HHUUMMAANN BBOODDYY IIII BBrriittaannnniiccaa IIlllluussttrraatteedd SScciieennccee LLiibbrraarryy Encyclopædia Britannica, Inc. Chicago ■ London ■ New Delhi ■ Paris ■ Seoul ■ Sydney ■ Taipei ■ Tokyo BBrriittaannnniiccaa IIlllluussttrraatteedd SScciieennccee LLiibbrraarryy © 2009 Editorial Sol 90 All rights reserved. Idea and Concept of This Work: Editorial Sol 90 Project Management: Fabián Cassan Photo Credits: Corbis, ESA, Getty Images, Graphic News, NASA, National Geographic, Science Photo Library Illustrators: Guido Arroyo, Pablo Aschei, Carlos Francisco Bulzomi, Gustavo J. Caironi, Hernán Cañellas, Leonardo César, José Luis Corsetti, Vanina Farías, Manrique Fernández Buente, Joana Garrido, Celina Hilbert, Inkspot, Jorge Ivanovich, Iván Longuini, Isidro López, Diego Martín, Jorge Martínez, Marco Menco, Marcelo Morán, Ala de Mosca, Diego Mourelos, Laura Mourelos, Pablo Palastro, Eduardo Pérez, Javier Pérez, Ariel Piroyansky, Fernando Ramallo, Ariel Roldán, Marcel Socías, Néstor Taylor, Trebol Animation, Juan Venegas, Constanza Vicco, Coralia Vignau, Gustavo Yamin, 3DN, 3DOM studio Composition and Pre-press Services: Editorial Sol 90 Translation Services and Index: Publication Services, Inc. Portions © 2009 Encyclopædia Britannica, Inc. Encyclopædia Britannica, Britannica, and the thistle logo are registered trademarks of Encyclopædia Britannica, Inc. Britannica Illustrated Science Library Staff Encyclopædia Britannica, Inc. Editorial Jacob E. Safra, Chairman of the Board Michael Levy, Executive Editor, Core Editorial John Rafferty, Associate Editor, Earth Sciences Jorge Aguilar-Cauz, President William L. Hosch, Associate Editor, Mathematics and Computers Michael Ross, Senior Vice President, Corporate Development Kara Rogers, Associate Editor, Life Sciences Rob Curley, Senior Editor, Science and Technology Dale H. Hoiberg, Senior Vice President and Editor David Hayes, Special Projects Editor Marsha Mackenzie, Director of Production Art and Composition Steven N. Kapusta, Director Carol A. Gaines, Composition Supervisor Christine McCabe, Senior Illustrator International Standard Book Number (set): Media Acquisition 978-1-59339-860-6 Kathy Nakamura, Manager International Standard Book Number (volume): 978-1-59339-873-6 Copy Department Britannica Illustrated Science Library: Human Body II 2009 Sylvia Wallace, Director Julian Ronning, Supervisor Printed in China Information Management and Retrieval Sheila Vasich, Information Architect Production Control Marilyn L. Barton Manufacturing Kim Gerber, Director www.britannica.com Human Body II Contents From Zygote to Embryo Page 6 Fetal Development and Childbirth Page 22 Microlife Page 46 The Most Common Diseases Page 58 Advanced Technology Page 78 The Miracle information, reviewed by professionals and digitally. That way a doctor can quickly accompanied by incredible illustrations, will access the medical record of the person of Life captivate you from the first page. The last through a remote communication network chapter is devoted to tracing the landscape such as the Internet. It is not strange to of future medicine. The surprising advances imagine that in coming years everyone will in molecular biology and genetics allow us to carry their medical records on a keychain have new therapeutic and diagnostic tools that, when connected to a computer, would that make it possible to think that, in the provide all their medical information. There future, humans will live eternally. The is real evidence that in the next decades the themes covered and shown here have a way that medicine will treat diseases scientific basis. We tell you, for example, requiring the replacement of organs or which mechanisms regulate the operation of tissues will also change. The tissue created in the genes and how these mechanisms can the laboratory will be genetically identical to correct certain errors in the DNA—the the patient's, so there will be no rejection. starting point for many illnesses of genetic Once this is achieved, transplants and origin, including many forms of cancer. In a artificial organ implants will be a thing of T his is a moving book. A guide for not too distant future, nanomachines (many the past. Today in the cases of heart failure, parents as well as young people, it times smaller than a cell) could be guided when the treatments do not work, a recounts in detail the almost magical inside the body to eliminate obstructions in transplant is sought. In a few more years, way in which babies evolve from the very blood vessels or to kill cancer cells. With this will be unnecessary. Ventricular moment that fertilization occurs. Thanks to particles the size of amino acids, sick cells assistance devices, combined