Development Weeks 2-8 Flashcards
activity during second week of development
implantation, formation of embryonic disc and extraembryonic structures
formation of embryonic disc will lead to …
hypoblast, epiblast
fetus
formation of extraembryonic structures will lead to …
amniotic cavity, amnion, yolk sac, connecting stalk, chorionic sac, uteroplacental circulation, placenta
invasion of syncytiotrophoblast cells and proliferation of cytotrophoblast cells
implantation
early embryo is supported by …
nutrient-rich development in endometrium
invasion of syncytiotrophoblast cells feeds of ____ ____ and produces ____ ____
decidual cells
HCG hormone
most common implantation site
posterosuperior wall of uterus
extrauterine implantation causes …
ectopic pregnancy, tubal pregnancy, abdominal pregnancy, placenta previa
embryonic disc forms what two layers?
epiblast, hypoblast
describe the hypoblast
root of exocoelomic cavity, continuous with exocoelomic membrane, forms primary yolk sac
space formed in the embryoblast, lined with amnion layer of cells from epiblast
amniotic cavity
extraembryonic mesoderm surrounds what two things?
yolk sac, amniotic cavity
what forms in syncytiotrophoblast during the development of uteroplacental circulation?
lacunae (spaces)
____ ____ are the primordia of the intervillous spaces of the placenta
lacunae networks
lacunae allows embryotroph to nourish the embryo via
diffusion
formed by proliferation of cytotrophoblastic cells into the syncytiotrophoblast
primary chorionic villi
formed by trophoblast and extraembryonic somatic mesoderm
chorion
formerly known as the extraembryonic coelom; changes names during development of chorionic sac
chorionic cavity
what is the morphology at the end of the second week?
bilaminar embryonic disc
amniotic sac (epiblast forms floor)
yolk sac (hypoblast forms roof)
chorionic sac
connecting stalk
weeks 3-8 in which all major body system begin development
organogenetic period
phases of embryonic development
growth, morphogenesis, differentiation
*anomalies
developmental event that occurs during the third week
changes in embryonic disc
- appearance of primitive streak
- development of notochord
- differentiation of three germ layers
development of three germ layers - called?
gastrulation
embryonic ectoderm, embryonic mesoderm, embryonic endoderm
process of the development of body form
morphogenesis
thickened linear line of epiblast
primitive streak
describe the development of the primitive streak
in medial plane
dorsal aspect of embryonic disc
identifies cephalo-caudal, medial-lateral
describe the characteristics of the primitive node
located on cranial end
contains the primitive pit
when does the primitive streak normally disappear?
end of 4th week
depression in the primitive streak
primitive groove
forms from cells on deep surface of primitive streak
mesenchyme
cells that make up the embryonic mesoderm
mesoblasts
embryonic mesoderm will differentiate into …
fibroblasts, chondroblasts, osteoblasts
epiblast cells displace hypoblast cells to create which intraembryonic layer?
embryonic endoderm
epiblast cells make up which intraembryonic layer?
embryonic ectoderm
describe the notochordal process
mesenchymal cells migrate from primitive pit through the notochordal canal, ending at the prechordal plate
no intervening mesoderm
this is the site of future oral cavity
contains a cloacal membrane
mesenchyme cells migrate in which direction to the margins of the embryonic disc, making contact with extraembryonic mesoderm?
laterally
mesenchyme cells migrate in which direction to form the cardiogenic area?
cranially
embryonic endoderm creates …
epithelial linings of respiratory passages and GI tract, linings of glands opening into GI tract and certain glandular cells
embryonic ectoderm creates …
epidermis, retina, central and peripheral nervous sysems
embryonic mesoderm creates …
smooth muscle coats, connective tissue, vessels, cardiovascular system, blood cells and bone marrow, skeleton and striated muscle, reproductive and excretory organs
events of the 4th week
neurulation, formation of somites, appearance of early thorax and abdomen cavities, “folding” of embryo into 3D structure
future site of vertebral bodies
primordial axis
notochord is the basis for development of the ____
skeleton
notochord process fuses with underlying embryonic mesoderm, which degenerates so that …
notochord is in contact with yolk sac, creating the notochordal plate
notochordal plate infolds to form the ____, inducing the formation of the ____ ____
notochord
neural plate
formation of neural plate, neural folds, and closure of neural folds
neurulation
when does neurulation occur?
during 4th week
what is the embryo called during neurulation?
neurula
how does the neural plate form? what does it become?
embryonic ectoderm thickens over notochord
CNS
how does the neural tube form?
neural groove forms from a depression in neural plate
neural folds approximate, separating surface from embryonic ectoderm
failure of caudal neuropore to close is called
spina bifida
neural folds are the first sign of what?
brain development
failure of cranial neuropore to close is called
anencephaly
what does the neural crest form from? what happens to it?
