Gas Exchange

Basic Principles Large animals, with high met rates need a circulatory system to deliver oxygen to the tissues b/c diffusion isnt fast enough to keep up They also have a dedicated gas exchange system This is the point at which O2 enters the animal and CO2 leaves the animal Regardless of looking at a small animal w/ a small met rate or a larger complex animal what drives oxygen movement is the same He partial pressure difference between the environment and the tissues Cells use O2 meaning there is a partial pressure gradient between the external environment and the cell O2 moves down that partial pressure gradient from out of the cell in CO2 moves from the cell other external environment The Oxygen Cascade What drives o2 into an animal is diffusion along its partial pressure gradient And this o2 movement can be thought of as a series of steps called the O2 Cascade High O2 levels in the external environment Low O2 in the mitochondria where o2 is being used for metabolism This difference of partial pressure between the environment and the tissue site of o2 use that allows for o2 movement in other tissues Depending the complexity of the animal there will be a series of steps Oxygen is delivered to the exchange surface by some type of ventilation Transfer of respiratory gases is Done in 4 steps in vertebrates Ventilation Brings o2 to gas exchange surface Diffusion Across the respiratory epithelium Carrying of O2 in the blood to the tissues Diffusion from the blood into the tissues When this is broken down one ca see 2 steps where diffusion is involved At the gas exchange surface At the tissues And there are 2 steps where o2 is being carried by the bulk flow of fluid Ventilation of air and water Blood flow These are convective steps Diffusion This is the movement of molecules by random Brownian motion Movement of gas by diffusion is driven by the diffusion gradient which in the case of gases is the partial pressure gradient pgas Diffusion depends on permeability Kgas=estimate of permeability Diffusion of gas is much faster in are than it is in water and this reflects the permeability Permeability in part depends on how readily the gas dissolves into the medium(air, water or blood) Gases are more mobile in air than in water b/c they are more mobile in air Depends on surface area Large the surface area the greater diffusion can occur And diffusion is inversely proportional to thickness For fast gas diffusion, a thin barrier is preferred Fick equation: Mgas = Pgas Kgas SA/T Diffusion depends on P, not C Convection The gas is being moved by the bulk flow of the medium and this medium can be air water or blood The individual o2 molecules are carried by the medium This is a much faster transport pathway allows higher rats of gas transfer In terms of o2 delivery; the movement/flow of medium and the conc of gas in the medium So how much o2 is present the medium The flow of the medium times the concentration difference tells you how much gas is being delivered Mgas = Vmedium Cgas Convection plays a role in boundary layers Boundary layers are regions next to the gas exchange surface that becomes depleted in o2 Area where o2 has diffused from and is now low inn o2 b/c they can become depleted in o2 they slow down diffusion convection eliminates boundary layers by delivering o2 directly to the gas exchange site/tissues how are partial pressure and convection are related for gases partial pressure determines movement in terms of metabolism what really matters is how much gas is present i.e. the conc of gas these two variable are related see graph in slide 6 capacitance is a way of relating concentration to partial pressure (slide 6) Capacitance = C/ P if pressure and capacitance is known, one could calculate conc Capacitance of Air and liquids need to considered separately Air looking at o2 and co2 in air they have exactly the same capacitance b/c in air they follow the ideal gas law when the ideal gas law equation is rearranges on can find the slope of the relationship= 1/rt so ALL gases have the same capacitance in air Fluid(blood/water) If air is put overtop of a fluid where initially there is no o2 O2 will move into the fluid according to its partial pressure gradient until the partial pressures are the same in the fluid and the air This will occur by diffusion Partial pressure of o2 in the fluid is going to equilibrate with the partial pressure of o2 in the air over top so there is the same partial pressure in both locations The concentration of o2 in the gas vs the liquid will be different b/c the conc of gas in the liquid will depend on the solubility of the liquid for oxygen for o2 and whether there is anything in the liquid to which o2 can bind Gas will physically dissolve in the liquid and this is determined by solubility Knowing solubility you can calculate the conc of gas in the liquid There is a chance that o2 will react with the liquid and this will increase the conc of o2 in the liquid 2 cases O2 physically dissolves in the liquid Amount hat physically dissolves is determined by the solubility coefficient= depends on the particular gas, temperature and salinity as temp goes up solubility goes down from we can calculate the physically dissolved o2 C= P O2 is involved with additional chemical binding Chemical biding of the gas The gas for o2 in blood and for CO2 in water and in blood

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When water is air equilibrated the CO2 concentration is water and air is equal but the concentration of O2 in water and air differ Conc of o2 is water depends on how much o2 can be physically dissolved in the water and this is given by the following equation: [O2]dissolved= PO2 x When going beyond water you end up with binding of o2 to respiratory pigments like hemoglobin If the gas chemically reacts with something in the solution then physically dissolved gas no longer describes all the gas that is present You will have to add in a term to described the amount of chemically bound gas that is present Ex blood contains hemoglobin and oxygen binds to hemoglobin therefore the conc of o2 in blood is the amount of oxygen that physically dissolves in the plasma plus the amount of o2 chemically bound to hemoglobin CO2 chemically reacts with water They react to form carbonic acid which then dissociates in bicarbonate and then this further dissociates to carbonate ions So the conc of co2 is not only the physically dissolved CO2 but on top of that you have to add the amount of co2 that has chemically reacted with the water This includes the bicarbonate ions, and the carbonate ions Note: the pH of a physiological system is one in which we are only worrying about the bicarbonate It dominates b/c the carbonate ions are pretty small and can be considered negligible most of the time Co2 in blood It is physically dissolved Co2 reacts with the water in blood and so the conc of bicarbonate and carbonate ions are included Co2 chemically reacts with respiratory pigments such as hemoglobin and co2 that is bound to hemoglobin