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Gerard J. Tortora / Bryan Derrickson 14th Edition
ANATOMY & PHYSIOLOGY 14th Edition
Gerard J. Tortora Bergen Community College
Bryan Derrickson Valencia College
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Jerry Tortora is Professor of Biology and former Biology Coordinator at Bergen Community College in Paramus, New Jersey, where he teaches human anatomy and physiology as well as microbiology. He received his bachelor’s degree in biology from Fairleigh Dickinson University and his master’s degree in science education from Montclair State College. He is a member of many professional organizations, including the Human Anatomy and Physiology Society (HAPS), the American Society of Microbiology (ASM), the American Association for the Advancement of Science (AAAS), the National Education Association (NEA), and the Metropolitan Association of College and University Biologists (MACUB). Above all, Jerry is devoted to his students and their aspirations. In recognition of this commitment, Jerry was the recipient of MACUB’s 1992 President’s Memorial Award. In 1996, he received a National Institute for Staff and Organizational Development (NISOD) excellence award from the University of Texas and was selected to represent Bergen Community College in a campaign to increase awareness of the contributions of community colleges to higher education. Jerry is the author of several best-selling science textbooks and laboratory manuals, a calling that often requires an additional 40 hours per week beyond his teaching responsibilities. Nevertheless, he still makes time for four or five weekly aerobic workouts that include biking and running. He also enjoys attending college basketball and professional hockey games and performances at the Metropolitan Opera House. Courtesy of Gerard J. Tortora
Courtesy of Heidi Chung
ABOUT THE AUTHORS
To Reverend Dr. James F. Tortora, my brother, my friend, and my role model.
Courtesy of Bryan Derrickson
His life of dedication has inspired me in so many ways, both personally and professionally, and I honor him and pay tribute to him with this dedication. G.J.T.
Bryan Derrickson is Professor of Biology at Valencia College in Orlando, Florida, where he teaches human anatomy and physiology as well as general biology and human sexuality. He received his bachelor’s degree in biology from Morehouse College and his Ph.D. in cell biology from Duke University. Bryan’s study at Duke was in the Physiology Division within the Department of Cell Biology, so while his degree is in cell biology, his training focused on physiology. At Valencia, he frequently serves on faculty hiring committees. He has served as a member of the Faculty Senate, which is the governing body of the college, and as a member of the Faculty Academy Committee (now called the Teaching and Learning Academy), which sets the standards for the acquisition of tenure by faculty members. Nationally, he is a member of the Human Anatomy and Physiology Society (HAPS) and the National Association of Biology Teachers (NABT). Bryan has always wanted to teach. Inspired by several biology professors while in college, he decided to pursue physiology with an eye to teaching at the college level. He is completely dedicated to the success of his students. He particularly enjoys the challenges of his diverse student population, in terms of their age, ethnicity, and academic ability, and finds being able to reach all of them, despite their differences, a rewarding experience. His students continually recognize Bryan’s efforts and care by nominating him for a campus award known as the “Valencia Professor Who Makes Valencia a Better Place to Start.” Bryan has received this award three times.
To my family: Rosalind, Hurley, Cherie, and Robb. Your support and motivation have been invaluable to me.
PREFACE An anatomy and physiology course can be the gateway to a gratifying career in a host of health-related professions. It can also be an incredible challenge. Principles of Anatomy and Physiology, 14th edition continues to offer a balanced presentation of content under the umbrella of our primary and unifying theme of homeostasis, supported by relevant discussions of disruptions to homeostasis. Through years of collaboration with students and instructors alike, this new edition of the text—integrated with WileyPLUS with ORION—brings together deep experience and modern innovation to provide solutions for students’ greatest challenges. We have designed the organization and flow of content within these pages to provide students with an accurate, clearly written, and expertly illustrated presentation of the structure and function of the human body. We are also cognizant of the fact that the teaching and learning environment has changed significantly to rely more heavily on the ability to access the rich content in this printed text in a variety of digital ways, anytime and anywhere. We are pleased that this 14th edition meets these changing standards and offers dynamic and engaging choices to make this course more rewarding and fruitful. Students can start here, and armed with the knowledge they gain through a professor’s guidance using these materials, be ready to go anywhere with their careers.
