A closer look at the heart and how it works

We spent most of class this week focused on the heart and circulatory system.  First, we watched this video, which illustrates how the heart works.  We talked about how hearts of mammals, which are four chambered.  See the illustration to the right to the right, to see what we discussed.

• The bottom line is that the heart from the body comes to the Superior vena cava at the top of the heart and then fills the right atrium.  
• At the right moment, the tricuspid valve opens and lets the deoxygenated blood go into the right ventricle.  
• The heart contracts and pumps the blood up to the lungs by going through the pulmonary valve and the pulmonary artery.  
• In the lungs, oxygen is added to the blood.
• Then, it comes back to the heart, through the pulmonary veins and into the left atrium.
• It gets dumped into the left ventricle by passing through the mitral valve.
• The heart contracts and pumps the oxygenated blood through the aortic valve, then the aorta and onto the body to bring oxygen and nutrients to our brain and other organs.
• The valves prevent blood from flowing backwards.

One cool thing we learned is that a fetal heart has a hole between the left and right atrium called the foramen ovale.  Because the fetus doesn't get its oxygen from breathing air into its lungs, there is no need to separate the blood flowing from the lungs from the blood flowing from the body.  The fetus gets its oxygen from the mom's blood, across the placenta.  

The hole normally closes shortly after birth, which is when the baby begins to breathe air and needs to keep the oxygenated and deoxygenated blood separate.  We looks at our fetal pig hearts and could not find the foramen ovale.

Actually, mammalian fetuses have their own form of hemoglobin, the molecule in blood that attracts oxygen.  Fetal hemoglobin has a higher affinity for oxygen than adult hemoglobin, which allows the fetus to take oxygen out of the mom's blood and into its own.  Pregnant women have to expand their lungs and breathe in more oxygen to make up for this, and it all happens automatically.  This curve below shows that fetal hemoglobin attracts oxygen better than adult hemoglobin.

We dissected the adult pig heart too, which was very large compared to the fetal pig hearts.  We weighed the adult heart, and found it was about 1.3 lbs, which was less than we predicted.  Then we weighed all 8 of the fetal hearts and found they were also less than we predicted, a total of about 70 grams, when we thought they would add up to about 150 grams.