is called carbamino co2 Carbamino co2 describes the amount of co2 that is bound to hemoglobin When there is more than just physically dissolved as, capacitance is especially useful If there is only dissolved gas then one can rely on the solubility coefficient to give the conc of gas present Beyond that(^^) the value of capacitance describes all of the different ways the gas can be carried in the liquid It includes things like O2 bound to hemoglobin, or co2 that is chemically reacted with water is a functional measure of solubility it will tell you how much gas is in the liquid whereas the solubility coefficient will only tell you the amount of gas that physically dissolved in the liquid movement of o2 into animal can be divided into 4 steps oxygen is brought to the gas exchange surface this involves ventilation so it involves air or water moving across the gas exchange surface this is a convective step the o2 has to move across the respiratory surface this is a diffusive step and so it relies on the Fick equation o2 is carried in the circulatory system to the tissues sites of use another convective step b/c the gas is being carried by the blood o2 moves from the blood into the tissue site of use this is a diffusive step relying on the Ficks equation can use this exact same model for co2 however its in reverse for any convective step, the amount of gas that Is moved Mgas=flow of medium carry it (air, water or blood) X the concentration mgas= amount of gas that is movedGas transfer revisited MO2 = Vm (CiO2-CeO2) i=inspired E=expired How much air youre breathing multiplied by the difference between your expired and inspired are in the amount of o2 that is present Or it's the amount of water a fish is breathing multiplies by the difference between inspired water and expired water in the o2 content Sometimes its difficult to measure concentration and its often easier to measure pressure Because we have a relationship between concentration and capacitance, concentration can be replaced with capacitance Vm mO2 (PiO2-PeO2) This tells how much O2 is being carried to the gas exchange surface by the flow of air/water V=flow(ml/min) MO2 = Vb (CaO2-CvO2) = Vb bO2 (PaO2-PvO2) Here we can calculate amount of O2 in the blood Here we use blood flow so Vb As well as arterial(a)and venous(v) content Or Pressure The flow of blood multiplied by the difference between the arterial venous blood in terms of how much blood is being carried Arterial blood brings O2 to the tissue and the Venous blood flows away from the tissue The difference between tells how much o2 the tissue has acquired In a well-designed gas exchange system, the amount of O2 moving through the system will be the same the whole way So at each step we can look at a calculation for mO2 but if our calculate the amount of oxygen that is being carried to the gas exchange surface we should also note the amount of o2 that is diffusing into the tissue(in s4) The amount of O2 moving should be constant within the system The end game is to get o2 to the tissues. Everything preceding that is just moving it into the system this is a handy property b/c it means we can use things that are easy to calculate such as the amount of o2 being delivered to the lungs in the air as a proxy for things can are really difficult to calculate like the amount of o2 being delivered to the tissues by diffusion its quite difficult to calculate movement by diffusion even when given the Fick equation b/c parts of the Fick equation are quite difficult to calculate MO2 constant across system so can rearrange equations to solve for unknown variables. MO2 = DPO2 KO2 SA/T Here is a eq of o2 consumption as a function of blood flow and blood o2 content If you want to calculate blood flow; the rearrangement of the eq will allow itBlood O2 transport O2 is carried in the blood both as physically dissolved gas and gas that is bound to a respiratory pigment(i.e. hemoglobin but there is a ton) Hemoglobin increases the amount of o2 the blood can carry See slide 14 The amount of just physically dissolved o2 in the blood is about 0.3 vol % The amount of o2 present in the blood when you have a respiratory pigment is 20 vol% Vastly more oxygen available b/c f chemical bind fo2 to the resp pigment Hgb is an awesome o2 carrier Without Hgb in order to deliver the necessary amount of o2 blood flow must increase Ex crustacean + fish Crusts have to have a higher blood flow b/c their hemoglobin holds less o2 How high does blood flow need to be in anemic human beings in order for the human to meet the normal o2 consumption of 1mmO2/g/hr. See There is a fish that lacks Hgb The ice fish see the blood in slide 16 Its clear w/out any Hgb This fish can survive without any Hgb by relying on dissolved o2 only This means that the fishes cardiac output will be very high This means the heart of an ice fish is fairly large The heart is actually 3x larger than the hearts of similar red blooded fish to accommodate for the need of a higher cardiac output It is an ectothermic living in very cold temperatures Has a low met rate Though the water is old and the solubility of o2 is really highRespiratory Pigments Hemoglobin is not the only respiratory pigment but it is the most common It is the respiratory pigment of vertebrates; also found in a lot of invertebrates Called a respiratory pigment because it changes colour depending on whether o2 is bound to it or not. Hgb where O2 is bound(Hb-O2) is bright red Deoxygenated blood deoxy-Hb is a blue-red (so purple...) In crustaceans there is hemocyanin This hemocyanin is copper based meaning when oxygenated their blood is blue Clear when deoxygenated In annelids they have chlorocruorins which are green when oxygenated and clear when deoxygenated Worms have hemerythrins and this is violet color when oxygenated and clear when its not. The Hgb molecule is a tetrameric molecule, so there are 4 subunits 2 alpha and 2 beta subunits And associated with each globin is an iron based prosthetic group called the heme group This is where o2 binds 1 molecule of hemoglobin can bind 4 molecules of o2 Due to the subunits each with their own heme groupLecture 9- Oct 3rd Which animals are blue-blooded- crustaceans. Can you distinguish between carrying capacity and binding affinity? Carrying capacity is the max amount of oxygen the blood can cary, and the binding affinity is how well the oxygen binds to hemoglobin. Sketch an oxygen equilibrium curve and use it to illustrate the bohr effect. On the x-axis: Partial pressure of Oxygen- y-axis- %saturation of hemoglobim or oxygen saturation in units and the curve looks like a shaped curve and with the Bohr effect we shift either right or left- if you shift right its because CO2 has gone up or the other way if CO2 has gone down. The capacitance of blood for CO2 is much higher than that of plasma yet Hb binds relatively little to CO2- explain. Its not because hemoglobin can bind CO2, so why does the red cell matter- because there is a possibility of getting rid of the products of the hydration reaction so