Gaseous Exchange-STPM

Gaseous exchange Transport of oxygen The red blood cells contain haemoglobin, the molecule that transports oxygen. Typically, Typically, the human body requires 3 3  between 250 cm  (at rest) and 000 cm (in strenuous exercise) o! oxygen per minute. "t human (3# o$) body temperature, about 0.%5 cm 3 o! oxygen can be dissol&ed in 00 cm 3 o! blood plasma, but the total oxygen transporting !acility o! blood is about 20 cm 3 per 00 cm3. Thus some ' per cent o! oxygen is transported by haemoglobin. Haemoglobin and oxygen transport aemoglobin is a compact molecule made up o! !our interloc*ing sub+units. The sub+units consist o! !our polypeptide chains called globin (two +chains and two -+chains), each attached to a haem group. aemoglobin there!ore has a quaternary structure. The haem groups comprise a porphyrin ring containing an atom o! iron () at the centre. The haem groups in haemoglobin are responsible !or its red colour, and are the site o! oxygen transport. "n "n iron atom combines with a molecule o! oxygen, but without oxidation o! the iron (). Thus, each haemoglobin molecule can carry !our molecules o! /2. i*e all respiratory pigments, haemoglobin must bind oxygen re&ersibly, loading oxygen in the lungs and unloading it in other parts o! the body. body. oading and unloading depends on cooperation among the sub+units o! the haemoglobin molecule. The binding o! oxygen to one sub+unit induces the remaining sub+units to change their shape slightly so that their a!!inity !or oxygen increases. "nd when one sub+unit unloads unloads its oxygen, the other three quic*ly !ollow suit as a con!ormational change lowers their a!!inity !or oxygen. The structure of haemoglobin aemoglobin is a con1ugated protein • The protein part (called globin) consists o! !our polypeptide chains. These chains are o! two types called alpha • and beta. They are about the same length (about %0 amino acids) but ha&e slightly di!!erent compositions. ach chain is combined with a non+protein prosthetic group called haem. aem consists o! an atom o! iron • enclosed in a ring structure (porphyrin ring) ach haem group can combine with one molecule o! oxygen. This process is called oxygenation. (t is not the • same as oxidation, because the iron does not lose any electrons and is not chemically oxidised). ach molecule o! haemoglobin can there!ore combine with a maximum o! !our molecules o! oxygen. Oxygen tension (partial pressure) n a mixture o! gases, each component gas exerts a pressure (its partial pressure or tension) in proportion to its • molar percentage in the mixture. The partial pressure o! a gas is the pressure contributed by one gas to the total pressure o! a mixture o! gases. • The partial pressure o! a gas is the pressure exerted by the particular gas in a mixture o! gases. • Partial pressures of the components of air $omp $ompon onen entt gas gases es erc ercen enta tage ge comp compos osit itio ion n art artia iall pre press ssur ure4 e4* *aa art artia iall pre press ssur ure4 e4mm mm g /xygen 2 2.2 0 $arbon dioxide 0.0% 0.0% 0.3  6itrogen #' 0.0 Partial pressure of the components of alveolar air $omp $ompon onen ents ts gas gases es erc ercen enta tage ge com compo posi siti tion on art artia iall pre press ssur ure4 e4* *aa /xygen 3. %.0 $arbon dioxide 5.5 5.  6itrogen 0.#

artial pressures o! the components in tissue cells $omp $ompon onen entt gas gases es erc ercen enta tage ge comp compos osit itio ion n art artia iall pre press ssur ure4 e4* *aa /xygen 7 5. $arbon dioxide 8 .3

art artia iall pre press ssur ure4 e4mm mm g g 0% %0

art artia iall pre press ssur ure4 e4mm mm g 7 %0 8 %5

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