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The Respiratory System

The Respiratory System. Requirements: Relies on diffusion across a membrane, so must be thin with large surface area Diffusion constant varies according to medium/temperature

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The Respiratory System

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  1. The Respiratory System • Requirements: • Relies on diffusion across a membrane, so must be thin with large surface area • Diffusion constant varies according to medium/temperature • Need bulk flow of water or air, slow enough to juxtapose medium and blood, fast enough to maintain diffusion gradient • Ventilation rates or respiratory area variable – according to level of activity of organism

  2. WATER PROBLEMS 1. O2 content in air = 210ml/L O2 content in fresh water = 6.6ml/L (at sea level) O2 content of sea water = 5.3ml/L 2. Water much denser and more viscous than air So requires large respiratory surface and move large volumes of water, but not at too high an energetic cost. • Other problems: • CO2 very soluble in water but pH may decrease • Proximity of blood and water means heat lost so same temp as environment

  3. Tunicates, cepahlochordates Small and inactive so NO Gills. Body & pharynx wall serve as respiratory membranes Pharyngeal slits

  4. GILLS External gills – many fish larvae and amphibian larvae

  5. Internal gills Brachiomere components – cartilage becomes gill ray, muscle, nerve, aortic arch = interbranchial septum

  6. 5 (no spiracle) 6 (1st = spiracle) 15! 7 Extinct jawless fishes Hagfish = 14 Chondrichthyans, early bony fish NUMBERS - variable

  7. Lamprey = POUCHED GILLS (present in internal chambers). Gill lamellae in jawless line all the pouches – through to be ancestral

  8. Elasmobranchs – SEPTAL GILLS (present all along the interbranchial septum). Gill rakers in pharynx stop food going into gills. Distal tips of interbranchial septae act as valves for closing

  9. Structure – interbranchial septum, primary gill lamellae, secondary gill lamellae Blood in from heart Blood out to body

  10. Water flows opposite direction to blood = countercurrent = far more efficient that both flowing in same direction – up to 95% of O2 taken up

  11. inspiration expiration Elastic recoil of visceral skeleton also important. Fast moving sharks also use open mouths

  12. BONY FISHES Operculum covers gills so only one external gill slit. Interbrachial septa reduced so gill lamellae extend freely in opercular cavity = ASEPTAL GILLS.

  13. Principles of flow the same as sharks, but because of opercular cavity water flow across gills during suction as well. Result is a CONTINUOUS flow of water across gills. Good diffusion because water:blood interface only 1 cell thick Active fish have 10X greater surface area of gills than sluggish, bottom dweller

  14. Air and water breathers – found in water with low O2 content (shallow warm pools, swamps) Accessory respiratory organs • Vascular skin – eels migrating over land • Modified gut – perches gulp air and keep it for 30 minutes • Climbing perch, walking catfish have dorsal outpocketing to form suprabranchial air chamber and one of the gill arches develops a vascular arborescent organ to protrude into it and make a ‘lung’

  15. Many bony fish have either lungs or swim bladders, most primitive ones have most ‘lung-like’ structures so evolved early – freshwater stagnant habitats, periodic drying out e.g. gar, reed fish, bowfin, pirarucu (Actinopterygians) Lungfish (Sarcopterygians) Lungs

  16. Pulse-pump system – lungs expand due to force of pushing air into them from the oral cavity. Aspiration pump already present in fishes

  17. Lungfish also has pulse-pump system but with mixed air – typical of Sarcopterygians Lung lining folded to some degree to compartmentalise for increased surface area. Surfactant present – lipoprotein – acts like an anti-glue to prevent cells sticking together.

  18. Swim bladders and gar lungs develop from dorsal foregut In these lungs develop from ventral floor of foregut so tetrapod lungs could be a primitive feature

  19. SWIM BLADDER Arises from the primitive Actinopyterygian lung O2 rich water, lungs converted into buoyancy organ, but can also take up O2 (so lung as well). Arises as dorsal outgrowth (previous slide). Contains 80% O2 – secreted into swim bladder from gas gland, against pressure gradient. Walls made of guanine plates to prevent diffusion out. Rete mirabile acts as a countercurrent system to prevent O2 leaving Considered to be a biological marvel

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