promotes more CO2 loading into the blood (there is also something catalyzing the reaction). Respiratory physiology short answer question- 30mL min-1 Haldane effect- related to the Bohr effect- oxygen binding is allosteric inhibitor of proton binding. Ties together CO2 transport and O2 transport in the blood. As the blood arrives to the tissues, oxygen is being given up to the tissues and this mean that hemoglobin is being deoxygenated and can bind more protons. When Hb is deoxygenated it can hold more protons which allows more CO2 to be entered into the blood. The difference between the line of deoxygenated blood and oxygenated is the Haldane effect. Blood moves from tissues to lungs/gills- then oxygen comes in, binds to Hb, lowering affinity for protons- which allows for dehydration to give you molecular CO2- benefits for CO2 unloading at tissue and benefits loading at gill or lung. Diagram- we have air on the left (Va) and blood on the right (Vb)- the red blood cell is loaded up with CO2- most CO2 thats in the blood is in bicarbonate ions in the plasma so we have to convert it back to molecular CO2 and then that has to diffuse out of blood into the air. And at the same time, oxygen is moving from the air into the blood. As CO2 diffuses out of the blood, its going to push the reaction towards CO2 formation (left) because its an equilibrium reaction. To make CO2 you need protons and bicarbonate ions- protons will be released by Hb, then Haldane effect will come into play when oxygen binds to Hb (gives you protons) nowyou need bicarbonate ions. Most of them are carried in plasma so they have to get back into the cell through anion exchanger while chloride ions are moving out (facilitated diffusion) and gives you more molecular CO2 which then diffuses out by partial pressure gradient . If there is any more HbCO2 (called carbomino CO2) (small amounts bound to Hb)- it gives up the rest of the CO2 because there is low levels of CO2 and that also diffuses out. CA- carbonic hydronaze. Water breathing teleost fish diagram- difference between lungs- when CO2 is let into the water it reacts with water and products are protons and HCO3 gooed because it gets rid of CO2 which keeps partial pressure constant. There is also no carbomino CO2 because its almost no importance in fish. Dogfish- they have carbonic anhydrase in the blood (floating in plasma), and its also on the gill membrane where it can catalyze plasma reactions. Up to about half of CO2 excretion happens in the plasma. There is also no Haldane effect. Gas exchange organs- gills are outfoldings of body surface and lungs are infoldings of the body surface. Tend to have high surface area, high permeability, thin membranes and richly visualized surface (lots of blood vessels). We can understand this MO2 (amount of O2 thats moving= deltaPO2 x KO2 x SA/T. Air vs water- the most important difference is that solubility of oxygen in water is very low compared to that of air. So water holds about 30x less O2 than air does. This means that water breathing animals have to move a lot more water to get the oxygen they need than air breathing animals do. MO2= Vm x concentration difference. Animal that has same rate of oxygen use, amount of oxygen is the same but however because capacitance for water for oxygen is so low, the water breather is going to have a much greater flow of water. Without Hb you can only get dissolved oxygen in water and thats very low so Hb is important. Vw (flow of water past the gill)- Vb (flow of blood past the gill) there is 10-20x more water. In air breathers Va:Vb = 1:1 at the gas exchange surface. This is called the ventilation to perfusion ratio. Not only do water breathers have to move more water, but water is also more dense and viscous than air and this has a huge impact on how its designed. Water goes in the mouth, goes through gas exchange organ and goes out through a separate cavity. Rather than in and out flow like you find in air breathers, you have unidirectional flow. There are a few exceptions- lamprae (jawless fish)- water goes in the mouth and comes out through gill pouches. When they are attached to prey, they cannot be used for breathing ther must be an in and out flow of water in and out of the gill pouches. Even with the one way design of water breathers, the cost of breathing is much higher for them . For a fish thats just respiring, its 10% of their energy just to breathe. Another difference between air and water is heat capacity- 1000x in water than in air. This means that animals that live in water live in a giant heat sink so most of them cant have body temperatures that are different than the environment. There is a difference between O2 and CO2 in water- capacitance of water for CO2 is much higher than it is for O2 (because it dissolves and CO2 reacts). Gas exchange through skin- very low usually in vertebrates except in amphibians. The skin in amphibians can be an important source of O2 and CO2 movement. In some amphibians, the skin is the only gas exchange organ. Oxygen moving from pool of air sitting near the skin. PO2 in blood starts low and then rises as oxygen moves into the blood. What drives the movement? Partial pressure of oxygen in the blood and partial pressure in the water- there is a large difference because there is no ventilation. The skin usually isnt permeable, but in amphibians it is- but its not as protective. There is limited surface area of the skin, its not ventilated, limits size/metabolic rate. Gills- surface area is important for how much O2 uptake can occur- and its usually linked to their lifestyle. Mackerel is a swimmer- so higher surface area. Internal gills are external gills that have a flap of tissue that protects them. It also has advatages for effective ventilation. Ventilation- water comes in the mouth and exits through the flap- mouth opens and closes to move the water- those two things together pump water across the gills. Its not only unidirectional, its non-stop. Ram ventilation- swimming fast. Tuna is obligate ram ventilators and they have lost the capacity to pump so if they stop swimming they cant breathe. They have very high metabolic rate, high rates of water across the gills. Gill structure- 4 gill arches on side of fishes head that are like a post supporting structure of the gil- after that there are 2 rows of filaments and then covering the filament are plate-like structures called lamellae (site where gas exchange occurs). Maximum contact between water and the gas exchange surface- lots of surface area. Why dont gills work in the air? They need the water to support the gill structure, when in air surface area is really low. There are exceptions- lamellae are connected so they dont collapse in air (mud skipper). If you look closely at regular gills- they are relatively flat, thin epithelial layers that are separated by cells that hold them apart called pillar cells. As water moves through blood space in one direction, water moves between lamellae in opposite direction- counter current of water and blood flow.

