Respiratory system Encouraging diffusion Function: • surface area - gill lamellae, infolding • Gas exchange with environment • Exchange CO2 for O2 depends on: Diffusion ~ SA x gradient distance lamprey X-section Encouraging diffusion Encouraging diffusion • distance across - thin walls of • gradient - counter-current exchange of capillaries, thin skin for cutaneous gills, tetrapod ventilation respiration. Cell thickness at aveoli 1 Fish respiratory systems Development of internal gills • Ectoderm meets endoderm Fish respiratory anatomy Countercurrent exchange • Lamprey, Chondrichthyes, Osteoichthyes 80-95 of O2 taken up Osmotic issues may cause fish to not ventilate or exchange 2 Ventilation mechanics – Water flows over gills via suction and Fish respiratory systems force pump, using branchial muscles Fig. 18-6 • Low oxygen-content environments Fish lungs – Solubility of O2 is better in cold water Dissolved O2 in water is only 3% of O2 in the o o (at O C ~10 ml O2 at 30 C ~5 ml O2) same volume of air Accessory respiratory surfaces: cloaca, mouth, esophagus, intestine, skin, lungs Lungs evolved early in Gnathostomata from an outpocketing of the gut Modified gill arches poke into air chamber in mouth 3 During the “age of fishes” Lungs and swim bladders • Early freshwater bony fish would have low • Even in fish, there is surfactant, glottis O2 environments • Pulse pump of most fish w/lungs, Lungs vs. swim bladders amphibians • Lungs later developed a hydrostatic fxn • (swim bladder) • Swim bladders became dorsally located 4 Physostomous vs. Physoclistous Physoclistous swim bladder • Gas still secreted against strong gradient • Countercurrent multiplier w/rete mirabile • Incoming O2 • Gas gland Result of exchange Tetrapod respiration Amphibian respiration, vocalization • Need moist surfaces, but little water loss • Cutaneous respiration usually dominates when ventilating • Septas provide SA – Frog lung 1 cm3, 20 cm2 surface area Vibrations here get resonated here – Mouse lung 1 cm3, 800 cm2 surface area 5 Reptile respiration • Because of longer neck, larynx and Crocodilian ventilation trachea are found in reptiles • Muscle extends from liver to pelvis, liver • Lungs primary gas exchange site movement is similar to mammal diaphragm • Aspiration pump in amniotes p.593 Evolutionary constraint: running Solutions to the constraint and breathing • Erect stance – movement in vertical plane • Tetrapods w/ sprawled limbs depend on lateral bending in locomotion. – Flexion of trunk interferes with lung expansion on that side • Bounding encourages breathing w/each gait 6 Solutions to the constraint Bird respiration • Most efficient respiration bc of flying and • Aquatic air breathers: endothermy constraints – Use dorsal ventral flexion • Lungs small, non expanding – Use limbs simultaneously • Air sacs hold great volumes, allow for unidirectional flow Bird respiration • Inhalation • Lungs - parabronchi – exchange at air capillaries • Exhalation Air through parabronchi 7 Bird ventilation Bird syrinx • Uncinate processes • Syrinx - similar to larynx, but after split increase lever arm for into bronchi. rib cage ventral expansion Mammal respiration Nasal and oral cavities • In mammals, the soft palate touches the • Larynx has vocal epiglottis, allowing constant separation of cords, epiglottis food and air Breathing Talking epiglottis 8 Humans are an exception Mammal respiration • Bidirectional ventilation – dead air (20%) • Humans - Epiglottis does not contact • Greatest SA of tetrapods soft palate. Modification for speech – Young babies have • Pleural cavity, diaphragm contact soft palate epiglottis Costal ventilation External Internal Intercostal Intercostal 9 .