Transport Of Gases

TRANSPORT OF GASES:

INSPIRED AIR

pO2 pCO2

158 0.3

ALVEOLAR AIR

100 40

ARTERIAL BLOOD

97 -100 40

VENOUS BLOOD.

40 46

O2 HB DISSOCIATION CURVE: 1. Curve relating percentage oxygen saturation of hemoglobin to the pO2. 2. SIGMOID IN SHAPE. 3. Because of binding of one O2 molecule to Hb, increases the affinity for next Hb. Combination of heme in the hemoglobin molecule with O2 increases affinity of second heme for O2. Therefore, affinity of Hb for the fourth O2 molecule is much greater than the first. 1g of HB can combine with 1.34 ml of O2

Factors affecting O2 – Hb DISSOCIATION CURVE: Curve shifted to the right

AFFINITY Between O2 and Hb decreases and O2 can be easily extracted from the blood. Higher pO2 is required for Hb to bind given amount of O2. z z z z z

Acidosis.- respiratory or metabolic Increase in body temperature. Increased 2-3 Di Phospho Glycerate.(2,3-DPG.) Anemia. Exercise.

Bohr’s effect Decreased O2 affinity of hemoglobin with decrease in blood pH unloading of O2 with increase in CO2. Haldane effect Reverse of Bohr’s effect Increase in affinity of O2 to Hb with rise in pH More O2 binds with Hb displacing CO2 O2 – Hb dissociation curve shift to left: MEANS INCREASE AFFINITY OF O2 TO Hb. z z z z z

Increased pH Decreased CO2 Decreased temperature Decreased 2,3, DPG Fetal hemoglobin

Factors affecting 2,3DPG: Decrease Acidosis Stored blood

Increase Anemia Exercise Chronic hypoxia Increased body temperature. High altitude Thyroid hormones

SIGNIFICANCE OF O2- Hb dissociation curve: 1. FLAT TOP PART (70- 100 mm Hg). If pO2 falls from 100 to 70 mm Hg, then HBO2 saturation falls from 97 to 92%.very little change in amount of O2 carried by blood. 2. Steep part, (below 40 mm Hg). When pO2 falls below 40 mmHg, more O2 is released from hemoglobin.

OXYGEN TRANSPORT: Modes of O2 transport: 1. Plasma 2. Hemoglobin. 3. Blood. BLOOD IS THE IDEAL VEHICLE FOR O2 TRANSPORT. IT GIVES MORE O2 TO TISSUES AT LOWER pO2.

pO2 100 mm Hg.

Arterial blood

Venous blood

40

mm

Hg

19 ml% 14 ml%

CO2 transport 1. Plasma 2. Bicarbonate solution 3. Blood Blood is ideal medium for carrying CO2 Venous blood pCO2 46mmHg Alveolar pCO2 40 mmHg

O2 CONTENT Dissolved 0.3ml% Bound to Hb 18.7 ml% Dissolved 0.12 ml% Bound to Hb 13.88ml%.

1. CO2 from dissolved solution and carbamino compound breaks up to liberate CO2 2. HB becomes oxygenated forming oxy-HB----Increase Acidity of cells----CL shift in reverse order----CL comes out of cell 3. HCO3 from plasma enters the cells 4. In RBC s oxy Hb release H that joins with HCO3 forming H2CO3 5. H2CO3 is broken up in RBC into H2O and CO2 6. CO2 is liberated from the lungs.

Plasma a. Dissolved form b. Carbamino compound c. Hydration CO2 + H2O ÙH2CO3ÙH + HCO3

BLOOD

FACTORS AFFECTING CO2 DISSOCIATON CURVE 1. Increase in temp. -----release of O2 from blood----increase take up of CO2 in blood 2. Decrease in O2 causes loading of CO2 NOTE deoxyHb carries more CO2

CHLORIDE SHIFT (HAMBURGER phenomenon) a) Blood passing through capillaries contains more HCO3 content in RBC than plasma b) HCO3 enters plasma from RBC down the concentration gradient.

c) Electrochemical equilibrium is maintained by shift of chloride from plasma into cells d) Cl content of venous content is significantly higher than arterial blood. e) For every One CO2 enters RBC ,there is an increase of HCO3 or CL in the RBC f) RBC takes up water and haematocrit of venous blood is 3 %greater than arterial blood