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40 Cards in this Set
- Front
- Back
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Ampulla
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site of fertilization, sperm moving from the cervix require 2-7 hours to reach the uterine tube. If ovulation has not occurred they become less mobile
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Phases of Fertilization
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1. capacitation: period of conditioning in female reproductive tract, lasting 7 hours
2. Acrosomal reaction: induced by zona proteins after binding to zona pellucida. Releases hyaluronidase that the sperm uses to penetrate ovum - which releases lysosomal enzymes to prevent additional entry 3. Fusion of plasma cell membranes: sperm leaves plasma membrane behind 4. Completion of second meiotic division: formation of female pronucleus 5. Formation of male pronucleus 6. Breakdown of pronuclear membranes, and restoration of diploid chromosomes |
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Cleavage
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division of zygote approx. 30 hours after fertilization. Mitotic division leads to formation of blastomeres, which is compacted for cell-cell interaction
Morula: 16-32 cell stage |
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Blastocyst formation
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morula enters uterus, where uterine fluid penetrates zona pellucida, fluid filled cavities combine to form blastocystic cavity
fluid separates blastomeres into embryoblasts (tissue), and trophoblast (placenta). Implantation occurs 6 days after fertilization at the endometrial epithelium |
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Day 8
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Trophoblast proliferates into inner layer of cytotrophoblast cells, and outer layer of syncytiotrophoblast (multinucleated), which begin to penetrate the endometrial epithelium
Embryoblast differentiates into bilaminar embryonic disc, composed of: -Epiblast (thick layer): small cavity which enlarges to form amniotic cavity. Those adjacent to cytotrophoblasts become amnioblasts - enclosing the amnion, which becomes amniotic cavity -Hypoblast (thin layer): adjacent to blastocyst cavity |
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Days 9-10
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trophoblast enters lacunar stage, where vacoules form in syncytium, later fusing into lacunae
hypoblast cells line blastocystic cavity, which becomes exocoelomic cavity; the cells form membrane called exocoelomic membrane (Heuser's membrane) exocoelomic membrane/cavity are modified to form primitive yolk sac (primary umbilical vesicle). Blastocyst is fully embedded by day 10, site of penetration is closed by fibrin coagulum |
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Days 11-12
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Lacunae appear, esp at embryonic pole; syncytiotrophoblast penetrates deeper, eroding endothelial lining of maternal capillaries (which become sinusoids), wherupon blood enters lacunar system, starting uterplacental circulation
cells derived from yolk sac form between inner surface of cytotrophoblast and outer surface of amnion/exocoelomic membrane, forming extraembryonic mesoderm cavities formed there coalesce into the extraembryonic coelom/chorionic cavity, which surrounds the primary umbilical vesicle as this forms, primary umbilical vesicle shrinks and secondary umbilical vesicle forms mesoderm lining cytotrophoblasts and amnion forms extraembryonic somatic mesoderm, lining of umbilical vesicle becomes extraembryonic splanchnic mesoderm |
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Days 13-14
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Formation of primary villi: cytotrophoblasts proliferate and penetrate into syncytio. forming columns surounded by syncytia. Combo is called primary chorionic villi.
other cytotrophoblasts reach maternal endometrium, and along with other villi form outer cytotrophoblast shell (attaches the chorionic sac to endometrium) Villi that extend from this shell are called secondary chorionic villi, stems of which are tertiary chorionic villi, and are the site of maternal exchange somatic mesoderm and trophoblast layers form chorion, which form walls of the chorionic sac embryo, amniotic sac, and umbilical vesicle are suspended in chorionic cavity by connecting stack, which becomes umbilical cord by day 14 embryo still has bilaminar embryonic disc, and thickened portion of endoderm called prechordal plate syncytiotrophoblasts produce detectable levels of hCG by 2nd week |
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Hydatidiform Mole
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trophoblast forms placental membranes, but oocyte lacks nucleus.
