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Chapter 42 Circulation and Gas Exchange Material Exchange The exchange of materials from inside to outside is an important function for organisms. It’s easy for unicellular organisms. It becomes more difficult for multicellular organisms. Complex organ systems have evolved to move materials throughout an organism. GAS Exchange in Animals RESPIRATORY SYSTEM – OXYGEN IS NEEDED FOR AEROBIC RESPIRATION – GAS EXCHANGE: UPTAKE OF O2 & DISCHARGE OF CO2 – RESPIRATORY MEDIUM: SOURCE OF OXYGEN AMOUNT OF DISSOLVED O2 IN WATER LESS THAN IN THE AIR RESPIRATORY SURFACE PART OF ANIMAL WHERE GAS EXCHANGE OCCURS DIFFUSION THIN AND LARGE MAXIMIZE DIFFUSION CELLS MUST BE BATHED IN WATER TO MAINTAIN PLASMA MEMBRANE – SURFACES THUS ARE MOIST – SIZE INFLUENCED BY SIZE OF ANIMAL – ENDOTHERM HAS LARGER R.S. THAN ECTOTHERM OF SAME SIZE Respiratory System EXTENSIVE FOLDING OR BRANCHING – ENLARGENS SURFACE AREA FOR GAS EXCHANGE In animals that don’t respire through their skin, there are three common respiratory surfaces: 1. Gills 2. Trachea 3. Lungs 1. Gills Are out-foldings of the body surface suspended in water. Creates a large surface area They are loaded with capillaries. Animals with gills ventilate them which moves water with a high concentration of O2 over them. This ventilation consumes a lot of energy!! 1. Countercurrent Exchange Gills Blood moves in an opposite direction to the movement of water past the gills. The O2 transfer is highly efficient. This is called counter-current exchange, and loads the blood with O2. It keeps a diffusion gradient over the entire length of the capillary. PROBLEMS ASSOCIATED WITH WATER AS A RESPIRATORY MEDIUM O2 CONCENTRATIONS ARE LOW THE WARMER, THE LES DISSOLVED OXYGEN IT CAN HOLD THE SALTIER, THE LES DISSOLVED OXYGEN IT CAN HOLD OVERCOME BY VENTILATION FISH OPENS WATER, WATER PASSES THROUGH PHARYNX & OVER GILLS (FISH EXPEND A LOT OF ENERGY VENTILATING GILLS!!) Terrestrial breathing: Air has advantages over water as a respiratory medium Higher O2 conc Gas exchange faster through air Less ventilation of Resp. Surfaces required AND DISADVANTAGES: Resp surfaces continuously desiccate ( dry out) Evolution overcomes this problem: surfaces within animal) 2. Tracheal System Found in insects. Tubes that branch through the body Delivers air to all body cells Air enters tracheae through pores (spiracles) at the surface, passes through smaller tracheoles; end at cellular membranes. Air sacks 3. Lungs Restricted to one location in body. Circulatory system connects respiratory surface with all body cells. They have a dense net of capillaries immediately below the epithelium on the respiratory surface. Air Pathway Nares, pharynx, larynx, trachea, bronchi, bronchioles, alveoli It is like a tree tipped upside down. The epithelial lining of the three major branches of the respiratory system are covered by cilia and a thin film of mucus. Air Pathway The mucus traps particulate matter and the cilia sweeps it out. O2 dissolves in the moist film covering the epithelium and quickly diffuses into the web of capillaries surrounding the alveolus. CO2 diffuses in the opposite direction. Alveoli Tips of smallest bronchioles Clusters of dead-ended air sacs Site of gas exchange Surrounded by web of capillaries Diffusion by differences in partial pressures (air is only part oxygen/CO2) High to low Oxygen Transport By respiratory pigments in the blood Hemoglobin –most vertebrates – Reversible binding – Iron Cooperative unloading – Unloading of O2 from one heme group stimulates unloading from the other three in a hemoglobin molecule Bohr shift is the lowering of hemoglobin’s affinity for oxygen upon a drop in pH. – This occurs in active tissues due to the entrance of Heme group CO2 into Ironthe atom blood O2 loaded in lungs O2 unloaded O2 Oxygen Transport Cooperative unloading – Unloading of O2 from one heme group stimulates unloading from the other three in a hemoglobin molecule Bohr shift is the lowering of hemoglobin’s affinity for oxygen upon a drop in pH. – This occurs in active tissues due to the entrance of CO2 into the blood Heme group Iron atom O2 loaded in lungs O2 unloaded In tissues O2 O2 Carbon Dioxide Transport Most transported in the plasma as bicarbonate ions: HCO3- CO2 enters RBC’s In RBC’s, CO2 converted into bicarbonate. Then diffuses out of RBC’s into the plasma 1 2 Carbon dioxide produced by body tissues diffuses into the interstitial fluid and the plasma. Over 90% of the CO2 diffuses into red blood cells, leaving only 7% in the plasma as dissolved CO2. Tissue cell Some CO2 is picked up and transported by hemoglobin. 