sonic hedgehog gene
made in base of limbs in the zone of polarizing activity ---anterior/posterior patterning; involved in CNS development
made at apical ectodermal ridge (distal end of growing limbs); for dorsal/ventral organization
made at apical ectodermal ridge; stimulates mitosis for limb lengthening
Hox (homeobox) genes
segmental organization of embryp in a craniocaudal fashion
hox mutation causes...
appendage in wrong place
10 weeks of early fetal development
day 0 - fertilization forms a zygote; embryogenesis initiated week 1 - hCG secretion and implantation of blastocyst week 2 - 2 wks = 2 layers --> bilaminar disc (epiblast and hypoblast) week 3 - 3 wks = 3 layers --> trilaminar disc; gastrulation; primitive streak, notochord, mesoderm, and neural plate begin to form weeks 3-8 - extremely susceptible to teratogens week 4 - heart begins to beat; limb buds begin to form (4wks = 4 limbs) week 6 - fetal cardiac activity visible by transvaginal ultrasound week 10 - sex specific genitalia
process that forms the trilaminar disc (ectoderm, mesoderm, and endoderm germ layers) starts with the epiblast invaginating to form the primitive streak
what forms the CNS? PNS?
cns = neuroectoderm pns = neural crest
VACTERL vertebral anal atresia cardiac trachea-esophageal fistula renal limb (bone and muscle)
what is derived from surface ectoderm?
eye lens, oral cavity linings, ear sensory organs and olfactory epithelium, anal canal below pectinate line, parotid/sweat/mammary glands
what is derived from the neuroectoderm?
CNS brain, retina, optic nerves, spinal cord
what is derived from neural crest?
pns dorsal root ganglia, schwann cells, melanocytes, bones of skull, odontoblasts, aorticopulmonary septum, chromaffin and parafollicular cells
what is derived from the mesoderm?
muscle, bone, CT, serous linings of cavties (peritoneum), spleen, CV structures, lymphatics, blood, wall of gut tube, vagina, kidneys, dermis, testes, ovaries,
endoderm forms the...
gut tube epithelium, anal canal above pectinate line, urethra and luminal epithelium derivatives (lungs, liver, gallbladder, Eustachian tube, thymus, etc)
absent organ due to absent primordial tissue
absent organ despite present primordial tissue
incomplete organ development
secondary breakdown of a previously normal structure
malformation vs deformation
M = intrinsic disruption; during the embryonic period (wks 3 - 8) D = extrinsic disruption; after the embryonic period
abnormalities result from a single embryological event ex: oligohydramnios --> potter sequence
when is embryo most susceptible to teratogens?
weeks 3-8 (embryonic period) during organogenesis before week 3 --> all or none effect after week 8 --> growth and function affected
fetal alcohol syndrome
mothers consume a lot of alcohol during pregnancy --> increased risk for congenital malformations ---intellectual disability, retardation, microcephaly, holopresencephaly, facial abnormalities, limb dislocation, and heart defects
arises from 2 eggs that are separately fertilized by 2 different sperm (always 2 zygotes) --2 different amniotic sacs and 2 separate placentas (chorions)
from 1 fertilized egg (1 egg + 1 sperm) that splits into 2 zygotes in early pregnancy
what determines degree of separation of monozygotic twins?
depends on when the fertilized egg splits into 2 zygotes --timing determines the number of chorions and amnions
amnion vs chorion
Amnion is the inner layer that surrounds the amniotic cavity while chorion is the outer layer that covers amnion, yolk sac and the allantois amnion does not contain any vessels or nerves
early separation of monozygotic twins? middle latest separation of monozygotic twins?
before morula (0-4 days) --> dichorionic diamniotic after morula, before blastocyst (4-8 days) --> monochorionic diamniotic after blastocyst stage (8+ days) --> monochorionic monoamniotic
where are nutrient and gas exchanged between mother and fetus?
three components forming the placenta?
cytotrophoblast, syncytiotrophoblast, and decidua basalis
inner layer of chorionic villi of placenta (fetal component)