Male chromosomes are duplicated to restore diploid number produces high levels of hCG, and may become malignant |
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Placenta previa
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placenta bridges the internal os of the cervix
potential for life-threatening bleeding in late pregnancy/delivery |
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Placenta accreta
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abnormal adherence of placenta to myometrium
Placenta percreta: chorionic villi penetrate all the way to the perimetrium |
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Exctopic pregnancy
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implantation outside of the uterus
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Third week of development
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1. Gastrulation
2. Formation of Notochord 3. Establishment of Body Axes 4. Fate map of epiblast migration is established 5. Growth of embryonic disc |
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Gastrulation
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1. Gastrulation: ectoderm, mesoderm, and endoderm formed
-primitive streak forms: narrow groove with elevations on either side -epiblast cells migrate towards primitive streak and invaginate beneath epiblast -invaginated cells displace hypoblast forming endoderm, others form mesoderm between this. Remaining cells become ectoderm |
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Formation of the notochord
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Mesenchymal cells migrate cranially from primitive node and forms notochordal process, which acquires a lumen called notochordal canal
-notochordal process grows cranially between extoderm and endoderm to reach prechordal plate (small disc of endodermal cells). -fused layers of ectoderm and prechordal plate form oropharyngeal membrane -cells migrate on each side of primitive streak and meet cranially to form cardiogenic mesoderm, in the cardiogenic area (primordium of heart begins forming) -floor of notochord process fuses with underlying endoderm and degenerates to interconnect amniotic cavity and umbilical vesicle -remaining notochordal process forms flattened/grooved notochordal plate -notochord cells proliferate and plate folds to become notochord -prechordal plate is important in forebrain, notochord is basis for parts of axial skeleton and spinal cord -cloacal membrane forms of fused ectoderm and endoderm -posterior wall of umbilical vesicle forms diverticulum (allantois) extending into the connecting stalk |
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Establishment of body axes
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-body axes (anteroposterior, dorsoventral, left-right) established before/during time of gastrulation
-Anteroposterior axis signaled by cells at cranial margin, called anterior visceral endoderm -primitive streak is initiaed and maintained by expression of Nodal gene, regulating formation of dorsal and ventral structures -Expression of Nodal and Lefty (left side) and snail gene (right side) |
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Fate Map of Epiblast migration
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Established during gastrulation
-cells migrating towards cranial region of primitive node become notochord -intraembryonic mesoderm proliferates to form longitudinal column of paraxial mesoderm -each column continues laterally to become intermediate mesoderm -this thins into layer called lateral plate mesoderm -extraembryonic mesoderm covering amnion and umbilical vesicle is continuous with lateral mesoderm |
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Growth of Embryonic disc
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-embryonic disc becomes elongated with growth, broad at the cephalic region, and caudal remains narrow
-disc enlargement is due to continuous cell migration from primitive streak until end of fourth week -cell layers in cephalic part differentiate in the third week, caudal part begins at the end of the fourth week -end of the fourth week, primitive streak regresses |
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Holoproscencephaly
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high doses of alcohol during gastrulation kill cells in anterior midline, producing deficiency of midline in craniofacial structures
-fore brain is small, two lateral ventricles often merge into single ventricle |
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Sirenomelia
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-insufficient mesoderm formed in caudal region
-contribues to abnormalities in lower limbs, urogenital system, lumbosacral vertebra -sometimes associated with maternal diabetes |
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Situs inversus
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left and right organ positions are reversed
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Sacrococcygeal teratoma
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-proliferation of remnants of primitive streak
-forms tumors comprised of three germ layers -most common newborn tumor |
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The Embryonic Period
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Period of organogenesis
embryonic disc forms a head fold, tail fold, and lateral folds |
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Derivatives of ectoderm layer
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central and peripheral nervous systems, sensory epithelium of eye/ear/nose, epidermis and epidermal derivatives
