This fifty-four-minute video module begins with an overview of external respiration. Then, we consider the chemical properties of a truly amazing plasma protein, hemoglobin. The affinity of fetal hemoglobin for oxygen is compared to that of its adult counterpart, adult hemoglobin. As the end of the third-trimester approaches, the fetus begins to manufacture adult hemoglobin, such that, at full term, the circulatory system of the newborn is populated by both fetal and adult hemoglobin. In light of this fact, it behooves us to evaluate the efficiency of oxygen transport by each category of the carrier, fetal and adult hemoglobin. The precise calculation of the comparative amounts of oxygen delivered from the lung of the newborn to his/her peripheral tissues is detailed in this module. The video concludes with an accurate determination of the effect on the whole-body oxygen economy of profound hypothermia. -Bob Demers