1.3 (Lecture 1) - Embryology - Differentiation + Implantation Flashcards
Zygote
cell that results from the union of the oocyte (female) and sperm (male) during fertilization
the first stage in human development
Embryonic stage of development
from fertilization until 8th week of development (D56)
by the end of this period all major structures are present
Fetal Stage of development
begins D57 extends until the fetus is completely outside of the mother
= a period of growth and differentiation of tissues and organs formed in the embryonic period
fertilization
complex sequence of events - begins with sperm and oocyte contact - results in intermingling of maternal + paternal chromosomes
cleavage divisions
- series of mitotic cell divisions of the zygote
- result information of the early embryonic cells (blastomeres)
- size of zygote remains unchanged with these divisions (blastomeres become smaller at each division)
blastocyst
stage of development that begins after the developing embryo (morula) enters the uterus a fluid filled cavity develops inside it - developing embryo is now called a blastocyst
Inner cell mass - what it is and its other name
- also called embryoblast
- group of centrally located blastomeres
- that will give rise to the embryo
Outer cell mass - what it is and its other name
- also called the trophoblast
- thing outer cell layer
- gives rise to the embryonic portion of the placenta
(remember: trophe = nutrition)
Endometrium
- internal layer of the uterus
- formed by simple columnar epithelium, with connective tissue stroma
Cytotrophoblast
- cytotrophoblast is a thin, mitotically active layer
- comes from the proliferation of the trophoblast following its attachment to the endometrium
Syncytiotrophoblast
- the outer mass of the trophoblast
- consists of a multinucleated mass, in which no cell boundaries are observed
chorion
- structure formed by the a) extraembryonic mesoderm, b) cytotrophoblast and c) syncytiotrophoblast
- contributes to the fetal portion of the placenta
ectopic pregnancy
implantation of the blastocyst outside of the uterus, most commonly int he ampulla of the oviduct
bilaminar disc
- flat bilaminar plate of cells
- originates from the changes occurring in the cells of the embryoblast (inner cell mass) during the 2nd week of development
epiblast (what is it and what type of cells)
- thick, dorsal aspect of the bilaminar disc
- top layer formed from the epiblast (inner cell mass)
- consists of high columnar cells
- related to the amniotic cavity
hypoblast (what is it and what type of cells)
- ventral layer of the bilaminar disc located below epiblast
- also called primitive endoderm
- small cuboidal cells
- related to the yolk sac formation and extraembryonic mesoderm
- do not contribute to tissues of the embryo
yolk sac
- ventral structure lined by hypoblast cells (below the hypoblast layer)
- important functions include:
a) origin of primordial germ cells
b) early blood cell development
c) regulation of nutrients to the embryo
amnion and amnionic cavity
- formed by cells that separate from the epiblast
- amnion encloses the amniotic cavity
- amniotic cavity surrounds the embryo and fetus + contains amniotic fluid - the amount of the fluid is critical to health of developing embryo
primitive streak
= thickened band of epiblast cells appearing at the beg. of week 3 in the caudal, dorsal aspect of the bilaminar disc
- epiblast cells will migrate through this streak to form endoderm and mesoderm during gastrulation
gastrulation
=period of epiblast proliferation, migration, and differentiation
- process by which the 3 germ layers develop
germ layers
= the three basic cell layers of ectoderm, mesoderm, endoderm
- gives rise to all of the cells, tissues, structures of the embryo
blastomeres
= daughter cells formed by the first mitotic (cleavage) divisions of the zygote
zona pelucida
= the protective layer surrounding the oocyte and the developing zygote/blastomeres/morula
- disappears after implantation
morula
= round, solid mass of cells produced by the cleavage divisions
- the 12-32 blastomere stage
- will enter the uterus ~ 3 days after implantation
amnioblast
= the rudiment of the amnion formed from the cells of the epiblast
- encloses a fluid-filled space (amniotic cavity) that developes b/w the epiblast and the adjoining cytotrophoblast
primitive groove/pit
= the epliblast covering the primitive streak becomes indented = primitive groove
- cranial end of the groove forms the primitive pit
- the primitive pit communicates with the yolk sac
prechordal plate
- arises from the cranial end of the primitive streak + inserts into the endoderm and forms a thickening
- contributes to the oropharyngeal membrane
- forms and important signaling center involved in formation of the forebrain of the CNS
- might contribute to connective tissue in the head region
important functions of yolk sac during the first four weeks of development
- major site of blood cell formation (hematopoiesis)
- primordial germ cells are first recognized on the wall of the yolk sac prior to the migration to the developing gonads
What cells during gastrulation will later form the endoderm?
- the early migrating cells
- they displace the hypoblast cells (primitive endoderm) to form a new sheet-like epithelial layer (definitive endoderm)
what cells during gastrulation will later form the mesoderm?
- the later migrating cells
- spread between the epiblast and the endoderm to form the embryonic mesoderm
what cells during gastrulation will later form the ectoderm?
- cells that remain in the epiblast
- sheet-like epithelial layer
oropharyngeal membrane
- one of the fates of the hypoblast
- cranial end membrane which will regress/breakdown during development to form the beginning of the GI tract
cloacal membrane
- one of the fates of the hypoblast
- caudal end membrane which will regress/breakdown during development to form the end of the GI tract
notochord
- forms during gastrulation in the area of the primitive pit
- extends cranially to the prechordal plate
- considered to be mesodermal derivative
- has important inductive roles in development
induction (inductive development)
= one tissue acts on another tissues to change its fate
- requires an inducing tissues + responding tissue
decidua
the functional layer of the endometrium (layer that is shed during menstruation and parturition)
decidua reactions
- seen early in pregnancy whenthe blastocyst contacts the endometrial decidua
- characterized by increased secretory functions of the endometrium at site of implantation and the surrounding stroma
(Decidua = functional layer of the endometrium during pregnancy)
