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Oxygen and Carbon Dioxide transport in the blood.

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Presentation on theme: "Oxygen and Carbon Dioxide transport in the blood."— Presentation transcript:

1 Oxygen and Carbon Dioxide transport in the blood

2 Majority of O2 and CO2 is transported in the blood by: O2 combing with hemoglobin CO2 transformed into bicarbonate (HCO 3 ¯)

3 Hemoglobin and O 2 transport ±99% of O 2 transported in blood is chemically bound to hemoglobin Hemoglobin is a protein found in red blood cells (erythrocytes) Each hemoglobin molecule can hold up to 4 O 2 molecules

4 O 2 combined with hemoglobin = oxyhemoglobin O 2 that is NOT combined with hemoglobin = deoxyhemoglobin

5 Oxyhemoglobin

6 The amount of O2 that can be transported depends on the concentration of hemoglobin Normal, healthy men = 150g/L of blood Normal, healthy women = 130g/L of blood When a hemoglobin molecule is completely saturated with O 2  it can transport 1.34ml of O 2

7 Therefore if hemoglobin if full (100% saturated with O 2 ): Healthy male can transport 200ml of O 2 Healthy female can transport 174ml of O 2 100% saturation occurs at sea level (low altitude)

8 Partial Pressure The amount of O 2 bound to hemoglobin is directly related to the partial pressure of O 2. PO 2 : All gases exert pressure on the walls of their container because the molecules of gas bounce off the walls. Partial pressure is used to describe a mixture of gases. Defined as the pressure that any one gas would exert on the walls of the container if it were the only gas present

9 In the lungs, where the alveoli and capillaries exchange gases, PO 2 is high Therefore O 2 binds instantly to hemoglobin. As the blood circulates to other body tissue  the PO 2 becomes lower Therefore hemoglobin releases O 2 into the tissue because the hemoglobin cant maintain its full capacity of O 2

10 Oxyhemoglobin Dissociation Curve In the alveolar capillaries in the lungs: O2 binding with hemoglobin is called loading Release of O2 from hemoglobin is called unloading Loading & unloading are reversible actions: Deoxyhemoglobin + O2 Oxyhemoglobin

11 Oxyhemoglobin Dissociation Curve An important tool for understanding how our blood carries and releases oxygen. Relates oxygen saturation (SO 2 ) and partial pressure of oxygen in the blood (PO 2 ) Determined by what is called "hemoglobin's affinity for oxygen“  how readily hemoglobin acquires and releases oxygen molecules from its surrounding tissue.

12 Oxygen hemoglobin dissociation curve

13 Oxygen Dissociation Curve Shows the percentage of O 2 that is bound to hemoglobin at each O 2 pressure. The curve is S-shaped with a steep slope between 10 and 60 mmHg and a flat portion between 70 and 100 mmHg. At rest the body’s O 2 requirement is low & only ±25% is unloaded into muscles At intense exercise, PO2 can reach 20mmHg and 90% of O2 is unloaded into muscles 13

14 Significance of the Flat Portion The flat portion of the curve shows that the PO 2 can fall from 100 to 60 mmHg and the hemoglobin will still be 90% saturated with O 2 At pressures above 60mm Hg, the dissociation curve is relatively flat. This means the O 2 content does not change much (even with large changes in the partial pressure of oxygen) E.g. PO2 can fluctuate between 90 – 100mmHg without a large drop in the percentage of hemoglobin that is saturated with O 2 *This is important because there is a drop in PO2 with aging and with climbing high altitudes 14

15 Haemoglobin Saturation at High Values Lungs at sea level: PO2 of 100mmHg haemoglobin is 98% SATURATED Lungs at high elevations: PO2 of 80mmHg, haemoglobin 95 % saturated Even though PO2 differs by 20 mmHg there is almost no difference in haemoglobin saturation. When the PO2 in the lungs declines below typical sea level values, haemoglobin still has a high affinity for O2 and remains almost fully saturated.

