Embryology 6 Flashcards
Describe the formation of the intraembryonic mesoderm during gastrulation.
cells migrate through primitive streak of embryo to form intraembryonic mesoderm
The intraembryonic mesoderm is partitioned into (3)
paraxial mesoderm
intermediate mesoderm
lateral mesoderm
What is the ultimate fate of the paraxial mesoderm? (2)
segmented into somites, which develop into bones of axial skeleton + associated musculature
develops into dermis
What is the ultimate fate of the intermediate mesoderm?
urogenital tract
The lateral mesoderm gets split into
two layers: parietal lateral mesoderm + visceral lateral mesoderm
Which embryonic structure develops into a “tube within a tube?”
lateral mesoderm
What embryonic structure gives rise to the cardiovascular system?
visceral portion of the lateral mesoderm
Label the following diagram.
When does the formation of the primitive heart begin?
week 3
What is the first step of primitive heart formation?
angioblastic cords form from lateral mesoderm
Describe how the angioblastic cords formed from lateral mesoderm further develop. (2)
angioblastic cords → 2 endothelial heart tubes
tubes fuse → primitive heart
What are the three layers of the primitive heart?
endocardium = lines cavity
myocardium = heart muscle
epicardium = outermost layer
All three layers of the primitive heart derive from what embryonic structure?
visceral portion of lateral mesoderm
Where is the primitive heart positioned relative to the foregut and oropharyngeal membrane?
ventral to foregut
caudal to oropharyngeal membrane
What five structures are distinguishable along the heart tube?
sinus venosus
primitive atrium
primitive ventricle
bulbus cordis
truncus arteriosus
When and how do heart contractions begin in the embryonic heart?
begin on day 21-22 as peristaltic waves in sinus venosus
What is the direction of embryonic heart blood flow by week 4?
unidirectional
Describe the pathway of embryonic blood flow in the primitive heart. (7)
blood enters heart through sinus venosus
enters primitive atrium
goes to primitive ventricle
exits primitive ventricle via bulbus cordis + truncus arteriosus
goes to aortic sac
goes to aortic arches
dorsal aorta
What structures feed blood into the sinus venosus of the embryonic heart? (3)
common cardinal veins
umbilical vein
vitelline vein
How does the embryo receive nutrients and oxygen?
from mother, via placental transfer
Describe the vascular resistance of the embryonic lung.
high vascular resistance, because the lungs are not yet filled with air
Describe blood supply to the lungs and liver in embryonic development.
lungs and liver don’t have much of a function in the embryonic stage, so they are bypassed in fetal circulation
Draw a diagram of fetal circulation after its heart has developed.
What are the two primary structures of the fetal heart that allow blood to bypass the lungs?
foramen ovale
ductus arteriosus
What are the three major changes to the cardiovascular system after birth?
lungs inflate = lower resistance to blood flow in lungs
foramen ovale closes
ductus arteriosus closes
What is the remnant of the ductus arteriosus in the adult heart?
ligamentum arteriosum
What is the effect of clamping the umbilical cord?
reroutes neonatal blood from oxygenation in placenta to oxygenation in aerated lungs
What is the remnant of the ductus venosus in the adult?
ligamentum venosum
What is the remnant of the umbilical vein in the adult?
ligamentum teres, a.k.a. round ligament of liver
What is the remnant of the umbilical artery/arteries in the adult?
medial umbilical ligaments
How many chambers are there in the primitive heart?
only 2 - one atrium and one ventricle
What does it mean for the heart to develop a double pump system?
right atrium and ventricle drive pulmonary circulation
left atrium and ventricle drive systemic circulation
What anchors the superior end of the primitive heart tube?
aortic arches
What anchors the inferior end of the primitive heart tube?
septum transversum
What is the embryonic precursor to the diaphragm?
septum transversum
What is the result of the rapid growth of the bulbus cordis and primitive ventricle in the embryonic heart?
formation of bulboventricular loop
Describe the positioning of the sinus venosus and bulbus cordis within the bulboventricular loop.
sinus venosus is dorsal and superior to bulbus cordis
What is the remnant of the bulboventricular loop in adults?
transverse pericardial sinus
What structures define the transverse pericardial sinus? (2)
anterior = aorta + pulmonary trunk
posterior = SVC + pulmonary veins
What is the structural function of the atrioventricular canal in the primitive heart?
connects primitive atrium to primitive ventricle
What structure connects the primitive atrium to the primitive ventricle in the primitive heart?
atrioventricular canal
What are endocardial cushions?
outgrowths of dorsal + ventral walls of atrioventricular canal
What eventually happens to the endocardial cushions?
grow until they fuse, at which point the atrioventricular canal is now separated into a right and left canal
Draw a diagram of the steps that occur in the partitioning of the primitive atrium.
