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Gas Exchange Chapter 22 The Air Up There • Air is a fixed ratio of partial pressures (Px) • Air thins with increasing altitude – Gas in same ratio, but less of – 3000 m 1/3 less O2 • Sherpas, athletic training, and blood doping • Mountain sickness Revisiting Respiration Gas Exchange Breathing • Organismal level • O2 in CO2 out via diffusion Cellular Respiration • Cellular level • Use O2 to produce CO2 and ATP Exchange Application Respiratory Surfaces • Thin – Diffusion distance – Speed • Moist – Gases dissolved in solution • Large – SA to volume ratio – Energy demands Respiratory Mediums Water • Pro Air • Pro – Direct contact of respiratory surface to medium • Con – Less O2 • warm and salty even less – O2 diffusion slower – More energy to ventilate • Larger structures • Water supports weight – High concentration of O2 – Less dense – O2 diffusion faster • Con – Desiccation of respiratory surface • Small openings externally • Indirect contact of respiratory surface to medium Gill Systems • Aquatic organisms • Convoluted extensions of body surface (pink) • Ventilation varies between organisms – Move respiratory medium across respiratory surfaces • Inefficient on land – Desiccation – Tissue Mass • Mollusks, annelids, arthropods, echinoderms, fish, and amphibians Countercurrent Exchange • Exchange between 2 oppositely flowing currents • Maximizes O2 diffusion out of H2O – Concentration gradient maintained entire length – Compare to concurrent ‘Skin Breathers’ • Earthworms and some amphibians • Skin is respiratory surface – Circulatory system to distribute (hemoglobin assists) – Lower invertebrates without • Moist environments Tracheal System • Insects • Internal branched tube system – Connect all cells to environment – Prevents desiccation • Direct exchange – Open circulatory system • Hemolymph = nutrients only • Body movements assist Lungs • Branched internal sacs – Moist epithelium • Pigmented, closed circulatory system – Nutrient and gas transport • Most terrestrial vertebrates – Elaboration with movement to land – Variations between classes Lung Adaptation • Amphibians – O2 via positive pressure into small sacs – Skin also for exchange • Birds – 1 way flow increases efficiency – 2 cycles to complete • Mammals – Negative pressure – Incomplete removal – Myoglobin content varies Mammalian Respiratory System • Upper respiratory system – Nasal cavity • Warms air • Smells – Pharynx – Larynx • Vocal cords tensed to create sound • Lower respiratory system – Trachea • Cartilage rings – Bronchi (2) – Bronchioles – Alveoli • Diffusion with capillaries through interstial fluid Respiratory Cycle Inhale • Rib muscles (up) and diaphragm (down) contract • Chest cavity increases • Lowers air pressure in alveoli Exhale • Rib muscles (down) and diaphragm (up) relax • Chest cavity decreases • Increases air pressure in alveoli Respiratory Disruptions • Smoking – Inhibit cilia movement causes ‘smoker’s cough’ • Thicken bronchioles and reduce elasticity • Alveoli rupture – Stopping allows cilia and alveoli damage to reverse • Premature birth (37 weeks or less) – Surfactant production incomplete • Keeps alveoli from collapsing – Each breath requires large effort • Emphysema – Bronchi swell, tearing alveoli – Reduced SA for gas exchange • Pneumonia – Fluid in alveoli • Bronchitis inflames of bronchioles Respiratory Gas Transport • Blood circulates to all cells – Hemoglobin binds/carries • Protein bound to a metal • Carry 4 O2 molecules, some CO2 too • PO2 and PCO2 vary within the circulatory system – Blue and red vessels – Lungs: high O2, low CO2 – Body tissues: low O2, high CO2 • Pressure gradient facilitates gas exchange in tissue capillaries (purple) Control of Human Breathing • Most is involuntary – Control centers in brain • Medulla: inhalation signaling • Pons: smoothes out rhythm and depth • Driven by [CO2] in blood – Reactions • CO2 + H2O • H2CO3 H2CO3 (carbonic acid) H+ + HCO3 – CO2 levels increase • pH in blood/CSF lowered • Respiratory centers signaled • Carotid arteries and aorta monitor O2 also – Severe deficit, i.e high altitude – Increase rate and depth Human Fetus • Amniotic sac in uterus – Lungs are fluid filled • Placental role – Blood exchange with mother – Fetal hemoglobin • Birth stops gas exchange – pH drop, why? – First breath