surface that keeps friction to a minimum and promotes smooth blood flow Just outside the endothelium is a layer composed primarily of smooth muscle with interwoven elastic connective tissue In most arteries this is the thickest of the three layers Steady partial contraction of the smooth muscle of large and medium-sized arteries stiffens the arteries and helps them resist the high pressures within, but it does not constrict them enough to alter blood flow The elastic tissue makes large and medium-sized arteries slightly distensible so they can stretch passively to accommodate the blood that enters with each heartbeat The outermost layer of large and medium-sized arteries consists of a tough supportive layer of connective tissue, primarily collagen This sturdy casing anchors vessels to surrounding tissues and helps protect them from injury The fact that arteries are constantly under high pressure places them at risk of injury If the endothelium becomes damaged, blood may seep through the injured area and work its way between the two outer layers, splitting them apart The result is an aneurysm, or ballooning of the artery wall Some aneurysms cause the smooth muscle and endothelial layers to bulge inward as they develop, narrowing the lumen enough to reduce blood flow to an organ or region of the body Others force the outer connective tissue layer to bulge outward Sometimes aneurysms cause severe chest pain, but in other cases they are completely symptomless until they rupture or “blow out,” causing massive internal bleeding and often death If you’ve ever seen a water line burst, you know how quickly it can be devastating Aneurysms of the aorta (see section 8.2) kill an estimated 25,000 Americans every year Actor John Ritter’s sudden death in 2003 was caused by a ruptured aneurysm Aneurysms often take years to develop During this time, many can be detected and repaired surgically Some physicians recommend that anyone with a family history of aneurysm should be examined, even if there are no symptoms Doctors can sometimes detect inward-bulging aneurysms with a stethoscope (an instrument for listening to sounds inside the body) because flowing blood produces characteristic sounds as it passes through a narrowed arterial lumen A computerized tomography (CT) scan may also locate aneurysms before they rupture Arterioles and precapillary sphincters regulate blood flow Eventually blood reaches the smallest arteries, called arterioles (literally, “little arteries”) The largest artery in the body, the aorta, is about 2.5 centimeters (roughly inch) Heart and Blood Vessels 193 wide In contrast, arterioles have a diameter of 0.3 millimeter or less, about the width of a piece of thread By the time blood flows through the arterioles, blood pressure has fallen considerably Consequently, arterioles can be simpler in structure Generally, they lack the outermost layer of connective tissue, and their smooth muscle layer is not as thick In addition to blood transport and storage, arterioles have a third function not shared by the larger arteries: They help regulate the amount of blood that flows to each capillary They this by contracting or relaxing the smooth muscle layer, altering the diameter of the arteriole lumen Right where an arteriole joins a capillary is a band of smooth muscle called the precapillary sphincter (Figure 8.2) The precapillary sphincters serve as gates that control blood flow into individual capillaries Relaxation of vascular smooth muscle is called vasodilation Vasodilation of arterioles and precapillary sphincters increases their diameter and thus increases blood flow to the capillaries Conversely, contraction of vascular smooth muscle is called vasoconstriction Vasoconstriction of arterioles and precapillary sphincters reduces their diameter and thus reduces blood flow to the capillaries A wide variety of external and internal factors can produce vasodilation or vasoconstriction, including nerves, hormones, and conditions in the local environment of the arterioles and precapillary sphincters If you go outside on a cold day, you may notice that your fingers start to look pale This is because vasoconstriction produced by nerves is narrowing your vessels Arteriole Vasodilation Relaxed precapillary sphincters Vasoconstriction Constricted precapillary sphincters Capillaries Venule (small vein) Figure 8.2  Precapillary sphincters control the flow of blood into individual capillaries In this diagram, the two precapillary sphincters on the right are vasoconstricted, reducing flow in that region Arrows indicate direction of blood flow 194 C HA P TE R Heart and Blood Vessels to reduce heat loss from your body On the other hand, hot weather will make your skin appear flushed as vasodilation occurs to speed up heat loss and cool you off Emotions can also have an impact: Vasodilation is partly responsible for the surge in blood