Transport of Gases by the Blood PDF

Transport of gases by the blood Prepared by : Prof. Dr. Marwa Nagy Emam Professor of physiology  ILOs By the end of this lecture, students should be able to: 1. Describe how O2 and CO2 are transported by the blood. 2. Explain physiological significance of oxyhemoglobin...

Transport of gases by the blood Prepared by : Prof. Dr. Marwa Nagy Emam Professor of physiology  ILOs By the end of this lecture, students should be able to: 1. Describe how O2 and CO2 are transported by the blood. 2. Explain physiological significance of oxyhemoglobin dissociation curve. 3. Differentiate factors affecting affinity of hemoglobin to O2.  ILOs By the end of this lecture, students should be able to: 4. Explain effect of carbon monoxide poisoning. 5. Explain the changes in red blood corpuscles as blood flow in systemic and pulmonary capillaries.  Oxygen transport by the blood ❖ Oxygen is transported by the blood in 2 forms: 1- Dissolved in plasma (physical 2- Chemically bound with solution) free hemoglobin (chemical combination) 3% of total oxygen 97% of total Oxygen. Amount: Amount: Arterial blood (PO2= 100 mmHg)= 0.3 ml Arterial blood = 19.5 ml O2 / 100 ml blood. O2 / 100 ml blood. Venous blood (PO2= 40 mmHg)= 0.13 Venous blood= 14 ml O2/ 100 ml blood ml/100 ml blood. ferrous Significance: - Oxygen bind with Fe+ in HB molecule by - Determine oxygen pressure or tension in a reversible reaction forming plasma. oxyhemoglobin. a 0 - Affects rate and direction of O2 diffusion. - Not important in supplying O2 to tissues. - O2 in chemical combination has no tension. Binding of Oxygen to Hb is characterized by: ❑The reaction is oxygenation not oxidation. i.e., the iron in heme molecule remains in the reduced form “Fe++ or ferrous iron”. ❑ Hemoglobin molecule binds to 4 molecules of oxygen as follows: Hb + O2 HbO2 (25 % saturation) So HbO2 + O2 HbO4 (50 % saturation) I.ws HbO4 + O2 HBO6 (75 % saturation) I TIME HbO6 + O2 HBO8 (100 % saturation) i I ❑ As Hb binds to O2, it undergo conformational changes which increases its affinity e to bind more O2 till hemoglobin molecule is fully saturated with O2.  ML 02 10ombood Physical chemical Artery 0.3 ml 02 02 HB Oxyhemoglobin looming free Arterial 19 5 mi 02 BI 100 Veinous i o 13 ml 02 100 ml BL Ven 14 ml 02 100 BI HB FeT Q oxygenation oxidation revetsible reaction ❖ Some important definitions: MCA 1- Oxygen capacity: It is the volume of O2 (in ml) 2 02 Or 02 present in chemical combination with Hb in 100ml of blood when Hb is fully saturated with O2. It equals 20 ml O2/ 100 ml blood. Calculation: I When Hb is fully saturated with O2: Each 1 gm of HB can bind to 1.34 ml O2. Normal adult contains 15 gm HB/ 100 ml blood. So, O2 content= 1.34 X 15 = 20 ml O2. ❖ Some important definitions: 2- Oxygen content: It is the volume of O2 (in ml) present in chemical combination with Hb in 100ml of blood.HbNotfullysaturatedwithO2 i) Arterial O2 content is about  19.5 ml O2/100 ml I blood. ii) Venous O2 content is about  14 ml O2 / 100 ml I blood. ❖ Some important definitions: WINsaturation 3- Percentage (%) of Hb with O2: It is the percentage ratio of O2 content to the O2 0 content capacity. 0 saturation 100 capacity i) In arterial blood = 97.5%. ii) In venous blood = 70%. 14 20 100 70 ❖ N.B: Try to solve: If oxygen content is 12 ml/100 ml blood, and oxygen capacity is 20 ml /100 ml blood. i sat 100 What is the % saturation of Hb with oxygen??? 12 100 60 If oxygen capacity is 20ml /100 ml blood, and blood is 75% saturated with O2. What is the oxygen content in 100 ml blood??? 75 con capx1 Sat 1 20 751 15  O2 Dissociation Curve ▪ This curve shows the relation between O2 pressure (tension) PO2& % saturation of Hb with O2. ▪ The curve is normally sigmoid in shape  i.e. S- shaped. sss B A tissue Arteria  Physiological significance of S- shaped curve 1) At pO2 of 100 mmHg (PO2 of arterial blood) : (A) If O2 tension in arterial blood was 100 mmHg (arterial blood)  Hb is 97.5% saturated with O2 this helps adequate O2 supply to the tissues (HB is nearly fully saturated with O2). This also means that , at high O2 tension  hemoglobin has high affinity to O2 (HB saturation with O2). In 2) As pO2 decreases from100 mmHg to 60 mm Hg (B) 0 The affinity of HB to oxygen is high. The percentage saturation of HB with O2 decreases slightly ( about 93% ). I.E: HB is still nearly saturated with O2 It This is important in high altitude ,where PO2 decreases but % saturation of HB with O2 is affected slightly  this enables these persons to get enough O2 from their blood. 