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Animals breathing Air summarized lectures notes along with relevant pictures and notes from the assigned readings

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Western University
Biology 2601A/B
Brent Sinclair

Organismal Phys Lecture 16 Gas Exchange 2: Animals Breathing Air Concurrent Gas Exchange  Medium and blood flow in the same direction  At end of flow, end up with intermediate level of O₂ in blood  As deoxygenated blood enter the gas exchange surface, it comes into contact with the fully oxygenated external medium  As blood flows through the gas exchange surface, the PO₂ approaches that of the exhaled medium Counter-current Gas Exchange  (refer to last lecture)  Medium and blood flowing in opposite ways  Get high O₂ in the blood  Always a concentration gradient between the medium and the blood  Heat transfers to incoming vessel; less heat is lost to the outside world  Less heat is required to re-heat the incoming blood Cross-current Gas Exchange  Medium intersects blood flow at various points  Multiple capillaries are arranged at an angle to the flow of the external medium  After they exit the gas exchange surface, these capillaries join into an efferent blood vessel  The first vessel that crosses the gas exchange surface encounters a fully oxygenated medium, yielding a high PO₂ in the capillary, but subsequent capillaries encounter a progressively O₂-depleted medium and thus have somewhat lower PO₂  PO₂ leaving the gas exchange surface is generally higher than concurrent, but lower than counter-current  The slower the flow of the medium in relation to blood flow, the lower the blood PO₂ will be leaving Lungs  Are undergoing tidal gas exchange (tidal volume is the normal amount of air displaced between normal inspiration and expiration when extra effort is not applied)  Highly vascularised; O₂ moves from inhaled air into the blood Mammal Lungs Are Inefficient: Tidal Ventilation & Dead Space in Alveoli  Similar to concurrent  As blood leaves gas exchange area, the blood contains approximately same O₂ as the medium  Animals that tidally ventilate are generally unable to completely empty their respiratory cavity with each ventilatory cycle  As the animal breathes in, the incoming fresh medium mixes with that of the medium in the respiratory cavity; therefore the PO₂ in the respiratory cavity is lower than that of the external medium  Also need to note that there is dead space in the alveoli when breathe in and out the tidal volume is only 500mL o When you breathe very deeply, you can increase your lung capacity (therefore, normally have extra volume in your lungs that you don’t use Breathing Air  Lots of O₂ available  Is not so easy to get rid of CO₂, but is not impossible  There are problems with water loss (especially if air is dry)  Use lungs for gas exchange (invaginations)  Fish can use their gut, swim bladder or mouth as an air breathing organ; the blood will go through air breathing organ in parallel to systemic tissues Ways to Maximize O₂ Uptake  The energetic costs of flying are 2.5-3x higher than running (very expensive)  Constraints for flying is O₂ availability  There are two groups of extant flying vertebrates (birds and bats)  Organisms can maximize O₂ uptake by o Counter-current exchange o Increase flow rate o Increase SA o Reduce diffusion distance Bird Lungs: A One-Way System  Are highly specialized and are extremely efficient (can extract high % of O₂ from air)  Lungs are relatively small in comparison to air sacs  Lungs consist of a one way tube for air The Bird Lung – Orientation  1° bronchus is the same as the human trachea  The is the gas exchange surface  The mesobronchus connects in parallel to the lungs  Birds can exchange large amounts of O₂; needed for flying Bird Lung – Breathing In  Expansion of the chest during the first inhalation causes fresh air to flow through the bronchi to the posterior air sacs (step 1)  Expansion of the chest during the second inhalation causes stale air to flow from the lungs into the anterior sac (step 3) Bird Lung – Breathing Out  Compression of the chest during the first exhalation pushes the fresh air from the posterior sac into the lungs (step 2)  Compressio
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