flow that causes the penis or clitoris to become erect when we are sexually aroused Later in this chapter, we will talk more about how the cardiovascular system is regulated to maintain homeostasis Capillaries: where blood exchanges substances with tissues Arterioles connect to the smallest blood vessels, called capillaries (Figure 8.3a) Capillaries are thin-walled vessels that average only about one-hundredth of a millimeter in diameter—not much wider than the red blood cells that travel through them In fact, they are so narrow that red blood cells (RBCs) often have to pass through them in single file or even bend to squeeze through (Figure 8.3b) Extensive networks of capillaries, called capillary beds, can be found in all areas of the body, which is why you are likely to bleed no matter where you cut yourself The branching design of capillaries and their thin, porous walls allow blood to exchange oxygen, carbon dioxide, nutrients, and waste products with tissue cells Capillary walls consist of a single layer of squamous epithelial cells (Figure 8.3c) Microscopic pores pierce this layer, and the cells are separated by narrow slits These openings are large enough to allow the exchange of fluid and other materials between blood and the interstitial fluid (the fluid that surrounds every living cell), yet small enough to retain RBCs and most plasma proteins in the capillary Some white blood cells (WBCs) can also squeeze between the cells in capillary walls and enter the tissue spaces In effect, capillaries function as biological strainers that permit selective exchange of substances with the interstitial fluid In fact, capillaries are the only blood vessels that can exchange materials with the interstitial fluid Figure 8.4 illustrates the general pattern of how water and substances move across a capillary At the beginning of a capillary, fluid is filtered out of the vessel into the interstitial fluid, accompanied by oxygen, nutrients, and raw materials needed by the cell The filtered fluid is essentially like plasma except that it contains very little protein because most protein molecules are too large to be filtered Filtration of fluid is driven by the blood pressure generated by the heart Waste materials such as carbon dioxide and urea (a nitrogen-containing substance) diffuse out of the cells and back into the blood Most of the filtered fluid is reabsorbed by diffusion back into the last half of the capillary before it joins a vein The force for this reabsorption is the presence of protein in the blood but not in the interstitial fluid In other words, fluid diffuses from an area of high water concentration (interstitial fluid) to an area of lower water concentration (blood plasma) However, the diffusional reabsorption of fluid does not quite match the pressure-induced filtration of fluid, so a small amount of filtered fluid remains in the interstitial space as excess interstitial fluid Why doesn’t exchange of gases and nutrients with the interstitial fluid occur in arteries and arterioles too, instead of just in capillaries? Put another way, what about the structure of an artery or an arteriole prevents such exchange from occurring? Capillary cell Slit between cells Pores through cells a) A medium-magnification view showing a rich network of capillaries surrounding and interconnecting small arteries and veins Nucleus Red blood cell b) A higher magnification showing a single branching capillary Notice the red blood cells traveling single file in the capillary Figure 8.3  Capillaries c) The structure of a capillary CH APTER Heart and Blood Vessels 195 Veins return blood to the heart Precapillary sphincter Capillary RBCs, most proteins Fluid (water) O2, nutrients, raw materials CO2, wastes Venule Arteriole Tissue cell Figure 8.4  The general pattern of fluid movement between capillaries, the interstitial fluid, and cells For simplicity, only a single tissue cell is shown, but a single capillary may supply many nearby cells Why does most of the fluid that was filtered out of the proximal (beginning) end of the capillary move back into the distal (far) end? The lymphatic system helps maintain blood volume Although the imbalance between the amount of plasma fluid filtered by the capillaries and the amount reabsorbed is not large, over the course of a day it would amount to about or liters This excess plasma fluid must be returned to the cardiovascular system somehow, or all the plasma would end up in the interstitial fluid The excess plasma fluid is absorbed by blind-ended capillaries that join together into a collection system of larger vessels, collectively called the lymphatic system The lymphatic system is somewhat similar to (and nearly parallel to) the venous system of blood vessels, except that the fluid of the lymphatic system (called lymph) does not contain plasma proteins or RBCs In addition to absorbing excess