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Water breathing teleost fish diagram-(Slide 31) Blood flow on one side of the gas exchange organ(gill) and water instead of air on the other side of the gill So when CO2 leaves the gills it is let into the water and reacts with water producing protons and HCO3 This is good because CO2 that reacts with water does not affect the partial pressure Co2 diffuses out of the gill down its partial pressure gradient and reacts with water Meaning it keeps partial pressure constant. This means water breather are able to get rid of CO2 more readily than air breathers There is also no carbamino CO2 because its almost no importance in fish. Elasmobranch Fish (dog fish; slide 32) Carbonic anhydrase is present, membrane bound in the gill and floating around in the plasma This means that the plasma reactions are catalyzed This plasma reaction is catalyzed, meaning it occurs quickly playing an important role in CO2 excretion The red cells become less important b/c these fish lack the Haldane effect Hb is a good buffer but in the absence of the Haldane effect the contribution of hemoglobin to proton binding is lessened Conclusion There less room in the blood cell to mop up protons and there are catalyzed CO2 reactions in the plasma Due to these two factors both plasma bicarbonate dehydration and red cell bicarbonate dehydration contribute to the excretion of CO2 These fish are very different than other fish in how this fundamental process occurs

Gas exchange Organs In vertebrates there are 3 possible gas exchange organs Integument Body covering/skin Gills Out folding of the skin Evaginated highly folded extension of the skin Lungs Infolding of the body surfaces Internalized invaginated, highly folded infolding of body surface All three of these gas exchange organs have a series of design features high surface area high permeability thin membranes and richly vascularized surface (lots of blood vessels) Fick equation=MO2=PO2 x KO2 x SA/T The respiratory medium has a big impact on the design of the gas exchange organ itselfEffects of respiratory mediums (Air vs Water) Water breathers Solubility of oxygen in water is very low compared to that of air. So water holds about 30x less O2 than air does. This means that water breathing animals have to move a lot more water to get the oxygen they need than air breathing animals do. MO2= Vm x concentration difference(can be replaced with KO2 and PO2) If we have 2 animal that have same rate of oxygen use and the same partial pressure difference however on is an air breather and the other is a water breather Because capacitance for water for oxygen is so low, the water breather is going to have a much greater flow of water. (if the carry capacity for oxygen is low then to deliver an appropriate amount of oxygen you will need a higher flow of respiratory medium) Water breathers have to breathe 10-20X more water to gain the same amount of oxygen as an air breather would have to breathe air The flow of medium relative to blood flow In water breathers the capacitance of water for oxygen is much lower than the capacitance of blood for oxygen Blood contain respiratory pigment and water doesnt When O2 moves from water to blood you need a high flow of water to deliver the oxygen And you need a low flow of blood to take the O2 away from the gas exchange organ. Water flow has to be 10-20X higher than blood flow to move the same amount of oxygen The Viscosity of water Water is both denser and more viscous than air When the water breather move the water against their gas exchange organs the water that they are moving is 800X more dense and 50X more viscous than air In order to overcome this water breathers use unidirectional flow Water goes in the mouth, passes of the gills and exits out through the apicular cavity These are the flaps on either side of the fishes heads There are a few exceptions- lamprey (jawless fish) This fish has a plat like mouth which it uses to suck on its prey When unattached water goes in the mouth and comes out through gill pouches. When they are attached to prey, theyre mouth cannot be used for ventilation So instead of a unidirectional flow of water it has to use tidal flow of water in and out of the gill pouches(less effective) Heat Capacity of Water Heat capacity is 1000x higher in water than in air. Water acts as giant heat sink, any heat that fish produces as the water passes across the gills the heat is transferred from the fish to the environment Consequence of this high heat capacity is that most water breathers are not endothermic animals In water the capacitance of water for CO2 is much higher than it is for O2 (because it dissolves and CO2 reacts). This makes it easy for water breathers to get rid of carbon dioxide even though its difficult for them to gain O2 When looking at what regulates ventilation in water breathers it is usually O2 This is b/c they have difficulty getting O2 from the environment For air breathers blood and air hold similar amounts of oxygen(the same capacitance) The flow of air and the flow of blood is the same The amount of air needed to deliver O2 to the lungs is equal to the amount in blood needed to carry that oxygen away from the lung Air breathers are tidal breathers Air is sucked into the lung and then back out In and out through the same set of tubes Ventilation in this case is regulated by CO2 This is because it is more difficult for them to get rid of CO2 This comparison of ventilation flow and blood flow is called the ventilation to profusion ration Profusion means the flow of blood through the gas exchange organ Able to distinguish a water breather from an air breather b/c the ventilation to profusion ration in a water breather is usually around 10-20:1 Ventilation: profusion is air breathers = 1:1

Integument Gas exchange through the skin is not very important in mammals/bird/reptile and most fish However this is important in amphibians Amphibians have thin permeable skin that is suitable for gas exchange Frog n slide 37- some O2 across the skin; large amount of CO2 This large amount of CO2 excretion could be accounted for by the fact that CO2 loss is easier in water The lungless salamanders They do not have lungs or gills and rely entirely on their sin for gas exchange They have a high SA: V ration, low met rate, For most vertebrates the skin is not a great gas exchange organ Oxygen moving from pool of air sitting near the skin. PO2 in blood starts low and then rises as oxygen moves into the blood. This movement is driven by the partial pressure of oxygen in the blood and partial pressure in the water/air Note: Slide 40; environmental partial pressure is still much higher than the PO2 of blood even when oxygenated This reflects the limitations of skin as a gas exchange organ This occurs because the skin is ventilated meaning there s=is no mechanism to move air/water across the skin other than the animal swimming or moving around This is a disadvantage b/c the pool of O2 sitting above the skin can become depleted leading to the formation of boundary layer Meaning less O2 moving into the animal Another problem is that there is a conflict between the skin as a protection covering and the skin as a gas exchange organ For the skin to be an effective