Cardiovascular system development timingAttach Images
First system to functionally develop. Begins to develop during the middle of the 3rd week. Blood circulates at beginning of 4th week. Done development by 8th week.
Angioblastic cords are originally found in the cardiogeic area (cranial end of the embryo). These cords canalize (hollow out) to form the endocardial heart tubes at the late 3rd week. Heart begins to beat at 22-23 days
Head fold effect on cardiac development
The head-folding of the embryo brings the developing heart and pericardial cavity ventral to the foregut and caudal to the oropharyngeal membrane
Lateral fold effect on cardiac development
the lateral folding brings the endocardial heart tubes together, fusing to form a single heart tube with three layers.
Three layers of the heart tube
Visceral pericardium cardiac jelly (connective tissue that will become the AV valves), and the wall of the heart tube
"Main drain vein" of the fetal heart. Receives venous blood flow from umbilical vein (chorion), vitelline vein (yolk sac) and cardinal vein (embryo). Develops right and left horns due to embryo shunting blood to the right side of the primitive heart.
Site of collection of fetal blood. Not differentiated into left and right. Receives blood from sinus venosus
Develops into blood inflow portion of adult ventricle. Site of inflow from primordial atrium. Pumps blood out. Largest part of fetal heart
Develops into conus arteriosus and aortic vestibule. Outflow portion of developing heart ventricle. Proximal to truncus arteriosus. Receives blood from primordial vestibule and sends blood to truncus arteriosus.
Outflow portion of developing heart. Continuous with aortic sac from which aortic arches develop
Develops into aortic arches. Primordial vascular channel anterior to the truncus arteriosus. Outflow of fetal heart
Cause for heart outflow in front and inflow in back
Bulbus cordis and ventricle (largest aspects) grow faster than other regions of the developing heart, causing the heart to bend upon itself. The bend is down and to the right side of the embryo. As the primordial heart bends at the bulboventricular loop, the atrium and sinus venosus come to lie dorsal to the truncus arteriosus, bulbus cordis, and ventricle. BENDING OCCURS AT INFERIOR BORDER OF HEART. Results in adult positioning of heart in mediastinum: inflow of blood on posterior aspect and outflow of blood on anterior aspect.
U shaped junction between bulbus cordis outflow and primordial ventricle inflow. Location of bending of heart at inferior border of heart.
Blood flow of primitive heart prior to folding
Sinus venosus --> primordial atrium --> (AV Canal) --> primordial ventricle --> bulboventricular jxn --> bulbus cordis --> truncus arteriosus --> aortic sac --> aortic arches
Development of Semilunar valves
Develop from three swellings of subendocardial tissue via blood flowing through and hollowing out/remodeling the endocardium. Swellings are restructured via this blood flow to form thin-walled cusps. The position of the cusps after rotation is the normal anatomical way of naming cusps
Development of AV valves
Proliferation of endocardial cushions (cardiac jelly!) around the AV canals. Endocardium at the atrioventricular junctions undergo remodeling TOWARD THE VENTRICLE --> chordae tendinae, papillary muscle. This development toward the ventricle is due to the DIRECTION OF BLOOD FLOW (from atrium to ventricle) pushing the valves toward the ventricle. Three cusps on right (Tricuspid valve) and two cusps on left (mitral valve)
Partitioning of primordial atrium
Two Walls and Two Holes (phrasing!). Goal: primordial atrium into left and right atrium.
"First wall". The first septum. Grows inferiorly to the atrioventricular junctions. Its job is to close the opening between the primordial atrium known as the Foramen Primum (first hole). The Septum Primum divides the atrium into the right and left atria.
First hole. Closed by foramen primum. Aka Ostium primum. The original opening between the right and left atria before they are separated by the septum primum.
Before the foramen primum is closed, a second hole forms in the septum primum. This hole is the foramen secundum. This hole allows for blood flow between the two atria as the fetal lungs are not yet sufficiently developed, so a bypass is necessary.