New for This Edition The 14th edition of Principles of Anatomy and Physiology has been updated throughout, paying careful attention to include the most current medical terms in use (based on Terminologia Anatomica) and including an enhanced glossary. The design has been refreshed to ensure that the content is clearly presented and easy to access. Clinical Connections that help students understand the relevance of anatomical structures and functions have been updated throughout and in some cases are now placed alongside related illustrations to strengthen these connections for students. The all-important illustrations that support this most visual of sciences have been scrutinized and revised as needed throughout. Nearly every chapter of the text has a new or revised illustration or photograph. ANTERIOR
PULMONARY VALVE (closed)
Right coronary artery
Left coronary artery
PULMONARY VALVE (open) AORTIC VALVE (open)
AORTIC VALVE (closed)
BICUSPID VALVE (open)
BICUSPID VALVE (closed) TRICUSPID VALVE (closed)
TRICUSPID VALVE (open) POSTERIOR Superior view with atria removed: pulmonary and aortic valves closed, bicuspid and tricuspid valves open
POSTERIOR Superior view with atria removed: pulmonary and aortic valves open, bicuspid and tricuspid valves closed
Axodendritic Perpendicular plate
Superior nasal concha
Superior nasal meatus Middle nasal meatus
Middle nasal concha
Inferior nasal concha Maxilla
Axosomatic Cell body
Inferior nasal meatus Frontal section through ethmoid bone in skull
Thyroid cartilage of larynx
Cricoid cartilage of larynx RIGHT LATERAL LOBE OF THYROID GLAND LEFT LATERAL LOBE OF THYROID GLAND ISTHMUS OF THYROID GLAND
Optic nerve Periorbital fat
Arch of aorta
Superior nasal concha Superior nasal meatus Nasal septum: Perpendicular plate of ethmoid
Vomer Inferior nasal concha Inferior nasal meatus Hard palate
Tongue Frontal section showing conchae and meatuses
SEM x4000 Extension Hyperextension
Hyperextension Extension Extension Hyperextension
Atlanto-occipital and cervical intervertebral joints
Lateral flexion Extension
c21TheCardiovascularSystemBloodVesselsAndHemodynamics.indd Page 747 9/16/13 8:35 AM f-481
Enhancing our emphasis on the importance of homeostasis and the mechanisms that support it, we have redesigned the illustrations describing feedback diagrams throughout the text. Introduced in the first chapter, the distinctive design helps students recognize the key components of a feedback cycle, whether studying the control manBody.indd Page 10 7/11/13 11:08 AM f-481 /204/WB00924/9781118345009/ch01/text_s of blood pressure, regulation of breathing, regulation of glomerular filtration Figure 21.14 Negative feedback regulation of blood rate, or a host of other functions involving negative or positive feedback. To pressure via baroreceptor reflexes. aid visual learners, color is used consistently—green for a controlled condition, When blood pressure decreases, heart rate increases. blue for receptors, purple for the control center, and red for effectors.
Figure 1.3 Homeostatic regulation of blood pressure by a negative feedback system. The broken return arrow with a negative sign surrounded by a circle symbolizes negative feedback.
Disrupts homeostasis by decreasing
If the response reverses the stimulus, a system is operating by negative feedback.
CONTROLLED CONDITION STIMULUS
Disrupts homeostasis by increasing
CONTROLLED CONDITION Blood pressure
Baroreceptors in carotid sinus and arch of aorta
– RECEPTORS Baroreceptors in certain blood vessels
Stretch less, which decreases rate of nerve impulses
CONTROL CENTERS CV center in medulla oblongata
CONTROL CENTER Brain
Return to homeostasis when the response brings blood pressure back to normal Output
Increased secretion of epinephrine and norepinephrine from adrenal medulla
Return to homeostasis when increased cardiac output and increased vascular resistance bring blood pressure back to normal
EFFECTORS Heart Blood vessels
EFFECTORS Heart Blood vessels
Increased stroke volume and heart rate lead to increased cardiac output (CO)
Constriction of blood vessels increases systemic vascular resistance (SVR)
RESPONSE Increased blood pressure RESPONSE A decrease in heart rate and the dilation (widening) of blood vessels cause blood pressure to decrease
What would happen to heart rate if some stimulus caused blood pressure to decrease? Would this occur by way of positive or negative feedback?
Does this negative feedback cycle represent the changes that occur when you lie down or when you stand up?
In addition, following the chapter or chapters covering each body system, a page is devoted to fostering understanding of how each system contributes to overall homeostasis through its interaction with other body systems. These Focus on Homeostasis pages have been redesigned for a more effective presentation of this summary material.
FOCUS on HOMEOSTASIS LYMPHATIC SYSTEM and IMMUNITY
Glucocorticoids such as cortisol depress inflammation and immune responses Thymic hormones promote maturation of T cells (a type of white blood cell)
Androgens stimulate growth of axillary and pubic hair and activation of sebaceous glands Excess melanocyte-stimulating hormone (MSH) causes darkening of skin
RESPIRATORY SYSTEM Epinephrine and norepinephrine dilate (widen) airways during exercise and other stresses Erythropoietin regulates amount of oxygen carried in blood by adjusting number of red blood cells