protective organ it needs to be thick/tough/impermeable However for the skin to be a gas exchange organ it should be the opposite(thin, permeable) The skin is also relatively limited in surface area In slide 39 this frog lives in a high altitude area with fairly hypoxic water causing it to remain immersed in the water Because its gas exchange organ on the sin it forms folds in the skin to increase surface area increasing gas exchange These fold of skin are not really ideal for protection or locomotionGills Specialized gas exchange organs Out folding/evagination of the body surface High folded to increase SA Surface area is important for how much O2 uptake can occur and its usually linked to their lifestyle. Ex. Mackerel is a swimmer- so higher surface area. Internal gills are external gills that have a flap of tissue that protects them. This provided protection and effective ventilation. The presence of the apicular flow allows for ventilation of the gills What happens is that water goes in the mouth which opens and closes to pump water the gill flaps also open and close to help move water across the gills(apicular pump) this gives 2 pump actions in order to in the mouth and exits through the flap this give a unidirectional non-stop motion of water this is essential b/c of the low solubility of O2 in water and the fact that water is dense and viscous even in this one way mechanism the cost of ventilation in water breathing fish is much higher than the cost of ventilation in an air breather at rest, breathing would cost water breathing fish about 20-30% or its resting met rate this is because they need to move more water and it is dense and viscous fish generally do whatever it takes to lower cost of ventilation ex. ram ventilation Ram ventilation When ram ventilation the fish opens its mouth and water is able to flow in the mouth and across the gills without having to pump water This involves swimming fast. This means they actively stop breathing and regain the energy that would be spent on pumping water across the gills Most fish will do this if they are swimming in a current, or do it when they are swimming fast enough; they can also get a ride in order to ram ventilate Ex the remora links/attaches to a shark and stops pumping instead using the flow of water generated by the sharks swimming for ventilation(facultative ram ventilation) Tuna is obligate ram ventilators as they have lost the capacity to pump so if they stop swimming they suffocate They have very high metabolic rate, high rates of water moving across the gills. Gill structure 4 gill arches on either side of fishes head that are like a post supporting structure of the gill These have cartilage to help support its shape On each gill arch there are 2 rows of filaments covering the filament are plate-like structures called lamellae this is the site where gas exchange occurs they are equivalent to alveoli in mammal lung and par bronchi in fish lung they form a type of sieve that that water passes through Maximum contact between water and the gas exchange surface- lots of surface area. Filaments and lamellae shape is supported by the flow of water Why dont gills work in the air? They need the water to support the gill structure, when in air the surface area is reduced. There are exceptions- lamellae are connected so they dont collapse in air (mud skipper). If you look closely at regular gills- they are relatively flat, thin epithelial layers that are separated by cells that hold them apart called pillar cells. As water moves through blood space in one direction, water moves between lamellae in opposite direction- counter current of water and blood flow. The lamellae structure Consists of Two respiratory epithelial sheets which are separated by blood space. Pillar cells These are cells that hold two epithelial cells at a good distance. oxygen has to travel from the water through the diffusion barrier to get to the blood cell the diffusion barrier is about 5um thick in most fish and consist of a mucus layer respiratory epithelium blood The epithelium is relatively thick because there is water on one side and blood on the other and it needs to be tough enough to withstand the movement of both passed it. the thickness of the diffusion barrier correlates with lifestyle The tuna has a thin epithelial layer because it has a high performance lifestyle- has to take up a lot of oxygen so has a very high surface area also. Model of gas exchange Blood flow and water flow along epithelium are in opposite directions(counter current) The counter current flow of blood and water is the basis of the fish gills efficiency Has the higher efficient In this counter current system the water that is entering the gill-the best oxygenated water- comes into contact with the blood that is leaving the gill (the most oxygenated blood) At the other end the water that is leaving the gill-which has been depleted of O2-meets the blood that is depleted of O2 In countercurrent exchange As blood leaves the gill it is trying to come to equilibrium with inspired PO2(PiO2) So the gradient may not be large at any point but the final PO2 achieved in the blood is high b/c the blood is trying to equilibrium with PiO2 water This makes the countercurrent system more efficient. In concurrent flow water and blood go in the same direction It starts off with a much higher gradient b/c the inspired water(highly oxygenated) meets the venous blood which has the lowest O2 giving a large gradient Here the blood that is entering the gills is coming into equilibrium with water that is leaving the grill Highest PO2 achieved is whatever the expired PO2(PeO2) isLungs Lungs are highly folded with the surface area correlating with the activity of the animal. Total surface area in a human lung is about 80m2- folded in. They are typically ventilated that moves air in and out of the lung. In amphibians that is a positive pressure mechanism where they gulp air and push down int the lung Lung in reptiles, mammals and birds/lungfish are suction lungs where the volume of the lung is increased and this pulls/sucks air into the lung Diaphragm in mammals helps with mechanism for breathing. Most reptiles cant move and breathe at the same time This is because muscles used for movement are also needed to help pull the lungs outward to allow for the drawing of air into the lungs. To be able to run and gain oxygen at the same time, they lift their front legs and run on the back so they can use the muscles in the front to breathe. Other lizards stop breathing when they move This is why you see relatively low metabolic rates in lizards. Mammalian lung- The functional unit as alveoli This is a small, balloon like structure- very large surface area required for maximizing oxygen uptake. The alveoli also provides High surface area, it is relatively permeable, thin, and it is actively ventilated (suction mechanism), It is also surrounded by a capillary network. Capillaries are pressed tight against respiratory epithelium The distance of the respiratory epithelium is about 0.5um (similar value of tuna) Low thickness=better/easier O2 transfer This is 10x thinner than a fish gill Birds around 0.1 (thickness of barrier). Air is moved through a series of conducting airways Air comes in through the