544 



ORGAN SYSTEMS OF MAN 



umbilicol 

 cord 



IBI blood rich in oxyqen 

 mm mixed blood 



blood low in oxyqen 



ductus orteriosus 



foron»en ovale 



umbilicol vein 

 umbilicus 



umbilicol orreries 



plocento 



uterus 



PRENATAL 



POSTNMAL 



Fig. 21-11. The blood pathway is quite different during fetal life than it is after birth. These changes are indicated 



in these sketches. 



there is no point in sending blood through 

 the non-functional lungs, the heart has 

 modified the main blood flow through itself, 

 and functions essentially as a single organ 

 rather than the double one of the adult. 

 This temporaiy detour has meant that the 

 fetal heart must be constructed on a slightly 

 different plan than the adult heart. There 

 is an opening between the auricles, the 

 foramen ovale, which allows incoming 



blood from the great veins to fill both auri- 

 cles simultaneously. When the blood is 

 forced out from the ventricles, that coming 

 from the right ventricle, which in the adult 

 goes to the lungs, is short-circuited through 

 a large, short connection, the ductus arterio- 

 sus, to the aorta. Very little blood goes to 

 the lungs so very little comes back to the 

 left auricle. Almost the entire output from 

 both ventricles therefore passes out into the 



