1 Respiratory system L4 Faisal I. Mohammed, MD, PhD University of Jordan

2 Transport of Oxygen and Carbon Dioxide Oxygen transport  Only about 1.5% dissolved in plasma  98.5% bound to hemoglobin in red blood cells Heme portion of hemoglobin contains 4 iron atoms – each can bind one O 2 molecule Oxyhemoglobin Only dissolved portion can diffuse out of blood into cells Oxygen must be able to bind and dissociate from heme University of Jordan

OXYGEN IN THE BLOOD in Milliliters: 200 ml in 1litre arterial blood. Oxygen in blood: Blood of a normal person contains about 15 gm of Hb in each 100 ml of blood. Each gram of Hb can bind with a maximum of 1.34 ml of O 2 - 6

5 Relationship between Hemoglobin and Oxygen Partial Pressure  Higher the P O2, More O 2 combines with Hb  Fully saturated – completely converted to oxyhemoglobin  Percent saturation expresses average saturation of hemoglobin with oxygen  Oxygen-hemoglobin dissociation curve In pulmonary capillaries, O 2 loads onto Hb In tissues, O 2 is not held and unloaded  75% may still remain in deoxygenated blood (reserve) University of Jordan

6 Hemoglobin and Oxygen Other factors affecting affinity of Hemoglobin for oxygen Each makes sense if you keep in mind that metabolically active tissues need O 2, and produce acids, CO 2, and heat as wastes  Acidity (pH)  P CO2  Temperature University of Jordan

Hemoglobin and 0 2 Transport 280 million hemoglobin/RBC. Each hemoglobin has 4 polypeptide chains and 4 hemes. In the center of each heme group is 1 atom of iron that can combine with 1 molecule 0 2. Insert fig

University of Jordan 8 Hemoglobin

How does Hemoglobin carry Oxygen?  Hemoglobin exists in two forms:  Oxyhemoglobin: HbO 2  O 2 + Hb HbO 2  Iron in Hb binds to O 2  4 O 2 molecules per Hb molecule  Deoxyhemoglobin  The fraction of all the Hemoglobin in the form of Oxyhemoglobin is expressed as Hemoglobin saturation.

Hemoglobin (continued) Methemoglobin:  Has iron in the oxidized form (Fe 3+ ). Lacks electrons and cannot bind with 0 2.  Blood normally contains a small amount. Carboxyhemoglobin:  The reduced heme is combined with carbon monoxide.  The bond with carbon monoxide is 210 times stronger than the bond with oxygen. Transport of 0 2 to tissues is impaired.

Hemoglobin ( continued ) Oxygen-carrying capacity of blood determined by its [hemoglobin].  Anemia: [Hemoglobin] below normal.  Polycythemia: [Hemoglobin] above normal.  Hemoglobin production controlled by erythropoietin. Production stimulated by PC02 delivery to kidneys. Loading/unloading depends:  P0 2 of environment.  Affinity between hemoglobin and 0 2.

Oxyhemoglobin Dissociation Curve Graphic illustration of the % oxyhemoglobin saturation at different values of P0 2.  Loading and unloading of 0 2. Steep portion of the sigmoidal curve, small changes in P0 2 produce large differences in % saturation (unload more 0 2 ). Decreased pH, increased temperature, and increased 2,3 DPG:  Affinity of hemoglobin for 0 2 decreases. Greater unloading of 0 2 :  Shift to the curve to the right.

13 Oxygen-hemoglobin Dissociation Curve University of Jordan

Oxyhemoglobin Dissociation Curve Insert fig.16.34

Effects of pH and Temperature The loading and unloading of O 2 influenced by the affinity of hemoglobin for 0 2. Affinity is decreased when pH is decreased. Increased temperature and 2,3-DPG:  Shift the curve to the right. Insert fig

Effect of 2,3 DPG on 0 2 Transport Anemia:  RBCs total blood [hemoglobin] falls, each RBC produces greater amount of 2,3 DPG. Since RBCs lack both nuclei and mitochondria, produce ATP through anaerobic metabolism. Fetal hemoglobin (hemoglobin f):  Has 2  -chains in place of the  -chains. Hemoglobin f cannot bind to 2,3 DPG.  Has a higher affinity for 0 2.

Inherited Defects in Hemoglobin Structure and Function Sickle-cell anemia:  Hemoglobin S differs in that valine is substituted for glutamic acid on position 6 of the b chains. Cross links form a “paracrystalline gel” within the RBCs.  Makes the RBCs less flexible and more fragile. Thalassemia:  Decreased synthesis of a or b chains, increased synthesis of g chains.

Muscle Myoglobin Red pigment found exclusively in striated muscle.  Slow-twitch skeletal fibers and cardiac muscle cells are rich in myoglobin. Have a higher affinity for 0 2 than hemoglobin.  May act as a “go- between” in the transfer of 0 2 from blood to the mitochondria within muscle cells. Insert fig May also have an 0 2 storage function in cardiac muscles.

19 Bohr Effect  As acidity increases (pH decreases), affinity of Hb for O 2 decreases  Increasing acidity enhances unloading  Shifts curve to right P CO2  Also shifts curve to right  As P CO2 rises, Hb unloads oxygen more easily  Low blood pH can result from high P CO2 University of Jordan

20 Temperature Changes  Within limits, as temperature increases, more oxygen is released from Hb  During hypothermia, more oxygen remains bound 2,3-bisphosphoglycerate  BPG formed by red blood cells during glycolysis  Helps unload oxygen by binding with Hb University of Jordan

21 Fetal and Maternal Hemoglobin Fetal hemoglobin has a higher affinity for oxygen than adult hemoglobin Hb-F can carry up to 30% more oxygen Maternal blood’s oxygen readily transferred to fetal blood University of Jordan

CO 2 produced by cells is carried by the blood in three forms In physical solution Plasma/Erythrocyte: 7% As Carbamino-Hemoglobin : 23%  CO 2 + Hb  HbCO 2 As Bicarbonate ions: 70%  Mostly in the Erythrocyte which has the enzyme, Carbonic anhydrase (Catalyses the formation of Carbonic acid 5000 times.)  CO 2 + H 2 O  H 2 CO 3  [H + ] + [HCO 3 - ] Carbon dioxide in blood

transported from the body cells back to the lungs (Tidal Co 2 ) as:

24 Chloride shift  HCO 3 - accumulates inside RBCs as they pick up carbon dioxide  Some diffuses out into plasma  To balance the loss of negative ions, chloride (Cl - ) moves into RBCs from plasma  Reverse happens in lungs – Cl - moves out as moves back into RBCs CO 2 + H 2 O ↔ H 2 CO 3 ↔ H + + HCO 3 - University of Jordan

25 University of Jordan

26 Thank You University of Jordan