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

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Presentation on theme: "1 Respiratory system L4 Faisal I. Mohammed, MD, PhD University of Jordan."— Presentation transcript:

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

2 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

3 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 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 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

7 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. 16.32

8 University of Jordan 8 Hemoglobin

9 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.

10 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.

11 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.

12 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 13 Oxygen-hemoglobin Dissociation Curve University of Jordan

14 Oxyhemoglobin Dissociation Curve Insert fig.16.34

15 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. 16.35

16 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.

17 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.

18 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. 13.37 May also have an 0 2 storage function in cardiac muscles.

19 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 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 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

22 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

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

24 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 25 University of Jordan

26 26 Thank You University of Jordan

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