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R E S P I R A T O R Y S Y S T E M GAS EXCHANGE
PULMONARY GAS EXCHANGE <ul><li>The movement of O 2  and CO 2  in and out of the capillaries both in the lungs and in the p...
GAS EXCHANGE IN THE LUNGS <ul><li>Gas exchange in the lungs depends on the partial pressure gradients between alveolar air...
GAS EXCHANGE IN THE LUNGS <ul><li>Although the average total pressure in the alveoli is equal to that in the atmosphere, a...
 
PULMONARY BLOOD GASES <ul><li>Gas diffusion gradients in the lung are determined by the differences between the partial pr...
 
PULMONARY BLOOD GASES <ul><li>Venous blood is mixed in the right ventricle, giving a PO 2  in the pulmonary arteries of 40...
PULMONARY BLOOD GASES <ul><li>Carbon dioxide, also driven by a partial pressure gradient, diffuses in the opposite directi...
 
PULMONARY BLOOD GASES <ul><li>Gas diffusion across the combined alveolar and capillary wall system is rapid, so that pulmo...
PULMONARY DIFFUSION <ul><li>Pulmonary gases must diffuse through several structures between the alveoli and the capillary ...
 
GAS EXCHANGE IN PERIPHERAL TISSUES <ul><li>The pressure gradients driving peripheral gas exchange are kept constant, with ...
GAS TRANSPORT IN BLOOD <ul><li>Both O 2  and CO 2  are transported between the lungs and the tissues in the blood.  </li><...
OXYGEN DISSOCIATION CURVE <ul><li>This sigmoid, or S-shaped curve describes the relationship between the partial pressure ...
 
CARBON DIOXIDE TRANSPORT <ul><li>Carbon dioxide is carried in three main forms in the blood: </li></ul><ul><li>Transport a...
 
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27. respiratory 2-07-08

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Transcript of "27. respiratory 2-07-08"

  1. 1. R E S P I R A T O R Y S Y S T E M GAS EXCHANGE
  2. 2. PULMONARY GAS EXCHANGE <ul><li>The movement of O 2 and CO 2 in and out of the capillaries both in the lungs and in the peripheral tissues depends on gas diffusion. </li></ul><ul><li>Diffusion is driven by partial pressure gradients. </li></ul><ul><li>The lungs are well adapted for gas diffusion, with a very large alveolar surface area and a very thin layer of fluid and tissue separating alveolar gas from pulmonary blood. </li></ul>
  3. 3. GAS EXCHANGE IN THE LUNGS <ul><li>Gas exchange in the lungs depends on the partial pressure gradients between alveolar air and pulmonary arterial blood for O 2 and CO 2 . </li></ul><ul><li>Effective gas exchange also requires easy diffusion between alveoli and blood and an appropriate balance between ventilation and perfusion within the lungs . </li></ul>
  4. 4. GAS EXCHANGE IN THE LUNGS <ul><li>Although the average total pressure in the alveoli is equal to that in the atmosphere, alveolar air differs from the air we breathe (the inspirate) in a number of ways. </li></ul><ul><li>Firstly, it has a higher water vapour pressure, since the inspired gases become fully saturated as they pass through the airways. </li></ul><ul><li>The other major differences reflect constant removal of O 2 by diffusion into the pulmonary blood and constant addition of CO 2 from the same source. This reduces the PO 2 and elevates the PCO 2 as compared with humidified air. </li></ul><ul><li>The limits the maximum possible alveolar PO 2 to about 150 mmHg. </li></ul><ul><li>Normally ventilation is homeostatically regulated so that alveolar PO 2 and PCO 2 remain relatively constant. </li></ul>
  5. 6. PULMONARY BLOOD GASES <ul><li>Gas diffusion gradients in the lung are determined by the differences between the partial pressures within the alveoli and those within the pulmonary capillaries. </li></ul><ul><li>Pulmonary arterial blood entering the capillaries contains partial pressures of O 2 and CO 2 , which are determined by the levels in systemic veins from peripheral tissues. </li></ul>
  6. 8. PULMONARY BLOOD GASES <ul><li>Venous blood is mixed in the right ventricle, giving a PO 2 in the pulmonary arteries of 40 mmHg and a PCO 2 of 45 mmHg. </li></ul><ul><li>Since the PO 2 in the alveoli is 103 mmHg, O 2 diffuses into the pulmonary blood. </li></ul>
  7. 9. PULMONARY BLOOD GASES <ul><li>Carbon dioxide, also driven by a partial pressure gradient, diffuses in the opposite direction, from the capillaries (PCO 2 = 45 mmHg) into the alveoli (PCO 2 = 40 mmHg). </li></ul>
  8. 11. PULMONARY BLOOD GASES <ul><li>Gas diffusion across the combined alveolar and capillary wall system is rapid, so that pulmonary blood normally equilibrates with alveolar gases before leaving the pulmonary capillary. </li></ul><ul><li>Thus, the gas pressures in pulmonary venous blood equal those in the alveoli. </li></ul>
  9. 12. PULMONARY DIFFUSION <ul><li>Pulmonary gases must diffuse through several structures between the alveoli and the capillary blood. The total thickness of the diffusion barrier can be as little as 0.2 nm. </li></ul><ul><li>Coupled with the large alveolar surface area (about 70 m2), this short diffusion distance makes the lungs very efficient gas exchange units, i.e. they have a high diffusion capacity. </li></ul>
  10. 14. GAS EXCHANGE IN PERIPHERAL TISSUES <ul><li>The pressure gradients driving peripheral gas exchange are kept constant, with a PO 2 of about 98 mmHg and a PCO 2 of 40 mmHg. </li></ul><ul><li>Tissue gas pressures may vary widely from organ to organ and time to time, depending on the balance between blood flow and local metabolic activity, which consumes O 2 and produces CO 2 . </li></ul>
  11. 15. GAS TRANSPORT IN BLOOD <ul><li>Both O 2 and CO 2 are transported between the lungs and the tissues in the blood. </li></ul><ul><li>The majority of the O 2 in blood is transported within red cells and is bound to haemoglobin, with only a negligible additional amount dissolved in the plasma. </li></ul><ul><li>The normal haemoglobin concentration is about 15 g/dl in males and 13 g/dl in females. </li></ul><ul><li>Since each gram of haemoglobin can carry 1.34 ml of O 2 . </li></ul>
  12. 16. OXYGEN DISSOCIATION CURVE <ul><li>This sigmoid, or S-shaped curve describes the relationship between the partial pressure of O 2 and the concentration of O 2 in blood. </li></ul>
  13. 18. CARBON DIOXIDE TRANSPORT <ul><li>Carbon dioxide is carried in three main forms in the blood: </li></ul><ul><li>Transport as bicarbonate ions (HCO 3 ) accounts for about 60-70% of the total CO 2 carried in the blood. The gas diffuses into the red blood cells where it reacts with water to form carbonic acid. </li></ul><ul><li>Transport as carbamino groups are formed by a reaction between CO 2 and amino acid residues in peptides and proteins. About 20-30% of circulating CO 2 is in this form. </li></ul><ul><li>Transport as dissolved CO 2 . This only accounts for about 10% of the total CO 2 transport. </li></ul>
  14. 20. Thank You For Your Attention!
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