Answer:
Development of the heart
Step-by-step explanation:
Already in the first weeks of development of the embryo the heart begins to form, from the accumulation of cells called mesenchymal.
At the beginning of its development, the future heart is a simple tube, the heart tube. However, due to its position among other structures, this tubular heart lengthens and dilates due to the different growth of some of its regions.
Completing the heart formation will develop the aortic and pulmonary heart valves and the mitral (left) and tricuspid (right) atrioventricular valves. There is also in the hearts of the fetuses a connection between the aorta and the pulmonary artery, called the ductus arteriosus, which should close after birth.
This whole process requires a heavy workload on the mother's body, which can result in serious bouts of morning sickness and tiredness around the 8th week of pregnancy.