interstitial fluid, the capillaries of the lymphatic system also pick up objects in the interstitial fluid that are too large to diffuse into the blood capillaries, such as lipid droplets absorbed during digestion and invading microorganisms The lymphatic system transports the lymph back to veins near the heart, where the lymph rejoins the venous blood Aside from its role in returning excess fluid and large objects to the blood, the lymphatic system also plays a major role in our immune defenses You’ll hear more about the lymphatic system when we discuss the immune system For now, just be aware that the lymphatic system, though technically not part of the cardiovascular system, plays a vital role in maintaining the proper volumes of blood and interstitial fluid There are certain parasitic worms that can enter the lymphatic system and completely block the lymphatic capillaries draining an arm or a leg Predict what would happen to the arm or leg if this occurs From the capillaries, blood flows back to the heart through venules (small veins) and veins (see Figures 8.1 and 8.4) Like the walls of arteries, the walls of veins consist of three layers of tissue However, the outer two layers of the walls of veins are much thinner than those of arteries Veins also have a larger diameter lumen than arteries The anatomical differences between arteries and veins reflect their functional differences As blood moves through the cardiovascular system, blood pressure becomes lower and lower The pressure in veins is only a small fraction of the pressure in arteries, so veins not need nearly as much wall strength as arteries The larger diameter and high distensibility of veins allows them to stretch like thin balloons to accommodate large volumes of blood at low pressures In addition to their transport function, then, veins serve as a blood volume reservoir for the entire cardiovascular system Nearly two-thirds of all the blood in your body is in your veins Thanks to their blood reservoir function, even if you become dehydrated or lose a little blood, your heart will still be able to pump enough blood to keep your blood pressure fairly constant The distensibility of veins, however, can lead to problems in returning blood to the heart against the force of gravity When you stand upright, blood tends to collect in the veins of your legs and feet People who spend a lot of time on their feet may develop varicose veins, permanently swollen veins that look twisted and bumpy from pooled blood Varicose veins can appear anywhere, but they are most common in the legs and feet In severe cases, the skin surrounding veins becomes dry and hard because the tissues are not receiving enough blood Often, varicose veins can be treated by injecting an irritating solution that shrivels the vessels and makes them less visible This should not affect blood flow because surrounding undamaged veins take over and return blood to the heart Fortunately, three mechanisms assist the veins in returning blood to the heart: (1) contractions of skeletal muscles, (2) one-way valves inside the veins, and (3) movements associated with breathing Let’s look at each in turn Skeletal muscles squeeze veins  On their path back to the heart, veins pass between many skeletal muscles As we move and these muscles contract and relax, they press against veins and collapse them, pushing blood toward the heart You may have noticed that you tire more easily when you stand still than when you walk around This is because walking improves the return of blood to your heart and prevents fluid accumulation in your legs It also increases blood flow and the supply of energy to your leg muscles One-way valves permit only one-way blood flow  Most veins contain valves consisting of small folds of the inner layer that protrude into the lumen The structure of these valves allows blood to flow in one direction only: toward the heart They open passively to permit blood to move toward the heart and then close whenever blood begins to flow backward Together, skeletal muscles and valves form 196 C HA P TE R Heart and Blood Vessels what is called the “skeletal muscle pump” (Figure 8.5) Once blood has been pushed toward the heart by skeletal muscles or drained in that direction by gravity, it cannot drain back again because of these one-way valves The opening and closing of venous valves is strictly dependent on differences in blood pressure on either side Pressures associated with breathing push blood toward the heart  The third mechanism that assists blood flow involves pressure changes in the thoracic (chest) and abdominal cavities during breathing When we inhale, abdominal pressure increases and squeezes abdominal veins At the same time, pressure within the thoracic cavity decreases, dilating thoracic veins The result is to push blood from the abdomen into the chest and toward the heart This effect is sometimes