2. Gas Exchange & Respiratory Systems

3. Why do we need a respiratory system? O2O2 food ATP CO 2 respiration for respiration Need O 2 in –for aerobic cellular respiration –make ATP Need CO 2 out –waste product from Krebs cycle

4. Gas exchange O 2 & CO 2 exchange between environment & cells –need moist membrane –need high surface area

5. Optimizing gas exchange Why high surface area? –maximizing rate of gas exchange –CO 2 & O 2 move across cell membrane by diffusion rate of diffusion proportional to surface area Why moist membranes? –moisture maintains cell membrane structure –gases diffuse only dissolved in water

6. Gas exchange in many forms… one-celledamphibiansechinoderms insectsfish mammals endotherm vs. ectotherm size cilia water vs. land

7. Evolution of gas exchange structures external systems with lots of surface area exposed to aquatic environment Aquatic organisms moist internal respiratory tissues with lots of surface area Terrestrial

8. Gas Exchange in Water: Gills

9. Counter current exchange system Water carrying gas flows in one direction, blood flows in opposite direction

10. Blood & water flow in opposite directions –maintains diffusion gradient over whole length of gill capillary –maximizing O 2 transfer from water to blood water blood How counter current exchange works front back blood 100% 15% 5% 90% 70%40% 60%30% 100% 5% 50% 70% 30% water counter- current concurrent

11. Gas Exchange on Land Advantages of terrestrial life –air has many advantages over water higher concentration of O 2 O 2 & CO 2 diffuse much faster through air –respiratory surfaces exposed to air do not have to be ventilated as thoroughly as gills air is much lighter than water & therefore much easier to pump –expend less energy moving air in & out Disadvantages –keeping large respiratory surface moist causes high water loss reduce water loss by keeping lungs internal Why don’t land animals use gills?

12. Terrestrial adaptations air tubes branching throughout body gas exchanged by diffusion across moist cells lining terminal ends, not through open circulatory system Tracheae

13. Lungs Exchange tissue: spongy texture, honeycombed with moist epithelium Why is this exchange with the environment RISKY?

14. Alveoli Gas exchange across thin epithelium of millions of alveoli –total surface area in humans ~100 m 2

15. Negative pressure breathing Breathing due to changing pressures in lungs –air flows from higher pressure to lower pressure –pulling air instead of pushing it

16. Mechanics of breathing Air enters nostrils –filtered by hairs, warmed & humidified –sampled for odors Pharynx  glottis  larynx (vocal cords)  trachea (windpipe)  bronchi  bronchioles  air sacs (alveoli) Epithelial lining covered by cilia & thin film of mucus –mucus traps dust, pollen, particulates –beating cilia move mucus upward to pharynx, where it is swallowed

17. Autonomic breathing control Medulla sets rhythm & pons moderates it –coordinate respiratory, cardiovascular systems & metabolic demands Nerve sensors in walls of aorta & carotid arteries in neck detect O 2 & CO 2 in blood

18. Medulla monitors blood Monitors CO 2 level of blood –measures pH of blood & cerebrospinal fluid bathing brain CO 2 + H 2 O  H 2 CO 3 (carbonic acid) if pH decreases then increase depth & rate of breathing & excess CO 2 is eliminated in exhaled air

19. Breathing and Homeostasis Homeostasis –keeping the internal environment of the body balanced –need to balance O 2 in and CO 2 out –need to balance energy (ATP) production Exercise –breathe faster need more ATP bring in more O 2 & remove more CO 2 Disease –poor lung or heart function = breathe faster need to work harder to bring in O 2 & remove CO 2 O2O2 ATP CO 2

20. Diffusion of gases Concentration gradient & pressure drives movement of gases into & out of blood at both lungs & body tissue bloodlungs CO 2 O2O2 O2O2 bloodbody CO 2 O2O2 O2O2 capillaries in lungscapillaries in muscle

21. Hemoglobin Why use a carrier molecule? –O 2 not soluble enough in H 2 O for animal needs blood alone could not provide enough O 2 to animal cells hemocyanin in insects = copper (bluish/greenish) hemoglobin in vertebrates = iron (reddish) Reversibly binds O 2 –loading O 2 at lungs or gills & unloading at cells cooperativity heme group

22. Cooperativity in Hemoglobin Binding O 2 –binding of O 2 to 1 st subunit causes shape change to other subunits conformational change –increasing attraction to O 2 Releasing O 2 –when 1 st subunit releases O 2, causes shape change to other subunits conformational change –lowers attraction to O 2

23. O 2 dissociation curve for hemoglobin Bohr Shift  drop in pH lowers affinity of Hb for O 2  active tissue (producing CO 2 ) lowers blood pH & induces Hb to release more O 2 P O 2 (mm Hg) 0 10 20 30 40 50 60 70 80 90 100 020406080100120140 More O 2 delivered to tissues pH 7.60 pH 7.20 pH 7.40 % oxyhemoglobin saturation Effect of pH (CO 2 concentration)

24. O 2 dissociation curve for hemoglobin Bohr Shift  increase in temperature lowers affinity of Hb for O 2  active muscle produces heat P O 2 (mm Hg) 0 10 20 30 40 50 60 70 80 90 100 020406080100120140 More O 2 delivered to tissues 20°C 43°C 37°C % oxyhemoglobin saturation Effect of Temperature

25. Transporting CO 2 in blood Tissue cells Plasma CO 2 dissolves in plasma CO 2 combines with Hb CO 2 + H 2 OH 2 CO 3 H+ + HCO 3 – HCO 3 – H 2 CO 3 CO 2 Carbonic anhydrase Cl– Dissolved in blood plasma as bicarbonate ion carbonic acid CO 2 + H 2 O  H 2 CO 3 bicarbonate H 2 CO 3  H + + HCO 3 – carbonic anhydrase

26. Releasing CO 2 from blood at lungs Lower CO 2 pressure at lungs allows CO 2 to diffuse out of blood into lungs Plasma Lungs: Alveoli CO 2 dissolved in plasma HCO 3 – Cl – CO 2 H 2 CO 3 Hemoglobin + CO 2 CO 2 + H 2 O HCO 3 – + H +

27. Adaptations for pregnancy Mother & fetus exchange O 2 & CO 2 across placental tissue Why would mother’s Hb give up its O 2 to baby’s Hb?

28. Fetal hemoglobin (HbF) What is the adaptive advantage? 2 alpha & 2 gamma units HbF has greater attraction to O 2 than Hb –low % O 2 by time blood reaches placenta –fetal Hb must be able to bind O 2 with greater attraction than maternal Hb

29. Don’t be such a baby… Ask Questions!!

30. If I roll a: 1 – On your own, no notes 2 – On your own, with notes 3 – With partner, no notes 4 - with partner, with notes 5 – as a class, no notes 6 – as a class, with notes

31. Relate the negative pressure system of the lungs to the negative pressure system of plants.