The process of breathing Air has much more oxygen than water (20% vs. 0. %) Gas effuses more rapidly in air; water is much more dense and viscous Therefore aquatic animals are highly efficient at extracting oxygen form water However, they must expend much more energy to do so (up to 20% vs. 1-2% of resting metabolism) Respiratory surfaces must be thin and wet so that gas can diffuse through an aqueous phase between environment and circulation (also to maintain cells themselves) Air breathers have adapted specialized investigation of the body to “take in” air Ventilation-mechanisms to move air into and out of the body Paginations gills) for water breathing Investigation (lungs and tracheae) for air Types of respiratory organs Direct diffusion (coetaneous respiration) protozoa, sponges, cnidarians, some worms Possible because these animals have large areas relative to their mass (and all cells are close to the outer surface). See where a circulatory system comes in?

Larger animals (amphibians, eels) supplements breathing with coetaneous respiration Skins are heavily visualized Hibernating frogs and turtles can exchange all gases through skin while submerged Presence of gills can vary through animal velveteen All chordates have gill slits at some point Gills: efficient gas exchange in water Many different types of gills external extensions of body surface dermal paella: sea stars breaches tufts: marine worms, aquatic amphibians internal gills- fishes, arthropods lots of vascular- blood flow is opposite to flow of water across gills (counterculture flow) Propeller (gill cover) closes when mouth opens Water passes over gills and out propeller Counterculture exchange Maximizes transfer of oxygen from water to blood Gills must be continuously in water (I. E. N aquatic animals) or they will collapse and dry out Terrestrial animals require internal tubes to move air into the body tracheal systems lungs Air vs. water Much higher concentration of oxygen in air Gases diffuse faster in air; less ventilation and less energy required of the animal Internalizing the respiratory tubes minimizes water loss

Breathing in amphibians: positive pressure Reptiles, birds and mammals use negative pressure: expand thoracic cavity to pull in air Frogs draw air into the mouth, then drive it into the lungs by closing mares , raising mouth floor and driving air into the lungs Mouth cavity is visualized; often frogs do not use their lungs Birds’ system has evolved to meet the demands of flight Birds have lost part of their digestive systems and make room for air sacs Mammalian respiratory system Properties of lungs Compliance- ability to expand when stretched Elasticity- ability to turn to original size Surface tension exerted by fluid in alveoli Surfactant helps prevent alveoli from collapsing RODS-surfactant lacking in the lungs of premature babies AWARDS- alveolar permeability and reduced surfactant Control of breathing; gas level detectors Why can’t you hold your breath indefinitely? Partial pressures to oxygen and carbon dioxide Most 02 in blood is bound to R (0. Ml out of 20 ml/100 ml blood is dissolved in plasma) Increasing POP in blood increases rate of diffusion to tissues Arterial levels are significant because they reflect lung function

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Respiratory pigments help transport gases (metallic ion confers color and binds oxygen) Hemoglobin- copper ion; found in arthropods and many mollusks Hemoglobin- iron; vertebrates Oxygen is bound reversibly Hemoglobin and oxygen transport Loading (in lungs) disemboweling becomes snowmobiling; reversed in tissues Affinity for oxygen decreases in lower pH and higher temperature 2,3-EDP (unique to Ribs) also reduces affinity of snowmobiling for oxygen (this works if oxygen levels are low or in anemia) Net effect: favors unloading of oxygen into tissues