called the “respiratory pump.” Recap A branching system of thick-walled arteries distributes blood to every area of the body Arterioles regulate blood flow to local regions, and precapillary sphincters regulate flow into individual capillaries Capillaries consisting of a single layer of cells exchange materials with the interstitial fluid The lymphatic system removes excess fluid The thin-walled veins return blood to the heart and serve as a volume reservoir for blood Valve (open) 8.2 The heart pumps blood through the vessels The human heart is a pump, but it’s a very special pump indeed The heart is constructed entirely of living cells and cellular materials, yet it is capable of greater reliability than some of the best pumps ever built by humans It can easily withstand 80–100 years of continuous service without ever stopping for repairs and without ever even resting for more than two-thirds of a second Its output is also fully adjustable on demand, over a range of about 5–25 liters of blood per minute At rest your heart pumps about 75 times every minute, speeding up to over 200 beats per minute during periods of exertion or in response to stress Under normal circumstances, the heart’s rate of pumping is controlled by nerve signals originating in the brain But unlike skeletal muscle, the heart can beat on its own without any nerve signals at all The heart is mostly muscle The human heart is a muscular, cone-shaped organ slightly larger than your fist (Figure 8.6) It consists mostly of a special type of muscle called cardiac muscle Unlike skeletal muscle, which attaches to bone and requires nerve signals for contraction, cardiac muscle contracts spontaneously and is not connected to bone The heart contracts in a cyclic, coordinated, squeezing motion that propels blood through the blood vessels One-way valves (closed) Left atrium (collapsed) Right atrium (collapsed) Calf muscles relaxed Calf muscles contracted Right ventricle Figure 8.5  The skeletal muscle pump With the calf muscle relaxed, blood accumulates in the vein, and backflow is prevented by one-way valves When the calf muscle contracts, skeletal muscles press on the vein, forcing blood toward the heart through the upper one-way valve, while the lower one-way valve remains closed, preventing backflow Left ventricle Figure 8.6  A human heart CH APTER In its natural position within the chest cavity, the heart is closely surrounded by a tough fibrous sac called the pericardium (not shown in Figure 8.6) The pericardium protects the heart and anchors it to surrounding structures The pericardium also prevents the heart from overfilling with blood, because although the heart is flexible, it is not very stretchable Between the pericardium and the heart is a space called the pericardial cavity The pericardial cavity contains a film of lubricating fluid that reduces friction and allows the heart and the pericardium to glide smoothly against each other when the heart contracts In cross section, we see that the walls of the heart consist of three layers: the epicardium, myocardium, and endocardium (Figure 8.7) The outermost layer, the epicardium, is a thin layer of epithelial and connective tissue The middle layer is the myocardium This is a thick layer consisting mainly of cardiac muscle that forms the bulk of the heart The myocardium is the layer that contracts every time the heart beats The structure of cardiac muscle cells allows electrical signals to flow directly from cell to cell An electrical signal in one cardiac muscle cell can spread to adjacent cells, enabling large numbers of cells to contract as a coordinated unit Every time the myocardium contracts, it squeezes the chambers inside the heart, pushing blood outward into the arteries The innermost layer of the heart, the endocardium, is a thin endothelial layer resting on a layer of connective tissue The endocardium is continuous with the endothelium that lines the blood vessels Heart and Blood Vessels 197 The heart has four chambers and four valves Taking a closer look at the details of the structure of the heart, we see that it consists of four separate chambers (see Figure 8.7) The two chambers on the top are the atria (singular: atrium), and the two more-muscular bottom chambers are the ventricles A muscular partition called the septum separates the right and left sides of the heart Blood returning to the heart from the body’s tissues enters the heart at the right atrium From the right atrium, the blood passes through a valve into the right ventricle The right ventricle is more muscular than the right atrium because it pumps blood at considerable pressure through a second valve and into the artery leading to the lungs Blood returning from the lungs to the heart enters the left atrium and then passes through a third valve into the left ventricle The very muscular left ventricle pumps blood through a fourth