Describe how the foramen ovale between the atria is closed after birth.
higher pressure in left atrium pushes septum primum against septum secondum, which closes foramen ovale
What is the remnant of the foramen ovale after birth?
fossa ovalis
Describe how the primitive ventricle is partitioned.
ridge from floor of common ventricle grows upward but a gap (interventricular foramen) persists
What is the fate of the interventricular foramen?
membranous septum bridges interventricular foramen in week 7, which completely separates the ventricles
Describe how the aorticopulmonary septum is formed. (2)
bulbar ridges grow out from bulbus cordis and extend into truncus arteriosus as truncal ridges
bulbar and truncal ridges spiral + fuse to produce aorticopulmonary spetum
In adults, the bulbus cordis become
conus arteriosus (infundibulum)
Describe the changes in the sinus venosus at week 7.
paired venous system (left and right common cardinal veins draining into sinus venosus) becomes unpaired w/ IVC and SVC
Describe the significance of the right portion of the sinus venosus integrating into the right atrial wall.
the point of integration is the crista terminalis:
rough surface derives from primitive atrium
smooth surface derives from sinus venosus
What is the crista terminalis?
the border between smooth and rough portions of the atrial wall
What is the embryonic origin of the coronary sinus?
left portion of sinus venosus
What is the function of the coronary sinus?
drains venous blood from heart muscle into right atrium
From where do the pharyngeal arches receive the aortic arches?
common aortic sac
The common aortic sac is a continuation of
the truncus arteriosus
The third pair of aortic arches develops into (2)
the common carotid arteries (from the proximal portion of the third aortic arches)
the internal carotid arteries (from the distal portion of the third aortic arches)
What is the embryonic origin of the common carotid arteries?
proximal portions of third aortic arches
What is the embryonic origin of the internal carotid arteries?
distal parts of the third aortic arches
The left fourth aortic arch becomes
the arch of the aorta
The right fourth aortic arch becomes
right subclavian artery
What is the embryonic origin of the arch of the aorta?
left fourth aortic arch
What is the embryonic origin of the right subclavian artery?
right fourth aortic arch
The left sixth aortic arch becomes
the left pulmonary artery (proximal portions)
ductus arteriosus (distal portions)
What is the embryonic origin of the left pulmonary artery?
proximal portions of the left sixth aortic arch
What is the embryonic origin of the ductus arteriosus?
distal portions of the left sixth aortic arch
The right sixth aortic arch becomes
the right pulmonary artery (proximal portions)
nothing/degenerates (distal portions)
What is the embryonic origin of the right pulmonary artery?
proximal portions of the right sixth aortic arch
Describe the location of the recurrent laryngeal nerves in the embryonic heart, and how this location changes. (3)
initially supply sixth pair of branchial arches and loop around sixth pair of aortic arches
degeneration of 5th/6th aortic arches causes:
right recurrent laryngeal nerve to hook around right subclavian artery
left recurrent laryngeal nerve to stay anchored around ductus arteriosus
What are cardiac shunts?
patterns of cardiac blood flow that deviate from normal pattern
How do cardiac shunts typically occur?
when two spaces of the heart (e.g. R and L atria) are abnormally connected
What is a left-to-right shunt? (2)
abnormal flow from systemic to pulmonary circuit
oxygenated blood is redirected to pulmonary circulation instead of going out to the periphery
What is a right-to-left shunt? (2)
abnormal flow from pulmonary circuit to systemic circuit
deoxygenated blood enters systemic circulation
What is cyanosis?
blue appearance of skin/mucous membranes due to lack of oxygen
What is the long term effect of a left-to-right shunt?
right atrial and ventricular hypertrophy, because the pulmonary circulation has to pump an increased amount of blood
What are three classes of congenital heart defects causing left-to-right shunts?
atrial septal defects
ventricular septal defect
patent ductus arteriosus
Give four subtypes of atrial septal defects.
foramen secundum defects
foramen primum defects
sinus venosus atrial septal defects
common atrium
If you have defects in the septa that divide the left and right atria in an embryo, what are the consequences?
no consequences [assuming this is prior to birth], because the atria are connected by the foramen ovale anyways
What are foramen secundum defects?
patent foramen ovale due to defects in formation of septum primum or septum secundum
What are foramen primum defects?
septum primum does not completely fuse with endocardial cushion, resulting in patent foramen primum
When do the symptoms of a foramen secundum defect typically manifest?
do not manifest in childhood or early adulthood, but typically start at the age of 30
What is a common symptom of foramen secundum defects?
pulmonary hypertension
How are foramen secundum defects treated?
with an easy and low-mortality-rate surgery
Foramen primum defects are often associated with what other heart defect?
cleft in one cusp of mitral valve
Sinus venosus atrial septal defects result from
incomplete integration of the right sinus venosus into the right atrium
A common atrium is the result of
complete failure to form septum primum and septum secundum
Ventricular septal defects are caused by
incomplete growth of membranous or muscular part of interventricular septum
Patent ductus arteriosus results from
failure of closure of ductus arteriosus after birth
Give four examples of congenital heart defects that cause right-to-left shunts, with cyanosis.
persistent truncus arteriosus (PTA)
transposition of great arteries
tetralogy of Fallot (TF)
coarctation of aorta
Persistent truncus arteriosus is the result of
the aorticopulmonary septum (separating aorta from pulmonary trunk) failing to form
Transposition of great arteries occurs when
aorticopulmonary septum develops in a non-spiral manner, causing aorta to arise from right ventricle and pulmonary trunk arising from left ventricle
How is the transposition of the great arteries treated?
it’s not compatible with life, unless there’s another shunt
Tetralogy of Fallot is caused by
defects in development of aorticopulmonary septum and endocardial cushions
List the four malformations associated with tetralogy of Fallot.
pulmonic stenosis
ventricular septal defect
overriding aorta
hypertrophy of right ventricle
What is coarctation of the aorta?
narrowing of aorta proximally or distally to junction of aorta and ductus arteriosus
What is the function of the ductus arteriosus?
connects pulmonary trunk to descending aorta
Label the following diagram.
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