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Respiratory Pigments: Oxygen and Carbon Dioxide Transport in the Blood

Learn about respiratory pigments such as hemoglobin that greatly increase the amount of oxygen that blood can carry, as well as their role in carbon dioxide transport. Explore how these pigments help regulate breathing in humans and the unique respiratory adaptations of birds, fish, and diving mammals.

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Respiratory Pigments: Oxygen and Carbon Dioxide Transport in the Blood

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  1. Chapter 42 Circulation and Gas Exchange

  2. Concept 42.7: Respiratory pigments bind and transport gases • The metabolic demands of many organisms require that the blood transport large quantities of O2 and CO2

  3. Respiratory Pigments • Respiratory pigments, proteins that transport oxygen, greatly increase the amount of oxygen that blood can carry

  4. Oxygen Transport • The respiratory pigment of almost all vertebrates is the protein hemoglobin, contained in erythrocytes (red blood cell) • Hemoglobin (Hb) contains 4 individual polypeptide chains; each of which also contains one heme group • Each heme group contains one iron atom that has an affinity for oxygen Heme group Iron atom O2 loaded in lungs O2 unloaded in tissues Polypeptide chain

  5. Oxygen Transport • Like all respiratory pigments, hemoglobin must reversibly bind O2, loading O2 in the lungs and unloading it in other parts of the body Heme group Iron atom O2 loaded in lungs O2 unloaded in tissues Polypeptide chain

  6. Loading and unloading of O2depend on cooperation between the subunits of the hemoglobin molecule • The binding of O2 to one subunit induces the other subunits to bind O2 with more affinity • Cooperative O2 binding and release is evident in the dissociation curve for hemoglobin • A drop in pH lowers affinity of hemoglobin for O2

  7. Oxygen dissociation curves - Tells us Hb’s affinity for O2 at a given pressure O2 unloaded from hemoglobin during normal metabolism 100 80 60 O2 saturation of hemoglobin (%) O2 reserve that can be unloaded from hemoglobin to tissues with high metabolism Hb is “saturated” with O2 when all heme groups have attached an O2 molecule. Greater % = greater affinity 40 20 0 0 20 40 60 80 100 (B) Tissues at rest (C) Tissues during exercise (A)Lungs P(mm Hg) O2 At higher altitudes, lower pressure, LESS oxygen is present

  8. Increase CO2 Increase acidity/decrease pH O2 affinity decreases Soooo… Hb readily gives up the oxygen to tissues during exercise 100 pH 7.4 80 Bohr shift: additional O2 released from hemoglobin at lower pH (higher CO2 concentration) O2 saturation of hemoglobin (%) 60 pH 7.2 40 20 0 0 20 40 60 80 100 P(mm Hg) O2

  9. Carbon Dioxide Transport • Hemoglobin also helps transport CO2and assists in buffering • Carbon from respiring cells diffuses into the blood plasma and then into erythrocytes and is ultimately released in the lungs

  10. Tissue cell CO2 transport from tissues CO2 produced Interstitial fluid CO2 CO2 Capillary wall Blood plasma within capillary CO2 H2O Hemoglobin picks up CO2 and H+ Red blood cell H2CO3 Carbonic acid Hb HCO3– Bicarbonate H+ + HCO3– To lungs

  11. CO2 transport to lungs HCO3– HCO3– H+ + Hemoglobin releases CO2 and H+ Hb H2CO3 H2O CO2 CO2 CO2 CO2 Alveolar space in lung

  12. Control of Breathing in Humans • In humans, the main breathing control centers are in two regions of the brain, the medulla oblongata and the pons • The medullaregulates the rate and depth of breathing in response to pH changes in the cerebrospinal fluid • pH changes are caused by concentration of CO2 in the blood • The medulla adjusts breathing rate and depth to match metabolic demands

  13. Cerebrospinal fluid • Sensors in the aorta and carotid arteries monitor O2 and CO2 concentrations in the blood • These sensors exert secondary control over breathing Pons Breathing control centers Medulla oblongata Carotid arteries Aorta Diaphragm Rib muscles

  14. Negative Feedback Loop Holding breath CO2 levels rise O2 /CO2 level returns to normal Control system forces exhale, inhale

  15. How a Bird Breathes • Birds have eight or nine air sacs that function as bellows that keep air flowing through the lungs • Air passes through the lungs in one direction only • How does air flow in mammals? • Every exhalation completely renews the air in the lungs Air Air Anterior air sacs Trachea Posterior air sacs Lungs Lungs Air tubes (parabronchi) in lung 1 mm INHALATION Air sacs fill EXHALATION Air sacs empty; lungs fill

  16. Swim Bladder • A swim bladder is an air-filled organ fish use to control buoyancy.

  17. Elite Animal Athletes • Migratory and diving mammals have evolutionary adaptations that allow them to perform extraordinary feats

  18. The Ultimate Endurance Runner • The extreme O2 consumption of the antelope-like pronghorn underlies its ability to run at high speed over long distances

  19. Diving Mammals • Deep-diving air breathers stockpile O2 and deplete it slowly • CO2 & lactic acid as a result from respiration is stored until animal “comes up” • Also have a slow heart beat (bradycardia)

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