valve into the body’s largest artery, the aorta From the aorta, blood travels through the arteries and arterioles to the systemic capillaries, venules, and veins and then back to the right atrium again The left ventricle is the most muscular of the heart’s four chambers because it must more work than any other chamber The left ventricle must generate pressures higher than aortic blood pressure in order to pump blood into the aorta (We’ll see how high aortic pressure is in a minute.) The right ventricle has a thinner wall and does less work because the blood pressure in the arteries leading to the lungs is only about one-sixth that of the aorta Aorta Superior vena cava Left pulmonary artery Right pulmonary artery Pulmonary trunk Left pulmonary veins Left atrium Pulmonary semilunar valve Right atrium Aortic semilunar valve Left atrioventricular (AV) valve Left ventricle Right atrioventricular (AV) valve Chordae tendineae Right ventricle Papillary muscles Septum Epicardium Inferior vena cava Myocardium Endocardium Figure 8.7  A view of the heart showing major blood vessels, chambers, and valves 198 C HA P TE R Heart and Blood Vessels Four heart valves enforce the heart’s one-way flow pattern and prevent blood from flowing backward The valves open and shut passively in response to changes in the pressure of blood on each side of the valve The right and left atrioventricular (AV) valves located between the atria and their corresponding ventricle prevent blood from flowing back into the atria when the ventricles contract The AV valves consist of thin connective tissue flaps (cusps) that project into the ventricles The right AV valve is called the tricuspid valve because it has three flexible flaps The left AV valve has two flaps, so it is referred to as the bicuspid or mitral valve These valves are supported by strands of connective tissue called chordae tendineae that connect to muscular extensions of the ventricle walls called papillary muscles Together, the chordae tendineae and papillary muscles prevent the valves from everting (opening backward) into the atria when the ventricles contract Two semilunar valves (the pulmonary and the aortic) prevent backflow into the ventricles from the main arteries leaving the heart when the heart relaxes Each semilunar valve consists of three pocketlike flaps The valve name reflects the half-moon shape of these flaps (semi means “one-half”; luna comes from the Latin word for “moon”) 12 Systemic Circuit Head and upper limbs 11 7 The pattern of blood flow through the cardiovascular system The heart pumps blood through two circuits simultaneously; the pulmonary circuit (lungs), where blood picks up oxygen and gets rid of CO2, and the systemic circuit (the rest of the body) where oxygen is used and CO2 waste is produced The pattern of blood flow within the cardiovascular system is shown in Figure 8.8 Let’s follow the flow of blood through the system, starting with the return of blood to the heart from the systemic circuit Deoxygenated venous blood returns to the heart and enters the right atrium From there it passes through the right atrioventricular valve into the right ventricle The right ventricle pumps blood through the pulmonary semilunar valve into the pulmonary trunk (the main pulmonary artery) leading to the lungs The pulmonary trunk divides into the right and left pulmonary arteries, which supply the right and left lungs, respectively Blood entering the lungs passes through the pulmonary capillaries This is where gas exchange occurs; blood gives up CO2 and receives a fresh supply of O2 from the air we inhale The freshly oxygenated blood flows into the Figure 8.8  pulmonary veins leading back to the heart On returning to the heart after its trip through the lungs, the now-oxygenated blood flows into the left atrium and then passes through the left atrioventricular valve to enter the left ventricle 10 The left ventricle pumps the blood into the 10 11 Systemic Circuit Torso and lower limbs 12 The pattern of blood flow through the cardiovascular system aorta 11 Some of the blood travels up the main arteries to the head and upper body, and the rest passes down the aorta to the torso and lower limbs 12 Upon arrival at the capillaries in the systemic circuit, blood delivers O2 to the ... Life 533 23 Ecosystems and Populations 551 24 Human Impacts, Biodiversity, and Environmental Issues 571 Michael D Johnson Human Biology CONCEPTS AND CURRENT ISSUES Eighth Edition Global Edition Acquisitions... asserted by him in accordance with the Copyright, Designs and Patents Act 1988 Authorized adaptation from the United States edition, entitled Human Biology: Concepts and Current Issues, 8th edition,... want to, not because they have to, and they’ll be more comfortable with science and with biology. ” —Michael Johnson, Author of Human Biology: Concepts and Current Issues BlogInFocus in-text references