لخّصلي

Normal fetal circulation is a unique system that allows the developing fetus to receive oxygen and nutrients from the mother's bloodstream. The circulation in the fetus differs from that in a newborn or adult due to the presence of certain structures that bypass the non-functional lungs and liver. Here is a simplified explanation of normal fetal circulation:

1. 
   

   Oxygenated blood supply: Oxygenated blood rich in nutrients is carried to the placenta through the umbilical arteries. These arteries arise from the fetus's internal iliac arteries and transport blood to the placenta.

   
   


2. 
   

   Oxygen and nutrient exchange: At the placenta, oxygen and nutrients diffuse across the thin walls of the placental villi and into the fetal capillaries. The exchange occurs through the process of diffusion and relies on the concentration gradient between the maternal and fetal blood.

   
   


3. 
   

   Umbilical vein: Oxygenated blood from the placenta returns to the fetus through the umbilical vein. The umbilical vein carries the blood into the fetal body through the umbilicus (belly button).

   
   


4. 
   

   Ductus venosus: Upon entering the fetal body, most of the blood in the umbilical vein bypasses the liver through a structure called the ductus venosus. The ductus venosus allows a portion of the oxygenated blood to directly enter the inferior vena cava, which carries blood from the lower body to the right atrium of the heart.

   
   


5. 
   

   Right atrium and foramen ovale: In the right atrium, the oxygenated blood from the inferior vena cava mixes with the deoxygenated blood returning from the upper body. A special opening called the foramen ovale exists in the atrial septum, allowing blood to pass directly from the right atrium to the left atrium, bypassing the right ventricle.

   
   


6. 
   

   Left ventricle and systemic circulation: From the left atrium, blood flows into the left ventricle, which then pumps it out into the aorta. The oxygenated blood is distributed to the fetal body through the systemic circulation, providing oxygen and nutrients to the developing organs and tissues.

   
   


7. 
   

   Deoxygenated blood and pulmonary circulation: Deoxygenated blood returns to the right atrium from the fetal body through the superior vena cava. A small portion of the blood enters the right ventricle and is then pumped into the pulmonary artery. However, the majority of the blood in the pulmonary artery is directed away from the non-functional fetal lungs through a shunt called the ductus arteriosus.

   
   


8. 
   

   Ductus arteriosus: The ductus arteriosus connects the pulmonary artery to the descending aorta, allowing most of the blood to bypass the lungs and flow directly into the systemic circulation. This shunt helps to ensure that the developing fetus receives oxygenated blood from the placenta instead of relying on its own non-functional lungs for oxygen exchange.