1 11 1 Respiratory Systems Air Breathing BIO 361T Fall 2014 1 It is common for desert insects to have spiracles that they can open and close Propose a proximate explanation for this observation Low moisture content in air danger of trachea ends drying out which would prevent O2 from dissolving and thus diffusing into the interstitial fluid or hemolymph for insects that have circulatory systems 2 Use Boyle s Law to explain how insects use abdominal muscle contractions to ventilate their trachea Contract abdominal muscles decrease volume in abdomen V2 increase pressure in abdomen P2 air follows pressure gradient out of trachea Relax abdominal muscles increase volume in abdomen decrease pressure in abdomen air follows pressure gradient into trachea 3 Air breathing has evolved multiple times in fish giving rise to about 400 species of fish that use air for part or all of their oxygen Some like lungfishes have one or two specialized pockets essentially lungs dedicated for gas exchange Others have modified the surface of their mouth or stomach for gas exchange a Explain how fish ventilate their respiratory surfaces by swallowing air Air enters buccal cavity part of mouth and is pushed further into body by raising buccal floor b What other adaptation do lungfish have to make them efficient air breathers Partially divided atrium that leads to double circuitry separate capillaries for lungs 9 2 HW 4 Use Boyle s Law to give a generic explanation for a How a fish or amphibian breathes air Positive pressure increase pressure in buccal cavity by decreasing volume which pushes air back towards respiratory surface b How a reptile bird or mammal breathes air Negative pressure decrease pressure in respiratory surface compartment by increasing volume which pulls air back towards respiratory surface 2 5 On the bird respiratory system below draw the progression of a single breath of air through two respiratory cycles then answer the questions that follow See homework figure a Inhalation 1 b Exhalation 1 c Inhalation 2 d Exhalation 2 e During Inhalation 2 and all subsequent inhalations which air sacs will inflate Both sets posterior and anterior 6 Some of the alveolar epithelia in mammals express a gene for ENaC channels a When this gene is knocked out it causes pulmonary edema or accumulation of fluid inside the alveoli What do you think the ENaC channel does normally and why does the knock out cause edema Regulates Na between inside and outside of alveoli Na builds up inside alveoli drawing H2O into alveoli from surrounding tissues pulmonary capillaries and accumulating fluid inside lungs b Predict the phenotype when this gene is mutated to be overactive It simulates the phenotype of cystic fibrosis causing accumulation of viscous mucous in the alveoli because too much Na is being transported out of the alveoli which draws too much H2O out causing the lung secretions to be too dry and thicken c Use Fick s Law to explain why animals with this mutation suffer from hypoxia low PO2 in tissues L increases with mucous accumulation so O2 cannot diffuse from inhaled air across alveolar epithelium then through endothelium into pulmonary capillaries 3 7 In mammals when the pleural sac is punctured it is called a pneumothorax a How will this affect pressure inside the pleural sac Will increase to equal atmospheric outside pressure b How will this affect the volume of the alveoli No longer pulls them open with pressure gradient so alveolar volume will decrease c How will this affect the animal s respiratory rate Lower surface area for diffusion so animal will become hypoxic and increase resp rate 8 The pressure gradient between the pleural sac intrapleural pressure and alveoli intra alveolar pressure is crucial to mammalian respiration During inspiration inhalation intrapleural pressure decreases a Use Boyle s Law to explain what happens to the volume of the pleural sac during inspiration Intrapleural pressure decreases P2 so volume must increase V2 b 9 During expiration exhalation intrapleural pressure returns to normal below atmospheric environmental pressure as shown in the graph below Fill in the top graph which illustrates intra alveolar pressure during inspiration and expiration Air breathers have chemoreceptors that detect changes in O2 CO2 and pH Respiration is primarily controlled by changes in CO2 not O2 a Why do you think it is typically unnecessary to monitor O2 levels in air breathers while respiration in water breathers is primarily driven by changes in O2 O2 is much more plentiful and diffuses faster in air than in water 4 b Central chemoreceptors are located in the medulla and detect pH changes in cerebrospinal fluid Why is this equivalent to measuring PCO2 Because of carbonic anhydrase if pH drops H increases it will react with HCO3 bicarbonate to form H2CO3 carbonic acid which will spontaneously dissociate into CO2 and H2O increasing PCO2 c Give a neural mechanism for how the medulla will respond to a decrease in pH and the resulting behavioral output Neurons in pre B tzinger complex CPG will increase endogenous rhythmic firing of action potentials which will increase respiratory rate This will increase O2 inhalation and increase CO2 exhalation bringing PCO2 back down to normal d Peripheral chemoreceptors are located in major arteries and detect PO2 and PCO2 pH Although PO2 is usually stable in air breathers it can become too low at very high altitudes causing hypoxia Why do you think there are chemoreceptors for O2 in major arteries like the aorta To monitor PO2 in oxygenated blood going out to the tissues e How do you think the medulla will respond when aortic chemoreceptors detect a decrease in blood PO2 Increase firing rate of CPG to increase ventilation rate and increase PO2 f Why will this cause a drop in blood PCO2 Because more CO2 will be exhaled as a result of increased rate and depth of ventilation PCO2 is monitored to regulate respiratory rate so when this drops mammal will have trouble breathing especially while sleeping due to lack of voluntary compensation also leads to low H high pH respiratory alkalosis See flow chart on next page Flow chart of high altitude hypoxia 5