Carriage of respiratory Carriage of respiratory GasesGases

ByBy

Y StockY Stock

ObjectivesObjectives

You should be able to:You should be able to: Describe the structure of Describe the structure of

erythrocytes.erythrocytes. Describe the role of respiratory Describe the role of respiratory

pigments.pigments.

Understand and interpret Understand and interpret dissociation curves.dissociation curves.

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Red blood cellsRed blood cells

Biconcave discsBiconcave discs 8 micrometers diameter8 micrometers diameter

No nucleusNo nucleus

Made in bone marrowMade in bone marrow Destroyed by liver/spleenDestroyed by liver/spleen

Function: To carry oxygen and Function: To carry oxygen and carbon dioxidecarbon dioxide

Adaptions:Adaptions:

Shape gives a large surface area, Shape gives a large surface area, encouraging diffusionencouraging diffusion

Full of haemoglobinFull of haemoglobin

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HaemoglobinHaemoglobin

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HaemoglobinHaemoglobin

Consists of 4 polypeptide chains, Consists of 4 polypeptide chains, each with an iron containing haem each with an iron containing haem group.group.

Each haem group combines with an Each haem group combines with an oxygen moleculeoxygen molecule

Haemoglobin+oxygen=oxyhaemoglobinHaemoglobin+oxygen=oxyhaemoglobin

Hb + 4OHb + 4O22 = HbO = HbO88

Reversible reactionReversible reaction

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Hb + 4OHb + 4O22 = HbO = HbO88

High partial High partial pressure oxygenpressure oxygen

LungsLungs

Oxyhaemoglobin Oxyhaemoglobin formedformed

Low partial Low partial pressure oxygenpressure oxygen

Active tissuesActive tissues

Oxyhaemoglobin Oxyhaemoglobin breaks downbreaks down

Oxygen releasedOxygen released

Oxygen dissociation curvesOxygen dissociation curves

Found by exposing haemoglobin to Found by exposing haemoglobin to

air mixtures of varying oxygen partial air mixtures of varying oxygen partial

pressures and determining its % pressures and determining its %

saturation.saturation.

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S shaped curveS shaped curve

Over the steep section a small fall inOver the steep section a small fall in

Oxygen partial pressure causes a Oxygen partial pressure causes a

sizeable drop in % saturation.sizeable drop in % saturation.

The curve shows that:The curve shows that:

at relatively low oxygen concentrations at relatively low oxygen concentrations there is uncombined haemoglobin in the there is uncombined haemoglobin in the blood and little or no oxyhaemoglobin, e.g. blood and little or no oxyhaemoglobin, e.g. in body tissue in body tissue

at relatively high oxygen concentrations at relatively high oxygen concentrations there is little or no uncombined there is little or no uncombined haemoglobin in the blood; it is in the form haemoglobin in the blood; it is in the form of oxyhaemoglobin, e.g. in the lungs. of oxyhaemoglobin, e.g. in the lungs.

Effect of increased carbon dioxideEffect of increased carbon dioxide

Bohr EffectBohr Effect

Curve shifted to rightCurve shifted to right

Increased COIncreased CO22 causes causes oxyhaemoglobin to unload some of oxyhaemoglobin to unload some of its oxygen.its oxygen.

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Fate of carbon dioxideFate of carbon dioxide

7-10% dissolves in plasma7-10% dissolves in plasma

20-30% in red cells as 20-30% in red cells as carbaminohaemoglobin (binds to carbaminohaemoglobin (binds to amino acids)amino acids)

60-70% converted to bicarbonate in 60-70% converted to bicarbonate in plasmaplasma

Conversion to bicarbonateConversion to bicarbonate

Carbon dioxide diffuses into red cellsCarbon dioxide diffuses into red cells

Enzyme:carbonic anhydraseEnzyme:carbonic anhydrase

COCO22 + H + H22O = HO = H22COCO33

This dissociatesThis dissociates HH22COCO3 3 = H= H++ + HCO + HCO33

--

HCOHCO33- - diffuses into plasmadiffuses into plasma

HH++ combine with oxyhaemoglobin forming combine with oxyhaemoglobin forming haemoglobinic acid.haemoglobinic acid.

HH+ + + HbO + HbO22 = HHB + O = HHB + O22

Oxygen displaced.Oxygen displaced. Haemoglobin buffering pH changesHaemoglobin buffering pH changes

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Myoglobin -Curve shifted to leftMyoglobin -Curve shifted to left

Myoglobin binds more tightly to Myoglobin binds more tightly to oxygen.oxygen.

Oxygen only given up at very low POOxygen only given up at very low PO22

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QuizQuiz

Haemoglobin quiz image search RSCHaemoglobin quiz image search RSC