with stem-cell new technological advances, today it is could be eliminated without damaging the implants, will be used to allow regeneration possible to visualize and re-create images of healthy ones. Like guided missiles, the of the damaged muscle. what happens inside a woman's body when molecules would go directly to the damaged a sperm travels through the uterus and the cells. This type of therapy has already been I gelatinous membrane that surrounds the demonstrated in mice and rats, and, n addition, the health of many people egg. Incredible photos show, day by day, how although the tests are still in development, it will be determined during fetal the embryo evolves, when the heart begins is expected that within the next few years development. As a result of the to beat, and even when the brain, eyes, legs, this type of revolutionary treatment, which advances in prenatal diagnostic methods, arms, mouth, and teeth are formed. This combines genetics with pharmacology, could the possibility has appeared in recent years SOURCE OF HEALTH book contains a wealth of information, with be applied. Currently there are patients on of carrying out surgical procedures to Breast milk is especially rich in antibodies, and photographic details that show you the whom certain drugs have toxic effects or do correct certain congenital problems inside when accompanied with inside of the body from a totally new not have the desired effect; in the future, the womb. It is not difficult to foresee the love and affection, it provides a sense of viewpoint. drugs could be made according to the development of medical units in which the security, warmth, and genetic makeup of each patient. fetus is a patient. Even though many of these well-being. advances are still in the research stage, it is T he book is divided into five chapters. not unrealistic to believe that they will end A The first two are dedicated to the nother aspect to highlight in the use up being useful. Several decades ago, nobody formation and development of the of new technologies is related to would have thought about replacing sick baby, and the rest deal with everything that health informatics, or medical organs with healthy ones or the possibility of happens to the body when it gets sick— informatics, in which all kinds of patient choosing a baby's sex. So why not fantasize from how the HIV/AIDS virus affects us to information is managed. Such a system about virtual medicine that is safer, simpler, what happens when arteries become already allows all hospitals in some cities, and more effective or even about the blocked because of fat deposits. The such as Vienna, Austria, to communicate possibility of living forever? From Zygote to Embryo FERTILIZED EGG THE ORIGIN OF SEX AND LIFE 8-9 After fertilization, the egg implants itself in the FERTILIZATION OF THE EGG 10-13 endometrium and begins FIRST HUMAN FORMS 14-21 to develop. F rom conception until the third embryonic stage, the most critical one implants itself in the endometrium and organ that gives the unborn baby the month of pregnancy, what takes during pregnancy? What changes does measures about 0.2 inch (5 mm). At what different nutrients and oxygen it needs place inside the mother's belly? the embryo go through? Here we present time do the heartbeats begin and the to continue developing? Turn the page. Day by day, during the phases of incredible images that show the embryo eyes, mouth, and legs begin to form? mitosis, what happens at this from its formation to the moment it Also, what is the role of the placenta, the 8 FROM ZYGOTE TO EMBRYO HUMAN BODY II 9 The Origin of Sex and Life The Menstrual Cycle Menstruation Thickening Maximum Ovulation Increase in Arrival of the egg The female The blood hormone levels occurs around progesterone If it is fertilized, it body disposes vessels of the Estrogen, luteinizing the 14th day The hormone that becomes implanted; The uterus is prepared for the implantation of the dead uterus hormone (LH), and after prepares the if not, menstruation T of the fertilized egg. For this, the woman's cells from the lengthen, and follicle-stimulating menstruation. endometrium for occurs. he origin of human reproduction is sexual. Men and women can have sex any time during the hormones have stimulated the uterus to endometrium. the wall grows. hormone (FSH) implantation thicken its internal wall (endometrium). If no year, unlike most other species, which have their specific times of heat. The ability to have sex egg is implanted, the thickened wall breaks begins at puberty, the age when the sexual organs develop. Women are fertile from their first down and the waste material is disposed of M U outside the body, together with the RI menstrual period until menopause at around age 45. Although their sexual activity continues after T unfertilized egg. This process is synchronized E M this age, they no longer produce eggs, the female sexual gametes capable of being fertilized by sperm. with ovulation and is repeated regularly O D throughout the woman's fertile life, from N E puberty until menopause. 