SKELETAL SYSTEM Human growth hormone (hGH) and insulinlike growth factors (IGFs) stimulate bone growth Estrogens cause closure of the epiphyseal plates at the end of puberty and help maintain bone mass in adults Parathyroid hormone (PTH) and calcitonin regulate levels of calcium and other minerals in bone matrix and blood Thyroid hormones are needed for normal development and growth of the skeleton
MUSCULAR SYSTEM Epinephrine and norepinephrine help increase blood flow to exercising muscle PTH maintains proper level of Ca2+, needed for muscle contraction Glucagon, insulin, and other hormones regulate metabolism in muscle fibers hGH, IGFs, and thyroid hormones help maintain muscle mass
NERVOUS SYSTEM Several hormones, especially thyroid hormones, insulin, and growth hormone, influence growth and development of the nervous system PTH maintains proper level of Ca2+, needed for generation and conduction of nerve impulses
CARDIOVASCULAR SYSTEM Erythropoietin (EPO) promotes formation of red blood cells Aldosterone and antidiuretic hormone (ADH) increase blood volume Epinephrine and norepinephrine increase heart rate and force of contraction Several hormones elevate blood pressure during exercise and other stresses
CONTRIBUTIONS OF THE
FOR ALL BODY SYSTEMS Together with the nervous system, circulating and local hormones of the endocrine system regulate activity and growth of target cells throughout the body Several hormones regulate metabolism, uptake of glucose, and molecules used for ATP production by body cells
Epinephrine and norepinephrine depress activity of the digestive system Gastrin, cholecystokinin, secretin, and glucose-dependent insulinotropic peptide (GIP) help regulate digestion Calcitriol promotes absorption of dietary calcium Leptin suppresses appetite
URINARY SYSTEM ADH, aldosterone, and atrial natriuretic peptide (ANP) adjust the rate of loss of water and ions in the urine, thereby regulating blood volume and ion content of the blood
REPRODUCTIVE SYSTEMS Hypothalamic releasing and inhibiting hormones, follicle-stimulating hormone (FSH), and luteinizing hormone (LH) regulate development, growth, and secretions of the gonads (ovaries and testes) Estrogens and testosterone contribute to development of oocytes and sperm and stimulate development of secondary sex characteristics Prolactin promotes milk secretion in mammary glands Oxytocin causes contraction of the uterus and ejection of milk from the mammary glands
We are most excited about the enhanced digital experience now available with the 14th edition of this text. WileyPLUS now includes a powerful new adaptive learning component called ORION that allows students to take charge of their study time in ways they have not previously experienced and prepares them for more meaningful classroom and laboratory interactions. WileyPLUS itself has been refreshed with a new design that allows easier discoverability and access to the rich resources including new 3-D animations, Interactions, Muscles in Motion, Real Anatomy, Anatomy Drill and Practice, and PowerPhys. New for the 14th edition is a digital alternative called All Access Pack for Principles of Anatomy and Physiology, 14th edition. This choice offers you a full e-text to download and keep, full access to WileyPLUS, and a Study Resource Guide to use as a basis for taking notes in class and studying. It provides you with everything you need for your course, anytime, anywhere, on any device.
BRIEF CONTENTS 1 AN INTRODUCTION TO THE HUMAN BODY 2 THE CHEMICAL LEVEL OF ORGANIZATION 3 THE CELLULAR LEVEL OF ORGANIZATION 4 THE TISSUE LEVEL OF ORGANIZATION 5 THE INTEGUMENTARY SYSTEM 6 THE SKELETAL SYSTEM: BONE TISSUE 7 THE SKELETAL SYSTEM: THE AXIAL SKELETON 8 THE SKELETAL SYSTEM: THE APPENDICULAR SKELETON 9 JOINTS 10 MUSCULAR TISSUE 11 THE MUSCULAR SYSTEM 12 NERVOUS TISSUE 13 THE SPINAL CORD AND SPINAL NERVES 14 THE BRAIN AND CRANIAL NERVES 15 THE AUTONOMIC NERVOUS SYSTEM 16 SENSORY, MOTOR, AND INTEGRATIVE SYSTEMS 17 THE SPECIAL SENSES 18 THE ENDOCRINE SYSTEM 19 THE CARDIOVASCULAR SYSTEM: THE BLOOD 20 THE CARDIOVASCULAR SYSTEM: THE HEART 21 THE CARDIOVASCULAR SYSTEM: BLOOD VESSELS AND HEMODYNAMICS 22 THE LYMPHATIC SYSTEM AND IMMUNITY 23 THE RESPIRATORY SYSTEM 24 THE DIGESTIVE SYSTEM 25 METABOLISM AND NUTRITION 26 THE URINARY SYSTEM 27 FLUID, ELECTROLYTE, AND ACID–BASE HOMEOSTASIS 28 THE REPRODUCTIVE SYSTEMS 29 DEVELOPMENT AND INHERITANCE
APPENDIX A: MEASUREMENTS A-1 APPENDIX B: PERIODIC TABLE B-3 APPENDIX C: NORMAL VALUES FOR SELECTED BLOOD TESTS C-4 APPENDIX D: NORMAL VALUES FOR SELECTED URINE TESTS D-6 APPENDIX E: ANSWERS E-8 GLOSSARY G-1 CREDITS C-1 INDEX I-1
An Introduction to the Human Body The human body and homeostasis Humans have many ways to maintain homeostasis, the state of relative stability of the body’s internal environment. Disruptions to homeostasis often set in motion corrective cycles, called feedback systems, that help restore the conditions needed for health and life.
Our fascinating journey through the human body begins with an overview of the meanings of anatomy and physiology, followed by a discussion of the organization of the human body and the properties that it shares with all living things. Next, you will discover how the body regulates its own internal environment; this unceasing process, called homeostasis, is a major theme in every chapter of this book. Finally, we introduce the basic vocabulary that will help you speak about
ar br Li
e Res oto
the body in a way that is understood by scientists and health-care professionals alike.
Mauro Ferm arie ll o / S cie nc e
Did you ever wonder why an autopsy is performed
• AN INTRODUCTION TO THE HUMAN BODY
1.1 Anatomy and Physiology Defined OBJECTIVE
• Define anatomy and physiology, and name several branches of these sciences.
