Early Development II Flashcards
Embryonic folding
. Longitudinal and transverse folding of embryonic disc
. Establishes recognizable vertebrate body plan
Longitudinal folding
. Rapid differential growth of axial structures causing cranial and caudal end to fold ventrally
. Cephalic rim folds ventrally and caudally for ventral surface of face, neck and chest
. Oropharyngeal membrane relocated to site of mouth
. Cardiogenic region and septum transversum carried into future thoracic region
. Caudal rim folds ventrally and cranially carrying cloacal membrane and connecting stalk onto embryo’s ventral surface
. Connecting stalk contacts neck of yolk sac
Septum transversum
. Thickened band of mesoderm that contributes to thoraco-abdominal diaphragm
Transverse folding
. Lat. edges of embryo fold ventrally and meet in midline where they fuse at cranial and caudal ends and proceed toward site of future umbilicus
. Midline fusion or endoderm and splanchnic mesoderm creates gut tube
. Lat. folds constrict neck of yolk sac creating Vitelline duct that contacts connecting stalk
. Midline fusion of somatic mesoderm and ectoderm creates definitive intraembryonic coelom/body cavity
Gut tube
. Foregut and hindgut: blind pouches
. Hindgut communicates w/ allantois
. Midgut: communicates w yolk sac
Folding causes embryo to be enveloped in ____
Amniotic cavity
Rupture of ____ and ___ opens gut tube to amniotic cavity at both ends
. Oropharyngeal and cloacal membranes
Late embryonic period
. Weeks 5-8
. Most active organogenesis
. By week 9 heart and limbs formed and foundation or other systems established
Fetal period
. Weeks 9-38
. Organ system maturation and growth
. Malformations unlikely
Fetal viability starts at ____
22 weeks
When does growth in length occur?
Months 3-5
T/F fetal crown-rump length is closely assoc. w/ fetal age
T
Length of body and limbs inc. relative to ____
Head size
Inc. weight occurs most rapidly when?
Months 8-9
What occurs in week 2 in regards to placenta?
. Syncytiotrophoblast proliferates and develops lacunae to form lacunae network and erodes uterine glands w/in endometrium releasing glycogen-rich secretions and maternal serum into lacunar network
. Vascularization and secretory activity in endometrium inc. (decidual rxn)
. Endometrium referred to as decidua
Decidua
. Decidua basalis: btw embryo and muscular uterine wall
. Decidua capsularis: separates embryo from uterine cavity
. Decidua parietalis: lines remainder of uterine cavity
Chorionic villi development
. Primary: finger-like folds of trophoblast (both layers) project into lacunae
. Secondary: extraembryonic mesoderm penetrates the villus core
. Tertiary: mesoderm core gives rise to blood cells and vessels that connect w/ developing vessels in embryo proper
. Villi bathed by maternal blood when maternal-placental circulation establishes
When does maternal-placental circulation occur?
