Gas Exchange

1. Gas Exchange Chapter 22

2. Gas Exchange • Respiration or the interchange of O2 and CO2 • 3 phases which use digested food to produce work • Breathing exposes large, moist internal surface to air • O2 diffuses from lungs into blood vessels and CO2 in reverse • Exhalation removes CO2 from body • Transport of gases by circulatory system • O2 attaches to hemoglobin in RBC’s • Red vessels = O2 from lungs, blue vessels = CO2 from tissues • Body cells take up O2from blood and release CO2 into it • Important for cellular respiration • Continuous supply of O2 and removal of CO2

3. Respiratory Surfaces • Part of an animal where gases are exchanged • Made of living cells that must be moist to function • Single layer to allow rapid diffusion of gases • Surface area must be large enough to take up sufficient O2 for every body cell and dispose of CO2 • 4 types which vary between species (pictures) • Skin, gills, tracheal systems, and lungs

4. ‘Skin Breathers’ • Outer skin is gas exchange organ • No specialized organs • O2 diffuses in capillaries just below outer surface • Must live in damp places • Generally small and long, thin, or flattened • High ratio of SA to body volume

5. Gill systems • Extensions of the body surface, specialized for gas exchange • O2 across gills to capillaries and CO2 in opposite direction -countercurrent • Found in most aquatic animals • Not a problem staying moist

7. Tracheal Systems • Branching internal tube system in insects • Surface at tips • Direct exchange with body cells • No circulatory system • Open to external environment via narrow tubes • Helps retain moisture • Most terrestrial animals

8. Lungs • Internal sacs with moist epithelium • Inner surfaces branch extensively to increase SA • Circulatory system carries gases between lungs and body cells • Most terrestrial vertebrates

9. Aquatic Environments • O2 as dissolved gas in bodies of water • Trade off: no limit to moisture, but decreased O2 • Warmer and saltier = less O2 • Structure of gills • Less O2 available so gill SA larger then rest of the body • Respiratory surfaces are so tiny that RBC’s flow singularly in close contact with O2 in water • Positioned so water can enter mouth, flow over gills, and exit • Gills remove 80% of O2, lungs only 25% • Gills outside body so H2O loss terrestrially would be large • Terrestrial animals house respiratory organs inside body

10. Countercurrent exchange: transfer of a substance from a fluid flowing in 1 direction to a fluid flowing in the opposite direction Sets up a concentration gradient to favor O2 diffusion from H20 Gill Systems

11. Terrestrial Organisms • Air has higher [O2] and easier to move than H2O • Less energy to ventilate, move O2 containing substances across respiratory organs • Higher probability of H2O loss from evaporation • Tracheal system allows exposure to all body parts and gas exchange independent of a circulatory system • Flight in insects can increase exchange rate to sustain high energy needs for flight

12. Tracheae open to external environment Smaller branches are tracheoles that participate directly in gas exchange O2 directly to body cells Tracheal Systems

13. Evolution of Tetrapods • Fossil evidence of skeletal tetrapod changes • Current hypothesis that pectoral girdle changes to enable pushing up out of water to gulp air • Had lungs and gills • Stronger & elongated snout and neck to lift head out of water • Diverged into amphibians, reptiles, and mammals • Amphibians with small lungs and heavy reliance on gas exchange across body surfaces • Reptiles and mammals have lungs whose size and complexity correlate with metabolic rate or O2 needed

14. Respiratory Pathway • Air into our nostrils to be filtered and warmed • Mouth breathing skips processing by the nose • Flows into pharynx where food and air paths cross before entering the trachea • Passes through the larynx or voicebox • When exhaling the vocal cords are tensed to produce sounds by changing the vibrations made • High pitch when stretched tight and vibrate fast • Rings of cartilage in the trachea prevent collapse • Rest of the path lined with moist, ciliated epithelium and mucus • Moves contaminates trapped in mucus to the pharynx • Trachea branches into 2 bronchi, 1 to each lung • Branching continues into bronchioles and dead end at alveoli, or dead end grape-like sacs • Increases SA to 50X’s greater than skin • Diffusion across epithelium cells into and out of capillaries around each

15. Human Lungs

16. Respiratory Problems • Bronchitis from inflammation of bronchioles which impede breathing • Premature babies have difficulty keeping alveoli open • Surfactants are secreted to combat surface tension, resulting from moisture surrounding the tiny sacs, which causes the alveoli to stick together • Don’t appear until about 33 weeks after conception • Alveoli highly susceptible to contaminants • Macrophages patrol, but extensive damage can decrease gas exchange • Pollutants from air and tobacco can inflame the lungs • Can lead to COPD

17. Smoking Risks • 1 drag exposes lungs to 4,000+ chemicals • Can irritate ciliated cells and inhibit flagellum movement • Kills macrophages in lungs • Can lead to emphysema, lung cancer, ‘smoker’s cough’, heart attacks, and stroke • 15 years of quitting can reverse effects

18. Ventilating Our Lungs • Breathing is the alternation of inhalation and exhalation • Maintains high O2 and low CO2 • Inhalation rib cage expands as rib muscles and diaphragm contract to enlarge chest cavity • Increases lung volume, pressure in alveoli less than atmosphere, are diffuses from nostrils to alveoli = negative breathing • Exhalation reverses muscle movements • Decreases lung volume, pressure is more so air pushed out, aided by upward movement of diaphragm • Vital capacity is max amount of air inhaled and exhaled

19. Breathing Techniques

20. Automatic Control • Breathing control centers in the brain include the pons and medulla • Voluntarily hold our breathe and change rate, but most breathing is involuntary • Nerves from brain signal contraction of rib muscles and diaphragm • Regulated in response to CO2 levels in blood • Exercise speeds up metabolism so more CO2 created • Forms carbonic acid, sensed by medulla which increases breathing rate • Aorta and carotid arteries also have CO2 sensors and O22 ones • Signals control centers accordingly

21. Respiratory Control System

22. Respiratory Gas Transport • Blue colored side is O2 poor • Blood from capillaries to heart which transports to alveoli for exchange • Red side is O2 rich • Blood from alveoli return to heart which transports to tissues • Gas exchange via diffusion across a pressure gradient • Air is a mix of gases with pressure • Each type of gas contributes a partial pressure • Each gas type moves down individual gradients

23. Hemoglobin • O2 is not soluble in H2O so must be transported by proteins called respiratory pigments, or colored molecules • Iron containing pigment that turns red with O2 • 4 polypeptide units of 2 types, each with an attached heme group and Fe atom in the center • 1 Fe to 1 O2 molecule • Helps transport CO2 and buffer blood • Upon entering RBC’s, hemoglobin binds some CO2, rest dissociates into H+ and HCO3- • Hemoglobin binds H + to minimize blood pH change • Remember pH drop increases breathing rate

24. O2 and CO2 Exchange CO2 + H2O H2CO3 H+ + HCO3- Carbon Water Carbonic Hydrogen Bicarbonate dioxide acid ion Reaction reverses as blood flows through the capillaries in the lungs

25. Human Fetus • Within the uterus the fetus survives in the amniotic fluid, a watery environment characteristic of most terrestrial animals • Lungs are nonfunctional and fluid filled • Gas exchange occurs through the placenta • A vascularized organ of maternal and fetal tissue • Capillaries branch to exchange gas within the maternal circulatory system • Fetal hemoglobin has a higher affinity than adult for O2 • Upon birth placental gas exchange stops • CO2 in fetal blood increases, pH drops, and breathing centers are stimulated = first breath