Human physiology : prepared with special reference to students of medicine / by Joseph Howard Raymond.
- Raymond, Joseph H. (Joseph Howard), 1845-1915
- Date:
- 1901
Licence: Public Domain Mark
Credit: Human physiology : prepared with special reference to students of medicine / by Joseph Howard Raymond. Source: Wellcome Collection.
Provider: This material has been provided by the Augustus C. Long Health Sciences Library at Columbia University and Columbia University Libraries/Information Services, through the Medical Heritage Library. The original may be consulted at the the Augustus C. Long Health Sciences Library at Columbia University and Columbia University.
659/712 page 647
![riiH'nce of c'xposiiro to the air, shows that tliis is not the essential, but only a contributinij;, cause. Jt is the Ht<>j)page of the placental circulation which starts the respiratory movements. Although durinti-fetal life some blood Hows through the pulmo- nary capillaries, still the amount is small, and, there being no air in the pidmonary alveoli, the lungs will sink if placed in water. The first respiratory movement causes an enlargement of the thoracic cavity and a conse<juent distention of the lungs, the air passing ii to the alveoli, and the blood, which is at the time in the ])ulmonary capillaries, becomes oxygenated and returns to the left auricle as arterial l)lood. The expansion of the thorax reduces the resistance to the flow of the blood through the pulmo- nary circulation, and as a result a large amount of blood goes to the lungs; this means a lessened amount through the ductus arteriosus, and, following the law that a diminution of function is followed by atrophy, this vessel begins to diminish in size, antl becomes closed between the fourth and tenth days, and in later life is to be found as a fibrous cord between the left pulmonary artery and the aorta. With the termination of the placental circulation the flow through the ductus venosus ceases, and within a few days this vessel closes, and remains only as a fibrous cord in the fissure of the same name in the liver : that portion of the umbilical vein which is within the body of the child becomes the round ligament of the liver. The blood flowing into the right auricle from the inferior vena cava finds it easier to pass into the right ventricle than into the left auricle, which is now filled with blood from the lungs, and hence takes this course, while the blood cannot flow into the right auricle through the foramen ovale by reason of the valve which has been forminp; in the left auricle during the latter part of intra-uterine life to close this opening. The opening is not permanently closed for a considerable time after birth, in some cases a year, and sometimes not at all. As a result of these various changes the fetal circulation becomes converted into that of the adult.](https://iiif.wellcomecollection.org/image/b21209893_0659.jp2/full/800%2C/0/default.jpg)