1 Blood plasma CO 2 within capillary Capillary wall 2 CO2 Carbonic acid dissociates into a biocarbonate ion (HCO3–) and a hydrogen ion (H+). HCO3– 7 Hemoglobin binds most of the H+ from H2CO3 preventing the H+ from acidifying the blood and thus preventing the Bohr shift. Figure 42.30 9 Carbonic acid is converted back into CO2 and water. 10 CO2 formed from H2CO3 is unloaded from hemoglobin and diffuses into the interstitial fluid. To lungs CO2 transport to lungs HCO3– 8 H2CO3 Hb 9 11 CO2 Hemoglobin releases CO2 and H+ H2O CO2 6 In the HCO3– diffuse from the plasma red blood cells, combining with H+ released from hemoglobin and forming H2CO3. 6 HCO3– + H+ 5 8 Red Hemoglobin H2CO3 blood Carbonic acid Hb picks up cell CO2 and H+ 5 + H+ Bicarbonate However, most CO2 reacts with water in red blood cells, forming carbonic acid (H2CO3), a reaction catalyzed by carbonic anhydrase contained. Within red blood cells. Most of the HCO3– diffuse into the plasma where it is carried in the bloodstream to the lungs. 3 4 HCO3– 4 7 Interstitial CO 2 fluid H2O 3 CO2 transport from tissues CO2 produced CO2 CO2 10 CO2 11 Alveolar space in lung diffuses into the alveolar space, from which it is expelled during exhalation. The reduction of CO2 concentration in the plasma drives the breakdown of H2CO3 Into CO2 and water in the red blood cells (see step 9), a reversal of the reaction that occurs in the tissues (see step 4). Elite Animal Athletes Migratory and diving mammals – Have evolutionary adaptations that allow them to perform extraordinary feats Diving Mammals-seals, dolphins, whales Google – Stockpile O2 Higher myoglobin concentration in their muscles Large spleen-store blood – and deplete it slowly Blood diverted FROM muscles Pulse slows upon diving Diving Mammals-seals, dolphins, whalesGoogle Image Result for http-bp3_blogger_com-_5v0u3ocGyrYRyLZteHqzUI-AAAAAAAAAxMgkbrVHneoMk-s400Cachalot_jpg.mht Breathing The diffusion of a gas depends on partial pressures. When water is exposed to air, the amount of gas dissolved in the water is proportional to the partial pressure in the air, and its solubility in water. Gases always diffuse from regions of high partial pressure to regions of low partial pressure. How an Amphibian Breathes An amphibian such as a frog – Ventilates its lungs by positive pressure breathing, which forces air down the trachea How a Mammal Breathes Mammals ventilate their lungs – By negative pressure breathing, which pulls air into the lungs Rib cage expands as rib muscles contract Air inhaled Rib cage gets smaller as rib muscles relax Air exhaled Lung Diaphragm INHALATION Diaphragm contracts (moves down) Figure 42.24 EXHALATION Diaphragm relaxes (moves up) Lung volume increases – As the rib muscles and diaphragm contract Breathing & Amount of air inhaled Tidal volume is the volume of air inhaled & exhaled with each breath.(.5 l) – Vital capacity: The MAXIMUM -- during forced breathing is 3-4.8L Residual volume is the amount remaining in the lungs after a forced exhale. Breathing Human breathing is mostly under autonomic control. 2 regions of the brain control this: – The pons and the medulla. The pons controls the medulla which sets a basic breathing rhythm. Breathing Sensors in the aorta and carotid arteries exert secondary control over breathing. These sensors monitor O2, CO2 and blood pH. The pH is largely controlled by CO2 levels. Breathing When CO2 levels increase, carbonic acid levels increase lowering the blood pH. When pH drops, the depth and rate of breathing increases helping to remove excess CO2. O2 levels only have an effect on breathing rate at high altitudes. Breathing In addition to transporting O2, hemoglobin helps transport CO2 and assists in buffering. Respiring cells produce CO2. Carbonic anhydrase catalyzes the reaction of CO2 with H2O to form H2CO3. H2CO3 dissociates into H+ + HCO3 Most of the H+ attaches to hemoglobin and other proteins minimizing the change in blood pH. Breathing HCO3- diffuses into the plasma. As blood flows through the lungs, the process is reversed. Diffusion of CO2 out of the blood shifts the chemical equilibrium in favor of the conversion of HCO3- to CO2.