Fetal Hemoglobin: Function and Structure

Hemoglobin is found in the red blood cells of every human being, child or adult.  It is necessary because hemoglobin binds and carries oxygen from the lungs to other tissues within the body.  Hemoglobin also transports carbon dioxide from tissues to the lungs.  In fact, hemoglobin represents over 95% of the solid components of red blood cells.  However, a developing baby has fetal hemoglobin while an adult, in most cases, carries adult hemoglobin.

Fetal Red Blood Cells

        A fetus is totally dependent on oxygen from its mother’s lungs and thus, must acquire a way in which to obtain the needed molecule.  The needed oxygen travels around the mother’s bloodstream attached to hemoglobin molecules in red blood cells.  Once at the placenta, the oxygen diffuses across into the fetal bloodstream and reaches the fetus at a much lower pressure than is found in the mother’s blood.  The oxygen pressure found in a fetus’ blood can be compared to the pressure at the top of Mt. Everest, not nearly enough pressure for an adult.  How then, can a fetus survive on such low oxygen pressure?

        A fetus is able to cope with this low amount of oxygen pressure in several ways:  

  1. A fetal heart beats extremely fast – an average of 150 times per minute.  A normal adult, on the other hand, has an average heartbeat between 70-80 times per minute.
  2. A fetus has more red blood cells per cubic millimeter than an adult (seven million compared to five million in an adult!).  A fetus’ heart must beat quickly in order to allow such large amounts of red blood cells to pick up the much-needed placental oxygen.  Keep in mind that it takes only about 30 seconds for a fetal blood cell to make a complete trip around the fetus’ body.   The number of red blood cells, combined with the increased heart rate, illustrates just how much oxygen the fetus requires.
  3. Fetal red blood cells have a greater affinity for oxygen at a lower oxygen pressure than adult red blood cells do.
  4. Fetal red blood cells are larger than adult cells (8.3 microns compared to 7.5 microns) and therefore each cell can carry more oxygen.
Join now!

               

The Bohr effect is important in the maternal-fetal O2 transport as well.  The blood that enters the placenta on the baby’s side has a high concentration of CO2.  This equilibrates with the mother’s blood rapidly.  As the mother takes up more Co2, she gives up more O2.  Likewise, as the baby gives up more CO2, he is able to bind more O2.  This effect favors the transport of O2 from mother to baby.  

Also interesting to note is that the formation of fetal red blood cells occurs ...

This is a preview of the whole essay