Transport of O2 and CO2Transport of O2 and CO2

AS LevelAS Level

O2 gas in the inhaled air

O2 dissolved in bloodstream

O2 transported

O2 dissolved in tissue

O2 used in the metabolism of glucose and the synthesis of ATP

The primary goal of respiration is to absorb O2 from the environment to fuel the body’s metabolism

Movement of O2 in the body is a result of its diffusion

• The pressure of a gas is proportional to its density of molecules and temperature

• In a mixture of gas, we refer to the density of any single molecular species as its partial pressure

• If a solution of dissolved O2 is at equilibrium with the adjoining air, the pO2 of the solution is the same as that of the air

Diffusion occurs because:

• The principle of diffusion: the gas will diffuse from a point of high partial pressure towards a point of low partial pressure

• pO2(air)>pO2(interstitial fluid)>pO2(blood plasma)

Oxygen O2

• 98% travels in oxyhaemoglobin (in red blood cells)

• 2% is dissolved in plasma

O2 is not very soluble – thus needs a carrier !

REMEMBER

Concentration of dissolved oxygen is often referred as the

PARTIAL PRESSURE TENSION

How is oxygen carried ? HAEMOGLOBIN

• Complex protein containing haem (iron)

• 1 molecule of haem combines with 4 molecules of oxygen to form oxyhaemoglobin

Hb + O2 HbO8

Haemoglobin oxygen oxyhaemoglobin

This reaction is reversible.

Cooperativity

• The haemoglobin molecule is a tetramer composed of 4 protein subunits, each of which can bind a single molecule to O2

• These subunits exhibit cooperativity when they bind to O2

• i.e. the binding of O2 to any subunits increases the likelihood that the other subunits will bind to O2

Release of O2

• The release of O2 begins because metabolically active tissue cells have consumed much of the O2 from the interstitial fluid around them

• i.e pO2 (interstitial fluid)> pO2 (blood plasma)

O2 diffuses out of the capillary – release of O2

bounded to haemoglobin

This property is called an

OXYGEN DISSOCIATION CURVE

Haemoglobin combines with oxygen when itis abundant and then releases it when theconcentration falls.

The cooperativity of O2 binding tohaemoglobin influences how much of theblood O2 is delivered to any particular tissue.

OXYGEN DISSOCIATION CURVE

• Shows the amount of O2 that is bound to haemoglobin (Y-axis) as a function of the partial pressure of O2 in the blood plasma (X-axis).

• Because of the cooperativity, this dissociation curve is S-shaped

OXYGEN DISSOCIATION CURVE

Bohr Effect or Bohr Shift

Niels Henrik David Bohr

Born: 7 Oct 1885 in Copenhagen, DenmarkDied: 18 Nov 1962 in Copenhagen, Denmark

Carbon Dioxide (CO2)

• 70% travels as HCO3- ions

(hydrogencarbonate ions)

• 23% travels as carbamino compounds

• 7% in plasma

In red blood cells

CO2 = waste product of cellular metabolism

About 70% of the blood

CO2 reacts with H2O to form carbonic acid

CO2 + H2O H2CO3

Carbonic acid rapidly dissociates into

H2CO3 H+ + HCO-3

ion H+ and bicarbonate ion

Carbonic anhydrase

Bohr ShiftBohr Shift

H2CO3

H+

Trapped in cytoplasm

acidification in the red blood cell

Bohr Shift

HCO-3

Leaves the red blood cell

CO2 enters

the blood

Tissues

With high level of activity

Hb affinity with O2

Release of O2

Bohr Effect or Bohr Shift

• The dissociation curve moves to the right at higher concentration of carbon dioxide. This shows that carbon dioxide lowers the affinity of Hb for oxygen.

• This means that when carbon dioxide concentration is higher, Hb does not hold on to its oxygen quite as well.

• Hb tends to give up O2 in area of high CO2 such as the respiring tissues that need it most.

Effect of pH (temperature = 38oC)Effect of pH (temperature = 38oC)

84 12

Normal acidity pH 7.4

pH 7.2 - low blood pH (High CO2)

High blood pH (Low CO2)

pH 7.6

Sat

urat

i on

of h

aem

oglo

bin

( %)

PO2/KPa

Foetal haemoglobin has a higher affinity for oxygen than adult haemoglobin.

This means that the foetus can receive oxygen from the mother across the placenta.

Foetal haemoglobin

Myoglobin is a pigment found in muscles, particularly in legs and heart muscles of mammals

Like Hb, myoglobin can reversibly bind O2 (only one), it acts like a temporary store of oxygen

Myoglobin

CO has a higher affinity with haemoglobin than O2 with haemoglobin

Example of Full Monty

Example of altitude Example of Fish

Hope this presentationwasn’t

Bohring