0 2 4 6 8 10 12 14 16 18 20 22 24 28 DAYS The Male Sexual Apparatus Gametes and Hormones The Sexual Organs of the Woman The testicles, or male sexual glands, lie below the pelvis within a structure Testicles and ovaries are glands that produce the sex cells, or gametes— With the exception of the vulva, which eggs, or sex cells, and hormones. Periodically called the scrotum. It is there that sperm—the mobile sex cells—are sperm and eggs, respectively. Gametes are haploid cells. In other words, is external, the female sexual a mature egg leaves the ovary and produced. During sexual intercourse, these cells, if they reach the female vaginal they possess half the chromosomes of any other human tissue cell, which apparatus (which allows a woman to have an installs itself in the uterus (ovulation). canal, head toward the egg so that one of them may fertilize it. The ductus contains a total of 46. Upon uniting at conception, each gamete active sexual life, become pregnant, and give There, if it has not been fertilized deferens is the path through which the sperm travels to be joined by materials contributes half of the genetic load of the new embryo. The sex birth) lies completely inside the abdominal in the fallopian tube, the body from the seminal vesicles and the prostate. This combination makes up the glands also produce hormones that determine secondary cavity, where it is supported and protected will expel it naturally together semen, which, in the moments of maximum sexual excitation, will move to the characteristics and, in women, ovulation. by the pelvis. Its basic shape is that of with the residues of the urethra to exit the man's body through the penis. a cavity formed by the vagina and endometrium the uterus. The ovaries produce the (menstruation). EJACULATION FALLOPIAN TUBE Ejaculation (the exit of the A tube 4 to 5 inches semen from the male body) (10-12 cm) in length is produced by the intense and about 0.1 inch (3 Bladder excitement of the erect mm) in diameter, sexual organ. with internal cilia 4 that propel the egg Urethra toward the uterus. Spongy Seminal erectile vesicle tissue 3 FIMBRIAE Prostate form a tunnel 5 through which the OVULATION CYCLE mature egg is Inside the ovary there are thousands of immature eggs, introduced into the each one wrapped in a follicle, or fallopian tubes. sac. In each cycle, a mature 2 egg is sent to the uterus. OVARY Ductus deferens 28 contains many follicles 6 Epididymis with immature eggs and Glans releases hormones Testicle DAYS A TYPICAL responsible for the MENSTRUAL CYCLE menstrual cycle and 1 7 LASTS female sexual activity. SEMINIFEROUS 1 FROM REST TO AN ERECTION TUBULE A physical or mental stimulus causes the cavernous bodies to fill FRONT VIEW 1 The egg begins to grow in a follicle, with blood and the penis to swell. stimulated by FSH. 2 Protection The follicular cells form an envelope Spermatocyte 2 EJACULATION around the egg. If the penis continues being stimulated, the seminal vesicle 3 Maturing of the egg contracts and expels the semen. UTERUS The egg bulges from the ovarian walls, and hormonal secretions increase. Ovary A pear-shaped cavity with thick, muscular 4 Maximum size Mspaetrumre SSpPeErmR Mori gPinRaOteDs UinCsidTeI tOhNe Fallopian Tube walls. Itthse i netnedronmale wtraiullm is. Tflhueid f-ofilllliecdle chaavsit fyo.rmed a 10,000 seminiferous tubules 5 Ovulation Halfway through the cycle, the follicle at a rate of 120 million a day Uterus bursts and releases a mature egg. and are stored in the BLADDER epididymis. This process VAGINA 6 Formation of the corpus luteum The ruptured follicle closes and requires a temperature of Cervix Cavity that is releases progesterone. Spermatid 93° F (34° C), which the anatomically prepared to testicles achieve by being receive the penis during 7 Degeneration of the corpus luteum occurs only if the egg has not been outside the abdomen. Vagina sexual intercourse fertilized. 