neuroepithelial cells between the surface ectoderm and neural tube
disperse into mesenchyme
what does the neural crest become?
sensory ganglia, neurilemma and meningeal coverings, pigment cells, adrenal medulla, skeletal and muscular components of the head
somites form due to changes in the intraembryonic mesoderm - what are the layers?
paraxial, intermediate, lateral
describe the somites that make up the paraxial mesoderm
44 pairs of blocks alongside the neural tube
gives rise to axial skeleton and associated muscles and dermis
embryonic body cavity becomes …
pericardial cavity, pleural cavities, and peritoneal cavity
what two structures form a single horseshoe-shaped cavity during the development of intraembryonic coelom?
coelomic spaces in lateral mesoderm, cardiogenic mesoderm
layers of the lateral mesoderm that the intraembryonic coelom divides into
parietal - continuous with extraembryonic mesoderm covering amnion
visceral - continuous with extraembryonic mesoderm covering yolk sac
folding of the embryo is caused by what?
rapid growth
describe the head fold of the embryo
brain grows cranially past oropharyngeal membrane to overhand developing heart, moving related future thoracic structures ventrally; part of yolk sac becomes foregut (esophagus, pharynx)
describe the tail fold of the embryo
connecting stalk moves ventrally, incorporating the hindgut
describe the horizontal plane folding of the embryo
midgut is incorporated and umbilical cord is formed
early development of the cardiovascular system begins in …
yolk sac, connecting stalk, chorion
describe vasculogenesis
angioblasts aggregate to form blood islands and cavities appear and angioblasts form endothelial lining of primitive blood vessels that undergo fusion and growth; blood cells originate from endothelial cells
describe the primordial cardiovascular system
in cardiogenic area, there are endocardial heart tubes that fuse, joining with blood vessels in embryo, connecting stalk, and yolk sac; heart ‘beat’ on 21st day
describe the development of chorionic villi
mesenchyme grows into primary villi, and eventually secondary villi. differentiation occurs to create capillaries and blood cells called tertiary chorionic villi. by the end of the third week, blood flows through capillaries. it has a cytotrophoblastic shell with stem villi and branch villi
highlights of week 4
open neural tube (caudal neuropore by end of week), pharyngeal arches visible, heart pumping blood, forebrain, limb buds, otic pits, lens placodes
highlights of week 5
rapid growth of head (cephalocaudal principle), limb buds present (UE first), lung buds push into developing thorax, heart separation starts, pharyngeal arches present, mesonephric kidneys
highlights of week 6
brain cortex areas present, trunk and neck straightening, face developing (lip and palate components), auricular hillocks present (external acoustic meatus), heart and lungs in thorax (separation of pulmonary and aortic outflow), elbow present, myoblasts oriented in parallel to limb buds, digital rays visible in hand plates, radial/median/ulnar nerves invade hand plate
highlights of week 7
umbilical herniation of intestines, yolk stalk present (formed from folding of embryo), endochondral ossification underway (intercartilaginous) and notches in digital rays
highlights of week 8
large head, neck noticeable,. umbilical herniation present, 33-34 cartilaginous vertebrae present, upper limbs rotate ventrally, webbed fingers, notches in distal rays of feet, purposeful limb movement, ossification of UE
how to estimate embryonic age?
ultrasound, greatest length (crown-rump)
disruptions via teratogens causes ____ of anomalies
7-10%
dosage of chemical or drug during critical periods of development (organogenetic period) that affects the genotype of the embryo
teratogenesis
duration of organogenetic period
brain 3-16 wks up to 2 yrs
examples of human teratogens
cigarette smoking, alcohol, androgens and progestogens, antibiotics, anticoagulants, anticonvulsants, etc
cigarette smoking causes what to an embryo?
slow intrauterine development
alcohol causes what to an embryo?
fetal alcohol syndrome, most common cause of mental disabilities
examples of androgens and progestogens that are teratogens
oral contraceptives, diethystibesterol
antibiotics, like tetracycline and streptomycin, can affect what in an embryo?
enamel, hearing
examples of anticoagulants and anticonvulsants that are teratogens
warfarin, trimethadione, phenytoin
environmental chemicals that are human teratogens
organic mercury (causes minamata disease - ataxia, sensory loss in distal limbs, weakness)
lead (slow growth)
polychlorinated biphenyls (cognitive development)
infectious agents that are human teratogens
rubella (cataract, cardiac defects, deafness)
cytomegalovirus (fatal)
herpes simplex virus (skin, eye, brain)
varicella (slow growth, clinodactyly)
in high doses, radiation is a human teratogen because it causes …
severe mental disabilities
maternal factors that are human teratogens
PKU (inability to breakdown phenylalanine - amino acid)
diabetes mellitus (if poorly controlled, elevates blood glucose)
