Cardiac embryology

Question 0

Lateral folding of heart

Answer 0

Endocardial tubes (lateral) and dorsal aortae (medial) are part of visceral mesoderm
Folding brings endocardial tubes together
Endocardial tubes fuse -> heart
Dorsal aortae still right/left, all connected cranially

Question 1

Cardiogenic region of intraembyonic ceolom

Answer 1

Forms from cranial end of intraembryonic ceolom (U)
Forms within visceral layer of lateral plate mesoderm
Lateral sides split into lateral endocardial tube and medial dorsal aortae
All still connected at cranial end

Question 2

Longitudinal folding of heart

Answer 2

Septum transversum begins in parietal layer, cranial end of embryo
Heart begins in visceral layer, cranial end

Fold anterior and inferior until in thorax, septum inferior to heart

Question 3

Segments of heart tube

Answer 3

Sinus venosus (R and L)
Primitive atrium
(atrioventricular sulcus)
Primitive ventricle (-> L ventricle)
(interventricular sulcus)
Bulbus cordis (-> R ventricle)
Conus cordis
Truncus arteriosus (connects to dorsal aortae R and L)

Question 4

Formation of cardiac loop

Answer 4

Heart grows while still attached at ends -> folding
Sinus venosus, primitive atrium, primitive ventricle move dorsal (sinus superior)
Bulbus cordis, conus cordis, truncus arteriosus anterior (truncus superior)
Forms overall structure of heart (assymetry, locations of chambers)

Question 5

Partitioning of AV canal

Answer 5

Endocardial cushions bulge out from endocardium
Superior/ventral vs inferior/dorsal
Meet in middle, form middle of X in heart
AV canal also shifts to R (primitive atria now connects to R and L ventricles)
Induced by neural crest cells

Question 6

Transverse pericardial sinus

Answer 6

Space between inflow (veins) and outflow (arteries)

Forms during formation of cardiac loop

Question 7

Partitioning of the atria

Answer 7

Septum primum grows from posterior, superior wall
Septum primum has osteum primum, then osteum secundum higher up (always has hole for blood flow)
Septum secundum grows to the right of septum primum
Foramen ovale is in septum secundum

Osteum secundum is in septum primum! Not septum secundum…wtf

Question 8

Closure of foramen ovale

Answer 8

In embryo, blood passes through foramen ovale and osteum secundum (high pressure in R atrium)
At birth, pressure drops in R atrium, pushes septum primum against foramen -> “valve” -> fuses closed

Question 9

Partitioning of ventricles

Answer 9

Myocardium grows up from base to form muscular portion of septum
Endocardial cushions form membranous portion of septum

Question 10

Formation of internal tissues of heart

Answer 10

Septum secundum -> atrial septum, right side
Septum primum -> valve over foramen ovale, left side
Endocardial cushions -> AV separations, membranous part of interventricular septum
Myocardium -> muscular part of interventricular septum

Question 11

Division of outflow tracts

Answer 11

Truncoconal ridges (R and L)  grow together in bulbus cordis and truncus arteriosus
Fuse in middle and fuse with endocardial cushions
-> aortico-pulmonary (spiral) septum

!Must twist in spiral so that vessels attach to the correct ventricles

Question 12

Formation of primitive veins

Answer 12

Everything begins symmetrical R and L
Cardinal veins - drain from most of body into sinus venosus
Vitelline veins - drain from yolk sac and gut tube, through liver
Umbilical veins - from placenta, originally go to cardinal veins

Question 13

Ductus venosus

Answer 13

Consolidation of umbilical and vitelline veins - shunts blood around liver sinusoids
(Primarily from left umbilical and right vitelline)
Drains into IVC
Degenerates and forms ligamentum venosum at birth

Question 14

Remodeling of great veins

Answer 14

Right sinus horn -> IVC, SVC
Right sinus venosus -> sinus venareum (smooth part of right atrium, separated by crista terminalis)
Left sinus venosus -> coronary sinus
Pulmonary veins sprout from left atrium, some moves back to become smooth portion of atrium

Question 15

Remodelling of great arteries

Answer 15

Multiple symmetrical arches from truncus -> dorsal aortae (original cranial connection is 1st arch)
Fourth arch: R -> R subclavian, L -> aortic arch
Sixth arch: proximal -> pulmonary trunk (R and L), distal L side remains as ductus arteriosus (distal R side disappears)
R and L dorsal aortae fuse -> descending aorta

Question 16

Formation of lymphatic ducts

Answer 16

All grow out from endothelium of veins
Six sacs: 2 jugular, cisterna chyli (anterior), retroperitoneal (posterior), 2 iliac
R and L thoracic ducts from jugular to cisterna chyli
Bottom of R and top of L duct form thoracic duct (runs into L veins at brachiocephalic)
Top of R drains right upper body into R brachiocephalic)

Question 17

Changes to circulation at birth

Answer 17

Lungs open -> R pressure falls -> foramen ovale closes (septum primum forms valve, then fuses)
Ductus arteriosus -> ligamentum arteriosum (bet pulmonary trunk and aorta)
Ductus venosus -> ligamentum venosum (on liver)
Umbilical arteries -> medial umbilical ligaments
Umbilical veins -> ligamentum teres hepatis

Question 18

Patent foramen ovale

Answer 18

Foramen ovale fails to close at birth
Most common atrial septal defect

• > hypoxia due to shunting of blood R->L
• > clots because not all blood is moving
• > pulmonary HTN, R hypertrophy if L->R shunting

Question 19

Congenital abnormalities of heart

Answer 19

Dextrocardia - reversed, not a huge deal…
Atrial septal defect - ex patent foramen ovale
Ventricular septal defect - usually hole in membranous portion
Transposition of great vessels - L ventricle to pulmonary trunk, R ventricle to aorta - super bad…
Patent ductus arteriosus - shunting from aorta -> lungs (causes CHF)
Coarctation of aorta - narrowing, flow only through collaterals
Tetrology of Fallot - see separate slide

Question 20

Tetrology of Fallot

Answer 20

Ventricular septal defect (hole)
Pulmonic stenosis (low flow to lungs)
Overriding aorta (flow from R ventricle -> aorta)
R ventricular hypertrophy

*Very little blood gets to lungs -> “blue baby”