trachea, which is a single tube, that splits into two bronchi Air continues down, until terminal bronchioles lead to alveoli. This structure is not involved in gas exchange at all instead it just gets air to where it needs to be. The only place where you can find gas exchange besides in the alveoli is in the smallest bronchioles leading to the alveoli These two are the respiratory airways. Small changes in radius in the airways causes a big difference in resistance Beta 2 receptors on muscle that allows them to dilate are the same receptors in lungs. People with asthma take 2 agonist to promote dilation. Ventilation lungs are bounded by thoracic cage which consists of ribs and diaphragm for them to expand properly, the lung cannot be physically attached to either structure So the lung is kept in a fluid filled space called pleural space which is filled with fluid called pleural fluid. This acts as a suction mechanism to hold lung on to the wall of the thoracic cage. If the seal is broken the lungs own tension will cause it to collapse The lungs are expanded by the outward movement of the ribcage and the downward movement of the diaphragm. Model of gas exchange- Mammalian lungs are not a very effective gas exchange surface Here there is a pool of air on top of the blood vessel in alveolus This pool of air is tuned over/refreshed meaning there is ventilation which improves the gas exchange model This is very similar to the mode of gas transfer across the skin PiO2 and PeO2 and there is diffusion of oxygen in the air from the alveolus into the blood PO2 starts high in the air and then decreases from inspired to expired O2 moves into the blood starting from a low pressure to a higher partial pressure The PO2 of air in the lung is lower than that in the environment making this model less efficient Meaning lungs contain stale air Po2 of air in lungs < PO2 of air in environment The reason for this poorer air quality is the fact that the lungs contain 2L of air but with each breath taken one only inhales 500mL So the bets one can do is to turn over about of the air in the lungs The conducting airways occupy about 150ml of volume and so of the 500ml that one breathe only about 350ml actually reach the alveoli Not much air is turn over in the lugs at any given breath Because of this alveolar PO2 sis lower than inspired PO2 and this limits the arterial PO2 that can be achieved arterial PO2 is one that matches expired PO2 If youre snorkeling, youre breathing through a tube. What happens to arterial PO2? And alveolar PO2? Arterial PO2+Aveolar Will decrease because you are increasing the amount of dead space(the tube that is used acts like an extended conducting airway) This make it more difficult for O2 uptake Less air in the lungs leading to arterial PO2 to fall This however doesnt happen because When a trend for arterial PO2 to fall the monitoring systems(chemocenters) that detect the blood kick in and increase tidal volume This compensates for the anatomical dead space Bird lungs They have relatively compact lungs which are about half the size of mammalian lungs Instead of alveoli their lungs are made up of tiny tubes made up of parabronchi (site of gas exchange). In addition there are respiratory sacs which are involved in ventilating the lung and they hold about 80% of the total volume of the system They are not involved in gas exchange, instead they are a part of the ventilatory mechanism This allows the bird lungs to be more efficient in comparison to mammalian lungs They also have a very low diffusion distance relative to mammals (0.1 micron) Correlation between lifestyle and thickness of respiratory epithelium Birds with thick respiratory epithelium are usually non flying birds(ostrich, emu, penguin)-similar to mammals This low diffusion distance however makes birds susceptible to respiratory problems Bird Lung Structure In terms of lungs as a whole, flow is tidal However when looking at gas exchange surface itself(parabronchus) flow is one-way and continuous This is the advantage of using tubes instead of balloons as the gas exchange site Air comes in through the bronchus and down to the mesobronchus from which it enters the dorsobronchus and goes through the parabronchi be collected by the ventobronchus and be collected again A loop through the lung itself with a tidal component in and out Capillaries surround the parabronchi O2 moves form air in parabronchi and into the capillaries In this model the PO2 of air depends on where it is in the air tube If blood meets air at the inspired end of the tub the air has a High PO2 If the capillary is at the expired end of the tube the blood is going to be meeting air with a low PO2 Air PO2 is low so PbO2 is low What comes out of the lung is a mix of all these diff situations On average experiment show that the arterial PO2 is just above expired PO2 So this model(cross current arrangement) is much better than the pool type arrangement in the mammalian lung but not as good as the counter current arrangement in fish lungs Air Movement through the bird lung Ventilatory innovation of bird lings are air sacs Two set of air sacs Posterior and anterior It takes 2 complete respiratory cycles to move a bolus of air through the lungs Inhalation 1 The bolus of air(green in slide59) is pulled into the air sacs and the dorsobronchus by the expansion of the air sac The bird exhales and this compresses the air sac pushing air out of them and forcing air through the parabronchi This completes one respiratory cycle and the bolus of air is halfway through the line Inhalation 2 The bird inhales again, expanding the air sacs pulling air in this continues movement through the parabronchi The bird exhales for the second time and this compresses the air out the ventobronchus and back out in a tidal fashion Because of these air sacs and the fact that the bird lung is made up of tubes other than balloons you end up with a functional gas exchange unit that is a continues one way flow of air This allows for a more efficient model of gas transfer Some recent work suggest that it may be found in realties with high metabolic rate Bird dont have counter current blood flow because there is a sea of capillaries winding around the air tube and so air is moving through the tube and blood Is going across at the same time This is a cross current way of blood flow Extraction efficiency This is the difference in inspired to expired PO2 divided by inspire Po2 Essentially saying how much O2 is removed from the air that is breathed as a percentage of the inspired Po2 For mammals efficiency is usually around 20-25% Pool type arrangement which isnt efficient at all Bird: can be up to 40% Cross current blood/air flow allow for higher efficiencies to be achieved Fish=20- 60% Design of fish gills allow for more efficient transmission of gas This is because they have the counter current arrangement of blood and water flow Mimic effects of high altitude on birds contrast and compare birds and mammals. Bird has been found at 9000 meters. Extraction efficiency is how much PO2 falls when gas exchange happens. In mammalian- 20-25%, bird is 40% and fish can be as high as 60%. So design of fish gill allows for more efficient transmission of gas. Why is the fish gill the most efficient design?