Two branches of science—anatomy and physiology—provide the foundation for understanding the body’s parts and functions. Anatomy (a-NAT-oˉ-me¯; ana- ⫽ up; -tomy ⫽ process of cutting) is the science of body structures and the relationships among them. It was first studied by dissection (dis-SEK-shun; dis- ⫽ apart; -section ⫽ act of cutting), the careful cutting apart of body structures to study their relationships. Today, a variety of imaging techniques (see Table 1.3) also contribute to the advancement of anatomical knowledge. Whereas anatomy deals with structures of the body, physiology (fiz⬘-e¯-OL-oˉ-je¯; physio- ⫽ nature; -logy ⫽ study of) is the science of body functions—how the body parts work. Table 1.1 describes several branches of anatomy and physiology. Because structure and function are so closely related, you will learn about the human body by studying its anatomy and physiology together. The structure of a part of the body often reflects its
functions. For example, the bones of the skull join tightly to form a rigid case that protects the brain. The bones of the fingers are more loosely joined to allow a variety of movements. The walls of the air sacs in the lungs are very thin, permitting rapid movement of inhaled oxygen into the blood. CHECKPOINT
1. What body function might a respiratory therapist strive to improve? What structures are involved? 2. Give your own example of how the structure of a part of the body is related to its function.
1.2 Levels of Structural Organization and Body Systems OBJECTIVES
• Describe the body’s six levels of structural organization. • List the 11 systems of the human body, representative organs present in each, and their general functions.
TABLE TABLE 1.1 1.3
Selected Branches of Anatomy and Physiology BRANCH OF ANATOMY
BRANCH OF PHYSIOLOGY
Embryology (em⬘-bre¯-OL-o¯-je¯; embry- ⫽ embryo; -logy ⫽ study of)
The first eight weeks of development after fertilization of a human egg.
Structural changes (gross to microscopic) associated with disease.
Chemical level. This very basic level can be compared to the letters of the alphabet and includes atoms, the smallest units
of matter that participate in chemical reactions, and molecules, two or more atoms joined together. Certain atoms, such as carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), calcium (Ca), and sulfur (S), are essential for maintaining life. Two familiar molecules found in the body are deoxyribonucleic acid (DNA), the genetic material passed from one generation to the next, and glucose, commonly known as blood sugar. Chapters 2 and 25 focus on the chemical level of organization.
Figure 1.1 Levels of structural organization in the human body. The levels of structural organization are chemical, cellular, tissue, organ, system, and organismal. 2 CELLULAR LEVEL 1 CHEMICAL LEVEL 3
Smooth muscle cell
Atoms (C, H, O, N, P) Smooth muscle tissue Molecule (DNA) 5 SYSTEM LEVEL
Which level of structural organization is composed of two or more different types of tissues that work together to perform a specific function?
The levels of organization of a language—letters, words, sentences, paragraphs, and so on—can be compared to the levels of organization of the human body. Your exploration of the human body will extend from atoms and molecules to the whole person. From the smallest to the largest, six levels of organization will help you to understand anatomy and physiology: the chemical, cellular, tissue, organ, system, and organismal levels of organization (Figure 1.1).
C H A P T E R
1.2 LEVELS OF STRUCTURAL ORGANIZATION AND BODY SYSTEMS
• AN INTRODUCTION TO THE HUMAN BODY
Cellular level. Molecules combine to form cells, the basic structural and functional units of an organism that are composed of chemicals. Just as words are the smallest elements of language that make sense, cells are the smallest living units in the human body. Among the many kinds of cells in your body are muscle cells, nerve cells, and epithelial cells. Figure 1.1 shows a smooth muscle cell, one of the three types of muscle cells in the body. The cellular level of organization is the focus of Chapter 3. Tissue level. Tissues are groups of cells and the materials surrounding them that work together to perform a particular function, similar to the way words are put together to form sentences. There are just four basic types of tissues in your body: epithelial tissue, connective tissue, muscular tissue, and nervous tissue. Epithelial tissue covers body surfaces, lines hollow organs and cavities, and forms glands. Connective tissue connects, supports, and protects body organs while distributing blood vessels to other tissues. Muscular tissue contracts to make body parts move and generates heat. Nervous tissue carries information from one part of the body to another through nerve impulses. Chapter 4 describes the tissue level of organization in greater detail. Shown in Figure 1.1 is smooth muscle tissue, which consists of tightly packed smooth muscle cells. Organ level. At the organ level different types of tissues are joined together. Similar to the relationship between sentences and paragraphs, organs are structures that are composed of two or more different types of tissues; they have specific functions and usually have recognizable shapes. Examples of organs are the stomach, skin, bones, heart, liver, lungs, and
brain. Figure 1.1 shows how several tissues make up the stomach. The stomach’s outer covering is a layer of epithelial tissue and connective tissue that reduces friction when the stomach moves and rubs against other organs. Underneath are three layers of a type of muscular tissue called smooth muscle tissue, which contracts to churn and mix food and then push it into the next digestive organ, the small intestine. The innermost lining is an epithelial tissue layer that produces fluid and chemicals responsible for digestion in the stomach. System level. A system (or chapter in our language analogy) consists of related organs (paragraphs) with a common function. An example of the system level, also called the organsystem level, is the digestive system, which breaks down and absorbs food. Its organs include the mouth, salivary glands, pharynx (throat), esophagus (food tube), stomach, small intestine, large intestine, liver, gallbladder, and pancreas. Sometimes an organ is part of more than one system. The pancreas, for example, is part of both the digestive system and the hormone-producing endocrine system. Organismal level. An organism (OR-ga-nizm), any living individual, can be compared to a book in our analogy. All the parts of the human body functioning together constitute the total organism.
