Embryology Flashcards
Where is the Cardiogenic Plate located at in the 3rd week
at the cranial part of
the trilaminar disc
What is the sequence of forming heart chambers
Primitive Blood Vessels → Two
Endocardial Tubes → Single
Endocardial Tube = Primitive Heart
Tube → Cardiac Loop → 4 Primordial
Heart Chambers
At the end of which week the fetal heart forms
By the end of the 8th week
Cardiac progenitor cells begin to form
in the middle of the 3rd week in the epiblast layer,
lateral to the primitive streak
These cells migrate through the primitive streak to an area that is rostral to the
buccopharyngeal membrane in the
splanchnic mesoderm.
The underlying endoderm induces these cells to differentiate into:
- Blood Islands: consists of precursor blood cells and angioblasts
- Myoblasts: will develop into the myocardium
the cardiogenic plate consists of two laterally placed endocardial tubes
surrounded by myoblasts and is
thus referred to as the
primordium of the heart
As the neural tube grows and closes, the primordium of the heart will shift
position from
rostral to the buccopharyngeal membrane to the thoracic region
The two endocardial tubes fuse to form the
primitive heat tube
As the primitive heart tube is forming, angiogenic cells appear on both sides,
close to the midline and will develop into the
paired dorsal aortae
At their cephalic end, the paired dorsal aortae bend around the developing
embryo and are attached to the cephalic end of the primitive heart tube
forming the
aortic arches
How many pairs of aortic arches will develop sequentially
6
The primitive heart tube shifts its
position into the pericardial cavity
which is formed by the
intraembryonic cavity
The primitive heart tube is held in
position by the
dorsal mesocardium
dorsal mesocardium which will disappear leaving a space
called the
transverse pericardial sinus
The myocardium thickens and
secretes an extracellular matrix called
the
cardiac jelly
the primitive heart tube has
three layers:
- Endocardium: the innermost lining
of the heart - Myocardium: the middle layer,
which contains muscle cells - Epicardium: the outer lining (or
visceral pericardium)
The primitive heart tube
consists of 4 subdivisions.
From caudal to cranial the
subdivisions are:
- Sinus Venosus
- Primitive Atrium
- Primitive Ventricle
- Bulbus Cordis
Sinus Venosus: paired structures which receives three sets of veins:
- Umbilical Veins: from the placenta
- Vitelline Veins: from the yolk sac
- Cardinal Veins: from the body of embryo
Primitive Atrium:
a single structure continuous with the sinus venosus
Primitive Ventricle:
will become the left ventricle
- That part of the endocardial tube between the atrium and ventricle is the
atrioventricular canal
Bulbus Cordis: 1. Caudal 1/3:
will become the trabeculated part of the right ventricle
Bulbus Cordis: Middle 1/3:
will become the conus cordis which will form the outflow tracts of
both ventricles
Bulbus Cordis: Cranial 1/3:
will become the truncus arteriosus, which is continuous with the
aortic arches and will form the roots and first part of the:
a. Aorta
b. Pulmonary trunk
The first heartbeat occurs at
22 days
The first heartbeat originates in the
myocardium,
forming peristalsis-like waves
beginning in the sinus venosus.
By the end of week ___ coordinated
contractions of the heart results in
unidirectional blood flow:
4
What is the route of blood at the end of week 4
Blood enters the sinus venous (from
the vitelline, cardinal and umbilical
veins) → the primitive atrium → the
primitive ventricle → the bulbus
cordis → the aortic sac → the aortic
arches → the dorsal aortae for
distributions to the embryo, yolk
sac and placenta
As the primitive heart elongates and grows rapidly, bends and forms the
cardiac
loop,
cardiac loop is finished by day
28
The cranial end grows
ventrally and to the right
The caudal end grows
dorsally and to the left
Sinus Vensous Derivatives
Left Horn →
the coronary sinus and
oblique vein of the left atrium.
Sinus Vensous Derivatives
Right Horn →
the smooth part of
the right atrium (sinus venarum)
The muscular part of the right atrium
(the auricle) is derived from
the primitive atrium
Sinus Vensous Derivatives
The opening between the sinus venosus and right atrium, called the sinoatrial
orifice, develops into:
Right and left venous valve
Right venous valve →
Valve of inferior vena cava & Valve of coronary sinus
Left venous valve:
becomes part of the septum secundum
The venous valves fuse dorsocranially and form ridge called
the septum spurium.
The primitive atrium on left side sprouts a pulmonary vein, which branches
and:
a. Grows towards the developing lungs
b. The trunk of the pulmonary vein is incorporated into atrium and will become the
smooth wall of the left atrium while the portion derived from the left side of the
primitive atrium retains a trabeculated appearance as the left auricle.
The trunk of the pulmonary vein is incorporated into atrium and will become the
____________________ while the portion derived from the left side of the
primitive atrium retains a trabeculated appearance as _________
smooth wall of the left atrium
left auricle.
