Brief description of the human circulatory system. Functions of hemoglobin in delivering oxygen and removing waste products such as acid protons and carbon dioxide. The brain’s unusual requirement for 20% of our blood flow to get enough oxygen. Explanation of hematocrit. Description of the many types of globin proteins. Explanation of using units of torr for the gas pressure, for concentrations of oxygen, and pO2 as the binding constant of hemes for oxygen. Explanation of how binding a compound by any protein, such as an enzyme or hemoglobin, is an on–off process. Normally, hemoglobins release one half of their bound oxygen molecules in the capillaries to be used by adjacent tissue cells. Explanation of why the different globin proteins must have different affinities for oxygen to achieve the net movement of oxygen from the lungs to the body’s tissues. Oxygen-binding curves by hemoglobin are sigmoid, indicating that the hemoglobin is changing its affinity for oxygen in response to the surrounding concentration of oxygen, acidity, or temperature. These allosteric effectors signal a greater need for oxygen. Fetal hemoglobin must bind oxygen more tightly than adult hemoglobin.