In the chapters that follow, you will study the anatomy and physiology of the body systems. Table 1.2 lists the components and introduces the functions of these systems. You will also discover that all body systems influence one another. As you study each of the body systems in more detail, you will discover how
The Eleven Systems of the Human Body INTEGUMENTARY SYSTEM (CHAPTER 5)
Components: Skin and associated structures, such as hair, fingernails and toenails, sweat glands, and oil glands. Functions: Protects body; helps regulate body temperature; eliminates some wastes; helps make vitamin D; detects sensations such as touch, pain, warmth, and cold; stores fat and provides insulation.
SKELETAL SYSTEM (CHAPTERS 6–9) Hair
Skin and associated glands Fingernails
Components: Bones and joints of the body and their associated cartilages. Functions: Supports and protects body; provides surface area for muscle attachments; aids body movements; houses cells that produce blood cells; stores minerals and lipids (fats).
1.3 CHARACTERISTICS OF THE LIVING HUMAN ORGANISM
C L INIC A L C ON N E C T ION |
Noninvasive Diagnostic Techniques
Health-care professionals and students of anatomy and physiology commonly use several noninvasive diagnostic techniques to assess certain aspects of body structure and function. A noninvasive diagnostic technique is one that does not involve insertion of an instrument or device through the skin or a body opening. In inspection, the examiner observes the body for any changes that deviate from normal. For example, a physician may examine the mouth cavity for evidence of disease. Following inspection, one or more additional techniques may be employed. In palpation (pal-PA¯-shun; palp- ⫽ gently touching) the examiner feels body surfaces with the hands. An example is palpating the abdomen to detect enlarged or tender internal organs or abnormal masses. In auscultation (aws-kul-TA¯-shun; auscult⫽ listening) the examiner listens to body sounds to evaluate the functioning of certain organs, often using a stethoscope to amplify the sounds. An example is auscultation of the lungs during breathing to check for crackling sounds associated with abnormal fluid accumulation. In percussion (pur-KUSH-un; percus- ⫽ beat through) the examiner taps on the body surface with the fingertips and listens to the resulting sound. Hollow cavities or spaces produce a different sound than solid organs. For example, percussion may reveal the abnormal presence of fluid in the lungs or air in the intestines. It may also provide information about the size, consistency, and position of an underlying structure. An understanding of anatomy is important for the effective application of most of these diagnostic techniques. •
1.3 Characteristics of the Living Human Organism OBJECTIVES
• Define the important life processes of the human body.
Basic Life Processes Certain processes distinguish organisms, or living things, from nonliving things. Following are the six most important life processes of the human body: 1. Metabolism (me-TAB-oˉ-lizm) is the sum of all chemical processes that occur in the body. One phase of metabolism is catabolism (ka-TAB-oˉ-lizm; catabol- ⫽ throwing down; -ism ⫽ a condition), the breakdown of complex chemical substances into simpler components. The other phase of metabolism is anabolism (a-NAB-oˉ-lizm; anabol- ⫽ a raising up), the building up of complex chemical substances from smaller, simpler components. For example, digestive processes catabolize (split)
MUSCULAR SYSTEM (CHAPTERS 10, 11)
NERVOUS SYSTEM (CHAPTERS 12–17)
Components: Specifically, skeletal muscle tissue—muscle usually attached to bones (other muscle tissues include smooth and cardiac).
Components: Brain, spinal cord, nerves, and special sense organs, such as eyes and ears.
Functions: Participates in body movements, such as walking; maintains posture; produces heat.
Skeletal muscle T Tendon
Functions: Generates action potentials (nerve impulses) to regulate body activities; detects changes in body’s internal and external environments, interprets changes, and responds by causing muscular contractions or glandular secretions.
TA B L E 1. 2
3. Define the following terms: atom, molecule, cell, tissue, organ, system, and organism. 4. At what levels of organization would an exercise physiologist study the human body? (Hint: Refer to Table 1.1.) 5. Referring to Table 1.2, which body systems help eliminate wastes?
C H A P T E R
they work together to maintain health, provide protection from disease, and allow for reproduction of the human species.
Development and Inheritance Development, inheritance, and homeostasis Both the genetic material inherited from parents (heredity) and normal development in the uterus (environment) play important roles in determining the homeostasis of a developing embryo and fetus and the subsequent birth of a healthy child.
Developmental biology is the study of the sequence of events from the fertilization of a secondary oocyte by a sperm cell to the formation of an adult organism. Pregnancy is a sequence of events that begins with fertilization; proceeds to implantation, embryonic development, and fetal development; and ideally ends with birth about 38 weeks later, or 40 weeks after the last menstrual period. Obstetrics (ob-STET-riks; obstetrix ⫽ midwife) deals with the management of pregnancy, labor, and the neonatal period ˉ -tal), the first 28 days after birth. Prenatal development (pre¯-NA ˉ -tal; pre- ⫽ before; -natal ⫽ birth) is the time from (ne¯-oˉ-NA and is divided into three periods of three calendar months each, ffertilization ertilization tto o birth an called trimesters. calle ed trimeste 1. The ffirst trimester is the most critical stage of development, during which the rudiments of all the major organ systems appear, and also during which the developing organism is the most vulnerable to the dur effects of drugs, radiation, and microbes. ef 22. The second trimester is characterized by the nearly complete development of organ systems. By the end of this stage, the fetus assumes distinctively human features. 33. The third trimester represents a period of rapid fetal growth. During the early stages of this period, most of the organ systems are becoming fully functional. this chapter, we focus on the developmental sequence from In thi fertilization through implantation, embryonic and fetal development, fertilizat labor, birth, aand the principles of inheritance (the passage of hereditary traits from one generation to another).