On the RIGHT side of the septum primum, the septum secundum grows inferiorly ONLY TO OVERLAP THE NEWLY FORMED FORAMEN SECUNDUM. This overlapping forms a flap-valve over the foramen (Foramen ovale)
Allows blood to flow between from right to left atria. USUALLY closes within minutes at birth, forming the fossa ovalis.
Formation of adult right atrium
Sinus venosus and primitive atrium. Right horn of sinus venosus becomes the posterior wall of right atrium --> sinus venarum (smooth portion of adult right atrium). Left horn of sinus venosus becomes coronary sinus. Primitve atrium becomes the rough anterior wall of adult right atrium (pectinate muscles)
Formation of adult left atrium
Smooth walls of left atrium formed by incorporation of primordial pulmonary vein IN NORMAL HEART.
Formation of left auricle
Primordial left atrium become left auricle (rough).
What happens if primordial pulmonary vein is incoporated into right side of interatrial septum?
Total Anomalous Pulmonary Vein. Heart defect. Blood is draining into right atrium instead of left (not good!)
Partitioning of primordial ventricle
Interventricular septum consists of muscular portion (inferior) and membranous portion (superior). The membranous portion of the IV septum is derived from tissue off of the right side of the endocardial cushion and the aorticopulmonary septum. This tissue along with muscular portion of the IV septum form a permanent partition between the left and right ventricles
Muscular portion of Interventricular septum
Infolding of primitive ventricle grows superiorly to meet the membranous portion. Divides primordial ventricle into a right and left side
Membranous portion of primordial ventricle
Forms from right side of fused endocardial cushions. Fuses with aorticopulmonary septum and comes down to meet muscular part of interventricular septum.
Partitioning of bulbis cordis
Bulbar ridges (mesenchymal cells) are derived from the neural crest within bulbis cordis. Form from swelling in wall of bulbar cordis.
Partitioning of Truncus arteriosus
Truncal ridges (mesenchymal cells) derived from neural crests within truncus arteriosus. Fromed from swelling in walls of truncus arteriosus.
Formation of outflow tracts
Starting with bulbar ridges, truncal and bulbar ridges approach each other to fuse via 180 degree spiraling around each other possibly due to streaming of blood from ventricles. When they fuse, they form the aorticopulmonary septum.
Separates aorta from pulmonary trunk in adults. Formation aorticopulmonary septum divides bulbus cordis and truncus arteriosus into conus arteriosus of right ventricle and aortic vestibule of left ventricle (OUTFLOW). Fuses with muscular portion of IV septum; requires the presence of endocardial cushions which seal the formation of the outflow tracts.
Gives rise to ascending aorta and pulmonary trunk
Atrial septal defects (ASDs)
Problems with the septum behind right and left atria. Secundum type, endocardial cushion defect with primum type, sinus venosus type, common atrium
Endocardial cushion defect with primum type
Aka Septum premum ASD. Septum premum is defective, atria are not separated. Needs to be fixed.
Secundum type ASD
Septum secundum did not make the overlap Foramen Secundum. Needs to be fixed
Sinus Venosus Type ASD
ASD in the region derived from the ASD; junction of SVC/IVC and RA.
Common atrium ASD
No separation between L and R atria
Ventricular septal defects (VSDs)
More significant than ASDs. Membranous, muscular, or absence of IV septum
Aorticopulmonary Septal Defect
Heart disorders from defects in development of aorticopulmonary septum. Persistent truncus arteriorsus, tetralogy of fallot, transposition of great vessels
Persistent truncus arteriosus
aka common arterial trunk. Truncus arteriosus never divides into aorta and pulmonary trunk. Ensures a VSD.
Transposition of great vessels
Aorta and pulmonary trunk are transposed. Blood goes to lungs, get O2, returns to heart, and goes back to lungs. Blood flow returning to body goes into heart before returning to body (no oxygen gets pumped into it).
Tetralogy of Fallot
Congential heart defect with 4 abnormalities of the heart. Pulmonic valvular stenosis, VSD, overriding aorta, and right ventricular hypertrophy
Unequal division of truncus arteriosus
Unequal division between aorta and pulmonary trunk. Can be large aorta (pulmonary valve stenosis) or large pulmonary trunk (aortic stenosis). VSD guarenteed in each case