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01:119:115 (825)
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Ch. 46

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Biological Sciences

Ch. 46 Respiration Gas exchange in water • Fish: gills for gas exchange • Gills are flaps of tissue richly supplied with blood vessels • Fish draws water into its mouth and across gills • O2 diffuses into blood vessels of gill • Co2 laves blood vessels and enters water Gas exchange in Air • Terrestrials: air has advantages over water: • Greater concentration of molecular oxygen • O2 diffuse faster Air is less dense/viscous and therefore more energy efficient • Terrestrial Adaptations for Gas Exchange • Fig 46-1a: Some invertebrates (most annelids) and some vertebrates (many amphibians): exchange gases across body surfaces with no specialized respiratory structures • Fig 46-2 insects and other arthropods - air (O2) enters spriacles, tracheal tubes, and then tracheoles which conduct 02 to cell systems e.g. Muscle cells needed for flight • Co2 (more dense than air) is expelled Evolution of Vertebrate Lungs Fig 46-4 • Birds: evolved elaborate system of lungs and air sacs. • Air is sucked into anterior sacs (via trachea) then on to lungs, and then posterior sacs before it is blown out of lung (via trachea) • Sacs also hold residual air volume to help in flight • Mammalian lungs: buried deep in body prevents dehydration; have millions of alveoli that increase the surface area available for gas exchange (Fig 46-6) The Human Respiratory System Fig 46-6 Each lung occupies thoracic cavity: covered with pleural membrane (pleura)- pleuritis • • Air passes: through nasal cavities - pharynx (throat) - larynx (voice box) - trachea - bronchi (lined with ciliated cells) - bronchioles - alveoli - where O2 and CO2 is exchanged • A flap or epiglottis closes off larynx to prevent food going into lower airways - swallow reflex Muscular diaphragm forms the flood of the thoracic cavity • ← Inhalation is an active process (Fig 46-8) • Contractions of external intercostal muscles (outside ribcage between the ribs): • Elevation of ribs and sternum increases front-to-back dimension of thoracic cavity Contraction of diaphragm: • • Moves diaphragm downward, expanding vertical dimension of thoracic cavity • Result: lowers air pressure in lungs: air (containing O2) moves into lungs ← Exhalation is a Passive Process (Fig 46-8) • Relaxation of external intercostal muscles and diaphragm • Returns diaphragm, ribs and sternum to resting position • Restores thoracic cavity to pre-inspiration volume • Result: increases pressure in lungs so air (containing CO2) is exhaled Fo
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