Lectures 13, 14 and 15: Embryology Flashcards
gastrulation definition/transformation
-formation of 3 germ layers
-go from bilaminar disk containing epiblast and hypoblast into trilaminar disc of 3 germ layers
corona radiata composed of
-zona pellucida
-layers of follicular cells
what is the zona pellucida
glycoprotein coat
acrosome cap definition and function
-specialized lysosome
-prevents sperm from getting to egg
capacitation process
-period between ejaculation and when the sperm is traveling to the egg
-get degradation of the acrosome cap so that sperm can fertilize egg
location and timing of ejaculation and capacitation is _________ specific
species
where does ejaculation and capacitation occur in dogs
uterus
where does ejaculation and capacitation occur in cats
vagina
purpose of cilia in oviduct
help fertilized egg
what makes oocyte impenetrable to other sperm
zona reaction
what causes the zona reaction
sperm in oocyte without its plasma membrane
how does sperm penetrate oocyte (process)
-as acrosome wall perforates, sperm moves through follicular cells
-sperm moves through corona radiata zona pellucida
-zona reaction
oocyte definition
-female gamete cell produced by ovaries
fertilized oocyte becomes
zygote
what is the female pronucleus
-oocyte after completing second meiotic division but before fertilization
male pronucleus
forms from enlarged sperm nucleus
what structure is absent/disappears in female pronucleus
corona radiata
how is diploid zygote formed from male and female pronucleus
-pronucleus membranes breakdown and fuse
blastomere definition
new embryonic cell produced by mitosis/cleavage
blastomeres get (bigger or smaller) with each cell division?
smaller
morula definition
superficial layer surrounding central core of compacted cells (i.e. blastomeres)
what structure surrounds the cluster of blastomeres following mitosis
morula
when are blastomeres no longer totipotent
when compaction occurs –> inner and outer cell masses created
what are the 2 layers of cell masses called in compacted blastomere
trophoblast = external layer
embryoblast = inner layer
what does trophoblast ultimately become
placenta
what does embryoblast become
fetus/conceptus
what is the first cavity created
blastocystic cavity
how is the blastocystic cavity created
secretions from blastomeres
structural function/location of zona pellucida
surround trophoblasts
2 poles of ovum/blastocyst
-animal pole
-vegetal pole
animal pole is located near what cell mass
embryoblast (inner cell mass)
vegetal pole is located where
away from embryoblast, closer to blastocystic cavity
function of trophoblast
protect embryoblast
what is rauber’s layer
layer of cells directly above embryoblast
what happens to rauber’s layer
disintegrates
early vs late embryoblast
late = hatching occurs out of zona pellucida
where does blastocyst emerge from (what is hatching?)
zona pellucida
when and why does hypoblast emerge
-as rauber’s layer disintegrates
-enclose blastocystic cavity
when does blastocystic cavity become exocoelemic cavity
when hypoblast emigrates to enclose blastocystic cavity (forms at ventral surface of embryoblast)
-see staggered clumps of hypoblast starting to surround cavity
at what stage is cavity named blastocystic cavity
at stage with trophoblast and embryoblast
how does name of blastocystic cavity change
blastocystic –> exocoelemic –> primitive yolk sac –> definitive yolk sac
when does exocoelemic cavity become primitive yolk sac
when hypoblast extends to surround exocoelemic cavity (see full enclosed layer of hypoblast around cavity)
what replaces rauber’s layer
tight junctions of epiblast
what 2 structures form the bilaminar embryonic disc
epiblast and adjacent hypoblast
location of ejaculation in cattle
vagina
location of ejaculation in horses
uterus
where does fertilization occur
oviduct
effect of zona reaction
hardens corona radiata so other sperm can’t enter
where is implantation in all domestic animals occur (relatively)
-centric/superficial
-conceptus fills up uterine lumen
pronucleus stage for female (4 things)
-2nd meiotic division complete
-corona radiata disappears
-zona pellucida remains and hardens
-have 2 polar bodies
pronucleus stage males (2)
-from enlarged sperm nucleus
-head and tail degenerate
steps from mature oocyte to blastocyst formation
-oocyte –>pronucleus –> zygote –> cleavage/mitosis –> marula formation –> blastocyst formation
when does extraembryonic mesoderm start forming
after conceptus implantation into uterine lumen
where will extraembryonic mesoderm be formed
between trophoblast and hypoblast layers
what will form the chorion
trophoblast
what cells form the amniotic membrane
epiblast
what forms after extraembryonic mesoderm
prechordal plate
how prechordal plate is formed
-some hypoblast cells become columnar and form thickened circular area = prechordal plate
what will prechordal plate become
mouth
what structure does gastrulation begin with
primitive streak
structures inside primitive streak (3)
-primitive groove in primitive streak
-primitive node at top of primitive streak
-primitive pit at top of primitive groove
where do all 3 germ layers originate from
epiblast
if nothing changes to cells (i.e. don’t migrate), what germ layer is formed
ectoderm
if cells do not become ectoderm, where do they go
migrate through primitive groove in primitive streak
mesenchymal cells =
migrating cells
endoderm will replace what cells
hypoblast
ectoderm becomes (main)
-epidermis
what does mesoderm form (important structure)
notochord
what happens first: gastrulation or notochord formation
gastrulation
function of notochord (4)
-defines axis of embryo
-provides rigidity
-future site of vertebral bodies (axial skeleton)
-primary inducer of future structures
how is notochord formed
