At what point does the embryo begin to develop the cardiovascular system.
Around three weeks. At this point the embryo can no longer survive via diffusion.
At what point in embryonic development do you see these developments?
If a baby was born with leukemia, from what lineage of cells did the neoplastic cells come from?
Splanchnic mesodermal cells -> Hemangioblasts -> Blood island development (endothelial lining and hematopoietic stem cells)
Why is it that embryos can generate blood cells even though they have not yet generated bone marrow?
Neonates utilize the yolk sac, spleen and liver to generate blood cells before the bone marrow is developed.
What role does angiogenesis play in blood vessel development in the embryo? When does blood vessel development start?
At about 18 days, vasculogenesis occurs and new blood vessels are formed from splanchnic mesodermal cells differentiating into endothelial cells. Angiogenesis remodels these new vessels to lengthen them and even split them into two separate vessels.
Where in the embryo does early vasculogenesis take place?
Yolk sac. This is where blood islands first begin to form around day 19.
How does the four-chambered heart function in the developing fetus? What happens when the baby is born?
The lungs are not yet functioning in the fetus, so the heart functions as one chamber with two shunts from the pulmonary trunk to the aortic arch inter-atrial and the ductus arteriosus (connects aorta and pulmonary arteries). When the baby is born, these shunts close and blood starts circulating through the lungs.
In a developing fetus, which side of the heart has a higher pressure (circulation resistance)? What happens when the baby is born?
Because the lungs are not functioning, pressure is high on the right, pulmonary side of the heart. The left side is low because it is included in systemic circulation which includes the low pressure placenta. When the baby is born pressure is relieved by opening pulmonary circulation and the left side now has higher pressure.
What pathways are turned on and what pathways are turned off during development of the cardiogenic field and cardiac progenitor cells?
NKX-2.5 is the master gene for developing cardiac progenitor cells. BMP 2,4 play a role in inducing NKX-2.5. WNT inhibitors are also turned on because WNT inhibits cardiac myocyte development.
What is the main event in fetal cardiac development around day 18?
The cardiogenic field is forming as blood islands aggregate in the splanchnic mesoderm. Also, the paired endocardial tubes and dorsal aorta begin to form.
What is the fate of the endocardial tubes in fetal cardiac development.
They fuse to form a single heart tube during lateral folding
Why is the pericardium connected to the diaphragm?
They develop from the same sac that surrounds the fetal heart tube, with the diaphragm coming from the septum transversum
A patient comes to see you with a coronary artery blockage. Where did this artery originate from during fetal development?
The septum transversum. This layer forms most of the epicardium and sinus venosus (veins of the heart that give rise to the coronary artery)
What are the different players in the heart tube that contribute to cardiac loop formation?
How does the heart tube actually fold to form a four-chambered heart?
The bulbs cordis grows and moves inferiorly and to the right, pushing the atrium superiorly and to the left.
What is the fate of the bulbs cordis?
It becomes the right ventricle.
When is dextrocardia a fatal congenital abnormality?
When none of the other organs are inverted.
How is the atrioventricular canal formed?
Endocardial cushions grow and fuse together to form a septum in the center of the heart that leave atria connected to ventricles via the AV canal.
What forms the wall that separates the two atria?
The septum primum and septum secundum. They each have a hole, but the two flaps fuse at birth to form a solid wall between the atria.
During the formation of the foramen secundum there is excess resorption of the septum primum. An adult with this condition will have blood flowing from where to where?
Left atrium to right atrium because pressure is higher in the left side of the heart.
What leads to formation of the muscular ventricular septum?
Ventricles grow and push the septum superiorly. This muscular septum meets up with the endocardial cushion from the AV canals and the conotruncal septum from the aortic and pulmonary arteries.
What is the role of neural crest cells in fetal cardiac development?
The form the secondary heart field that by populating the truncus arteriosus.
What structures are formed as a result of spiraling of the outflow tract?
The pulmonary artery coming from the right ventricle and the aorta coming from the left ventricle.
What does the truncus arteriosus give rise to as the heart develops?
It forms the septum between the aorta and pulmonary artery. It also gives rise to the semilunar valves.
If the conotruncal septum did not spiral during development, blood will from from the ___ to the ____.
Right ventricle to the aorta. This condition is called transposition of the great vessels.
How do the AV valves form?
Cells apoptose in the AV septum and endocardial cushion remodels to form the valves.
During fetal vascular development, how do the internal, external and common carotid arteries develop? Right subclavian? 7th intersegmental artery? Aorta? Pulmonary artery?
The internal and external carotid arteries are remnants of aortic arches 1 and 2. The common carotid artery formed from aortic arch 3. On the right side, aortic arch 4 becomes the right subclavian artery and the 7th intersegmental artery. It also becomes the arch of the aorta on the left side. The pulmonary artery comes from aortic arch 6.
Why do the recurrent laryngeal nerves loop around different structures on different sides of the body?
On the right, it loops around the right subclavian artery. On the left, it loops around the ligamentum arteriosum. This happens because during development you lose aortic arch 6 on the right side and the nerve loops around aortic arch 4 (right subclavian artery). Aortic arch 6 stays on the left side (ductus arteriosus)
How does blood flow in the fetus differ from that in the newborn baby?
In the fetus, blood from the umbilical vein flows in, bypasses the liver and the lungs via the ductus arteriosus. Blood then flows out the umbilical artery. At birth the ductus arteriosus constricts due to lack of maternal prostaglandins and bradykinin release (smooth muscle contraction). You now have blood flow into the liver, into the vena cava, coronary veins, through the pulmonary artery, pulmonary vein and out the aorta.
What are the main adult remnants of the embryological structures?
Ligamentum arteriosum and ligamentum teres hepatis.