Hi, this is Tom, and in this episode I'm going to be going through fetal hemoglobin,

and you can find notes at 0.0.5.com and in the 0 to Finals Pediatrics book,

and you can find flashcards and questions at members.0.0.5.com. So let's jump straight in. Hemoglobin is the

molecule responsible for transporting oxygen around the body. It's found in red blood cells. It picks up

oxygen in the lungs, transports it through the blood and releases it in the tissues.

In a fetus, hemoglobin picks up oxygen in the placenta,

where oxygen diffuses across the placenta from the mother's hemoglobin.

We need to talk about the difference between fetal hemoglobin and adult hemoglobin. Hemoglobin is formed of two

pairs of protein subunits, four protein subunits in total. Fetal hemoglobin, or HBF, has two alpha

and two gamma subunits.

Adult hemoglobin, or HBA, has two alpha and two beta subunits.

Fetal hemoglobin has a higher affinity for oxygen than adult hemoglobin.

That means oxygen binds to fetal hemoglobin more easily,

and it dissociates or separates from hemoglobin less easily.

This allows fetal hemoglobin to essentially steal oxygen from the mother's hemoglobin in the placenta.

If the fetal hemoglobin and the maternal hemoglobin had the

same oxygen affinity, then oxygen transfer to the fetus would be less efficient. Let's talk about

the oxygen dissociation curve. The oxygen dissociation curve shows the affinity of fetal and adult hemoglobin for oxygen.

Along the x-axis is the partial pressure of oxygen, or the PO2, which reflects the oxygen concentration

in the blood. On the y-axis is the percentage saturation of hemoglobin with oxygen,

essentially how full the hemoglobin molecule is with oxygen. As the partial pressure of oxygen

increases, more oxygen will be bound to hemoglobin. Adult hemoglobin requires a higher

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