;Bio3302Lec 12-13Control of Ventilation There are two parts to ventilation generating basic ventilatory movements (breathing movements) how you match ventilation to the requirements of the animal flying bird is at a high need There is a fairly complex set of brain neurons that generate motor output to breathing muscles (located in brain stem, medulla). On top of that, there are levels of control that allow breathing methods to be controlled Brain centers that allow you to hold your breath, or voluntary control. In addition to conscious control, there are mechanisms to match size and frequency of breaths to match needs of animal. Most important of these are chemoreceptors that are involved to detecting o2 and co2 levels in body, and matching requirements. Mammalian chemoreceptors 2 sets of chemoreceptors that regulate ventilation central (in brainstem) The most important component in the frequency and size of breaths in mammals. The chemoreceptors are proton sensors (detect hydrogen ions) however, they typically respond to Co2, because of the blood brain barrier Protons dont readily pass blood brain barrier but CO2can and so it reacts with water to form protons. As CO2 levels rise, more of it enters, reacts with water, and proton detecting cells respond to increase in proton levels by increase in breathing. A fall in pH (increase in proton levels) stimulates breathing (brings CO2 levels back to where they should be). peripheral chemoreceptors These are capable of detecting O2, CO2 and protons, but more sensitive to CO2 and protons than they are to O2. Found in two locations (called glomus cells) one in the carotid body, and the aortic bodies, Detect blood going to the brain to make sure that the brain gets sufficient oxygen delivery. Fish chemoreceptors There are no central chemoreceptors (nothing in the brain). They have peripheral chemoreceptors and are located on the gills and called neuroepithelial cells- similar to glomus. Through evolution, the structure in the gill arch in the fish became incorporated in the homologous structure in mammal, leading people to believe that neuroepithelial cells and glomus are homologous. However this is not the case Neuroepithelial cells detect CO2+ O2levels of blood and water They are not sensitive to protons Glomus are found only blood levels(not found in the fish doe) Why is ventilation keyed to O2 in water breathers, but CO2/pH in air breathers? In Fish ventilation is keyed to O2 In fish ventilation primarily response to oxygen levels In water O2 is limiting and therefore animals that breathe water need to monitor O2 very carefully in order to get sufficient O2 Remember CO2 is able to react with water but not with air making to easier to get of CO2 In mammals Ventilation changes primarily to changes in CO2 or pH It is more difficult to get rid of CO2 in air For air breathers it is much more easier to get O2 in air and so they breathe less to get the same amount of O2 as water breather By breathing less CO2 levels become higher So here there are 2 factors at play O2 is difficult to obtain in O2 so water breathers maintain O2 but in air breathers they are able to breathe less to get the required amount of O2 and therefore CO2 levels tend to accumulate So the convection requirement(how much one has to breather in ait much lower than in water in air and b/c of the low convection requirement in air CO2 levels tend to higher Humans PCO2=40Torr Fish PCO2= 4TorrDiving and Divers-respiratory and cardiovascular adjustments Divers are air breathers that go under water, where they no longer have access to respiratory medium, and have to cope. Often they are exercising at this time (swimming) without oxygen. Those that dive to great depths can run into problems because of pressure and temperature. Animals that are adapted divers use the same responses as animals that arent; they just take it to a higher level. Opportunistic nature of natural selection is the result. First problem is holding their breath. When you hold your breath, CO2 levels rise, which are the strongest ventilatory stimulus for air breathers. Slide 70 This line on the left is a just ordinary humans that are subjected to the test, so as CO2 levels rise, breathing rises. The three lines on the right are for 3 people who are trained as divers, you can see that they tolerate much higher levels of CO2 before ventilation starts to go up. Adapted divers exhibit blunted ventilatory sensitivity to CO2 By hyperventilating before diving they lower Co2 levels so that the levels dont go up as fast when holding breath. What about exercising? For divers, the only oxygen available is what they take with them (blood, lungs and muscles). Most adapted divers dont take oxygen into their lungs. So whatever is left is in the blood and muscle. The bottom figure in slide 71 shows total oxygen thats available. In general, most is available in the blood. Adapted divers increase blood volume and hematocrit (Hb levels). In some cases, they also have high levels of muscle oxygen levels, which they achieve by having higher levels or myoglobin. A problem with high hematocrit is the strain on the heart but they deal with it by only releasing red blood cells when they dive (hematocrit increases during the dime, and decreases when it emerges). They use the spleen as RBC reservoir, release it then re-sequester into the spleen after the dive Another way of maximizing oxygen stores is stripping as much oxygen as possible from blood to bring to muscle. For animals that have a lot of blood oxygen have a right shifted oxygen curve (high p50 value, lower affinity for Hb to oxygen makes it easier for oxygen to unload from blood). As animal mass increases, p50 values fall because small mammals have higher metabolic rates and need to enhance oxygen delivery. Both seals have higher p50 than expected and large caticaious. This is thought to be adaptation for oxygen delivery during a dive. Small cateceans (dolphins) have higher affinity for oxygen (lower p50) than you would expect- easier to take up oxygen from low- oxygen environments. The reason is because they dive on a breath of air- shallow divers so their high affinity Hb is useful for taking oxygen from that lung full of air as oxygen gets depleted. Some have strong Bohr effect- shifts curve to right to maximize oxygen delivery. In addition, these animals use oxygen as slowly as possible. One strategy is to not exercise when they dont have to. Rather than actively swimming, these animals glide down and then swim up and by gliding; they use less oxygen and can stay down longer. The other strategy is to become slightly hypothermic. Its been difficult to document this in free diving animals. It looks like body temp falls when animal dives. These animals allow themselves to become a bit hypothermic because it lowers metabolic rate, they suppress the shivering only when theyre diving; make oxygen stores last much longer

