11.12.08 organ systems: cardiovascular development 2

this is the second lecture in the cardiovascular development series and focuses on development of prenatal circulation and the transition to post natal circulation. it starts with where we left off with the last lecture, looking at the development of the larger structures in the heart, like the aortic arch being formed from the truncus arteriosus, forming the aorta on the left. the left recurrent laryngeal nerve is underneath the aorta and the right recurrent laryngeal nerve is underneath the right subclavian artery.

then we go back to some possible defects in structural development in the BC/TA trunk. when the spiral aortic-pulmonary septum forms from the endocardial cushion, there are several possibilities for abnormal development. these are: lack of septum altogether, called persistent truncus arteriosus, lack of a spiral in the septum, causing transposition of the aorta and pulmonary trunks, and an unequal divide in the trunk, causing one of the trunks to be bigger than the other. the tetralogy of fallot is a condition that combines the unequal divide with a VSD, resulting in right ventricular hypertrophy (induced by the pulmonary stenosis) as well as "aortic override".

finally, we look at the development of fetal circulation on a larger scale, as it interacts with its placenta. the trophoblast that is embedded in the endometrium differentiates into two layers: the syncytiotrophoblast, which contains spiralling maternal blood vessels and interstitial spaces, and the cytotrophoblast, which has "choroinic villi" that extend into the interstitial spaces and contain the fetal blood vessels. we then shift over to look at the difference between pre and post natal circulation, which is mainly in prenatal's use of shunts which divert blood from the liver and lungs. the ductus venous diverts blood from the liver, the ductus arteriosus and foramen ovale divert blood from the lungs, instead going directly back into circulation, which apparently "reduces oxygenated blood" in the lower limbs. two more random facts: blood supply from umbilical cord and vena cava remain in separate streams when entering the right atrium. the right ventricle and pulmonary trunk receives more deoxygenated blood and the left ventricle receives more oxygenated blood.