Gas Exchange Study Notes PDF

Gas Exchange: Animals  Gas Exchange Across Respiratory Surfaces For gases to move across a membrane involves diffusion surface must be moist to dissolve gases  Multicellular & Gas Diffusion Oxygen will only penetrate < 0.5mm into a group of cells, for most multicellular...

Gas Exchange: Animals  Gas Exchange Across Respiratory Surfaces For gases to move across a membrane involves diffusion surface must be moist to dissolve gases  Multicellular & Gas Diffusion Oxygen will only penetrate < 0.5mm into a group of cells, for most multicellular organisms sufficient O2 cannot be obtained by diffusion across body surface alone. God designed multicellular organisms to enhance gas exchange through 1. Increasing ventilation[moving air/water around] 2. Increased vascularisation 3. Increasing surface area 4. Specialization of cells 5. Specific Oxygen carrying molecules  1. Increasing ventilation[moving air/water around] To keep high gradient difference for O2/CO2, many organisms create air or water currents that continuously keep concentration of gases high at the desired level for diffusion over the respiratory surfaces e.g counter current systems Done by, muscular activity causing inhalation/exhalation, fish operculum beat and fish swim, cilia beating Carry gases away internally to keep gradient high. e.g vascularisation/ moving internal fluids  Ventilation of water in fish Fish need water flow past the gills to keep a high concentration of oxygen compared to their blood. Mobile fish (such as tuna) swim with their mouth open to continuously move water passed the gills Most bony fish use pumping action to ventilate; some can alternate  2. Increasing surface area and decreasing diffusion distance Some multicellular organisms are flat and thin so no cells are far from external supply e.g flatworms, tapeworm, leaves Specialized respiratory organs that increase the surface area available for diffusion – Gills, tracheae, and lungs – These adaptations bring the external environment (air or water) close to the internal fluid such as blood or hemolymph, which is circulated throughout the body Maximization of Gas Diffusion Maximization of Gas Diffusion Gill diffusion using counter-current flow  Specialized cells Specialised tasks include carrying oxygen. E.g. Red blood cell - only function is to carry oxygen.  Gas attracting molecules Molecules such as haemoglobin [iron based in mammals and others] or heamocyanin [copper based in arthropods and others] leghemoglobin [in plants such as legumes] chemically attract oxygen to increase their solubility. This means that body fluids such as blood can absorb and carry more oxygen than without.  Hemoglobin Oxygen has a low solubility; blood plasma can only contain a maximum of 3mL O2 per liter However, whole blood contains ~200mL O2 per liter since most of the O2 in the blood is bound to hemoglobin O2 is transported by respiratory pigments  Structural & functional adaptations for gas exchange What does this graph tell you?  Mediums: Air vs Water Carbon dioxide is more soluble than Oxygen in water The warmer the water the less oxygen is dissolved Oxygen concentration is 100x more available in air than water. e.g. air 20% O2 water 1-2% O2 Need more efficient gas exchange design when living in water to extract sufficient oxygen. What design features are they?  Gills Gills are specialized extensions of tissue that project into water – External gills are not enclosed within body structures; many fish and amphibian larvae – External gills require constant movement to ensure contact with fresh (high O2) water axolotl Gills  Gills In bony fishes, the gills are located between the oral cavity and the opercular cavities These two cavities operate as pumps that alternately expand – Water is moved into the mouth, through the gills and out of the fish through the open operculum, or gill cover  Videos https://www.youtube.com/watch?v=_2kjL9 BV3SA Bony fish have four gill arches on each side of their heads Each gill arch is composed of two rows of gill filaments, which consist of lamellae, thin membranous plates that project out into the flow of water Water flows past the lamellae in one direction only; blood flows opposite to this direction (countercurrent gas exchange)  Maximization of Gas Diffusion H 20 http://life.bio.sunysb.edu/marinebio/o2countercurrent.jp g Large surface area, high blood flow Countercurrent exchange – deoxygenated blood flows in one direction, while oxygenated blood flows in the other; maintains a high concentration gradient Countercurrent gas exchange Blood circulation in fish  Skin surface as a respiratory organ O2 and CO2 are able to diffuse across the skin [mucous membranes] in some vertebrates – amphibians – turtles Requires skin to be constantly moisture Supplements lung respiration Tracheal systems in Arthropods Tracheal systems are found in arthropods Respiratory system consists of small, branched