1. Gas Exchange Part I

2. Respiration – taking up O 2 giving up CO 2 Photosynthesis – taking up CO 2, giving up O 2.

3. Respiratory medium (air or water) Organismal level Cellular level Energy-rich fuel molecules from food Respiratory surface Circulatory system Cellular respiration CO 2 O2O2 ATP

4. What is diffusion? epswww.unm.edu/.../eps462/graphics/diffusion.gif

5. Depends on  partial pressure,  surface area A gas always diffuses from an area of high partial pressure to low partial pressure. What is equilibrium?

6. Partial pressure of gases: pressure exerted by a particular gas in a mixture of gases. We need to know:  Pressure that is exerted by mixture  Fraction of mixture represented by the particular gas  Atmosphere is 21% by volume O 2. At sea level atmospheric pressure is 760mm Hg.  P O 2 is 760mm Hg X 0.21 = 160mm Hg

7. What happens in water? Amount of gas dissolved in water is proportional to  partial pressure in air  solubility in water.

8. At equilibrium partial pressure of a gas in air (P O 2 of 160mm Hg) = partial pressure of that gas in solution (P O 2 of 160mm Hg) Concentration of a gas depends on the solubility of the gas.  Solubility decreases with increase of temperature and dissolved solids.  Concentration of O 2 [O 2 ] is about 40 times more in air than water.

9. Comparison of the two respiratory media: AirWater densitylessmore viscositylessmore [O2][O2] higherlower

10. Aquatic animals have had to evolve very effective and efficient gas exchange strategies.

11. Respiratory surfaces are plasma membranes which must be moist. Gas exchange takes place by diffusion. Rate of diffusion is  directly proportional to the surface area across which it occurs  inversely proportional to the square of the distance the molecules have to travel. To speed up the rate of diffusion, respiratory surfaces have to be LARGE and THIN.

12. In unicellular and simple animals diffusion occurs between all cells and environment.

13. If body surface is enough then skin can be a respiratory organ.  Earthworm – surface is moist, supplied richly by capillaries LE 42-3 A closed circulatory system. Auxiliary hearts Ventral vessels Dorsal vessel (main heart)

14. If body surface area is insufficient – need for specialized respiratory organs Larger animals have respiratory organs consisting of respiratory surfaces and other structures. Size of respiratory surface depends on  Size of organism  Metabolic demands

15. To accommodate large respiratory surfaces inside the body –  Folded  Branced Examples: gills, trachea, lungs

16. Gills: outfoldings of the body that are suspended in water; surface area much larger than the rest of the body. There are a large variety of gills

17. Gill Parapodia Marine worm Marine Worm

18. LE 42-20d Gills Crayfish

19. LE 42-20a Gills Coelom Tube foot Sea star Sea Star

20. Gill arch Water flow Operculum Gill arch Blood vessel Oxygen-rich blood Water flow over lamellae showing % O 2 Gill filaments O2O2 Oxygen-poor blood Lamella 15% 40% 70% 100% 90% 60% 30% 5% Blood flow through capillaries in lamellae showing % O 2 Countercurrent exchange

21. Ventilation: movement of respiratory medium over respiratory surface. Promoted by  moving the gills  moving water over the gills  swimming

22. Countercurrent exchange: exchange of substance between two fluids (blood and water) flowing in opposite directions and thereby maximizing gas exchange efficiency (about 80%)

23. Gills are unsuitable for land:  water supports the filaments and keep them separate  gills would dry up

24. Tracheal systems: Most common respiratory structure. Consists of:  Large tubes (trachea – supported by chitin rings) branch into…  Smaller tubes, tracheoles (fluid at terminal end); bring enough O2 to the tissues and removes enough CO2 from the tissues.  Air sacs: supply air to organs with higher O2 needs. Air sacs Tracheae Spiracle

25. Body cell Tracheole Air sac Trachea Air Body wall MyofibrilsTracheoles Mitochondria 2.5 µm

26. O 2 demand can go up during flight by up to 200X. The demand is met by:  Contraction and relaxation of the flight muscles pumps air through the tracheal system  Flight muscles rich in mitochondria.  Withdrawal of fluid from tracheole into body increases surface area.

