Ch. 42

1. Gas Exchange Ch. 42

2. Gas Exchange Respiratory exchange, respiration…but NOT cellular respiration Supplies oxygen for cellular respiration and disposes of carbon dioxide Respiratory medium • air • 21% oxygen

3. Partial Pressure Gradients in Gas Exchange Partial pressure • The pressure exerted by a particular gas in a mixture of gases • Allows us to predict the net result of diffusion at gas exchange surfaces • A gas always diffuses from a region of high partial pressure to a region of lower partial pressure

4. Specialized surfaces Oxygen exchange easy with air…not so much with water Respiratory surfaces • Part of body where gas exchange occurs • Must always be moist • Are large and thin to make diffusion speedy Surfaces can be… • Thin, moist epithelium • Skin • Gills, tracheae, lungs

5. Gills in Aquatic Animals Outfoldings of the body surface that are suspended in water Huge surface area Ventilation • Movement of the respiratory medium over the respiratory surface • Maintains the partial pressure

6. Gills … Countercurrent Exchange Exchange of a substance or heat between 2 fluids flowing in opposite directions Very efficient

7. Tracheal Systems in Insects Insects Air tubes that branch throughout the body Tracheae  largest of the tubes air enters through spiracles small insects rely only on diffusion larger insects may use rhythmic body movements for ventilation do not use circulatory system to transport O2 and CO2

8. Lungs • Localized respiratory organs • Highly vascularized invaginations of the body surface that are restricted to one area • Circulatory system must then transport the O2 and CO2 • Land snails: internal mantle as their lung • Spiders: booklungs • Amphibians: small & little SA • Turtles: lungs and membranes of mouth and nose

9. Mammalian Respiratory Systems • Thoracic cavity • Enclosed in a fluid filled sac • Air enters nostrils and is filtered by hairs, warmed and moistened • Air enters pharynx  glottis  larynx  trachea  bronchi  bronchioles  alveoli (respiratory surface) • Surfactant • Lines the alveoli to reduce surface tension

10. How an Amphibian Breathes Breathing • Process that ventilates the lungs Positive Pressure Breathing • Muscles lower floor of oral cavity • Air is drawn in through nostrils • Nostrils and mouth closed, floor of oral cavity rises • Air is forced down the trachea • Elastic recoil of lungs and compression of muscles in body wall causes exhalation

11. How a Bird Breathes Air only passes over gas exchange surface in one direction Incoming fresh air does not mix with air that has already carried out gas exchange Parabronchi replace alveoli Utilize air sacs

12. How a Mammal Breathes Negative pressure breathing Use diaphragm to expand thoracic cavity during inhalation Tidal volume • Volume of air inhaled and exhaled with each breath Inhalation mixes air that has already undergone gas exchange

13. Control of Breathing Medulla Oblongata • Contains neurons responsible for regulating breathing • Neural circuits form a breathing control center

18. Human Respiration

19. Coordination of Circulation & Gas Exchange

20. Respiratory Pigments Oxygen has a low solubility in water Respiratory pigments • Proteins that bind oxygen • Vertebrate hemoglobin • Four subunits; each with a heme group • Myoglobin • Oxygen storing molecule in muscles Carbon Dioxide Transport • Carbaminohemoglobin (23%) • 7% transported in plasma • 70% transported as bicarbonate ions

21. Deep Diving Mammals • Stockpile O2 and consume it slowly • Contain more myoglobin • Higher percentage of oxygen load is in the lungs (70%; 51% in humans) • Large spleen to store up to 24L of blood • Diving reflex slows the pulse • Reduce blood flow to muscles