The transport of oxygen in blood- Haemoglobin

• Hb + 4O2 → Hb(O2)4

• Over 95% of O2 is carried in this way

• Red blood cell (erythrocyte)

Adaptation of RBC in transport of gases

• Lack a nucleus

• Biconcave disc

Haemoglobin4 x Haem group + 4 x Polypeptide chain

The transport of oxygen in blood

The myogenic control of heartbeat

Bundle of His

Purkinje fibre

Body tissue身體

肺 Lung

心臟

肺循環pulmonary ci

rculation- to obtain O2 from

the atmosphere

體循環systemic circ

ulation- to release O2 to t

he body tissue

∴ Haemoglobin is exposed to places having different O2 concentration (partial pressure) during the circulation of blood.

Oxygen dissociation curve

100%

% saturation of haemoglobin

partial pressure of O2 (mmHg)

LungBody tissue

Significance of the S-shape curve

100%

% saturation of haemoglobin

partial pressure of O2 (mmHg)

Plateau:

► haemoglobin highly saturated with O2 at relatively low O2 partial pressure

► favour the loading of O2 in lung

Steep slope:

► small drop of O2 partial pressure leads to a rapid decrease in % saturation of haemoglobin

► favour the release of O2 in tissue cells

∴ highly effective in the uptake large amount of O2 from environment but release it so easily to the tissue cells !

Bohr effect – the effect of [CO2] on haemoglobin

100%

% saturation of haemoglobin

partial pressure of O2 (mmHg)

Higher [CO2] e.g. tissue cells

► curve shift to the right

► always at a value of lower % saturation of haemoglobin than the curve at the left

► haemoglobin has a lower affinity to O2

∴ in actively respiring tissue cells, O2 is more easily released by haemoglobin !

Bohr effect – the effect of [CO2] on haemoglobin

100%

% saturation of haemoglobin

partial pressure of O2 (mmHg)

Lower [CO2] e.g. in lung

► curve shift to the left► haemoglobin has a higher affinity to O2

∴ in well-ventilated alveolus, O2 is more easily taken up by haemoglobin !

Oxygen dissociation curve of haemoglobin in different animals

% saturation of haemoglobin

partial pressure of O2 (mmHg)

Human

LlamaLugworm

→ Haemoglobin adapted to obtain O2 more easily from the environment !

Oxygen dissociation curve of haemoglobin in different animals

% saturation of haemoglobin

partial pressure of O2 (mmHg)

Human

→ Haemoglobin adapted to release O2 more easily for active respiring tissues !

Small mammals or birds

Oxygen dissociation curve: Haemoglobin VS Myoglobin

% saturation of haemoglobin

partial pressure of O2 (mmHg)

Haemoglobin

→ Myoglobin stores O2 in muscles and release it only when the O2 partial pressure is very low.

Myoglobin

Oxygen dissociation curve:Foetal VS Maternal

% saturation of haemoglobin

partial pressure of O2 (mmHg)

Maternal

→ Foetal haemoglobin has higher affinity to O2 so as obtain O2 from maternal blood in the placenta.

Foetal