10 FROM ZYGOTE TO EMBRYO HUMAN BODY II 11 Fertilization of the Egg Day 4 Mitosis PHASES OF MITOSIS 1 TCheell pdrivoicseiosns bofe ggiennse wraittihn gth nee rwe pcleicllast.ion 1 PThroep DhNaAse of the chromosomes F of the DNA. In this way, a “mother” has already been copied. Two ertilization is the starting point for the development of pregnancy. After cell generates two identical “daughter” identical strands are formed, joined at the center by a intercourse, two sex cells, or gametes, fuse together, giving rise to an cells that contain the same genetic structure called a centromere. information as the mother cell. The ovum, or zygote, where the chromosomes of the two gametes are united. process of replication for cell division Nucleus In humans, these sex cells are the sperm and the egg. For conception of a new occurs for each of the 46 life, a sperm must fertilize the egg in a tough competition with hundreds of chromosomes in each cell. The cells of Cytoplasm the embryo divide through mitosis, just millions of other sperm. like most adult tissue cells. Centromere The Journey of a Sperm Chromatin ZONA PELLUCIDA After ejaculation, millions of sperm begin walls of the vagina and the uterus. Inside the Thick, translucent layer Sister their journey through the genital tract. egg, the sperm loses its tail and midsection, outside the cell Chromatids Only 200 will reach the egg. The trip toward the which dissolve. The head, which contains the membrane. It is Filament Centriole ftaol lsoepviearna lt uhboeusr st.a Tkoe sr eaancyhw thheerme ,f sropmer m15 u msein tuhteeisr gmeenmetbirca mnea toefr tiahle, megogv.e Ts hteo wmaarrdc ht hteo wplaarsdma penetrated by the sperm. 2 MTheet ampehmabserane that covers the tails, and they are helped by contractions in the fertilization is underway. cell nucleus disappears, and filaments form in the cell. The chromosomes align themselves along these filaments across the middle of the cell. FROM PENETRATION TO FERTILIZATION Daughter chromosomes CELL MEMBRANE ENLARGED AREA protects the egg. The 3 Anaphase sperm goes through it The filaments “tug” the duplicated chromosomes. after passing through The duplicated individual the zona pellucida. 3 Fertilization chromosomes move toward Fallopian Tube A zygote, or ovum, is the two ends of the cell. produced from the union of 3 FIne rtthilei zfaatllioopnian tubes, a Uterus Ovary the egg and the sperm. The sperm fertilizes the egg. cell will begin its cell division 250 through mitosis. Cervix 4 Telophase 2 E25ja0c umlailtliioonn sperm are NUCLEUS OF THE EGG Tanhde fai lnaemwe nntusc dleisaarp epnevaerl,ope released into the vagina. Vagina MILLION SPERM contains the genetic ma- forms around each group of terial made up of DNA. 46 chromosomes. The begin their journey nucleus has divided in two. through the genital tract 1 PTheen eetrreactti opnenis enters Penis after ejaculation. Only one the widened and will fertilize the egg. moistened vagina. 2 Only One The Egg Winner When the egg is fertilized by a sperm, pregnancy starts. 5 Late telophase The sperm that will finally The new cells have been Fertilization occurs in the exterior portion of the fallopian formed. The daughter cells fertilize the egg will release tube where the sperm meets and joins with the egg. Two contain the same genetic enzymes that allow it to cross days after fertilization, the egg travels toward the material as the original cell. The Sperm MIDSECTION through the external uterus, pushed along by the muscular action of the contains mitochondria membranes of the egg. When that release energy to fallopian tube. The egg, once fertilized, thickens its The male sex cell. With a tail, a head, it enters, it loses its tail and move the tail. outer surface to prevent the entrance of any and a midsection, millions of sperm fight midsection. What remains in new sperm. After fertilization, the zygote to fertilize the egg, a mission that only the egg is the head with the begins to divide through mitosis. one of them will accomplish. It measures genetic material. 0.002 inch (0.05 mm) in length. HEAD 0.1 inch contains the genetic Zona pellucida information (DNA). A membrane of glycoproteins that surrounds the plasma (3 mm) membrane of an oocyte, a female sex cell. This structure TAIL hethlprso utgheh sthpee remx tmeronvael 1 In the Race DISTANCE SPERM TRAVELS ahtetarda.c Itns thhuem sapnesr,m th aen md eism vbitraaln feo dr etgheen reerlaetaesse aonfd t hber esapkesrm membranes of the egg. Hundreds of millions of sperm IN A MINUTE down five days after fertilization. go in search of the egg immediately after ejaculation during reproduction. 