Longman Embryology _TOP_
Embryo Images Normal and Abnormal Mammalian Development -- Embryo Images Normal and Abnormal Mammalian Development is a tutorial that uses scanning electron micrographs (SEMs) as the primary resource to teach mammalian embryology. Formats include 3-D like quality of the micrographs and line drawings. The majority of micrographs are of mouse embryos and the remainder are human.
Note: Contents data are machine generated based on pre-publication provided by the publisher. Contents may have variations from the printed book or be incomplete or contain other coding.Contentspart oneGeneral Embryologychapter 1Development: Old and New Frontiers and an Introduction to Molecular Regulation and SignalingClinica relevanceA brief history of embryologyIntroduction to molecular regulation and signalingchapter 2Gametogenesis: Conversion of Germ Cells Into Male and Female Gametes Primordial germ cellsClinical correlatesThe chromosome theory of inheritanceClinical correlatesMorphological changes during maturation of the gametesClinical correlateschapter 3First Week of Development: Ovulation to Implantation Ovarian cycleClinical correlatesFertilizationClinical correlatesCleavageBlastocyst formationClinical correlatesUterus at time of implantationchapter 4Second Week of Development: Bilaminar Germ DiscDay 8Day 9Days 11 and 12Day 13Clinical correlateschapter 5Third Week of Development: Trilaminar Germ DiscGastrulation: formation of embryonic mesoderm and endodermFormation of the notochordEstablishment of the body axesFate map established during gastrulationGrowth of the embryonic discClinical correlatesFurther development of the trophoblastchapter 6Third to Eighth Weeks: The Embryonic PeriodDerivatives of the ectodermal germ layerDerivatives of the mesodermal germ layerClinical correlatesDerivatives of the endodermal germ layerPatterning of the anteroposterior axis: regulation by homeobox genesExternal appearance during the second monthClinical correlateschapter 7Third Month to Birth: The Fetal Period, Fetal Membranes and Placenta Development of the fetusClinical correlatesFetal membranes and placentaClinical correlatesStructure of the placentaClinical correlatesClinical correlatesAmnion and umbilical cordClinical correlatesPlacental changes at the end of the pregnancyAmniotic fluidClinical correlatesFetal membranes in twinsClinical correlatesParturition (birth)Clinical correlateschapter 8Birth Defects & Prenatal DiagnosisBirth defectsClinical correlatesPrenatal diagnosisFetal therapypart twoSystems Based Embryologychapter 9Skeletal System SkullClinical correlatesLimbClinical correlatesVertebrae and the vertebral columnClinical correlatesRibs and sternumchapter 10Muscular SystemStriated skeletal musculatureMolecular regulation of muscle developmentPatterning of musclesDerivatives of precursor muscle cellsHead musculatureLimb musculatureClinical correlatesCardiac muscleSmooth musclechapter 11Body Cavities Formation of the intraembryonic cavityClinical correlatesSerous membranesDiaphragm and thoracic cavityFormation of the diaphragmClinical correlateschapter 12Cardiovascular System Establishment of the cardiogenic fieldFormation and position of the heart tubeFormation of the cardiac loopClinical correlatesMolecular regulation of cardiac developmentDevelopment of the sinus venosusFormation of the cardiac septaClinical correlatesClinical correlatesClinical correlatesFormation of the conducting system of the heartVascular developmentClinical correlatesClinical correlatesCirculation before and after birthchapter 13Respiratory System Formation of the lung budsClinical correlatesLarynxTrachea, bronchi, and lungsMaturation of the lungsClinical correlateschapter 14Digestive System Divisions of the gut tubeMolecular regulation of gut tube developmentMesenteriesForegutClinical correlatesClinical correlatesMolecular regulation of liver inductionClinical correlatesClinical correlatesMidgutClinical correlatesHindgutClinical correlateschapter 15Urogenital System Urinary systemClinical correlatesClinical correlatesClinical correlatesGenital systemClinical correlatesClinical correlatesClinical correlatesClinical correlateschapter 16Head and NeckPharyngeal archesFirst pharyngeal pouchPharyngeal cleftsMolecular regulation of facial developmentClinical correlatesTongueClinical correlatesThyroid glandClinical correlatesFaceIntermaxillary segmentSecondary palateClinical correlatesNasal cavitiesTeethMolecular regulation of tooth developmentClinical correlateschapter 17Central Nervous SystemSpinal cordClinical correlatesBrainClinical correlatesMolecular regulation of brain developmentClinical correlatesCranial nervesAutonomic nervous systemClinical correlateschapter 18Ear Internal earMiddle earExternal earClinical correlateschapter 19EyeOptic cut and lens vesicleRetina, iris, and ciliary bodyLensChoroid, sclera, and corneaVitreous bodyOptic nerveMolecular regulation of eye developmentClinical correlateschapter 20Integumentary SystemSkinClinical correlatesClinical correlatesHairClinical correlatesMammary glandClinical correlatespart threeAppendixGlossary of Key TermsAnswers to ProblemsFigure CreditsIndex
Embryology (from Greek ἔμβρυον, embryon, "the unborn, embryo"; and -λογία, -logia) is the branch of animal biology that studies the prenatal development of gametes (sex cells), fertilization, and development of embryos and fetuses. Additionally, embryology encompasses the study of congenital disorders that occur before birth, known as teratology.
