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 O₂entering lungs

Adequacy of pulmonary gas exchange

O₂carrying capacity of blood

Blood flow to tissue

Inturn,

Blood flow to tissue depends:

Degree of constriction of tissue vascular bed

Cardiac output

Amount of O₂in 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 PO_2,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):

CO₂elimination mechanism is a reversal of O₂.

Steps:

CO₂transfer –

CO₂ collected from tissue capillaries

CO₂Transport – 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 CO_2.

– 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 CO_2.

– 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.

CO₂finally expelled from alveoli during expiration.

200 ml of CO₂ per minute at rest is transported from tissues to lungs & excreted.

Exam Important

INTERACTION BETWEEN CO₂ & O₂ TRANSPORT

O₂ tissue delivery depends

Amount of O₂entering lungs

Adequacy of pulmonary gas exchange

O₂carrying capacity of blood

Blood flow to tissue

Inturn,

Blood flow to tissue depends:

Degree of constriction of tissue vascular bed

Cardiac output

Amount of O₂in 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 PO_2,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