27. Lungs:  localized respiratory organs;  inflodings of the body surface separated consisting of numerous small pockets. Circulatory system transports O 2 to the body from the lungs and CO 2 from the body to the lungs

28. Most reptiles, all birds and mammals use lungs for gas exchange Amphibians and some reptiles (turtles) supplement lungs with parts of their skin. Some aquatic animals (lungfishes) use lungs for gas exchange

29. GillsTracheaLungs habitat of organismswaterland involves circulatory system yesnoyes location in body hangs outside in localized areas through out the body localized organs inside the body

30. For animals with gills or lungs – endotherms have greater surface area than ectotherms.

31. Gas Exchange Part II

32. Pathway of air to the gas exchange surface in mammals: Nasal cavity Pharynx Larynx Glottis (covered by epiglottis during swallowing) Trachea Bronchi Bronchioles Alveoli Nasal cavity Left lung Heart Larynx Pharynx Esophagus Trachea Right lung Bronchus Bronchiole Diaphragm

33. Mucus traps dust, beating cilia move the mucus to esophagus Millions of alveoli in lungs, total area about 100 m 2.

34. Alveoli are surrounded by capillaries. Surface is coated by moist fluid that helps in gas exchange. Surfactants keep alveoli from collapsing. Branch from pulmonary vein (oxygen-rich blood) Terminal bronchiole Branch from pulmonary artery (oxygen-poor blood) Alveoli 50 µm Colorized SEM SEM 50 µm

35. Breathing: process to ventilate lungs. Amphibian breathing: positive airflow. Mammalian breathing: negative pressure breathing.

36. Mammalian breathing  During inhalation - expand thoracic cavity, causes lower air pressure in thoracic chamber, air rushes in; opposite process for exhalation.  Rib muscles, diaphragm, double layered membrane between lungs and thoracic cavity participate.  During exercise muscles of neck, back and chest are also involved.

37. LE 42-24 Rib cage expands as rib muscles contract Air inhaled Lung Diaphragm INHALATION Diaphragm contracts (moves down) Rib cage gets smaller as rib muscles relax Air exhaled EXHALATION Diaphragm relaxes (moves up)

38. Tidal volume: volume of air inhaled and exhaled at each breath (~ 500ml) Vital capacity:  maximum volume of air that a person can exhale after maximum inhalation, ORexhaleinhalation  maximum volume of air that a person can inhale after maximum exhalation. 3.4L in college age women, 4.8L in college age men.  decreases with age. Residual volume: Air that remains after forced exhalation.

39. Avian breathing:  Ventilation is more efficient and more complex.  Maximum P O 2 is higher than that of mammals.  Birds are better adapted to higher altitudes than humans.

40.  Airflow over gas exchange surface is in one direction only  No mixing of fresh and used air.  8 – 9 pairs of air sacs that act as bellows.  Parabronchi in the lungs, no alveoli  2 sets of inhalation and exhalation are needed to completely pass air through the system.

41. LE 42-25 Anterior air sacs Lungs Posterior air sacs Trachea Air Lungs Air Air tubes (parabronchi) in lung 1 mm EXHALATION Air sacs empty; lungs fill INHALATION Air sacs fill

42. Breathing is controlled (involuntarily) to ensure  Gas exchange coordinates with circulation  Metabolic needs are met

43. Breathing is controlled by two regions at the base of the brain – pons and medulla oblongata Breathing control centers Cerebrospinal fluid Medulla oblongata Pons

44. During respiration cells produce CO 2. CO 2 concentration in blood goes up. CO 2 diffuses from blood to cerebrospinal fluid (CSF).

45. In CSF CO 2 + H 2 O H 2 CO 3 HCO 3 - + H +

46. Increased metabolic activity (exercise) – [CO 2 ] increases Results in increase in [H + ] Results in decrease in pH.

47. pH in CSF is an indicator of blood [CO 2 ]. Decrease in pH is an indicator of increased [CO 2 ] Decreased pH in cerebropspinal fluid results in control centers of the brain increasing the rate and depth of breathing. When CO 2 is exhaled, pH increases and breathing is returned to normal.

48. Breathing control centers Cerebrospinal fluid Medulla oblongata Pons Carotid arteries Aorta Diaphragm Rib muscles

49. CO 2 concentration is primarily used to control breathing O 2 concentration influences breathing only when it is very low.  Aorta and carotid arteries have O 2 sensors which signal the brain ti increases breathing  Increased breathing is always coupled with increased cardiac output.

50. Coordination of circulation and gas exchange.

51. Heart is a dual pump. Circulatory system is divided into pulmonary circuit and systemic circuit. Blood with higher P CO 2 and lower P O 2 comes from the heart to the lungs. LE 42-5 Anterior vena cava Pulmonary artery Capillaries of right lung Aorta Pulmonary vein Right atrium Right ventricle Posterior vena cava Capillaries of abdominal organs and hind limbs Pulmonary vein Left ventricle Left atrium Aorta Pulmonary artery Capillaries of head and forelimbs Capillaries of left lung

52. Air in the alveoli has higher P O 2 and lower P CO 2 than blood in the capillaries. O 2 in the alveoli dissolves in the fluid coating the alveolar epithelium and diffuses into the blood. CO 2 dissolves from blood to the air in the alveoli.

