A treatise on the science and practice of midwifery . from thence into the pulmonary arteries, and theductus arteriosus soon collapses and becomes impervious. The mass ofblood in the descending aorta no longer finds its way into the hypogas-tric arteries, but passes into the lower extremities, and the adult circula-tion is established. Changes in Foetal Circulation after Birth.—The changes which takeplace in the temporary vascular arrangements of the foetus prior to theircomplete disappearance are of some practical interest. The ductus arte-riosus, as has been said, collapses, chiefly because
A treatise on the science and practice of midwifery . from thence into the pulmonary arteries, and theductus arteriosus soon collapses and becomes impervious. The mass ofblood in the descending aorta no longer finds its way into the hypogas-tric arteries, but passes into the lower extremities, and the adult circula-tion is established. Changes in Foetal Circulation after Birth.—The changes which takeplace in the temporary vascular arrangements of the foetus prior to theircomplete disappearance are of some practical interest. The ductus arte-riosus, as has been said, collapses, chiefly because the mass of blood isdrawn to the lungs, and partly, perhaps, by its own inherent contract-ility. Its walls are found to be thickened, and its canal closes, first inthe centre, and subsequently at its extremities, its aortic end remaininglonger pervious on account of the greater pressure of blood from theleft side of the heart (Fig. 71). Practical closure occurs within a fewdays after birth, although Flourens states that it is not completely oblit-. THE ANATOMY AND PHYSIOLOGY OF THE FCETUS. 131 eratecl until eighteen months or two years have According toSchroeder, its walls unite without the formation of any thrombus. Theforamen ovale is soon closed by its valve, which contracts adhesion withthe edges of the aperture, so as effectually toocclude it. Sometimes, however, a small canal FlG- of communication between the two auriclesmay remain pervious for many months, oreven a year and more, without, however, anyadmixture of blood occurring. A perma-nently patulous condition of this aperture,however, sometimes exists, giving rise to thedisease known as cyanosis. The umbilical arteries and veins and theductus venosus soon also become impermeable,in consequence of concentric hypertrophy oftheir tissue and collapse of their Avails. The Diagram of Heart of of the former is aided by the forma- (AfterDalton) ,• n i»it*j_mk t 1- Aorta. 2. Pulmonary artery. tio
Size: 1504px × 1662px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1880, booksubjectobstetrics, bookyear1
