Today I confronted the monster that is Anatomy. It is not that I do not like Anatomy as if it were a monster, it is that the amount of material on my upcoming Anatomy is monstrous. My Anatomy prof told the class that out of the four exams we have in Anatomy this academic year (Fall midterm, Fall final, Winter midterm, Winter final) the upcoming exam (Winter midterm) will be the most difficult. Oh, joy.
The most difficult part in prepping for this exam is learning about the body's blood supply. We started learning about the heart, then the lungs (especially in regards to their role in pulmonary circulation), then finally focused our attention on all the major veins and arteries in the body. Obviously this is a quite difficult task as there are SO MANY blood vessels in the body.
We also learned about fetal blood circulation (which is oh-so-complicated). Did you know that fetuses don't use their lungs to breath until birth? I mentioned before that ...fetuses don't pump blood into the lungs as the amniotic fluid contains all the oxygen they need. Only after their first breath of air (after birth) do babies start pumping blood into the lungs for oxygenation. Allow me to explain a bit further.
Prior to birth, their lungs are completely filled with fluid (amniotic fluid) and are closed-off, blocking any blood from entering the lungs to receive oxygen. Instead, the fetus' blood is oxygenated via the amniotic fluid, which is rich in oxygen that is received from the mother's blood. Blood is pumped from the right side of the heart straight to the left side (note: from birth onwards blood is normally pumped from the right atrium of the heart, to the right ventricle, to the lungs (to pick-up oxygen (this is called pulmonary circulation), then back to the heart through the left atrium, then to the left ventricle where it is pumped out to the entire body (this is called systemic circulation)). When a baby is born, its lungs are emptied of any amniotic fluid and are thus empty and hollow. As the pressure in the lung cavities is lower than atmospheric pressure, air moves into the lungs upon birth. The lungs expand to their full capacity for the first time at birth; this is quite painful and is why babies cry their "first cry" upon leaving the womb. Once the lungs start operating, the hole between the right and left atriums of the heart is closed off, allowing pulmonary circulation to proceed prior to systemic circulation.
...back to the books!