2Assessment Statements H Define partial pressure.H Explain the oxygen dissociation curves of adult hemoglobin, fetal hemoglobin and myoglobin.H Describe how carbon dioxide is carried by the blood, including the action of carbonic anhydrase, the chloride shift and buffering by plasma proteins.H Explain the role of the Bohr shift in the supply of oxygen to respiring tissues.H Explain how and why ventilation rate varies with exercise.H Outline the possible causes of asthma and its effects on the gas exchange system.H Explain the problem of gas exchange at high altitudes and the way the body acclimatizes.
3Define the term partial pressure partial pressure is the pressure exerted by a given gas in a mixturethe symbol for partial pressure is P, and the partial pressure for a gas x is Px. So, PO2 denotes the partial pressure of oxygenwhat is the partial pressure of the oxygen in the air around us?At sea level, the atmospheric pressure is typically about kPa of which 21.0% is O2, So, PO2 is given by:101.3 𝑥 = 21.3 kPaAtmospheric air is a mixture of gases; nitrogen, oxygen, carbon dioxide, water vapour & inert gases.At sea level, the atmospheric pressure is about kPa.What proportion of atmospheric pressure is due to oxygen?
4Role of haemoglobin1 molecule of oxygen will combine with each haem group, meaning, each haemoglobin molecule is able to transport 4 molecules of oxygen:oxyhaemoglobin is the form in which oxygen is transported from the lungs to the respiring body tissuesat respiring tissue cells, oxyhaemoglobin breaks down, releasing oxygen & haemoglobinoxygen is used up by tissue cells while haemoglobin is returned to the lungs to pick up more oxygenhaemoglobin occurs in the red cellshaemoglobin molecule is built of four interlocking subunitseach subunit is composed of a large globular protein with a non-protein haem group attached, containing iron
5Oxygen dissociation curve the affinity of haemoglobin for oxygen is measured experimentally by finding the percentage saturation with oxygen of blood exposed to air mixtures containing different partial pressures of oxygenthe result is called an oxygen dissociation curveoxygen dissociation curve is S-shaped, the amount of oxygen held by haemoglobin depends on the partial pressure of oxygenin the body, too, the amount of oxygen held by haemoglobin depends on the partial pressurein respiring tissues, the oxygen partial pressure is much lower than that in the lungsat lower partial pressures, oxyhaemoglobin breaks down, releasing oxygen in solution and this rapidly diffuses into the surrounding tissues
6Oxygen dissociation curve of adult haemoglobin oxygen dissociation curve for oxyhaemoglobin is S/sigmoid-shapedit shows how the saturation of haemoglobin with oxygen varies with partial pressure of oxygenhaemoglobin has an increasing affinity for oxygen, initial uptake of one oxygen molecule by haemoglobin facilitates the further uptake of oxygen moleculeslow partial pressure of oxygen corresponds to the situation in the tissue, when partial pressure of oxygen is low, oxygen is releasedlow pH, increased carbon dioxide & increased lactic acid causes the curve to shifts the to the right and oxygen is more readily released to respiring tissues – this is known as the Bohr effecthigh partial pressure of oxygen corresponds to the situation in the lungs, when partial pressure of oxygen is high, oxygen is taken up by haemoglobinShift to the right; (decreased affinity) low pH, increased CO2, increased lactic acid
7Oxygen dissociation curve of fetal haemoglobin like adult haemoglobin, fetal haemoglobin have S-shaped oxygen dissociation curvesfetal haemoglobin have a high affinity for oxygen at high partial pressure of oxygenfetal haemoglobin always has a higher affinity for oxygen at corresponding partial pressures of oxygen than adult haemoglobin, thus fetal haemoglobin dissociation curve lies to the left of the adult dissociation curvein the placenta where maternal and fetal blood come into close proximity there is a low oxygen partial pressurefetal haemoglobin must have a greater affinity for oxygen otherwise the maternal oxy-haemoglobin would not dissociaterelationship between fetal and adult haemoglobin dissociation curves does NOT change at all partial pressures of oxygenthe difference in adult and fetal haemoglobin structures lead to differences in affinitybetween foetal & adult haemoglobin, which one has a higher affinity for oxygen?why it is advantageous that fetal haemoglobin higher affinity for oxygen than adult haemoglobin?