Did you ever wonder why the heart, blood vessels, and blood begin to form so early in the developmental process
• Explain the major developmental events that occur during the embryonic period.
First Week of Development The embryonic period extends from fertilization through the eighth week. The first week of development is characterized by several significant events including fertilization, cleavage of the zygote, blastocyst formation, and implantation.
Fertilization ˉ -shun; fertil- ⫽ fruitful), the geDuring fertilization (fer⬘-ti-li-ZA netic material from a haploid sperm cell (spermatozoon) and a haploid secondary oocyte merges into a single diploid nucleus. Of the 200 million sperm introduced into the vagina, fewer than 2 million (1%) reach the cervix of the uterus and only about 200 reach the secondary oocyte. Fertilization normally occurs in the uterine (fallopian) tube within 12 to 24 hours after ovulation. Sperm can remain viable for about 48 hours after deposition in the vagina, although a secondary oocyte is viable for only about 24 hours after ovulation. Thus, pregnancy is most likely to occur if intercourse takes place during a 3-day window—from 2 days before ovulation to 1 day after ovulation. Sperm swim from the vagina into the cervical canal by the whiplike movements of their tails (flagella). The passage of sperm through the rest of the uterus and then into the uterine tube results mainly from contractions of the walls of these organs. Prostaglandins in semen are believed to stimulate uterine motility at the time of intercourse and to aid in the movement of sperm through the uterus and into the uterine tube. Sperm that reach the vicinity of the oocyte within minutes after ejaculation are not capable of fertilizing it until about seven hours later. During this time in the female reproductive tract, mostly in the uterine tube, sperm undergo ˉ -shun; capacit- ⫽ capable of), a series of capacitation (ka-pas-i-TA functional changes that cause the sperm’s tail to beat even more vigorously and prepare its plasma membrane to fuse with the oocyte’s plasma membrane. During capacitation, sperm are acted on by secretions in the female reproductive tract that result in the removal of cholesterol, glycoproteins, and proteins from the plasma membrane around the head of the sperm cell. Only capacitated sperm are capable of being attracted by and responding to chemical factors produced by the surrounding cells of the ovulated oocyte. For fertilization to occur, a sperm cell first must penetrate two layers: the corona radiata (koˉ-RO¯-na ⫽ crown; raˉ-de¯-A-ta ⫽ to shine), the granulosa cells that surround the secondary oocyte, and the zona pellucida (ZO¯-na ⫽ zone; pe-LOO-si-da ⫽ allowing passage of light), the clear glycoprotein layer between the corona radiata and the oocyte’s plasma membrane (Figure 29.1a). The acrosome (AK-roˉ-soˉm), a helmetlike structure that covers the head of a sperm (see Figure 28.6), contains several enzymes. Acrosomal enzymes and strong tail movements by the sperm help it penetrate the cells of the corona radiata and come in contact with the zona pellucida. One of the glycoproteins in the zona pel-
lucida, called ZP3, acts as a sperm receptor. Its binding to specific membrane proteins in the sperm head triggers the acrosomal reaction, the release of the contents of the acrosome. The acrosomal enzymes digest a path through the zona pellucida as the lashing sperm tail pushes the sperm cell onward. Although many sperm bind to ZP3 molecules and undergo acrosomal reactions, only the first sperm cell to penetrate the entire zona pellucida and reach the oocyte’s plasma membrane fuses with the oocyte. The fusion of a sperm cell with a secondary oocyte sets in motion events that block polyspermy (POL-e¯-sper⬘-me¯), fertilization by more than one sperm cell. Within a few seconds, the cell membrane of the oocyte depolarizes, which acts as a fast block to polyspermy— the inability of a depolarized oocyte to fuse with another sperm. Depolarization also triggers the intracellular release of calcium ions, which stimulate exocytosis of secretory vesicles from the oocyte.
Figure 29.1 Selected structures and events in fertilization. During fertilization, genetic material from a sperm cell and a secondary oocyte merge to form a single diploid nucleus. Sperm cell
PATH OF SPERM CELL: Corona radiata
Zona pellucida Plasma membrane of secondary oocyte First polar body
Cytoplasm of secondary oocyte
(a) Sperm cell penetrating secondary oocyte Head of sperm cell
(b) Sperm cell in contact with secondary oocyte
What is capacitation?
(c) Male and female pronuclei
29.1 EMBRYONIC PERIOD
Blastocyst Formation By the end of the fourth day, the number of cells in the morula increases as it continues to move through the uterine tube toward the uterine cavity. When the morula enters the uterine cavity on day 4 or 5, a glycogen-rich secretion from the glands of the endometrium of the uterus passes into the uterine cavity and enters the morula through the zona pellucida. This fluid, called uterine milk, along with nutrients stored in the cytoplasm of the blastomeres of the morula, provides nourishment for the developing morula. At the 32-cell stage, the fluid enters the morula, collects between the blastomeres, and reorganizes them around a large fluid-filled cavity called the blastocyst cavity (BLAS-toˉ-sist; blasto- ⫽ germ or sprout; -cyst ⫽ bag), also called the blastocoel (BLAS-toˉ-se¯l) (Figure 29.2e). Once the blastocyst cavity is formed, the developing mass is called the blastocyst. Though it now has hundreds of cells, the blastocyst is still about the same size as the original zygote.
