Interaction Between Co2 & O2 Transport

Interaction Between Co2 & O2 Transport


INTERACTION BETWEEN CO2 & O2 TRANSPORT

Introduction to O2 transport:

  • O2 delivery system consists of,
  • Lungs & cardiovascular system.
  • O2 tissue delivery depends 
  • Amount of Oentering lungs
  • Adequacy of pulmonary gas exchange
  • Ocarrying capacity of blood
  • Blood flow to tissue
Inturn, 

Blood flow to tissue depends:

  • Degree of constriction of  tissue vascular bed
  • Cardiac output

Amount of Oin blood determined:

  • Amount of dissolved O2
  • Amount of hemoglobin in blood 
  • Affinity of hemoglobin for O2

TRANSPORT OF OXYGEN (O2)

  • Mechanism by which atmospheric oxygen is provided to tissues.
  • Has 3main components-
  • Oxygen trap –
  • Entrapment of oxygen by pulmonary capillaries from alveoli.
  • Transport of oxygen in blood
  • Transfer of oxygen from blood

1. Oxygen trap:

  • Oxygen diffuses into blood & combines with hemoglobin
  • Diffused oxygen does not contribute to blood PO2
  • Hence, alveolar-capillary gradient of PO2 is maintained much longer (provided, hemoglobin were not present)
  • Presence of hemoglobin makes an enormous difference to amount of oxygen transferred. 
  • By mopping up oxygen without letting PO2 rise, lets diffusion of oxygen continue much longer. 
  • PO2 gradient determines direction of oxygen diffusion
  • Hemoglobin lays trap for carrying large amounts of oxygen in blood.

2. Oxygen transport:

  • Orygen traped by hemoglobin in alveoli travels in blood in 2 forms – 
  • In dissolved form in plasma
  • In association with hemoglobin (as Oxyhemoglobin)

2a) Dissolved form:

  • Amount of O2 transported in dissolved form – 1.5 – 3% (0.3 ml/100 ml) of total amount transported
  • With higher PO2, unlimited O2 carried in dissolved form 
  • Concentration of dissolved O2  is directly proportional to PO2)

2b) As oxyhemoglobin:

  • Bulk of oxygen (97%) in blood is normally transported as Oxyhemoglobin
Oxyhemoglobin content:
  • Hemoglobin concentration in normal blood is about 15g/dl (15 g/100ml).
  • Each gram of hemoglobin normally carries 1.34 ml of O2
  • Hence,1 dl (100ml) of blood contains 20.1 ml (1.34 ml x 15) of oxyhemoglobin.
  • Hemoglobin in systemic arterial blood is only 97% saturated.
  • Hence, arterial blood contains a total of about 19.8 ml of O2/dl
At rest:
  • Tissues remove about 4.6 ml of O2 each deciliter of blood passing through them.
  • Hence, 230 ml (by 5 liters of blood) of O2 per minute is transported from blood to tissue, at rest.
3. Oxygen transfer:
  • Transfer from blood to tissue takes place in tissue capillaries.
  • Driving force is partial pressure gradient
  • Diffusion of O2 from capillaries to tissue – 
  • Along pressure gradient.

PO2

  • At arterial end of capillaries – about 95 mm Hg
  • At tissues – about 40 mm Hg.
TRANSPORT OF CARBON DIOXIDE (CO2):
  • COelimination mechanism is a reversal of O2.
Steps:
  • COtransfer – 
  • CO2 collected from tissue capillaries
  • COTransport – Venous blood
  • Expulsion – Via lungs.
1. CO2 transfer:
  • Accumulation of CO2 from tissue capillaries.
  • Driving force is partial pressure gradient
  • PCO2 –
  • In tissues – 46 mm Hg
  • At arterial end of capillaries – 40 mm Hg. 
  • Hence, CO2 diffuses from tissues to capillaries

2. CO2 transport in blood:

Blood transport 3 forms of CO2:

  • As bicarbonate
  • As carbamino compounds of hemoglobin 
  • As dissolved CO2.

Metrics:

  • 100 ml (1 dl) of blood takes away 4 ml of CO2.
  • 100 ml (1 dL) of venous blood carries 53 ml of CO2
  • 100 ml (1 dL) of arterial blood carries 49 ml of CO2.
  • (53 – 49 ml) from tissues.
  • Hence, 5L of blood transports 200 ml of CO2 from the tissues each minute

2a) As plasma bicarbonate

  • Major mechanism of CO2 transport,
  • 7O%  of CO2 transport.
  • RBCs play a major role,
  • Enzyme carbonic anhydrase catalyzes reaction generating HCO3– ions.

Chloride shift/Hamburger phenomenon:

  • Movement of chloride ions into RBC,
  • HCO3 ions generated diffuse out into plasma in exchange for Cl ions.
  • Diffuse into RBCs simultaneously.

