Cardiac Embryology Flashcards
Fertilization occurs in
the ampullary region of the fallopian tube
Sperm + Oocyte
= Zygote undergoes cell divisions
Reaches 2 cell stage about
30 hours post fertilization
4 cell stage at about
40 hours post fertilization
12-16 cell stage at about
72 hours (3 days)
Cells are called
Blastomeres
Cells are loosely arranged until
8 cell stage
cells have maximized contact with each other after
3rd cleavage
compaction
Cells separate into inner and outer cells.
Morula
16 cell stage
morula has defined
inner and outer cells
Inner cells =
inner cell mass (will become the embryo)
outer cells=
outer cell mass (will become the trophoblasts, which will be the placenta)
called blastocyst when
Fluid penetrates into the intercellular spaces of Inner
Cell Mass. Spaces become a single cavity
Blastocele
Blastocyst is comprised of
Trophoblast – outer covering
Formed from cells of the outer cell mass.
Cells flatten and eventually form the epithelial wall of the blastocyst
Blastocele – Internal fluid filled space
Embryoblast – Inner cell mass
Located at one pole
Trophoblast and part of inner cell mass will become
the placenta
Rest of inner cell mass will become
the embryo
Blastocyst remains free in the uterus for
2 days
implantation occurs
Around day 6 (after fertilization)
Trophoblastic cells over the embryoblast pole penetrate
between the epithelial cells of the uterine wall.
Blastocyst attaches to
uterine epithelium, and subsequently the endometrium
blastocyst oriented so
inner cell mass is near the endometrium
Blastocyst is partially embedded at
day 8
at day 8 blastocyst differentiates into
Syncytiotrophoblast – multi-nucleated, outer zone no cell boundries
Cytotrophoblast – mononucleated cells, inner layer distinctcells
Both layers become part of the chorion (one of the fetal membranes)
ICM differentiates into
Hypoblastlayer Layer of small cuboidal cells adjacent to the blastocyst cavity
Epiblastlayer Layer of high columnar cells adjacent to amniotic cavity
blastocyst completely embedded at
Day 11-12
day 11-12 cells of Syncytiotrophoblast
penetrate deeper into endothelial lining of maternal capillaries
Syncytiotrophoblast capillaries are
congested and dilated
Called Sinusoids
Causes blood to flow through the trophoblastic system
Beginning of the uteroplacental circulation
Cytotrophoblast proliferates to form:
Amnion
Thin Protective membrane that surrounds the developing embryo.
AmnioticCavity Space, eventually filled with fluid.
Gastrulation – starts at
day 8
Gastrulation is the process for
establishing 3 germ layers
ICM differentiates. Ectoderm Endoderm Mesoderm These are the major embryonic tissues from which all tissues and organs of the body develop.
gastrulation starts with the formation of
he primitive streak on the epiblast
By day 15-16, it is clearly visible as a narrow groove.
which cells migrate to primitive streak
Cells of the epiblast
source of germ layers
epiblast
Inner Cell Mass now called an______ as amniotic cavity starts to form
Embryonic Disc
Layer of cells of the inner cell mass closest to the amniotic cavity.
ectoderm
layers of inner cell mass that borders the blastocele.
endoderm
Lies inbetween the ectoderm and endoderm.
Mesoderm
Ectoderm Becomes:
Skin, teeth, mouth glands, nervous system, some
endocrine glands.
Endoderm Becomes:
Epithelium of digestive tract, respiratory system, bladder, vagina, urethra
Mesoderm Becomes:
All connective tissue, the muscular, skeletal, lymphatic, and circulatory systems.
Cardiovascular System appears in the middle of the
3rd week. At this point the embryo is no longer able to survive via diffusion alone.
The Cardiovascular System reaches
a functional state long before any of the other systems
Vascular system develops from a
simple symmetrical plexus, into an asymmetrical complex system of arteries, veins and capillaries.
