Cardiac Embryology Flashcards
Outline the events in lateral and cephalocaudal folding related to the heart.
Folding necessary as elongation as reduced the amount of space available to grow in
How do lateral folding and cephalocaudal folding help form the heart?
LATERAL: creates heart tube
CEPHALOCAUDAL: brings tube into thoracic region
What is looping?
Continued elongation of the heart that results in bending (folds into pericardial space) from day 23-28
From superior to inferior, what are the components of the heart tube?
Aortic roots
Bulbus cordis
Ventricle
Atrium
Sinus venosus
How do the portions of the heart tube move?
Cephalic: moves ventrally, caudally, and right
Caudal: moves dorsally, cranially, and left
What does looping achieve?
- creates transverse pericardial sinus by moving arteries in front of veins
- primordium of right ventricle closest to outflow tract
- primordium of left ventricle closest to inflow tract
- atrium dorsal to bulbus cordis (inflow dorsal to outflow)
- atrioventricular canal (pinched junction between atria and ventricles) allows atria and ventricles to communicate
Describe the development of the sinus venosus.
At first, the left and right sinus horns are equal in size
Venous return shifts to the right hand size, so the left sinus horn recedes
Right sinus horn is absorbed by the enlarging right atrium
Describe the development of the atria.
LEFT ATRIUM develops from:
- small portion of primitive atrium
- absorbs proximal parts of the pulmonary veins
- receives oxygenated blood from the lungs
note: oblique sinus formed as left atrium expands, absorbing the pulmonary veins
RIGHT ATRIUM develops from:
- most of the primitive atrium
- sinus venosus
- receives venous drainage from the body (venae cava) and the heart (coronary sinus)
Outline the foetal circulation and what shunts are present. Why are these necessary?
Placenta —–> DUCTUS VENOSUS —–> Inferior vena cava
(bypasses liver)
Right atrium —–> FORAMEN OVALE ——> left atrium
(bypasses lungs, which are non-functional)
Pulmonary trunk —–> DUCTUS ARTERIOSUS —–> aorta
(bypasses lungs, which are non-functional, and heart)
Why do the shunts close at birth?
Respiration begins ——> pressure in the left atrium increases ———–> foramen ovale closes & ductus arteriosus contracts (sensitive to pO2)
Placental support removed ———> ductus venosus closes
What are the aortic arches? What are the most important features?
Bilaterally symmetrical system of arched vessels
6 arches (no 5th) 4th = arch of aorta & proximal part of right subclavian artery 6th = pulmonary arch (recurrent laryngeal nerve)
As heart “descends” the left recurrent laryngeal nerve hooks around the 6th aortic arch (ductus arteriosus) and turns back on itself
Left recurrent laryngeal nerve descends to T1-T2
Right recurrent laryngeal nerve descends to T4-T5
What factors influence the course of the recurrent laryngeal nerves on the left and right sides?
- caudal shift of the developing heart and expansion of the developing neck region
- need for a foetal shunt between pulmonary trunk and aorta
What are the endocardial cushions? What do they do during development?
Neural crest cells that have migrated into the cardiac region (neural crest cells migrate throughout the mesoderm)
Grow towards each other to narrow the atrioventricular canal and from the primary interventricular foramen
Outline the stages of atrial septation.
Septum primum present with large hole present (ostium primum)
Ostium secundum forms in septum primum (by apoptosis)
Septum secundum forms in front of (ventral?) septum primum
Foramen ovale forms in septum secundum
Right to left shunt formed (foramen ovale —-> ostium secundum)
Outline the stages of ventricular septation.
Muscular portion of ventricle grows up towards endocardial cushions, and the membranous portion of the interventricular septum is formed by connective tissue derived from the endocardial cushions