12 FROM ZYGOTE TO EMBRYO HUMAN BODY II 13 9 days Day Formation of the Morula Implantation 2 The zygote goes through three stages word morum, meaning “mulberry”). The After cellular division to 64 cells, the morula the blastocyst. Nine days after fertilization, the of cell division. While it travels morula continues its journey through the becomes a blastocyst, a more compact and embryo will already be in the uterine wall. After AFTER FERTILIZATION through the fallopian tube, it divides first fallopian tube until it reaches the uterus. The blastocyst, the stage prior to solid mass. Once formed, the blastocyst moves implantation, the embryo begins to grow. If the into two and then into four identical cells. Cell division continues until a more solid ball the embryonic stage, implants itself freely in the uterine cavity for 48 hours before woman has very low levels of estrogen and After 72 hours, it will have reached the with 64 cells, the blastocyst, is formed. in the uterine wall. finding a place to implant itself in the endometrium. progesterone, the endometrium can rupture and stage of 16 cells, at which point a mulberry- Once the blastocyst attaches itself to the The endometrium relaxes to ease implantation of cause implantation to occur in the wrong place. shaped cell agglomerate called the morula interior of the uterus, the formation of the is formed (the name comes from the Latin embryo begins. X-ray of the Day Blastocyst TROPHOBLAST forms the embryonic part morula 4 The last step before growth of of the placenta. the embryo. The cellular mass is The morula is made up of 16 covered with an external layer CAVITY, OR BLASTOCOEL cells in its initial state. As it called the trophoblast. The contains liquid that passes divides, it will reach 64 cells, at trophoblast releases enzymes through the zona pellucida which time it becomes a that help the blastocyst adhere from the uterine cavity. blastocyst. to the endometrium. MASS OF CELLS They make up the embryo, 0.004 or embryoblast. Zygote BLASTOMERES Small cells that Tofh eth ree smualtlaen gta cmelel tfer o(smp etrhme )u wnioitnh inch mthaek me ourpu tlahe body of IT IMPDLAAYNST SA NFTINERE Day the female gamete (egg) in 9 FERTILIZATION. sexual reproduction is called the zygote. Its cytoplasm and (0.1 mm) MEMBRANE organelles are from the maternal covers the cellular egg. It contains all the necessary mass; made up of genetic material for fetal DIAMETER OF proteins. development. THE ZYGOTE LIQUID Fluid develops within the Fertilization intercellular spaces. Fertilization occurs in the upper part of the fallopian tube. When the head of the sperm penetrates a mature egg, the nuclei of both sex Morula cells, each one with 23 chromosomes, fuse to form the Trilaminar AMNIOTIC PRIMITIVE ECTODERM zygote, or ovum. With 46 chromosomes, the zygote will The second important stage of CAVITY GROOVE is the outermost layer. It development prior to the formation of disk begin the process of successive cell divisions through mitosis. It develops into skin, hair, the blastocyst. It forms from the will begin the journey from the fallopian tubes toward the repeated mitosis of the zygote. Initially its begins to form from the fingernails, the central nervous endometrium, where it will implant itself. interior contains 16 blastomeres, which are the embryonic bilaminar disk and is system, parts of the eye, the first cells that develop from the zygote. Inside the complete by day 15. From the nasal cavity, and tooth enamel. 12 hours morula, these cells are uniform in shape, size, and trilaminar disk, three physiological potential. germinative layers will develop; they will give rise to the distinct parts of the How long it takes the zygote, or ovum, body: mesoderm, endoderm, to divide through mitosis. Compact and ectoderm. masses are successively formed in MESODERM forms the bones, muscles, these cellular multiplications. cartilage, connective tissue, Unfertilized egg heart, blood, blood vessels, The Zygote's Journey Fertilized egg ZYGOTE The Endometrium lymphatic cells, lymphatic MORULA vessels, and various glands. YOLK SAC Once the sex cells have formed the zygote, it begins the journey The inner layer of the uterine wall, it is made up toward the uterus through the fallopian tube. During this journey, of the myometrium—the external musculature— ENDODERM several cellular divisions will take place. Before entering the and the endometrium—the internal mucosa. Its is the innermost layer. It forms the uterine cavity, a mulberry-shaped compact cellular mass is function is to receive the ovum for implantation. lining of the digestive and respiratory formed (the morula). Within the uterus, cellular divisions take When there is no pregnancy, the endometrium is tracts, liver ducts, pancreatic ducts, place every 12 hours until the blastocyst stage (about 64 cells) the bloody tissue lost during menstruation. and glands such as the thyroid has been reached. Once on the uterine lining, the blastocyst Uterine gland and the salivary gland. adheres to it, and shortly thereafter implantation takes place. Endometrium cavity Fallopian From that moment, embryonic growth begins. Tube Ovary BLASTOCYST