Figure 29.2 Cleavage and the formation of the morula and blastocyst. Cleavage refers to the early, rapid mitotic divisions of a zygote. Polar bodies Blastomeres
(a) CLEAVAGE OF ZYGOTE, TWO-CELL STAGE (day 1)
Nucleus Cytoplasm (b) CLEAVAGE OF ZYGOTE, FOUR-CELL STAGE (day 2)
(c) MORULA (day 4)
(d) BLASTOCYST, EXTERNAL VIEW (day 5)
Cleavage of the Zygote After fertilization, rapid mitotic cell divisions of the zygote called cleavage (KLE¯V-ij) take place (Figure 29.2). The first division of the zygote begins about 24 hours after fertilization and is completed about 6 hours later. Each succeeding division takes slightly less time. By the second day after fertilization, the second cleavage is completed and there are four cells (Figure 29.2b). By the end of the third day, there are 16 cells. The progressively smaller cells produced by cleavage are called blastomeres (BLAS-toˉ-me¯rz; blasto⫽ germ or sprout; -meres ⫽ parts). Successive cleavages eventually produce a solid sphere of cells called the morula (MOR-uˉ-la ⫽ mulberry). The morula is still surrounded by the zona pellucida and is about the same size as the original zygote (Figure 29.2c).
During the formation of the blastocyst two distinct cell populations arise: the embryoblast and trophoblast (Figure 29.2e). The embryoblast (EM-bre¯-oˉ-blast), or inner cell mass, is located internally and eventually develops into the embryo. The trophoblast ¯ F-oˉ-blast; tropho- ⫽ develop or nourish) is the outer superfi(TRO cial layer of cells that forms the spherelike wall of the blastocyst. It will ultimately develop into the outer chorionic sac that surrounds the fetus and the fetal portion of the placenta, the site of exchange of nutrients and wastes between the mother and fetus. Around the fifth day after fertilization, the blastocyst “hatches” from the zona pellucida by digesting a hole in it with an enzyme, and then squeezing through the hole. This shedding of the zona pellucida is
What is the histological difference between a morula and a blastocyst?
C H A P T E R
The molecules released by exocytosis inactivate ZP3 and harden the entire zona pellucida, events called the slow block to polyspermy. Once a sperm cell enters a secondary oocyte, the oocyte first must complete meiosis II. It divides into a larger ovum (mature egg) and a smaller second polar body that fragments and disintegrates (see Figure 28.15). The nucleus in the head of the sperm develops into the male pronucleus, and the nucleus of the fertilized ovum develops into the female pronucleus (Figure 29.1c). After the male and female pronuclei form, they fuse, producing a single diploid nucleus, a process known as syngamy (SIN-game¯). Thus, the fusion of the haploid (n) pronuclei restores the diploid number (2n) of 46 chromosomes. The fertilized ovum now is called a zygote (zygon ⫽ yolk). Dizygotic (fraternal) twins are produced from the independent release of two secondary oocytes and the subsequent fertilization of each by different sperm. They are the same age and in the uterus at the same time, but genetically they are as dissimilar as any other siblings. Dizygotic twins may or may not be the same sex. Because monozygotic (identical) twins develop from a single fertilized ovum, they contain exactly the same genetic material and are always the same sex. Monozygotic twins arise from separation of the developing cells into two embryos, which in 99% of the cases occurs before 8 days have passed. Separations that occur later than 8 days are likely to produce conjoined twins, a situation in which the twins are joined together and share some body structures.
DEVELOPMENT AND INHERITANCE
necessary in order to permit the next step, implantation (attachment) into the vascular, glandular endometrial lining of the uterus.