8-10 week
Smooth chorion (chorion laeve)
. During 2nd month
. Villi on abembryonic (away from. Embryo) side of the chorion degenerate forming this
Villous chorion (chorion frondosum)
. Portion of the chorion in contact w/ decidua basalis retains its villi
. Inc. in length and complexity throughout pregnancy
Intervillous space
. Lacunae enlarge and coalesce to form blood-filled intervillous space
. Lined by syncytiotrophoblast
Hydatidiform mole
. Trophoblastic hyperplasia in absence of viable embryo
. Complete mole contains only paternal chromosomes and lacks embryo
. Partial mole has triploid karyotype (from polyspermy) and a nonviable embryo
. Elevated hCG levels, proliferation and edema of chorionic villi, bleeding, and 1st trimester pre-eclampsia
Choriocarcinoma
. Malignant trophoblastic cancer
. 5% moles progress to this
Placental circulation
. Week 8: maternal blood in intervillous space via 100 spiral arteries
. Drained by endometrial veins
. Placental blood volume (150 ml) replaced 3-4 times per minute
. Capillaries w/in chorionic villi supplied w/ fetal blood by chorionic branches of umbilical arteries and drained by chorionic veins of umbilical veins
. Gas exchange occurs at placental membrane (chorionic villus wall)
Basal plate
. Maternal surface of placenta formed by decidua basalis and syncytiotrophoblast lining intervillous space
Chorionic plate
Fetal surface of placenta formed by villous chorion and chorionic vessels covered by amnion
Anchoring villi
. Specialized villi attach chorionic plate to basal plate
Cotyledons
. Occurs in months 4-5
. Protrusions of decidua basalis subdivide intervillous space into 15-25 segments
. Placental septae incomplete allow blood flow here
Placenta at birth
. Placenta weighs 500g and covers 30% of internal uterine surface
Placental membrane in early pregnancy
. Formed by trophoblast, fetal CT, and blood vessel endothelium
. Restricts broad range of substances from entering fetal circulation
Placental membrane in later pregnancy
. 2 layers: syncytiotrophoblast and endothelium to allow more substances to cross into fetal circulation
Beneficial substances that freely cross placental membrane
. Gasses . Electrolytes . Glucose . Nutrients . Fetal waste products . Maternal and fetal rbcs . Maternal serum proteins . Steroid hormones . Antibodies
Potentially harmful substances hat cross placental membrane
. Viruses . Environmental toxins . Pharmaceuticals . Bacteria and parasites . Maternal antibodies (anti-Rh)
Substances that can’t cross placental membrane
.most bacteria
. Large lipid molecules
. Protein hormones
. Some pharmaceuticals
Erythroblastosis Fetalis
. 2nd Rh+ child will have severe hemolytic anemia with mothers that do not have Rh factor w/o preventative measures
. 1st chid will be fine
Placental endocrine functions
. Placenta produces hormones crucial to maintenance of pregnancy and fetal growth and development
. HCG, human placental lactogen (fetal growth hormone), steroids hormones, and progesterone
Placenta previa
. Implantation on lower uterine wall causing placenta to expand and cover the internal os (opening) of the cervical canal
. Causes vaginal pleading in late pregnancy
. C-section performed to avoid life-threatening bleeding
Placenta accreta/increta/percreta
Abnormal implantation into (accreta/increta) or through (percreta) myometrium (muscular uterine wall)
. Can cause placental retention, massive hemorrhage, and/or uterine rupture
.Prior C sections inc. risk for this
. Life threatening
Primitive umbilical ring
, opening at conclusion of gastrulation on ventral embryo surface
Structures passing through primitive ring
. Connecting stalk
. Allantois: narrow yolk sac diverticulum w/in connecting stalk that communicates w/ hindgut
. Vitelline duct: connects yolk sac and midgut
Primitive umbilical cord formation
. Expansion of amniotic sac compresses and binds structures inside primitive umbilical ring
. Bound w/ sheath of amniotic membrane
Formation of umbilical vessels
. Weeks 2–3
. Vasculogenesis w/in extraembryonic mesoderm of the yolk sac extends into connecting stalk
. Gives rise to umbilical arteries and umbilical vein
Umbilical vessels
. Connected to vessels w/in embryo to eastablish fetal-placental circulation
. Embedded in Wharton’s jelly
. Umbilical arteries spiral around umbilical vein
Umbilical abnormalities
. Abnormal coiling assoc. w/ abnormal amniotic fluid volume and other fetal anomalies
. Presence of single umbilical artery is sign of cardiovascular abnormalities
Amniotic sac formation
. Week 8 amniotic sac has expanded to fill chorionic cavity
. Amnion fuses w/ chorion laeve to form amniochorionic membrane
. Uterine cavity disappears as amniotic sac grows
. Decidua capsularis and decidua parietalis fuse
Amniotic fluid
. Composed of maternally-derived H2O, electrolytes, biomolecules, and fetal waste products
. Supports fetus, prevents fetal membranes from adhering to it
. Permits movement
. AIDS in temp. Regulation
How is amniotic fluid produced?
. Direct transfer from maternal circulation and excretion of urine by fetus
Fluid resorption in fetus
. Occurs via fetal gut
. Fluid swallowed, absorbed into bloodstream across gut wall, and returned via placenta to maternal circulation
How much amniotic fluid at term?