The size of the embryonic heart in relation to the size of the embryo
is enormous compared to an adult heart in an adult size body.
progenitor heart cells Lie in
Epiblast. Adjacent to the cranial end of the primitive streak
Move through the streak and into the splanchnic layer of the mesoderm and form around day 16-18
Primitive Heart Field (PHF)
horse-shoe shaped cluster of cells
PHF specified on both sides to become the
Atria, LV, RV, Conus Cordis and Truncus Arteriosus
secondary ear field consists of and shows up when
Conus and Truncus come from the Secondary Heart field and show up around Day 20-21
blood island and cardiac myoblasts come from
Progenitor Heart Cells
Blood islands unite and form
a horse-shoe shaped tube Endothelial cell lined
Surrounded by myoblasts. More blood islands appear bilaterally, parallel and close
to the midline. Will form dorsal aortas.
Intraembryonic Celom (Body Cavity) Formed by the joining
small (initially isolated) spaces
which appear in the lateral mesoderm
Intraembryonic Celom (Body Cavity Bilateral cavities extend
cranially and fuse with each other forming a horseshoe-shaped cavity
Eventually becomes the pericardial cavity
Heart development starts at the and occurs in
end of the 3rd week of gestation. the ventral region of the embryo, inferior to the foregut.
Scattered masses of angiogenic cells appear
in the mesenchyme derived from PHF
blood islands occur in
ventral (in front of) the intraembryonic celom.
Anterior part of the celom will develop
the pericardial cavity.
Angiogenic cells form
clusters (Blood Islands) which increase in size and number. Acquire a lumen, unite and form a plexus of blood vessels
, bilateral endocardial tubes develop from
plexus of blood vessels from blood islands
The Endocardial tubes unite to form
a common tube
Primitive Heart Tube
the single heart tube starts to beat.
By Day 21-22
Cells are added from the secondary heart field to the
cranial end of the tube
If lengthening doesn’t occur, where outflow tract defects
come from
DORT, VSD, TOF, PA, PS
Meanwhile, Other blood islands appear inferior to the endocardial tubes
Eventually give rise to ______ and give rise to ______
dorsal aortas. Will connect with the endocardial tubes Establish the arterial end of the heart
Other end of the future endocardial tubes will make contact with the
vitelline veins (via the sinus venosus) and establish a venous pole.
newly formed heart tube starts to bend on day
23
Cephalic part bends
ventrally, caudally, and to the right.
Caudal part bends
dorsocranially, and to the left
attaches to dorsal wall by
mesoderm
Becomes the common outflow tract
Dorsal Aorta and Aortic Sac
primitive RV
bulbis cordis
primitive LV
primitive ventricle
Divides atria from ventricles
atrioventricular sulcus
Will form common atria
Paired Primitive Atria
Eventually forms the coronary sinus and oblique vein of the LA
sinus venosus
Heart undergoes a series of folding that leads to the
formation of the bulboventricular loop during
day 23- 28
proximal 1/3 Bulbus Cordis Will form
trabeculated part of RV
Junction between the ventricle and the bulbus cordis externally is the
bulboventricular sulcus
bulboventricular sulcus
aka primary interventricular foramen
Atrial portions of the Heart Tube dilate Form
common atrium
Atrium “climbs up” the ______ and takes the
dorsal pericardial wall TakesAtrioventricularjunctionwithit
Diverticula appear
Along front of endocardial tube
Just proximally and distal to the primary interventricular foramen
These diverticula expand
the capacity of the heart. Give them the densely trabeculated appearance
The trabeculae inside the heart leads to
valves, chordeae tendinae, papillary muscles, and atrioventricular valves.
Abnormalities in Cardiac looping, is responsible for cardiac defects
Ventricular inversion (corrected transposition), juxtaposition of the atrial appendages, and Double outlet right ventricle.
the sinus venosus receives blood from the right and left sinus horns during
the 4th week
each horn of the sinus venosus receives blood from three veins
Vitelline vein Umbilicalvein Common Cardinal vein
Communication between sinus and atrium is
wide open
Communication between sinus and atrium will eventually______ and is caused by
shift to the right. Caused by shift in blood in venous system Occurs at about 4-5 weeks.
Obliteration of the right umbilical vein and left vitelline vein Occurs
5th week. Left sinus horn loses importance
At week 10 the left common cardinal vein become and all that remains
obliterated
All that remains of the left sinus horn is the oblique vein of the left atrium and the coronary sinus
Shunt of blood left to right enlarges
right sinus horn
Right horn and vein are the only communication
between the original sinus venosus and the atrium
Forms the smooth walled part of the right atrium.
