Development of the Cardiovascular System 3 Flashcards
Explain the division of the primitive atrium
- To be divided into the right and left atrium
- The septum primum and septum secundum being involved
- the SP grows down from the roof of the atrium, with the foramen primum (FP) between it and the endocardial cushions
- The FP disappears leaving the SP to fuse with the endocardial cushions = foramen secondum
- The SS then grows down beside the FS
- SS leaves an oval opening = foramen ovale allowing +O2 blood flow between the two atria R →L
What are the 3 important bypasses?
- Ductus venosus
- Foramen ovale
- Ductus arteriosus
What is the difference between before and after birth in the heart
Before birth
- The right atrium has higher pressure than the left
- The septum secundum has the foramen ovale to regulate blood flow
After birth
- The left atrium has higher pressure than the right
- Instant physiological closure of the foramen ovale = oval fossa
- septum primum acts as a valve
how is the primitive ventricle divided
- The primitive ventricle needs to be divided to left and right
- The muscular part of the interventricular (IV) septum grows upward as a muscular ridge
- Growth stops short of the endocardial cushions = IV foramen (communication btw the ventricles)
- at the end of week 7, the membranous part of the IV septum grows down to complete the growth
Explain the closure of the IV foramen
This closure results in the fusion of tissues from
- The right and left bulbar ridge
- The endocardial cushion
- After its closes, the pulmonary trunk communicates with the right ventricle and the aorta communicates with the left ventricle
What changes happen to the sinus venosus
- There are initially left and right horns opening into the atrium
- Shift of blood flow from L → R with R horn increasing and L decreases
- An orifice (opening) moves to the R horn to open into the right atrium (RA) which then gets incorporated into the wall of the RA with SVC and IVC
- The L horn becomes the coronary sinus
How is the left atrium (LA) formed
- The primordial pulmonary vein is incorporated into the LA making most of the wall smooth
- The expanding atrium gets the pulmonary vein and its branches are incorporated into its wall
- 2 branches on both left and right main veins then split into 4 individual pulmonary veins bringing -O2 blood from the lungs
Explain the partitioning of the BC and TA
- Muscular, bulbar and truncated ridges (derived from the neural crest mesenchyme) fuse at the aorticopulmonary septum
- The neural crest cells move thru the pharynx and it’s arches to form the ridges
- The partitioning is a 180º spiral dividing the BC and TA into 2 channels: pulmonary trunk (RV) and aorta (LV)
what does the spiral partitioning of the TA and BC channels prevent
- The LV sends +O2 blood to the aorta and the RV sends -O2 blood to the lungs
- without the spiralled septum, +O2 blood will go to the lungs and -O2 blood goes to the aorta
what is the fate of the bulbus cordis
- It ends up being incorporated into the walls of the ventricles
- RV: it is the conus arteriosus giving origin to the pulmonary trunk
- LV: forms the walls of the aortic vestibule which is inferior to the aortic valve
What are some structural anomalies of the CV system
- Atrial Septum Defects (ASD): excessive reabsorption of the septum primum, defective development of the septum secundum. Can result in patent foramen ovale/primum
- Ventricular septal defects (VSD): involves the membranous part of the septum. Results in patent interventricular foramen
- Transposition of the Great Arteries (TGA): happens when aorticopulmonary septum doesn’t spiral
Explain the fetal circulation
- +O2 blood returns to the fetus from the umbilical vein
- Half goes through the liver and half goes through the ductus venosus to the IVC
- IVC → RA either goes through the foramen ovale to the LA or to the RV
- RV → pulmonary trunk to either the aorta via the ductus arteriosus or the lungs
- ~O2 blood leaves lungs to the LV to the aorta the intersegmental arteries has umbilical arteries carrying blood to the placenta
what is the difference between the pre and postnatal circulation
- The lungs are nonfunctional
- The placenta serves in gas exchange
Explain postnatal circulation
- At the time of birth, placental circulation is replaces with pulmonary circulation
- ductus venosus and arteriosus and foramen ovale close
- Decrease in pressure in the IVC and right side of the heart bc the placental blood flow is lost and inflation of the lungs decrease the pulmonary vascular resistance
- Increase in pressure of the left side of the heart be of increase in pulmonary flow
- blood pressure LA > RA so septum primum is pressed against secundum and the foramen ovale closes
What are the adult derivatives of fetal structures
- Umbilical vein = ligamentun teres
- Ductus venosus = ligamentum venosum
- Umbilical arteries = medial umbilical arteries and vesicular arteries
- Foramen ovale = fossa ovalis
- ductus arteriosus = ligamentum arteriosum
