Anatomy and Embalming / A Treatise on the Science and Art of Embalming, the Latest and Most Successful Methods of Treatment and the General Anatomy Relating to this Subject

by Albert John Nunnamaker; Charles Otto Dhonau

—The foetal circulation is that circulation existing between mother and unborn child.

The placenta constitutes, from the third month of intra uterine life, the nutritive and respiratory organ of the foetus. The placenta consists of a maternal portion and a foetal portion. The maternal portion is that portion of the placenta next to the uterine wall of the mother. In this are intervillus blood spaces, which may be regarded as derivations from the eroded maternal blood vessels. In the non-pregnant state the uterus is supplied with branches from the internal iliac artery, which end in capillaries in the wall of the uterus. In the pregnant state the numerous branches of the arteries supplying the uterus do not end as capillaries, but pierce the basal plate of the placenta, where the arterial vessels lose their muscular coat and open directly into the intervillus or intraplacental blood spaces. Maternal capillaries are wanting within the placenta, since they become early replaced by the intervillus spaces. The maternal blood is carried away from these spaces by wide venous channels, forming networks from which proceed the larger venous trunks.

Fig. 44—Plan of the foetal circulation. (Gray)

The foetal portion of the placenta is that portion next to the child. Here end the terminal loops of the foetal blood vessels, the blood being conveyed to and from the placenta along the umbilical cord, by the umbilical arteries and vein. Although coming into close relation, the blood streams of the mother and of the child never actually mingle, because of the delicate septum which intervenes. The delicate septum, however, allows the free interchange of gases necessary for the respiratory function as well as the passage of nutritive substances into the foetal circulation.

The umbilical cord connects the body of the foetus with the placenta, and conveys the foetal blood to and from the placenta to the child. This blood is carried by means of two umbilical arteries and one umbilical vein.

The umbilical vein originates by means of capillaries in the placenta, traverses the cord and enters the body of the child at the umbilicus. The umbilical vein now enters the substance of the liver and passes from that organ to the ascending vena cava by means of the ductus venosus. The blood now enters the right auricle of the heart and the eustachian valve is so placed that this blood is thrown directly into the left auricle of the heart, from there into the left ventricle, and out into the aorta to find itself in the general circulation of the child. The blood coming from the upper extremities of the child finds its way into the right auricle of the heart by means of the descending vena cava, thence into the right ventricle, and out into the pulmonary artery. This artery after birth will lead the blood to the lungs, but before birth, in as much as the lungs are not functioning, the lungs can not accommodate this amount of blood, so it passes directly into the arch of the aorta by means of the ductus arteriosus, and thence into the general circulation. The umbilical or hypogastric arteries leave the internal iliacs, pass one on each side of the bladder to the umbilicus, and thence down the cord to the placenta, end there in capillaries, where the blood is now purified, and nourished for its return flow.

The Collateral Circulation.

—By collateral circulation is meant the anastomoses of arteries, or veins through a side branch. There are three great arterial collateral circulations in the body. One is in the arm, the deep brachial artery, and the anastomotica magna, coming off of the brachial artery and anastomosing with the recurrent radial and ulnar artery. One is in the leg, the deep femoral artery, and the anastomotica magna coming off of the femoral artery and anastomosing with the recurrent anterior and posterior tibial arteries. One over the front part of the body, the superior and inferior mammary arteries branches of the subclavian artery and anastomosing with the superior and inferior epigastric arteries, branches of the external iliac and femoral arteries.