Sinuatrial orifice (entrance to the common atrium) is flanked on each side
by valvular folds.
left venous valves fuse with
the atrial septum
Superior part of the right venous valve
disappears
Inferior part of the right venous valve becomes
he valve of the inferior vena cava and the valve of the coronary sinus.
During atrial septation, the left atrium begins
to form sprouts of the pulmonary veins that grow towards the lungs.
Cardiac Septation
Starts at _____ and lasts
Day 27
Lasts 10 days (Day 27-37)
the embryo grows from _____ to _______ during septation
5mm to 16-17mm
During ventricular development, 2 important processes occur simultaneously, that result in the “chamberization” of the ventricles
Division of the AV Canal into a Right and Left AV orifice via the endocardial cushions
VentricularSeptation
Endocardial Cushions
Develop in the
Atrioventricular and Conotruncal regions
endocardial cushions assist in the formation
of the atrial and ventricular (membranous) septa, AV Canals, Valves, Aortic and Pulmonary Channels.
Atrioventricular endocardial cushions appear at the AV Canal.
at the end of week 4
The role of the endocardial cushions is to:
Form a barrier between the atria and ventricles Right –left division of the canal
The resulting canals are eventually occupied by the mitral and tricuspid valves.
End of week 4
The ventricular septum is formed by the
outgrowth of the muscular ridge at the interventricular foramen.
he ventricular septum grows upward from the
apex of the heart to the base of the heart
Interventricular foramen is the space above
the membranous septum
Shrinks when the conus septum is complete
Outgrowth of tissue from the endocardial cushion along the top of the muscular interventricular septum
closes the foramen
Fuses with the abutting part of the conus septum.
he paired atria fuse together for form a common atrium at day
27-28
Atrial septation occurs ________ with ventricular septation
simultaneously and in cooperation
Atrial septation also lasts approximately
10 days.
Sickle-shaped crest grows from
the roof of the common atrium
Sickle-shaped crest is first part of
Septum Primum
septum primum extends
toward the endocardial cushions in the AV Canal.
septum primum does not connect to
endocardial cushions. Leaves a space called the Ostium Primum
Ostium Primum
Formed by the opening between
he lower rim of the septum primum and the endocaridal cushions.
Extensions of the endocardial cushions grow
along the edge of the septum primum, closing the Ostium Primum
Before closure, Apoptosis (cell death) makes perforations in the ________ and forms the
upper part of the septum primum
FormstheOstiumSecundum Allows for blood flow to shunt from the right to the left
Lumen of the Right Atrium expands (result of incorporation of the sinus horns)
New crest-shaped fold appears called
SeptumSecundum
septum secundum extends
downward to the septum in the AV canal
Overlaps with the Ostium Secundum RemainingholeiscalledtheForamenOvale
By the 5th week opposing ridges
appear in the truncus
Both cushions grow toward
the aortic sac
cushions form
aorticopulmonary septum Divides the truncus into aortic and pulmonary channels.
Similar cushions appear along the right dorsal and left ventral walls of
conus cordis. Grow toward each other and distally Unite with the truncus septum. Divides the conus into anterolateral portion (RV outflow) and posteromedial portion (LV outflow)
Outflow Tract Septation – Day 29
Partitioning of the outflow tract
Truncus Arteriosus – Aorta Conus Cordis – Pulmonary
Artery
Createdbyaseptumthat forms in the outflow tract from these swellings
Each AV orifice is surrounded by
local proliferations of
mesenchymal tissue. vBlood hollows out and thins the tissue on the ventricular surface
Valves form
Remain attached to ventricular wall by muscular cords Muscular tissue degenerates and is replaced by connective tissue over time.
Semilunar Valves
Small tubercles found on main truncus swellings Tubercles hollow out on the upper surface
Day 1-2:
fertilization
day 6-7
Implantation of blastocyst into uterine wall
day 16-20
Appearance of Celom and Blood Islands
Day 20
Endocardial tubes are present and begin fusing
day 22
Main heart tube begins to beat
day 23-38
Heart Folding
day 27-37
Atrial and Ventricular septation and development
Day 29
Outflow tract septation
Day 55
complete