16 Significance of Steep Portion PO 2 reductions below 40 mm Hg produce a rapid decrease in the amount of O 2 bound to hemoglobin. When the PO 2 falls below 40 mm Hg, the quantity of O 2 delivered to the tissue cells may be significantly reduced. As PO 2 decrease in this steep area of the curve, the O 2 is unloaded to peripheral tissue as hemoglobin’s affinity for O 2 diminishes. Therefore, small changes in PO2 will release large amounts of O2 from hemoglobin. * This is critical during exercise when O2 consumption is high. 16

17 Haemoglobin Saturation at Low Values

18 Factors that affect the O 2 Dissociation ◦ pH - Change in the blood pH ◦ Temperature- temp increases = the curve moves to the right ◦ Carbon Dioxide – increased PCO 2 18

19 Factors Altering Haemoglobin Saturation

20 Factors Altering Haemoglobin Saturation (Exercise)

21 Example During exercise, the oxyhemoglobin dissociation curve will shift to the RIGHT This is because the pH in the body is decreased (from increased lactic acid) AND Temperature increases during exercise

22 O 2 Transport in muscle Myoglobin: - Protein that binds with O 2 - Found in Skeletal and Cardiac muscle fibers (not in blood) - Acts as a shuttle to transport O 2 from muscle cell membrane to the mitochondria - Found in large quantities in slow-twitch fibers (high aerobic capacity) - Smaller amounts in intermediate fibers - Limited quantity in fast twitch fibers

23 Myoglobin has a similar structure to hemoglobin, but is ¼ weight Difference in structure = difference in affinity for O 2 Myoglobin has a greater affinity for O 2 : Therefore the myoglobin-O 2 dissociation curve is much steeper = myoglobin releases O 2 at very low PO 2 values NB because PO 2 in mitochondria of contracting skeletal muscle can be as low as 1mmHg.

24 Myoglobin stores O 2 = reserve O 2 for transition from rest to exercise At the start of exercise there is a lag time from the onset of muscular contraction and increased O 2 delivery to the muscles Therefore O 2 bound to myoglobin before exercise acts as a buffer  so that muscles can receive O 2 until the cardiopulmonary system can meet the new O 2 demand

25 At the end of exercise: - myoglobin- O 2 stores must be replenished to ensure O 2 is available for the next time exercise begins Therefore O 2 consumption above rest contributes to the O 2 debt i.e. O 2 consumption continues after exercise has stopped  leading to an O 2 debt (O 2 deficit) (Anaerobic metabolism of lactate – also called EPOC  Post Exercise Oxygen Consumption)

26 Carbon Dioxide Transport in Blood CO 2 transported in the blood by: 1. Dissolved CO 2 (±10%) 2. CO 2 bound to hemoglobin (±20%) 3. Bicarbonate (HCO 3 ¯)(±70%)

27 CO 2 is converted to bicarbonate in red blood cells: A high PCO2 causes CO 2 to combine with water, forming carbonic acid. This reaction is rapidly catalyzed by the enzyme Carbonic Anhydrase The carbonic acid then dissociates into bicarbonate ion and hydrogen ion. The hydrogen ion then binds with hemoglobin The bicarbonate ion diffuses out of the red blood cell into the blood plasma

28 Transport of CO 2 Carbon Dioxide Transport H 2 CO 3 CO 2 + H 2 O H 2 CO 3 H + + H - CO 3 CA Carbonic Acid Bicarbonate ion

29 Bicarbonate Ion Exchange Because bicarbonate carries a negative charge (anion), removal of a negatively charged molecule from a cell = electrochemical imbalance Therefore the negative charge must be replaced Bicarbonate is replaced by chloride (Cl¯) which diffuses from the plasma into the red blood cell This is called chloride shift  the shift of anions into red blood cells as blood moves through tissue capillaries

30 When blood reaches the pulmonary capillaries: PCO 2 of the blood is greater than that of the alveolus = CO 2 diffuses out of the blood across the blood-gas interface At the lungs: Binding of O 2 to hemoglobin causes a release of the hydrogen ions (which are bound to hemoglobin) to promote the formation of carbonic acid H + + HCO 3 ¯ H 2 CO 3

31 In conditions where PCO 2 is low (at the alveolus), carbonic acid then dissociates into CO 2 and H 2 O H 2 CO 3 CO 2 +H 2 O The release of CO 2 from the blood into the alveoli is removed from the body in expired gas (CO 2 we breathe out)

32 Revision Questions 1. What is the amount of hemoglobin found in a normal male and female? (2) 2. What is the amount of oxygen carried in a normal male and female? (2) 3. What is partial pressure? (2) 4. Explain the oxghemoglobin dissociation curve, focusing on the use, flat and steep portions (10) 5. What factors affect the oxghemoglobin dissociation curve? (3)

33 Revision Questions 6. How does exercise affect the oxghemoglobin dissociation curve? (3) 7. What is myoglobin and where is it found? (4) 8. How is myoglobin different to hemoglobin? (4) 9. What are the differences in myoglobin and oxygen at the start and end of exercise? Why does this happen? (8) 10. What are the way in which carbon dioxide is transported? (3) 11. How is carbon dioxide converted to bicarbonate? (5) 12. Explain bicarbonate exchange. (8)

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