8Oxygen dissociation curve of myoglobin myoglobin is specialized for oxygen storagemyoglobin has a higher affinity for oxygen than haemoglobin, its dissociation curve is to the left of that for haemoglobinin normal conditions, at rest myoglobin is saturated with oxygenmyoglobin is used during intense muscle contraction when the oxygen supply is insufficient i.e. when muscle is very active its oxygen concentration may fall below 0.5 kPawhen this happens myoglobin releases oxygen to muscle cellsmyoglobin oxygen dissociation curve is not sigmoid shaped, it has a steep rise below 5 kPa with no lag & has slower rise approaching 100 % above 5 kPamyoglobin is a respiratory pigment built of a single haem–globin unit, similar to the four units in haemoglobinmyoglobin is only found in skeletal muscle cells, where it acts as a reserve of oxygen
9Oxygen dissociation curves of adult haemoglobin, fetal haemoglobin and myoglobin rapid saturation of oxygen in the lungsrapid dissociation of oxygen as the oxygen concentration decreasesoxygen released in the tissues where it is neededfetal haemoglobin:fetal haemoglobin curve to the left of adult haemoglobinhigher affinity for oxygen than adult haemoglobinoxygen moves from adult haemoglobin to fetal haemoglobinmyoglobin:myoglobin to the left of fetal haemoglobinonly releases oxygen at very low oxygen concentrations in tissuesacts as oxygen reserve in muscle cells
10How carbon dioxide is carried by the blood carbon dioxide is carried in three forms in the blood:carbon dioxide can be dissolved in the blood plasma forming carbonic acid (5 %)carbon dioxide can be carried as dissociated carbonic acid i.e. H H CO3 − in red blood cells (85 %)carbon dioxide can be carried as carbaminohemoglobin when it is bound to haemoglobin (10 %)carbonic anhydrase is an enzyme found in red blood cells (erythrocytes)carbonic anhydrase speeds up production of hydrogen carbonate (H CO3 −)chloride shift i.e. movement of chloride ions into red blood cell, occurs to balance movement of hydrogen carbonate ion out
11Role of the Bohr shift in the supply of oxygen to respiring tissues hemoglobin carries up to four oxygen moleculesBohr shift promotes the release of oxygen in respiring heart muscleactive respiration releases CO2 causing the partial pressure of CO2 increasesrelease of CO2 increases acidity i.e. lowers the pH due to formation of hydrogen ions (H+)hydrogen ions bind to hemoglobin decreasing hemoglobin’s affinity for O2 so O2 is released from the oxyhemoglobinthis occurs due allosteric effect i.e. conformational change in hemoglobin which releases O2 more readily
13How and why ventilation rate varies with exercise during exercise the rate of tissue respiration increases i.e. more carbon dioxide producedcarbon dioxide production in the tissues exceeds the rate of breathing it outincrease in carbonic acid (H2CO3), increase in H+ ions , pH drops in the blood plasmalactic acid produced during strenuous exercise reduces pHchemoreceptors, located in the carotid & aortic bodies, detect change in pH, increase in carbon dioxide & decrease in oxygenIncreased CO2 in the blood & lower pH are also detected by chemoreceptors in medullanerve impulses sent to the breathing Centre in the medulla of the brain from the chemoreceptorsnerve impulses are then sent to diaphragm & intercostal muscles from the breathing Centre in medulla to increase the rate & the depth of breathingventilation rate is controlled through negative feedback mechanism
15Possible causes of asthma and its effects on the gas exchange system asthma is a chronic inflammatory disease of the airwayit is caused by allergic reaction to allergens such as; dust, mites droppings, pollen, toxins, pets hairs, fungi etc.immune responses releases histamine which causes:constriction of muscles of wall of bronchiolesmore mucus is producedthese restricts air flow thus ventilation is hard & gas exchange is reduced
16Problem of gas exchange at high altitudes at high altitudes partial pressure of oxygen is lower, at 7000m PO2 is 8.1 kPaas air is exchanged in lungs hemoglobin does not become fully saturated with O2oxygen deprivation of tissues occurs causing fatigue i.e. Monge diseasemountain sickness (increased pulse rate, nausea, headaches, sore throat, muscular weakness, dizziness ) may developventilation rate & depth increases
17How the body acclimatizes to high altitudes ventilation rate increasesred blood cell (erythrocyte) concentration in blood increasesmyoglobin concentration in muscles increasescapillary networks in the muscles develop greater densitylung working volume, vital capacity, increasespeople living permanently at high altitude develops greater lung surface area
18Revision QuestionsExplain why ventilation rate varies with exercise Explain how and why ventilation rate varies with exercise Outline one possible cause of asthma and its effect on the gas exchange system Outline how the body acclimatizes to high altitudes. Explain the problem of gas exchange at high altitudes and the way the body acclimatizes Define the term partial pressure Explain the oxygen dissociation curves of adult haemoglobin, fetal haemoglobin and myoglobin. Describe how carbon dioxide is carried by the blood Explain, with the use of a diagram, the role of the Bohr shift in the supply of oxygen to respiring heart muscle. Explain the Bohr shift of an oxygen dissociation curve during gas exchange 
19The oxygen dissociation curve is a graph that shows the percentage saturation of haemoglobin at various partial pressures of oxygen. Curve A shows the dissociation at a pH of 7 and curve B shows the dissociation at a different pH.(i) State the possible cause of the curve shifting from A to B (ii) On the graph, draw the curve for myoglobin 
20Explain the oxygen dissociation of myoglobin, completing the graph below to support your answer. Po2 is the partial pressure of oxygen.