OXYGEN(O2) & CARBONDIOXIDE(CO2) GAS TRANSPORT OXYGEN(O2) & CARBONDIOXIDE(CO2)

Gas Transport O2 which is taken up by the blood at the lungs is transported to the tissues for use by the cells. CO2 produced at the cell level is transported to the lungs for elimination.

Oxygen (O2) Transport Most of the O2 in the blood is transported bound to hemoglobin. Method of O2 Transport Chemically bound to Hemoglobin – 98.5% Physically Dissolved in plasma – 1.5%

Oxygen Transport Most O2 in the blood is transported bound to hemoglobin. Method of O2 Transport Chemically bound to Hemoglobin – 98.5% Physically Dissolved in plasma – 1.5%

Oxygen Transport Hb is present inside red blood cells [RBC]. Hb is iron bearing protein molecule. It makes reversible combination with oxygen. When Hb combines with O2, we call Oxyhemoglobin [HbO2]. Hb + O2  HbO2 When O2 not combined with Hb, we call it reduced Hemoglobin or Deoxyhemoglobin.

Gas Transport Hemoglobin promotes the net transfer of oxygen at both the alveolar and tissue levels. There is a net diffusion of oxygen from the alveoli to the blood. This occurs continuously until hemoglobin is as much saturated as possible (97.5% at PO2 of100 mm of Hg). At the tissue cells hemoglobin rapidly delivers oxygen into the blood plasma and on to the tissue cells. Various factors promote this unloading.

Factors producing unloading of O2: An increase in carbon dioxide from the tissue cells into the systemic capillaries increased hemoglobin dissociation from oxygen (shifts the dissociation curve to the right). Increased acidity has the same effect. This shift of the curve to the right (more dissociation) is called the Bohr effect. Higher temperatures also produces this shift, as does the production of BPG. Hemoglobin has more affinity for carbon monoxide as compared to oxygen.

CO POISONING Hemoglobin has more affinity for carbon monoxide(240 times) as compared to oxygen. CO a poisonous gas, liberated by burning of carbon products, eg. automobile gasoline, coal, wood & tobacco. Not detected, because it is colorless, odorless & non irritating and may be lethal.

Oxygen-Hemoglobin (O2-Hb) dissociation(or saturation) curve

Factors at the tissue level promoting the unloading of O2 from Hb (Summary) Shifting of O2 dissociation curve to right or more dissociation [giving] of O2 to tissues or less affinity of O2 for Hb. The factors are 1- Increase PCO2 2- Increase Acidity [increase H+ ion] 3- Increase Temperature 4- Increase 2,3-BPG [bisphosphoglycerate] or 2,3-DPG [diphosphoglycerate]

CO2 Transport CO2 is transported in the blood by three ways: 1. Physically dissolved in Plasma- 10% 2. Bound to Hb- 30% Carbamino-Hb(Hb-CO2) 3. As Bicarbonate- 60%

CO2 Transport Most carbon dioxide (about 60%) is transported as the Bicarbonate Ion. Carbon dioxide combines with water to form carbonic acid. The enzyme carbonic anhydrase facilitates this in the erythrocyte. Carbonic acid dissociates into hydrogen ions and the bicarbonate ion. 2-step, reversible process is favored at the tissue cells. The reverse of this process (bicarbonate ions forming free molecules of carbon dioxide) occurs in the lungs. 30% of the carbon dioxide is bound to hemoglobin in the blood. This is another means of transport. About 10% of the transported carbon dioxide is dissolved in the plasma.

Gas Transport Most carbon dioxide (about 60%) is transported as the Bicarbonate Ion. By the chloride shift, the plasma membrane of the erythrocyte passively facilitates the diffusion of bicarbonate ions (out of the red cell) and chloride ions (inside of the red cell). By the Haldane effect the removal of oxygen from hemoglobin at the tissue cells increases the ability of hemoglobin to bind with carbon dioxide.

Abnormalities in Arterial PO2 Hypoxia Condition of having insufficient O2 at the cell level Categories Hypoxic hypoxia (low arterial blood PO2) eg. high altitude, inadequate gas exchange Anemic hypoxia (reduced O2 carrying capacity of blood) eg. Less RBC /Hb, CO poisoning Circulatory hypoxia(too little oxygenated blood is delivered to tissue); Stagnant hypoxia eg. congestive heart failure or circulatory shock Histotoxic hypoxia (inability of cells to use O2) eg. cyanide poisoning Hyperoxia condition of having an above-normal arterial PO2 Can only occur when breathing supplemental O2 Can be dangerous

Abnormalities in Arterial PCO2 Hypercapnia Condition of having excess CO2 in arterial blood Caused by hypoventilation Hypocapnia Below-normal arterial PCO2 levels Brought about by hyperventilation which can be triggered by Anxiety states Fever Aspirin poisoning

Things to be learn from this lecture Gas transport Methods of O2 transport Role of hemoglobin (Hb)in O2 transport O2-Hb dissociation curve Factors affecting Hb-O2 dissociation curve Methods of CO2 transport Abnormalities of PO2 & PCO2