Exercising, swimming around without oxygen they can increase blood volume, try and minimize way that they use the oxygen by Lowering body temperature and directing the blood flow to the tissues that need it most. Brain, heart, lungs This happens across a variety of tissues. It is important to note that blood flow to the heart is greatly reduced during diving, even though its oxygen sensitive- when it dives, the heart doesnt beat as fast and therefore doesnt need as much oxygen/blood flow. Slide 77 A- Animal at surface, dives then comes back up (HR falls when diving). Dive response This is a fall in heat rate and a selective O2 delivery system It is present in most air-breathing vertebrates, Particularly strong to animals who have diving lifestyle (natural selection). B)Adapted divers show unusual tolerance to low blood oxygen levels(tolerance of hypoxia) Divers have a pronounced tolerance for hypoxemia Data for seals as they did natural dives, as it dives blood oxygen levels fall and lowest levels are very low. The critical PO2 for a seal is about 10mmHg They deplete 90% of blood O2 reserves during a routine dive This is the point where there is irreversible brain damage, when they dive they are barely above that value For us, lowest PO2 are 20-30mmHg This measurement was taken from human blood that was subjected to climbing Mount Everest. Anaerobic metabolism during the dive vasoconstriction of the arterioles going to skeletal muscles occurs however muscles are able to work anaerobically and when they do they produce lactic acid This acid accumulates in the muscle not in the blood. This is a benefit of peripheral vasoconstriction because it traps the acid. When animal gets back to the surface, the lactic acid is released into the blood and has to metabolize the acid, get rid of CO2 (recovery) and its anaerobic. Adapted divers have high blood buffer values so they can tolerate high levels of lactic acid. Because of the costs of recovery of diving, most divers dont use this type of diving unless they have to. Only for dives that are longer than 20 mins in length lead to the accumulation lactic acid. Dives that are over this length are a lot less frequent because the animal avoids this recovery period. In addition to exercise without oxygen, the animals have another problem to face and its the high pressure at depth. Every 10m, pressure increases by 1atm so at 30m, its 4atm. At the depth gas exchange between lung and tissues means that the tissues experience these high partial pressures that are in the lungs This isnt really a problem for the tissues, but high pressure compresses the lung which results in high partial pressure thats in the lung. When the animal surfaces, the gases come out of solution which causes gas bubbles and this could be a fatal problem. This problem can be avoided if the animal comes up slowly enough, to allow the blood to equilibrate with the new partial pressures. Animals that dive however dont have this option Animals avoid the bends by doing the following1. dive on empty lungs as much as possible (exhale rather than inhale before they dive), They have larger tidal volumes than usual so they are more effective at emptying the lungs than humans would be. 2. When they dive their alveoli collapse and when this occurs air is pushed into the conducting airways This is an advantage because the gas thats trapped here cant equilibrate with the blood. Humans have opposite response, its not alveoli that collapse but lungs. High pressure depth causes the rib to collapse inwards and helps to empty the lungs to minimize equilibration between air in lungs and blood. 3. There is also strong peripheral vasoconstriction Blood isnt circulating to the tissues so minimizes chance of equilibration of tissues. Summarize specialization of vertebrate divers- vasoconstriction of peripheral vasculature, lower heart rate (both are for dive response) blunted ventilation (CO2), high levels of Mb and Hb (expand oxygen stores), ability to cope with high levels of lactic acid (blood buffering), strong facility for anaerobic metabolism, drop in body temperature Gliding rather than active swimming. Pulmonary alveoli can collapse dive on an exhalation rather than inhalation. Birds are ableto perform better at higher altitudes thanmammasl This can be attributed to Higher SA of gas exchange surface Blood to air diffusion barrier is thinner They are able to withdtasn ntracranial pressure better than mammals do When you put birds and mammals at high altitudes they hyperventilate and as s result of this CO2 levels fall When co2 levlesfallthis affects brian blood flow in mmamals but not in birds Birds are able to cope with hypercapnia(low co2 levels) Better neurons are more tolerant of low O2than mammalian neurons there fore they can withstand hypoxia better Because birds use tubes ratherthen balloons they can have unidirectional constsnt air flow They can also use coress current blood/air flowgivinfgimproved efficiency of O2 extraction Theu do not show hypoxic pulmonary vascontrciiton This helps at high atlitudes as you are breathing air of low O2 levels In this situation there would be vasoconstriction in mammalian lungs This cnan lead to oedoma Capillary to muscle cells ditacnce is lower in bird than in the muscles making it easy to deliver O2 under hypoxic condiions Birds have larger hearts and lungs for better o2 delivery This suggest that birds seem to do better These mechanism occurred more in birds than in mammals because of the birds ability for flight O2 delivery requirement for flight are much higher than they ar for swimming or running and therefore all of these adaptaions came into play for O2 delivery during flight One mammal where one cn see these suit of traits are in bats They have larger than normal hearts, larger than normal lung SA, thinner than typical blood to air diffusion ditnces.