why is a continuous communication between left and right sides is maintained to:
- Permit blood to flow directly from
the right atrium to the left atrium - Bypass the nonfunctioning lungs
Septation of the heart include:
A. Formation of the atrioventricular canal
B. Septation of the atrium
C. Separation of the Ventricles
D. Formation of the outflow tracts
which week does this happen:
they approach each
other and fuse, dividing the
atrioventricular canal into right
and left canals
5
The Septum ______
‐ Grows toward the endocardial cushions
‐ Leaving a large temporary opening: the ostium _____
‐ Fuses with the endocardial cushions: closing the ostium ______
‐ The upper part of the septum undergo cell death: the ostium ______
The Septum( Primum)
‐ Grows toward the endocardial cushions
‐ Leaving a large temporary opening: the ostium
(primum)
‐ Fuses with the endocardial cushions: closing the
ostium (primum)
‐ The upper part of the septum undergo cell death:
the ostium (secundum)
The Septum Secundum
‐ Appears on the _____ of the septum primum
‐ Grows downward to cover the foramen ______
‐ Does NOT fuse with the endocardial cushions:
foramen ______
The Septum Secundum
‐ Appears on the right of the septum primum
‐ Grows downward to cover the foramen secundum
‐ Does NOT fuse with the endocardial cushions:
foramen ovale
Foramen Ovale
‐ Permits blood flow from ____ atrium to ___ atrium
‐ Opposite flow is prevented by the flap valve
(_______)
‐ After birth, ↑ pressure in the ____ atrium increases
causing → closing the foamen ____ = solid wall
separating the right and left atria
‐ The site of the foramen ovale becomes the _____
Foramen Ovale
‐ Permits blood flow from Rt atrium to Lf atrium
‐ Opposite flow is prevented by the flap valve
(septum primum)
‐ After birth, ↑ pressure in the left atrium increases
causing → closing the foamen ovale = solid wall
separating the right and left atria
‐ The site of the foramen ovale becomes the fossa
ovalis
interventricular septum:
Consists of two components:
1. A ____ part: endocardial tissue
2. A _____ part: muscular tissue
Consists of two components:
1. A membranous part: endocardial tissue
2. A muscular part: muscular tissue
After closure:
‐ The right ventricle communicates with ______
‐ The left ventricle with the ____
After closure:
‐ The right ventricle communicates with pulmonary trunk
‐ The left ventricle with the aorta
Formation of the Outflow Tracts
Partitioned by _________ into
pulmonary and aortic trunks:
Partitioned by endocardial cushion into
pulmonary and aortic trunks:
What contribute in septum
Neural crest cells
the membranous part of the interventricular septum
The caudal ends
The cranial ends →
the semilunar
valves
In the middle of _____, blood islands
(mesoderm origin)are found in the
following areas:
1. Body of the embryo
2. Chorion
3. Connecting stalk
week 3
Within each blood island the
peripherally located cells flatten and
give rise to the
endothelial cells: the
walls of arteries and veins
what circulation develops in the wall of the yolk sac
Vitelline circulation:
What circulation: gives rise to umbilical vessels delivering blood to and from
the placenta
Chorionic circulation:
what circulation: circulates blood through the body of the developing
embryo
Intra-embryonic circulation:
Six pairs of aortic arch arteries:
- 1
ST pair → maxillary arteries - 2
nd pair → the hyoid and
stapedial arteries - 3
rd pair→ the common carotids
and roots of internal carotids - 4
th pair → contributes to
subclavian and left to arch of
aorta - 5
th pair → completely
disappears. - 6
th pair→ the proximal part of
the pulmonary arteries. The left
6
th arch also forms the ductus
arteriosus
Fate of the paired dorsal aortae,
the descending aorta (the suprarenal gland, the gonads, and the
kidneys)
Fate of the vitelline artery
Vitelline arteries → form arteries in the dorsal mesentery that supply the gut (the
celiac, superior and inferior mesenteric arteries)
fate of the umbilical arteries
Umbilical arteries → the internal iliac arteries and medial umbilical ligaments
paired veins drain into the heart at ___
weeks:
4
The right vitelline vein develops into the
hepatic portion of the inferior vena cava,
the portal vein and the superior
mesenteric vein
The left vitelline vein
disappears
which veins Bring oxygenated blood from placenta
Umbilical veins:
The right umbilical vein
disappears
The left umbilical vein
connects the placenta to the
inferior vena cava via the ductus venosus
what veins Drain the head and neck and body wall
of the embryo
Common cardinal veins:
Anterior cardinal veins: The cranial portion →
cerebral veins, intracranial dural sinuses
and internal jugular veins
Anterior cardinal veins: The cervical portions →
the left and right brachiocephalic veins
The right anterior cardinal vein
and the right common cardinal
vein →
the superior vena cave
Posterior cardinal veins:
Drain the lower body
Subcardinal veins:
‐ Drain the kidneys, gonads and
suprarenal glands
‐ The right subcardinal vein → the
renal segment (between liver and
kidney) of the inferior vena cava
Supracardinal veins:
‐ Appear lateral to sympathetic
trunk
‐ In thoracic region→ azygos and
hemiazygos veins
‐ In pelvic region → the pelvic
segment (below kidneys) of
inferior vena cava.
Sacrocardinal veins →
lower part
of inferior vena cava and
continue as common iliac veins
The inferior vena cava develops
from:
- Right vitelline vein
- Right subcardinal vein
- Supracardinal veins
- Sacrocardinal vein
Fetal Circulation
Oxygenated blood from the placenta:
umbilical vein → ductus venosum →
inferior vena cava → the right atrium
(mixing deoxygenated and
oxygenated blood):
Most oxygenated blood →
Most oxygenated blood → the
foramen ovale → the left atrium →
left ventricle → aorta → the fetal
body
Most deoxygenated blood →
Most deoxygenated blood → the right ventricle → the pulmonary trunk → the ductus arteriosus → aorta (bypassing the non- functioning lungs)
Blood is returned to the placenta for
oxygenation via
the umbilical arteries
The ductus venosus →
the ligamentum venosum.
The umbilical arteries →
the medial umbilical ligaments.
The umbilical vein →
the ligamentum teres hepatis.
The ductus arteriosus →
the ligamentum
arteriosum → increased pressure in the
left atrium → closes the foramen ovale
