4 27 2014 CHAPTER 45 Gas Exchange and Circulation PPT Notes 4 steps of gas exchange 1 ventilation occurs when air or water moves through a specialized gas exchange organ i e lungs gills 2 gas exchange takes place as CO2 and O2 diffuse btwn air water blood ventilatory surface 3 circulation dissolved CO2 and O2 transported through body 4 cellular respiration gas exchange btwn blood cells occurs in tissues where cellular respiration occurs CO2 and O2 diffuse btwn blood cells CO2 and O2 diffuse into water from atmosphere but amt of gas that dissolves depends on the solubility of gas in water o o water temperature o o presence of other solutes partial pressure of gas in contact w water Fick s Law Law of Diffusion Rate of diffusion kA P D where k is a diffusion constant A is the area for gas exchange P is the partial pressure gas on either side of barrier to diffusion and D is the thickness of the barrier to diffusion rate of diffusion of a gas depends on 5 parameters gas solubility temperature surface available for diffusion differences in partial pressures of the gas across gas exchange surface thickness of the barrier in diffusion identifies traits that allow animals to maximize rate which CO2 and O2 diffuse across surfaces all gases including CO2 and O2 diffuse in largest amounts when 3 conditions are met SA for gas exchange is large respiratory surface is extremely thin partial pressure gradient of the gas across the surface is large gills function as a countercurrent system external gills direct contact w water internal gills must have water brought to them flow of blood through capillaries is in opposite direction to the flow of water over the gill surface sets up countercurrent exchange system in each lamella exchange system creates large partial pressure of CO2 and O2 in water over blood efficient gas exchange over gills water flow over lamellae O2 as blood flow through lamellae O2 in aquatic habitats ventilation tends to disrupt water electrolyte balance homeostasis maintained by an active osmoregulatory system in insects trachea air filled tubes within insects that open to outside through pores called spiracles air moves into trachea and then by diffusion into cells sufficient for gas exchange in small insects in terrestrial animals air enters body through mouth nose o trachea carries inhaled air to narrow tubes called bronchi bronchioles narrower tubes of bronchi o o o o o o o o o o o o o o o o o o o lung organ for gas exchange encloses bronchioles portions of bronchi in human lungs airways into the human lungs alveoli alveolar gas exchange surface lungs expand contract in response to changes in pressure inside the chest cavity ventilary forces can be modeled by a balloon in a jar pressure more negative when breathing in breathing leads to loss of water by evaporation in terrestrial environments 4 27 2014 vertebrae ventilate lungs by pumping air via muscular contractions positive pressure ventilation mechanism for pumping air used by frogs air pushed into lungs negative pressure ventilation mechanism for pumping air used by humans other mammals air pulled into lungs pumping action in humans achieved by the diaphragm muscle ventilation in birds airflow through the avian lung is unidirectional continuous crosscurrent pattern of capillaries birds must be able to extract enough oxygen for extremely long flights at high elevations through 4 steps inhalation of air trachea air sacs posterior to lungs exhalation of air parabronchi in posterior portion of lungs inhalation of air air moves through parabronchi onto system of air sacs anterior to lungs exhalation of air air moves to atmosphere air from second inhalation moving through lungs blood connective tissue consisting of cells water o functions transportation of CO2 and O2 transportation of nutrients to cells from digestive system conveys hormones to target tissues organs delivers cells of immune system distributes heat plasma water portion of water extracellular matrix o platelets cell fragments that minimize blood loss o o white blood cells WBCs part of immune system o red blood cells RBCs transport oxygen from the lungs to body tissues participate in transporting CO2 from tissues to lungs in humans RBCs make up 99 9 of formed elements o hemoglobin oxygen carrying molecule consists of 4 polypeptide chains binds to a nonprotein group called heme heme contains iron ion Fe2 that can bind to O2 molecule each hemoglobin molecule can bind up to 4 O2 molecules in blood 98 5 O2 bound to hemoglobin 1 5 O2 dissolved in plasma oxygen hemoglobin equilibrium curve is sigmoidal sensitive to s in pH and temperature Bohr shift in pH and in temperature hemoglobin s conformation shape so it is more likely to release O2 at all levels of partial pressure of O2 makes hemoglobin more likely to release O2 during exercise in which pCO2 is high pH is low and tissue are under oxygen stress o o o cooperative binding large amounts of O2 delivered to resting exercising tissues noncooperative binding smaller amounts of O2 delivered to resting exercising tissues blood vessels 3 types arteries capillaries veins arteries tough thick walled vessels that take blood away from heart under high pressure arterioles small arteries contain fibrous tissue muscle tissue elastic tissue endothelium capillaries smallest vessels one cell thick allows gases other molecules to exchange w tissues in capillary beds networks 4 27 2014 contain nucleus endothelial cells basement membrane pressure differences in capillaries create interstitial fluid lymph veins vessels that return blood to heart under low pressure venules small veins contain fibrous tissue muscle tissue endothelium as vertebrae circulatory systems evolved of atria ventricles interstitial space area between cells interstitial fluid fluid that leaks into area btwn cells systemic circulation hypertension blood pressure higher than 140 90mmHg blood pressure given w systolic pressure as numerator diastolic pressure as denominator the cardiac cycle signals from sinoatrial SA node ensure that the atria contract simultaneously then relax signals from the atrioventricular AV node ensure that the ventricles contract while the atria are relaxed contraction phase systole relaxation phase diastole electrical activation of the heart SA node originates a signal signal from SA node propagated over the atria which contract simultaneously fill ventricles signal conducted to AV node which relays the signal to the ventricles after
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