trachae, or air ducts, which branch into tracheoles, a series of tubes which transfer gases directly to cells. Air enters into trachea through spiracles Body fluid circulates around tracheal system, obtaining oxygen and losing carbon dioxide, by diffusion  Figure 42.22 Tracheal systems Arthropod Gas exchange [Nelson txtbok]  Lungs in terrestrial vertebrates Air is less (structurally) supportive than water Unlike gills, internal air passages such as trachea and lungs can remain open because the body provides the necessary structural support Water evaporates Terrestrial organisms constantly lose water to the atmosphere; gills would provide an enormous surface area for water loss Most terrestrial exchange surfaces are internalised are thin and highly vascular protected and physically supported prevent moisture loss. lung minimizes evaporation by moving air through an internal tubular passage  Lungs Air drawn into the respiratory passages becomes saturated with water vapor prior to reaching the inner region of the lungs A thin, wet membrane permits gas exchange A two-way flow system (gases move into and out of lungs through same airway passages)  Air characteristics Air contains a constant proportion of gases – 78.09% nitrogen – 20.95% oxygen – 0.93% argon and other inert gases – 0.03% carbon dioxide Lungs work by changing air pressure. Because of gravity, air exerts a downward pressure (atmospheric pressure; 760mm Hg) it enters the lungs which are at a lower pressure  Lungs of Amphibians The lungs of amphibians are saclike outpouchings of the gut Surface area increased by folds Amphibians breathe by forcing air into their lungs: positive pressure breathing Also use their body surface as a respiratory organ. Thus it must be moist and is convoluted Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Nostrils Air open External nostril Buccal cavity Esophagu s Lung s a. Nostrils closed Air b.  Lungs of Reptiles Terrestrial reptiles have dry, scaly skins which prevent surface respiration Expand their rib cages by muscular contraction; this creates a lower pressure inside the lungs compared to the atmosphere, which moves air into the lungs: negative pressure breathing Same in mammals  Lungs of Mammals Endothermic (“warm-blooded”) animals, such as birds and mammals, require more efficient respiratory systems than ectothermic (“cold-blooded”) animals due to their increased metabolic oxygen demands The lungs of mammals are packed with millions of alveoli, sites of gas exchange – Provides lung with enormous surface area for gas exchange Lungs of Mammals Maximization of Gas Diffusion Large surface area/highly vascularised/moist The alveolus (singular) is composed of epithelium only 1 cell thick, and is surrounded by capillaries with walls that are also only 1 cell layer thick. The distance across which gas must diffuse is very small, only 0.5-1.5μm  In summary: lung design Alveoli are surrounded by an extensive capillary network Gas exchange between the air and blood occurs across the thin walls of the alveoli Red blood cells pass through capillaries in single file; O2 from alveoli enters the red blood cells and binds to hemoglobin Surface area of respiratory system is greatly enhanced; much more than amphibians and reptiles  Lungs of Birds Most efficient respiration of all terrestrial vertebrates Gas exchange occurs in parabronchi Air flows through the parabronchi in one direction only In other terrestrial vertebrates, inhaled (fresh) air is mixed with O2-depleted air from the previous breath In birds, the unidirectional flow allows only fresh air to enter the site of gas exchange  Lungs of Birds Respiration in birds occurs in 2 cycles: – 1. Inhaled air is drawn in from the trachea into posterior air sacs, and exhaled into lungs – 2. Air is drawn in from the lungs into anterior air sacs, and exhaled through the trachea http://people.eku.edu/ritchisong/birdrespiration.html  Features of Gas exchange surfaces are 1. Large SA 2. Moist 3. Vascularised 4. Thin 5. Ventilated  Hemoglobin Oxygen has a low solubility; blood plasma can only contain a maximum of 3mL O2 per liter However, whole blood contains ~200mL O2 per liter since most of the O2 in the blood is bound to hemoglobin O2 is transported by respiratory pigments – Bound to hemoglobin inside red blood cells (all vertebrates, most inverts), or hemocyanin in the plasma (arthropods and some molluscs) Hemoglobin  Heamoglobin Hemoglobin acquires O2 in the alveolar capillaries – O2-bound haemoglobin (oxyhaemoglobin) appears bright red – Haemoglobin without O2 (deoxyhaemoglobin) appears dark red, but has a bluish hue in tissues – Hemoglobin provides an oxygen reserve Only 1/5 of oxygen is released to muscles by oxyhemoglobin; the reminder serves as a reserve during physical exertion, and ensures enough O2 to maintain life for 4-5 minutes if breathing is interrupted or the heart stops In Summary: Types of gas exchange structures/designs