This document summarizes oxygen and carbon dioxide transport in the blood. It states that oxygen is transported in the blood in two forms: 1.5% dissolved in plasma and 98.5% bound to hemoglobin in red blood cells. Hemoglobin binds oxygen reversibly through an iron-containing heme group. The binding and release of oxygen depends on factors like partial pressure of oxygen, acidity, temperature, and partial pressure of carbon dioxide. Carbon dioxide is transported in three forms: 7% dissolved in plasma, 23% bound to hemoglobin as carbamino compounds, and 70% transported as bicarbonate ions through a series of reactions catalyzed by carbonic anhydrase.

1. Ms.Anu Sebastian: B.Pharm; M.Pharm
Assistant Professor,
Dept. Of Pharmacology
Nirmala College Of Pharmacy
Muvattupuzha,Ernakulam,Kerala

2.  Blood transports gases between the lungs & body tissues.
 When O2 and CO2 enter the blood, certain chemical reactions
occur that aid in gas transport & gas exchange.
OXYGEN TRANSPORT
 Oxygen does not dissolve easily in water, so only about 1.5% of
inhaled O2 is dissolved in blood plasma, which is mostly water.
 About 98.5% of blood O2 is bound to hemoglobin in red blood
cells.
 The heme portion of hemoglobin contains four atoms of iron,each
capable of binding to a molecule of O2.

3.  Oxygen & hemoglobin bind in an easily reversible reaction to
form oxyhemoglobin.
Hb + O2 ↔ Hb − O2
(Reduced Hb) (Oxygen) (Oxyhemoglobin)
 The 98.5 % of the O2 that is bound to hemoglobin is trapped
inside RBCs, so only the dissolved O2 (1.5%) can diffuse out of
tissue capillaries inti tissue cells.
 The binding & dissociation of oxygen from haemoglobin depends
on:
 Partial pressure of oxygen
 The higher the the PO2 ,the more O2 combines with Hb.

4.  When reduced Hb is completely converted to oxyhemoglobin
(Hb—O2), the hemoglobin is said to be fully saturated; when
hemoglobin consists of a mixture of Hb & Hb– O2 , it is partially
saturated.
 For eg: If each hemoglobin molecule has bound to two O2
molecules, then the hemoglobin is 50% saturated because each Hb
can bind a maximum of four O2.
 Acidity(pH)
 As acidity increases(pH decreases), the affinity of hemoglobin for
O2 decreases & O2 dissociates more readily from haemoglobin.
 Therefore. More oxygen is available to the metabolically active
tissues which produce acids.Eg:, Lactic acid,carbonic acid, etc..

5.  Temperature
 If the body temperature increases, oxygen dissociates more readily
from hemoglobin. Hence more amount of oxygen is available for
active tissues which liberate heat due to metabolic reactions.
 Partial pressure of carbon dioxide
 CO2 also can bind to hemoglobin. As PCO2 rises, hemoglobin
release O2 more readily.
 PCO2 & pH are related factors because low blood pH(acidity)
result from high PCO2.

6.  As CO2 enters blood, much of it is temporarily converted to
carbonic acid(H2CO3), a reaction catalyzed by an enzyme in
red blood cells called carbonic anhydrase(CA):
CO2 + H2O H2CO3 H+ + HCO3 –
 The carbonic acid thus formed in red blood cells dissociates
into hydrogen ions & bicarbonate ions.
 As the H+ concentration increases , pH decreases. Thus an
increased PCO2 produces a more acidic environment which
helps release O2 from hemoglobin.

7. Fig: Transport of gases

8. CARBON DIOXIDE TRANSPORT
 CO2 produced by the body cells as a metabolic waste
product is transported in the blood in three forms:
(I) Dissolved Oxygen
 The smallest percentage(7%) is dissolved in blood
plasma. On reaching the lungs, it diffused into alveolar
air & is exhaled
 (II) Carbamino compounds : about 23%, combines with
the amino groups of aminoacid & proteins in the blood to
form carbamino compounds.

9.  The main CO2 binding sites are the terminal aminoacids in the
two alpha & two beta chains.
 Haemoglobin that has bound CO2 is termed as
carbaminohemoglobin( Hb–- CO2) :
Hb + CO2 Hb – CO2
(Hemoglobin) (Carbaminohemoglobin)
(III) Bicarbonate Ions: Most of the C)2( about 70%) is
transported as bicarbonate ions in the blood.
 As CO2 diffuses into systemic capillaries & enters red blood
cells, it reacts with water in the presence of the enzyme
Carbonic anhydrase (CA) to form carbonic acid, which
dissociates into H+ & HCO3

10.  CO2 + H2O H2CO3 H+ + HCO3
 Thus as blood picks up CO2 ,HCO3- accumulates inside
RBCs. Some moves out into the blood plasma, in
exchange Cl- ions move from plasma into the RBCs.
 The net effect of these reactions is that CO2 is removed
from tisssue cells & transported in blood plasma as
HCO3- .As blood passes through pulmonary capillaries
in the lungs, all these reactions reverse & CO2 is exhaled.

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