53. Blood leaving the lungs and going to the heart has higher P O 2 and lower P CO 2 than the blood entering the lungs. From the heart the blood goes into the systemic circulation. In the tissues cellular respiration removes the O 2 from the cells and adds CO 2. P O 2 is higher and P CO 2 is lower in the blood in the tissue capillaries than in the tissues. O 2 diffuses out of the blood and enters the cells and CO 2 diffuses out of the cells and enters the blood. This blood is returned to heart and sent to lungs. Inhaled air Blood entering alveolar capillaries Alveolar epithelial cells Alveolar spaces Alveolar capillaries of lung Exhaled air Blood leaving alveolar capillaries Pulmonary veins Pulmonary arteries Tissue capillaries Heart Systemic veins Systemic arteries Blood leaving tissue capillaries Blood entering tissue capillaries Tissue cells CO 2 O2O2 O2O2 O2O2 O2O2 < 40> 45 4045 CO 2 O2O2 10040 CO 2 O2O2 O2O2 4045 CO 2 O2O2 10440 O2O2 CO 2 O2O2 O2O2 O2O2 10440 12027 1600.2

54. Diffusion of O 2 in the blood alone is inadequate for meeting metabolic needs. O 2 transport is done to a large degree by respiratory pigments.

55. During exercise cardiac output is 12.5L of blood per minute with respiratory pigment 555L without the pigment

56. Respiratory pigments: protein bound to metal, have distinctive color Hemoglobin: protein and iron (vertebrates) Hemocyanin: protein and copper (some arthropods and molluscs)

57. Hemoglobin (Hb): 4 polypeptide subunits each with an iron atom cofactor. Found in red blood cells. Polypeptide chain O 2 unloaded in tissues O 2 loaded in lungs Iron atomHeme group

58. Functions of hemoglobin:  carries O 2,  carries C O 2,  acts as a buffer in blood

59. Binds to oxygen reversibly. Subunits show co- operativity in binding and release. O 2 unloaded from hemoglobin during normal metabolism O 2 reserve that can be unloaded from hemoglobin to tissues with high metabolism P O 2 and hemoglobin dissociation at 37°C and pH 7.4 P (mm Hg) O2O2 Tissues during exercise Tissues at rest Lungs 10080 6040200 0 40 60 80 100 O 2 saturation of hemoglobin (%)

60. Cellular respiration increases CO 2 production. CO 2 production lowers pH Lower pH decreases Hb affinity for oxygen. (Bhor shift) Bohr shift: additional O 2 released from hemoglobin at lower pH (higher CO 2 concentration) pH and hemoglobin dissociation P (mm Hg) O2O2 10080 6040200 0 40 60 80 100 O 2 saturation of hemoglobin (%) pH 7.2 pH 7.4

61. When cellular respiration is higher Hb releases more O 2.

62. CO 2 transport.  In solution (7%)  Bound to Hb (23%)  Bicarbonate (HCO 3 - ) 70%

63. CO 2 transport from tissues to alveolar space CO 2 transport from tissues CO 2 produced Tissue cell CO 2 Interstitial fluid Blood plasma within capillary Capillary wall Hemoglobin picks up CO 2 and H + CO 2 transport to lungs To lungs H 2 CO 3 Carbonic acid H2OH2O Hb HCO 3 – Bicarbonate Red blood cell H+H+ + HCO 3 – Hemoglobin releases CO 2 and H + H+H+ + HCO 3 – CO 2 H 2 CO 3 H2OH2O CO 2 Hb Alveolar space in lung

64. From tissue and interstitial fluid to plasma Large part (~90%) diffuses into the red blood cells Some picked up by Hb CO 2 and water in red blood cells react forming carbonic acid Carbonic acid dissociates into bicarbonate and hydrogen ions. Hb binds most of the H + ; this helps maintain pH, preventing Bhor sift. CO 2 transport from tissues CO 2 produced Tissue cell CO 2 Interstitial fluid Blood plasma within capillary Capillary wall Hemoglobin picks up CO 2 and H + To lungs H 2 CO 3 Carbonic acid H2OH2O Hb HCO 3 – Bicarbonate Red blood cell H+H+ + HCO 3 –

65. HCO 3 - diffuses into the plasma. At the lungs HCO 3 - diffuses back into the red blood cells. Combines with H + to form CO 2 and water CO 2 is unloaded from Hb. Diffuses from plasma into interstitial fluid. CO 2 diffuses into alveolar space, exhaled out. CO 2 transport to lungs To lungs HCO 3 – Hemoglobin releases CO 2 and H + H+H+ + HCO 3 – CO 2 H 2 CO 3 H2OH2O CO 2 Hb Alveolar space in lung

66. Animals like cheetah, pronghorned antelope have been selected enhancement normal physiological mechanisms at every stage of O 2 metabolism.

67. Diving mammals have myoglobin that have higher affinity for O 2 than human myoglobin.