Early embryology was proposed by Marcello Malpighi, and known as preformationism, the theory that organisms develop from pre-existing miniature versions of themselves. Aristotle proposed the theory that is now accepted, epigenesis. Epigenesis is the idea that organisms develop from seed or egg in a sequence of steps. Modern embryology developed from the work of Karl Ernst von Baer, though accurate observations had been made in Italy by anatomists such as Aldrovandi and Leonardo da Vinci in the Renaissance.
The competing explanation of embryonic development was epigenesis, originally proposed 2,000 years earlier by Aristotle. Much early embryology came from the work of the Italian anatomists Aldrovandi, Aranzio, Leonardo da Vinci, Marcello Malpighi, Gabriele Falloppio, Girolamo Cardano, Emilio Parisano, Fortunio Liceti, Stefano Lorenzini, Spallanzani, Enrico Sertoli, and Mauro Ruscóni. According to epigenesis, the form of an animal emerges gradually from a relatively formless egg. As microscopy improved during the 19th century, biologists could see that embryos took shape in a series of progressive steps, and epigenesis displaced preformation as the favored explanation among embryologists.
Evolutionary embryology is the expansion of comparative embryology by the ideas of Charles Darwin. Similarly to Karl Ernst von Baer's principles that explained why many species often appear similar to one another in early developmental stages, Darwin argued that the relationship between groups can be determined based upon common embryonic and larval structures.
Until the birth of modern embryology through observation of the mammalian ovum by Karl Ernst von Baer in 1827, there was no clear scientific understanding of embryology, although later discussions in this article show that some cultures had a fairly refined understanding of some of the principles. Only in the late 1950s when ultrasound was first used for uterine scanning, was the true developmental chronology of human fetus available. Karl Ernst von Baer along with Heinz Christian Pander, also proposed the germ layer theory of development which helped to explain how the embryo developed in progressive steps. Part of this explanation explored why embryos in many species often appear similar to one another in early developmental stages using his four principles.
Medical embryology is used widely to detect abnormalities before birth. 2-5% of babies are born with an observable abnormality and medical embryology explores the different ways and stages that these abnormalities appear in. Genetically derived abnormalities are referred to as malformations. When there are multiple malformations, this is considered a syndrome. When abnormalities appear due to outside contributors, these are disruptions. The outside contributors causing disruptions are known as teratogens. Common teratogens are alcohol, retinoic acid, ionizing radiation or hyperthermic stress.
Many principles of embryology apply to invertebrates as well as to vertebrates. Therefore, the study of invertebrate embryology has advanced the study of vertebrate embryology. However, there are many differences as well. For example, numerous invertebrate species release a larva before development is complete; at the end of the larval period, an animal for the first time comes to resemble an adult similar to its parent or parents. Although invertebrate embryology is similar in some ways for different invertebrate animals, there are also countless variations. For instance, while spiders proceed directly from egg to adult form, many insects develop through at least one larval stage.For decades, a number of so-called normal staging tables were produced for the embryology of particular species, mainly focussing on external developmental characters. As variation in developmental progress makes comparison among species difficult, a character-based Standard Event System was developed, which documents these differences and allows for phylogenetic comparisons among species.
The study of embryology has a long pedigree. Knowledge of the placenta goes back at least to ancient Egypt, where the placenta was viewed as the seat of the soul. There was even an Egyptian official who held the title Opener of the Kings Placenta. Furthermore, one Egyptian text from the time of Akhenaten claims that a human originates from the egg that grows in women.
A variety of conceptions on embryology appeared in ancient Asia. A more advanced understanding of the embryological process was known from ancient India. Descriptions of the amniotic sac appear in the Bhagavad Gita, Bhagavata Purana, and the Sushruta Samhita. For example, the Sushruta Samhita claims that an embryo emerges from semen and blood, both of which in turn find their origins in chyle. In the third month, differentiation of body parts such as arms, leg, and head occurs, and this is followed in the fourth month by the development of the heart, thorax, and abdomen. In the sixth month, the hair, bones, sinews, nails, and veins develop, and in the eighth month the vital force (the ojas) is drawn from the mother and to the developing child. The father donates the hard parts of the body to the developing fetus whereas the soft parts come from the mother. Just as with Aristotle, the Sushruta Samhita compares the developing embryo to the clotting of milk into cheese. It claims that conditions of heat result in seven layers of skin being formed around the fetus, just as the creamy layers in cheese form from milk. One of the Upanishads known as the Garbhopanisaḍ states that the embryo is "like water in the first night, in seven nights it is like a bubble, at the end of half a month it becomes a ball. At the end of a month it is hardened, in two months the head is formed". The Indian medical tradition in the Ayurveda also has conceptions of embryology from antiquity. Then Dalhana, a medieval commentator on the Sushruta Samhita, also describes embryological development. Dalhana claims that in the first month, the fetus has a jelly-like form, whereas cold and heat cause a change to hardness during the second month. Limb differentiation occurs in the third to four months and intelligence even later.