Hematocrit value: 

  • For venous blood is normally 3% > arterial blood
  • Due to increased osmolarity and larger ionic concentration within RBC of venous blood.
2b) As carbamino compounds
  • 20% of CO2 transport.
  • CO2 binds to hemoglobin & other plasma proteins forming carbamino compounds.
  • Carbhemoglobin is major carbamino compound in blood.
  • Since hemoglobn is abundant protein in blood.
Haldane effect:
  • Binding of O2 reduces affinity of hemoglobin to CO2.
  • Deoxyhemoglobin binds more H+ ions than oxyhemoglobin.
  • Forms carbamino compounds more readily.
  • Hence, venous blood carries more CO2 than arterial blood.
  • Facilitating tissue CO2 uptake &release into lungs.

2c) As dissolved form

  • Volume of dissolved CO2 is proportional to PCO2
  • Accounts only 6-7% of total volume carried in blood.

3. EXPULSION OF CO2:

  • CO2 is removed from pulmonary capillaries by diffusion. 
  • PCO2 – 
  • Venous blood – 45 mm Hg 
  • Alveolar air – 40 mm Hg. 
  • CO2 diffuses along pressure gradient from alveolar capillaries into alveoli. 
  • COfinally expelled from alveoli during expiration.
  • 200 ml of CO2 per minute at rest is transported from tissues to lungs & excreted.
Exam Question
 

INTERACTION BETWEEN CO2 & O2 TRANSPORT

O2 tissue delivery depends 

  • Amount of Oentering lungs
  • Adequacy of pulmonary gas exchange
  • Ocarrying capacity of blood
  • Blood flow to tissue
Inturn, 

Blood flow to tissue depends:

  • Degree of constriction of  tissue vascular bed
  • Cardiac output

Amount of Oin blood determined:

  • Amount of dissolved O2
  • Amount of hemoglobin in blood 
  • Affinity of hemoglobin for O2

TRANSPORT OF OXYGEN (O2)

1. Oxygen trap:

  • Oxygen diffuses into blood & combines with hemoglobin.
  • Hemoglobin lays trap for carrying large amounts of oxygen in blood.

2. Oxygen transport:

  • Orygen traped by hemoglobin in alveoli travels in blood in 2 forms – 
  • In dissolved form in plasma
  • In association with hemoglobin (as Oxyhemoglobin)

2a) Dissolved form:

  • Amount of O2 transported in dissolved form – 
  • 1.5 – 3% (0.3 ml/100 ml) of total amount transported
  • With higher PO2, unlimited O2 carried in dissolved form 
  • Concentration of dissolved O2  is directly proportional to PO2

2b) As oxyhemoglobin:

  • Bulk of oxygen (97%) in blood is normally transported as Oxyhemoglobin
Oxyhemoglobin content:
  • Hemoglobin concentration in normal blood is about 15g/dl (15 g/100ml).
  • Each gram of hemoglobin normally carries 1.34 ml of O2
  • Hence,1 dl (100ml) of blood contains 20.1 ml (1.34 ml x 15) of oxyhemoglobin.
  • Hemoglobin in systemic arterial blood is only 97% saturated.
  • Hence, Arterial blood contains a total of about 19.8 ml of O2/dl

At rest:

  • Tissues remove about 4.6 ml of O2 each deciliter of blood passing through them.
  • Hence, 230 ml (by 5 liters of blood) of O2 per minute is transported from blood to tissue, at rest.
3. Oxygen transfer:
  • Diffusion of O2 from capillaries to tissue – Along pressure gradient.
  • PO2
  • At arterial end of capillaries – about 95 mm Hg
  • At tissues – about 40 mm Hg.
TRANSPORT OF CARBON DIOXIDE (CO2):
1. CO2 transfer:
  • Driving force is partial pressure gradient.
  • PCO2 –
  • In tissues – 46 mm Hg
  • At arterial end of capillaries – 40 mm Hg. 
  • Hence, CO2 diffuses from tissues to capillaries

2. CO2 transport in blood:

  • As bicarbonate

Metrics:

  • 100 ml (1 dl) of blood takes away 4 ml of CO2.
  • Hence, 5L of blood transports 200 ml of CO2 from the tissues each minute

2a) As plasma bicarbonate

  • 7O%  of CO2 transport – Major mechanism of CO2 transport.
  • Enzyme carbonic anhydrase catalyzes reaction generating HCO3– ions in RBC
  • Chloride shift/Hamburger phenomenon:
  • Movement of chloride ions into RBC.
  • HCO3 ions generated diffuse out into plasma in exchange for Cl ions.

Hematocrit value: 

  • For venous blood is normally 3% > arterial blood. 
  • Carbhemoglobin is major carbamino compound in blood.
Haldane effect:
  • Binding of O2 reduces affinity of hemoglobin to CO2.Deoxyhemoglobin binds more H+ ions than oxyhemoglobin and forms carbamino compounds more readily.
  • Hence, venous blood carries more CO2 than arterial blood facilitating tissue CO2 uptake &release into lungs.

3. Expulsion of CO2:

  • CO2 is removed from pulmonary capillaries by diffusion. 
  • PCO2 –
  • Venous blood – 45 mm Hg 
  • Alveolar air – 40 mm Hg.
  • CO2 diffuses along pressure gradient from alveolar capillaries into alveoli. 
  • 200 ml of CO2 per minute at rest is transported from tissues to lungs & excreted.
  • Don’t Forget to Solve all the previous Year Question asked on Interaction Between Co2 & O2 Transport

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