1 L
Oligohydramios
. Low. Amniotic fluid volume
. Due to fetal kidney abnormalities
. Inc. pressure on fetus causes additional abnormalities (Potter syndrome)) and hypoplasia
Polyhydramnios
Excess amniotic fluid caused by maternal diabetes or fetal abnormalities in gut or CNS
Amniotic band syndrome
. Occurs when bands of amniotic membrane constrict counter parts of fetus causing amputation or deformation of structures
Premature membrane rupture
. Leads to oligohydramnios and premature labor
Dizygotic twins
. 2 ova fertilized and implanted separately
. Each twin normally has separate placenta, chorion, and amnion
. Placentas or membranes may fuse
. Placental fusion may result in rbc exchange and genetic mosaicism
Monozygotic twins
. Single fertilized ovum splits into 2 embryos
. Organization of fetal membranes determined by stage at when splitting occurs
2-blastomere through morula separation for twins
. Resulting blastocysts implant separately
. Each twin forms a separate placenta, chorion, and amnion
Early blastocyst separation for twins
. Splitting forms 2 inner cell masses w/in common trophoblast
. Twins have common chorion but separate amnions
Bilaminar germ disc separation in twins
. Share single placenta, chorion, and amnion
Twin-twin transfusion syndrome
. Occurs when placental vascular anastomoses preferentially direct blood to 1 twin
. Results in gross size disparity
. Death of both twins occurs in 50-70% of cases
Congenital abnormalities
. Structural, functional, metabolic, or behavioral disorders present at birth
. Clinically significant anomalies present in 3% of live births
. Leading cause of infant mortality in US and major cause worldwide
. Cause unknown in 50% of cases, 15% genetic factors, 10% environmental factors, 25% combo factors
. Twinning <1% anomalies
Malformation
. Absence or abnormal configuration of structure due to abnormal processes of development
. Occurs in weeks 3-8 of development
Disruption
. Morphological change in normal structure by mechanical forces
. Most common in musculoskeletal system
Dysplasia
Abnormal organization of cells into tissues
Syndrome
. Group of anomalies occurring together that have common specific etiology
. Often genetic
Association
. Non random co-occurrence of a group of anomalies whose etiology is unknown
Prenatal testing
. Performed when risk factors inc. likelihood of genetic or other congenital anomalies
Preconception screening
. During IVF procedures blastomere can be removed for genetic screening prior touterine insertion
Ultrasound screening
. Reveals structural abnormalities of the embryo/fetus and placenta beginning at implantation
Chorionic villus sampling (CVS)
. Biopsy of chorionic tissue can diagnose genetic abnormalities
. Early as 8 weeks
. Carries higher risk of miscarriage than amniocentesis
Amniocentesis
. Needle aspiration of amniotic fluid provides fetal cells for genetic analysis
. Tests for presence of alpha-fetoprotein assoc. w/ neural defects and Downs
Teratology
. Study of congenital anomalies
Teratogens
. Agents that disturb development of an embryo/fetus causing congenital anomalies and/or death
Principles of teratology
. Susceptibility to teratogens depends on genotype of conceptus and manner in which genotype interacts w/ environment
. Susceptibility varies w/ developmental stage at time of exposure
. Act in specific ways on developing cells and tissues o cause abnormal embryogenesis
. Abnormal development inc. as dose/duration of exposure inc.
. Abnormal development includes death, malformation, growth retardation, and functional disorder
Resistant period (weeks 1-2)
. Conceptus will die from exposure or survive unharmed (all or nothing)
. Sensitive period
. Weeks 3-8
. Max susceptibility to teratogens
. Corresponds to embryonic period and period of organogenesis
Lowered susceptibility period
. Weeks 9-38
. Exposure may cause altered function and minor anomalies but less is likely to cause significant malformations
TORCH infections
. Toxoplasma, rubella, cytomegalovirus, herpes, HIV, Zika
. Prenatal exposure can cause miscarriage, stillbirth, retinal damage, microcephaly, hydrocephalus, encephalomyelitis, and cerebral calcification
