Appendix B: The Heart Oxygen Transpor The Heart and Oxygen Transport Anatomy of the Heart Blood Flow Through the Heart Electrical Conduction Through the Heart Hemoglobin Found in blood. It has four polypeptide chains (tetramer), each combined with an iron-containing heme group. Most oxygen transport takes place through the use of hemoglobin. A small amount of oxygen will still dissolve in the plasma and be transported on its own. Each RBC contains2.7$ ×$10( hemoglobin molecules. Cooperative When an O2 binds to one of the four binding sites, it becomes more Binding: likely that the remaining sites will bind to O 2. CO2 and H+ Allosterically inhibits Hemoglobin. That means CO2 and H+ will Inhibition: trigger the heme group to release its O2. Binding of Oxygen to a Heme Prosthetic Group Without O2, the Fe atom sits below the plane. When O2 binds, the electrons in the Fe atom rearrange so it fits in the hole and becomes level with the plane; also pulls His up towards the plane. The process starts when CO2 enters the RBC where carbonic anhydrase resides (the enzyme for the bicarbonate buffer). The CO2 combines with H2O to make H2CO3 which dissociates into H+ and HCO3-. The H+ allosterically inhibits hemoglobin, e.g. changes the shape of hemoglobin, so it can’t hold onto the O2. Since CO2 initiates this process, the result is O2 is released near lots of CO2, which is Found in muscle tissue, it stores and releases oxygen. It is a monomer and contains where respiration is happening and O2 is needed. only 1 heme group. Myoglobin is NOT pH sensitive. Myoglobin ¯pH Þ ¯heme affinity for O2, curve shifts RIGHT (Bohr shift). O2 Affinity: Myoglobin has a much HIGHER oxygen affinity than hemoglobin. This means it can bind more securely to the oxygen. 2,3-BPG Another allosteric regulator. It places itself in the center of the Heme Group: Myoglobin has only 1 heme group. This is why it cannot exhibit Inhibition: tetramer and causes a and b subunits to release their O2. Note, fetal cooperative binding and it has a hyperbolic curve. hemoglobin has a and g (gamma) subunits. g subunits do not respond to 2,3-BPG, so HbF ends up with more O2 than HbA. 2,32,3-BPG: 2,3-BPG has NO AFFECT on myoglobin. BPG causes a RIGHT shift on the dissociation curve, like CO2 and H+. &2,3-BPG means your body needs more oxygen. Hemoglobin and Myoglobin Dissociation Curves CO2 Transport: After delivering O2 to a muscle, the CO2 that triggered the release of O2 will remain in the hemoglobin. The RBC then travels back to the lung, bringing the CO2 with it. p50: Oxygen pressure when 50% of hemoglobin has an O2 bound. P50 is LOWER for HbF due to the high affinity HbF has for oxygen. % O2 Saturation Fetal HbF has a higher affinity for O2compared to adult hemoglobin (HbA). Hemoglobin: This is because its tetramer contains g subunits, which don’t respond to 2,3-BPG. HbF dissociation curve has a LEFT shift, as if 2,3-BPG levels are low. Myoglobin, hyperbolic, NOT cooperative Hemoglobin, sigmoidal, cooperative Sickle Cell A disease that affects hemoglobin. Caused when Val replaces Glu. Anemia: Hemoglobin aggregates into insoluble fibers. Glu Þ Val Hypoxia: Oxygen deprivation. 𝐏𝐎𝟐 (torr)