3) At PO2 below 60 mmHg : The affinity of HB to oxygen decreases. The curve becomes S – shaped and steep which means that the slight decrease in PO2  produces marked decrease in percentage saturation of HB with O2. 4) At PO2 of 40 mmHg (PO2 of venous blood ) : V At O2 tension in venous blood during the rest  Hb is 70% 5 saturated  this means that a tissues take 25% of O2 of arterial blood at rest (Coefficient of O2 utilization). 5) At PO2 below 40 mmHg(during muscular exercise): The affinity of HB to oxygen decreases markedly (dissociation). The curve becomes steeper (vertical) ; this helps in supplying more oxygen to active muscles. defeislise HBbading 25  Factors affecting the oxy-hemoglobin dissociation curve Factors that shift the curve to right Factors that shift the curve to left ❖ Shifting to right means  Hb gives more O2 ❖ Shifting to the left means  increased to the tissues (i.e unloading). affinity of Hb to O2 (i.e loading). ❖ These factors decrease affinity of Hb to O2. ❖ These factors increase affinity of Hb to O2. 1) Increased H+ concentration(acidosis). 1) Decreased H+ concentration(alkalosis). 2) Increased partial pressure of CO2. 2) Decreased partial pressure of CO2. 3) Increased temperature. 3) Decreased temperature. 4) Increased 2,3 DPG. 4) Decreased 2,3 DPG. 5) Carbon monoxide poisoning. NB: These changes occur when tissue activity increases (as in muscular exercise) 6) Fetal hemoglobin.  Significance of determining PO2 50 ❑Def: It is the PO2 at which hemoglobin is 50 % saturated with O2 ❑NL = 27 mm Hg ❑It is used as index for the affinity of hemoglobin to O2 ❑The more the affinity of hemoglobin to O2 the lower PO250 and vice versa  Factors affecting O2 dissociation curve ❑If PO2 50 is decreased: this means affinity of HB to bind O2 is increased ( shift the curve to the left). ❑If PO2 50 is increased: this means affinity of HB to bind O2 is decreased ( shift the curve to the right).  Carbon monoxide(CO)poisoning II CO is very toxic product (from incomplete combustion ofsee coal), as: ❑The affinity of hemoglobin to CO is 200 times than that of oxygen ❑When CO binds to hemoglobin , it forms carboxy-hemoglobin which can not carry oxygen ❖Carboxy-hemoglobin shifts the curve to the left. ❖When 70% of hemoglobin is changed to carboxyhemoglobin , death occurs.  2.CO2 Transport ▪ The arterial Co2 content is about 48 ml/100 ml of blood. ▪ The venous content of Co2 is 52 ml/100 ml of blood. ▪ This means that as blood passes in capillaries , Each 100 ml blood accept 4 ml CO2. ▪ These 4 ml of CO2 are called tidal CO2, which are added by tissue to venous blood. ▪ This tidal CO2 should be buffered , unless it could produce fatal drop in blood PH. CO2 + H20 H2CO3 H+ + HCO3- ▪ This reaction is catalyzed by carbonic anhydrase enzyme (present only in RBCs).  Forms of tidal CO2 transport in venous blood 1. Dissolved in physical solutions (5%) : It is dissolved in the plasma & RBCs. It is called free CO2. It determines CO2 tension (pCO2). 2. In Chemical combination (95%): a. Bicarbonate (90%): (The major form of CO2 transport) ▪ NaHCO3 in plasma. soldium bicarbonate ▪ KHCO3 in RBCs. Potassium bicarbonate b. Carbamino compounds (5%). formed by binding of CO2 with free amino groups in proteins as Hb& plasma proteins.  Chloride Shift Phenomenon A. At tissues: CO2 diffuse from the cells → tissue fluid →plasma →RBCs In RBC: 1) CO2 reacts with water, in the presence of carbonic anhydrase enzyme, to produces H+ and HCO-3 ions. 2) Bicarbonate increases and diffuses into plasma in exchange with chloride. 3) As bicarbonate and chloride ions increase inside RBCs , water moves by osmosis from the plasma to inside RBCs. 4) So, the size of RBCS in venous blood is more than that in arterial blood. 5) PH slightly decreased in RBCs and venous blood than arterial blood B. At lung: The whole process is reversed. attend  A weak acid  Effects of chloride shift at the tissues RBC Plasma HCO3- Increases Increases Chloride ions Increases Decreases Water - (Water shift): Water diffuses into RBCs from the plasma due to increased osmolality of RBCs (by increased HCO3- & Cl- ions). -This causes increased size of RBCs in venous blood than arterial blood. pH - The pH of venous blood is slightly less than the arterial blood. - Due to small amount of physically dissolved CO2 which is not buffered. THANK YOU.  RBCS Plasma HCO2 CI osmotic pressure onstant water cheff RBCS volume Hematocritvalue PH