notochord and prechordal mesoderm form neural plate during process of neurulation, neural folds and neural groove form in neural plate neural folds fuse, forming neural tube (begins in cervical region). at this stage, neural tube communicates with amniotic cavity via cranial and caudal neuropores day 25-27: neuropores close forming closed CNS of brain vesicles and spinal cord as neural folds fuse into neural tube, neuroectodermal cells at lateral border form neural crest cells at the trunk, neural crest cells migrate *along dorsal pathway to form melanocytes, and *ventral pathway to form sensory, sympathetic, enteric ganglia, and Schwann cells -neural crest cells form parts of craniofacial skeleton, cranial nerve ganglia, and parasympathetic ganglia |
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Derivatives of mesoderm layer
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by the 17th day the mesoderm begins to differentiate into three subdivisions:
Paraxial Intermediate Lateral mesoderm |
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Paraxial mesoderm
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beginning at week 3, paraxial mesoderm is organized into segments called somatomeres, which form somites
Somite formation begins around day 20 in occipital region -> caudal until end of week 5, forming occipital, cervical, thoracic, lumar, sacral, and coccygeal pairs of somites. Week 4, somites differentiate into sclerotome (bones, cartilage, tendons), myotome (muscles), and dermatome (dermis of the skin). |
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Intermediate mesoderm
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differentiates into urogenital organ components
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Lateral mesoderm
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Splits into 2 layers:
Parietal (somatic) mesoderm lining the intraembryonic cavity Visceral (splanchnic) mesoderm surrounding organs parietal cells form thin mesothelial serous membranes that line the pleural, pericardial, and peritoneal cavities visceral cells form thin serous membrane around the organs |
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Blood/Vessel formation
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Vasculogenesis: blood islands forming in mesoderm and lateral mesoderm from hemangioblasts
-hemangioblasts in the periphery of the blood islands become angioblasts that form blood vessels Angiogenesis: once vessels form, new vessels branch from these Blood cells: hemangioblasts form first cells in blood islands of umbilical vesicle, that form hematopoietic stem cells. Definitive hematopoietic stem cells arise from mesoderm that surrounds aorta, these migrate to liver (10-30 weeks of major blood formation) and spleen (15-30 weeks of minor blood formation). Later stem cells from the liver migrate into the bone marrow |
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Derivatives of endodermal layer
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anterior endoderm forms foregut, middle forms midgut, and tail forms hindgut.
-midgut communicates with umbilical vesicle via vitalline duct -foregut is closed off by oropharyngeal membrane, and hindgut is closed by cloacal membrane -These rupture at weeks 4 and 7 respectively, forming continuities between gut and amniotic cavity -as embryonic disc forms head/tail/ and lateral folds, the allantois is partially incorporated to become cloaca -endodermal germ layer gives rise to epithelial lining of organs (respiratory and urinary tracts, parenchyma of thyroid, liver and pancreas |
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Crown-rump Length
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(CRL) during the second month, age of the embryo is determined by millimeters between vertex of the skull to midpoint between apices of the buttocks
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Birth Defects
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3-8 week period is main organogenesis, and when gross structural birth defects occur
during this stage, mother may not realize she is pregnant, and not avoid alcohol/drug use |
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Third Month to birth
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maturation of organs, and rapid growth of body
greatest length increase in months 3, 4, and 5. greatest weight increase in months 8 and 9 length of pregnancy = 38 weeks after fertilization |
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9-12 weeks
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external genitalia develop enough that sex can be determined by week 12
week 10, liver is the major site of erythropoiesis |
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13-16 weeks
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growth is very rapid
limb movements become coordinated by week 14 face becomes human-looking week 16, ovaries are differentiated and contain primordial follicles with oogonia |
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17-20 weeks
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growth slows down, but CRL increases by 50mm
fetal movements (quickening) felt by mother Brown fat forms, and is a site of heat production for newborn 20-week, testes have begun to descend, but are located on the posterior abdominal wall |
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21-25 weeks
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substantial weight gain
24 weeks, the secretory epithelial cells (interalveolar walls) secrete surfactant sucking movements and reactive to sounds 22- 25 week old fetus may survive premature birth, but respiratory system is still immature |
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26-29 weeks
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lungs have developed enough to usually survive birth
CNS has matured enough to direct rhythmic breathing and body temperature formation of blood cells has moved to the bone marrow |
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30-34 weeks
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pupillary light reflex
32+ weeks usually survive |
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35-38 weeks
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circumferences of the head and abdomen are equal
growth slows, and most fetuses have: -CRL of 36 cm -CHL of 50 cm -3000-3400 g |