-prenotochordal cells invaginate into primitive pit and move cranially toward the midline until they reach the prechordal plate to form notochordal process
when does neurulation occur
at same time as gastrulation
neurulation definition
process of forming neural tube which will form brain and spinal cord
steps of neurulation (3)
-ectoderm thickens
-neural place invaginates to form neural groove with neural folds on either side
-neural folds form neural tube
ancephaly
-abnormal neurulation
-no/partial brain
-rostral pore doesn’t develop properly
spina bifida
-abnormal neurulation
-caudal pore doesn’t develop properly
where does neural crest form
between neural tube and ectoderm/epidermis
differentiation of mesoderm occurs when
same time as neurulation
endoderm goes on to form
gut tube/lining of GI
before differentiation, mesoderm was called
intraembryonic mesoderm
3 parts of mesoderm
-paraxial
-intermediate
-lateral plate
paraxial mesoderm
-located near neural tube
-forms somites
3 somites (mesoderm)
-dermatome
-myotome
-sclerotome
dermatome
somite
-forms dermis of skin over dorsal regions
myotome
somite
-voluntary muscles
scleratome
somite
-vertebrae, axial skeleton
intermediate mesoderm
forms gonads and portions of urogenital system
2 layers of lateral plate mesoderm
somatic and visceral
somatic lateral plate mesoderm
body wall structures
visceral lateral plate mesoderm
smooth muscle of gut
orientation of somites in mesoderm
outer = dermatome
middle = myotome
inner/medial = scleratome
body folding is important for formation of what structure
gut tube
2 major folds that transform flat embryonic disc into 3D
-meidan plane
-horizontal place
median plane body folding
-head and tail folds
-forms allantois
what does allantois become
membrane that cradles developing fetus
allantois is a derivative of what (hint: gut)
hindgut
body folding in horizontal plane
-right and left lateral folds
-allantois obliterates extraembryonic coelem
-yolk sac separates from body
2 parts of placenta
-fetal part
-maternal part
fetal part of placenta derived from
chorionic sac = trophoblast
maternal part of placenta derived from
endometrium
what separates fetus from endometrium
fetal part of placenta and fetal membranes
formation of choriovitelline membrane (first placenta)
fusion between yolk sac (vitelline sac) and chorion
definitive yolk sac is continuous with what structure
midgut
how are blood vessels developed from extraembryonic mesoderm
blood vessels grow through yolk sac –> penetrate body of embryo –> grow into allantois –> vascularize chorion
what happens as choriovitelline membrane recedes
chorioallantoic membrane increases
chorioallantoic membrane
membranes that have fused between allantois and chorion
placenta type is defined by
number of tissue layers between mother and fetus
placental type in horses
epithliochorial
placental type in cattle
synepitheliochorial
placenta type in dogs and cats
endotheliochorial
simplest placenta type
horses = epitheliochorial
most complex placenta type
dogs and cats = endotheliochorial
epitheliochorial placenta type
-horses
-endometrial epithelium remains in tact and is apposed to chorionic epithelium
-fetus and maternal parts are pretty separated (least invasive)
2 specializations of horse placentation
-chorionic girdle
-endometrial cups
chorionic girdle (horses) function
-destroy uterine cells
endometrial cups location (horses)
interdigitate in chorionic girdle
equine microcotyledons
fetal and maternal microvillous interdigitate (one big digitation)
precocial infant
ready to live after birth (horses)
cattle synepitheliochorial type
-attenuated layer of combined maternal and fetal epithelium
-union of fetal and maternal cells
-some connection between mother and fetus (but blood supply still separated)
union of fetal and maternal cells = what kind of epithelium
cryptal
cotyledonary placentation in cattle
placentome = caruncle and cotyledon
caruncle = maternal, stuck to cotyledon on fetus side
cotyledons fit into maternal crypts in caruncles
endotheliochorial placenta dogs and cats
-uterine epithelium and connective tissue are removed and chorionic epithelium comes in direct contact with endometrial capillaries (still have separated blood supply)
zonary placentation in dogs and cats
no connections on sides because of multiple fetuses
altricial infants
need care very early in development (dogs and cats)
2 types of twinning in calves
-monozygotic
-diazygotic
monozygotic =
one ovum
dizygotic =
2 ova
65% of monozygotic twinning begins at what stage of embryonic development
blastocyst
how monozygotic twins are formed 65% of the time
2 embryoblasts –> 2 amniotic sacs + 1 trophoblast (1 placenta + 1 chorionic sac) –> 2 amnions with single placenta
how monozygotic twins are formed 35% of the time
2 morulas –> 2 blastocysts –> 2 amnions, 2 placentas and 2 chorions
when does separation occur in monozygotic twins (35% of the time way)
before formation of blastocystic cavity
other way monozygotic twins originate
division of embryonic disc in week 2
how monozygotic twins originate from embryonic disc
fused embryos –> embryonic disc divides = 2 individuals in 1 amniotic sac –> parasitic twins, conjoined twins or separate twins
What kind of placentation do horses use
Diffuse
Diffuse placentation
-placenta with villi scattered around surface of chorion (entire surface of chorioallantoic membrane is involved in formation of placenta)
Function of microcotyledons in horse (diffuse) placentation
Fundamental unit of fetal-maternal interface
-consist of chorionic villi that invaginate into endometrium
what fluid is deep allantoicamniotic membrane
amniotic fluid
what fluid is deep to chorioallantoic membrane and superficial to allantoicamniotic membrane
allantoic fluid
what membrane attaches to the uterine lumen
chorioallantoic membrane