Implantation The blastocyst remains free within the uterine cavity for about 2 days before it attaches to the uterine wall. At this time the endometrium is in its secretory phase. About 6 days after fertilization, the blastocyst loosely attaches to the endometrium in a process ˉ -shun) (Figure 29.3). As the called implantation (im-plan-TA blastocyst implants, usually in either the posterior portion of the fundus or the body of the uterus, it orients with the inner cell mass toward the endometrium (Figure 29.3b). About 7 days after fertilization, the blastocyst attaches to the endometrium more firmly, endometrial glands in the vicinity enlarge, and the endometrium becomes more vascularized (forms new blood vessels). The blastocyst eventually secretes enzymes and burrows into the endometrium, and becomes surrounded by it. Following implantation, the endometrium is known as the decidua (de¯-SID-uˉ-a ⫽ falling off). The decidua separates from the endometrium after the fetus is delivered, much as it does in normal menstruation. Different regions of the decidua are named based on their positions relative to the site of the implanted blastocyst
(Figure 29.4). The decidua basalis is the portion of the endometrium between the embryo and the stratum basale of the uterus; it provides large amounts of glycogen and lipids for the developing embryo and fetus and later becomes the maternal part of the placenta. The decidua capsularis is the portion of the endometrium
Figure 29.3 Relationship of a blastocyst to the endometrium of the uterus at the time of implantation. Implantation, the attachment of a blastocyst to the endometrium, occurs about 6 days after fertilization. BLASTOCYST
Opening of endometrial gland
ENDOMETRIUM OF UTERUS Uterine cavity
C L I NI C AL C ON N E C T ION |
Stem Cell Research and Therapeutic Cloning
Stem cells are unspecialized cells that have the ability to divide for indefinite periods and give rise to specialized cells. In the context of human development, a zygote (fertilized ovum) is a stem cell. Because it has the potential to form an entire organism, a zygote is known as a totipotent stem cell (to¯-TIP-o¯-tent; totus- ⫽ whole; -potentia ⫽ power). Inner cell mass cells, called pluripotent stem cells (ploo-RIP-o¯-tent; plur- ⫽ several), can give rise to many (but not all) different types of cells. Later, pluripotent stem cells can undergo further specialization into multipotent stem cells (mul-TIP-o¯-tent), stem cells with a specific function. Examples include keratinocytes that produce new skin cells, myeloid and lymphoid stem cells that develop into blood cells, and spermatogonia that give rise to sperm. Pluripotent stem cells currently used in research are derived from (1) the embryoblast of embryos in the blastocyst stage that were destined to be used for infertility treatments but were not needed and from (2) nonliving fetuses terminated during the first 3 months of pregnancy. Scientists are also investigating the potential clinical applications of adult stem cells—stem cells that remain in the body throughout adulthood. Recent experiments suggest that the ovaries of adult mice contain stem cells that can develop into new ova (eggs). If these same types of stem cells are found in the ovaries of adult women, scientists could potentially harvest some of them from a woman about to undergo a sterilizing medical treatment (such as chemotherapy), store them, and then return the stem cells to her ovaries after the medical treatment is completed in order to restore fertility. Studies have also suggested that stem cells in human adult red bone marrow have the ability to differentiate into cells of the liver, kidney, heart, lung, skeletal muscle, skin, and organs of the gastrointestinal tract. In theory, adult stem cells from red bone marrow could be harvested from a patient and then used to repair other tissues and organs in that patient’s body without having to use stem cells from embryos. •
(a) External view of blastocyst, about 6 days after fertilization
Frontal plane Uterine cavity
Frontal section through uterus
ENDOMETRIUM OF UTERUS
Endometrial gland Opening of endometrial gland
EMBRYOBLAST (INNER CELL MASS) BLASTOCYST CAVITY
(b) Frontal section through endometrium of uterus and blastocyst, about 6 days after fertilization
How does the blastocyst merge with and burrow into the endometrium?
29.1 EMBRYONIC PERIOD
located between the embryo and the uterine cavity. The decidua parietalis (par-ri-e-TAL-is) is the remaining modified endometrium that lines the noninvolved areas of the rest of the uterus. As the embryo and later the fetus enlarges, the decidua capsularis bulges into the uterine cavity and fuses with the decidua parietalis, thereby obliterating the uterine cavity. By about 27 weeks, the decidua capsularis degenerates and disappears. The major events associated with the first week of development are summarized in Figure 29.5.
Figure 29.4 Regions of the decidua. The decidua is a modified portion of the endometrium that develops after implantation. Implanted embryo
CLINICAL CONNECTION | Ectopic Pregnancy Ectopic pregnancy (ek-TOP-ik; ec- ⫽ out of; -topic ⫽ place) is the development of an embryo or fetus outside the uterine cavity. An ectopic pregnancy usually occurs when movement of the fertilized ovum through the uterine tube is impaired by scarring due to a prior tubal infection, decreased movement of the uterine tube smooth muscle, or abnormal tubal anatomy. Although the most common site of ectopic pregnancy is the uterine tube, ectopic pregnancies may also occur in the ovary, abdominal cavity, or uterine cervix. Women who smoke are twice as likely to have an ectopic pregnancy because nicotine in cigarette smoke paralyzes the cilia in the lining of the uterine tube (as it does those in the respiratory airways). Scars from pelvic inflammatory disease, previous uterine tube surgery, and previous ectopic pregnancy may also hinder movement of the fertilized ovum. The signs and symptoms of ectopic pregnancy include one or two missed menstrual cycles followed by bleeding and acute abdominal and pelvic pain. Unless removed, the developing embryo can rupture the uterine tube, often resulting in death of the mother. Treatment options include surgery or the use of a cancer drug called methotrexate, which causes embryonic cells to stop dividing and eventually disappear. •
DECIDUA CAPSULARIS DECIDUA PARIETALIS
Frontal section of uterus
Details of decidua
Which part of the decidua helps form the maternal part of the placenta? CHECKPOINT
1. 2. 3. 4.
Where does fertilization normally occur? How is polyspermy prevented? What is a morula, and how is it formed? Describe the layers of a blastocyst and their eventual fates. 5. When, where, and how does implantation occur?
Figure 29.5 Summary of events associated with the first week of development. Fertilization usually occurs in the uterine tube. 2. CLEAVAGE (first cleavage completed about 30 hours after fertilization)
1. FERTILIZATION (occurs within uterine tube 12–24 hours after ovulation)
3. MORULA (3–4 days after fertilization)
4. BLASTOCYST (41/2 –5 days after fertilization)
Ovary Uterus: Endometrium Myometrium
Frontal section through uterus, uterine tube, and ovary
In which phase of the uterine cycle does implantation occur?
C H A P T E R
5. IMPLANTATION (occurs about 6 days after fertilization)
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