Gas Exchange and Circulation Notes PDF

GAS EXCHANGE AND CIRCULATION Biol 1215, Ch. 39/42...

GAS EXCHANGE AND CIRCULATION Biol 1215, Ch. 39/42 Dr. Kyra Janot Summer Term 2024 Impact of the Environment on Gas Exchange Gas Exchange in Animals All animals need to have a way to acquire _______________________ from their environment and eliminate _______________________from their body, and the mechanisms involved are collectively referred to as gas exchange Most gas exchange involves five steps: 1. Ventilation – movement of air or water through a specialised gas exchange organ (e.g., lung or gill, involves the ____________________________) 2. Diffusion at the respiratory surface – O2 moves from air or water into circulatory fluid, CO2 moves from circulatory fluid into air or water (also called external respiration, involves the ____________________________) 3. Circulation – transport of dissolved O2 and CO2 throughout the body (involves the ____________________________) 4. Diffusion at the body tissues – O2 moves from circulatory fluid into tissues, CO2 moves from tissues into circulatory fluid (involves the ____________________________) 5. Cellular respiration – cells within tissues produce ATP, which uses O2 and produces CO2 Movement of Gases by Diffusion Gases diffuse from regions of ____________________________ partial pressure to regions of ____________________________ partial pressure o Partial pressure is the pressure exerted by a given gas in a mixture of gases; it is ____________________________ to concentration (# of molecules/unit volume), but also impacted by ____________________________ Typically, tissues have ____________________________ PO2 and ____________________________ PCO2 relative to the surrounding environment o O2 tends to move from the environment into the tissues, CO2 tends to move from the tissues into the environment  GAS EXCHANGE AND CIRCULATION Biol 1215, Ch. 39/42 Dr. Kyra Janot Summer Term 2024 Rate of Diffusion The rate of diffusion in gas exchange is impacted by five key factors: 1. Solubility of the gas in the liquid layer that lines the gas exchange surface (____________________________solubility → faster diffusion) 2. Temperature (____________________________ temperature → faster diffusion) 3. Surface area available for diffusion (____________________________surface area → faster diffusion) 4. Partial pressure gradient of the gas across the gas exchange surface (____________________________ gradient → faster diffusion) 5. Thickness of the barrier to diffusion (____________________________ barrier → faster diffusion) Adaptations for increasing gas exchange efficiency usually involve increasing ____________________________, or decreasing ____________________________ Diffusion of Gases in Air Partial pressure of a gas in air is determined by two factors: 1. Proportion of the atmosphere that is taken up by that gas ▪ Generally around 76% N2, 21 O2, and 0.04 CO2 in the external environment 2. Total air pressure ▪ Increases when # of molecules/unit volume increases ▪ Higher at __________________________, due to force of gravity pulling molecules downwards Pgas = total air pressure x proportion of gas Diffusion of Gases in Water O2 has very low solubility in water in general, and it varies based on two factors: 1. Temperature – as temperature ________________, solubility of O2 and other gases ________________ ▪ Warm-water habitats have less O2 available than cold-water habitats do 2. Presence of other solutes – the __________________ solutes there are in the water, the __________________ room there is for gases to also dissolve ▪ Marine habitats typically have less O2 available than freshwater habitats do O2 availability in water is also impacted by the following: o Presence of photosynthetic organisms o Presence of organisms that undergo cellular respiration, e.g., decomposers o The amount of mixing that occurs o Surface area of the body of water Briefly describe how each of the above factors impacts O2 availability in water.  GAS EXCHANGE AND CIRCULATION Biol 1215, Ch. 39/42 Dr. Kyra Janot Summer Term 2024 Adaptations for Gas Exchange The Relationship Between Form and Function Challenges of gas exchange will be different depending on the overall ____________________________and ____________________________of the animal in question When considering animal adaptations, biologists look at both the anatomy and physiology of the parts involved, from proteins to organ systems o Natural selection impacts anatomy of structures by impacting the ____________________________ that code for different proteins o A change in anatomy (structure) will typically result in a change in physiology (function) Surface Area to Volume Ratio Surface area impacts the rate at which substances can be ____________________________between the external and internal environment of an animal, while volume impacts that rate at which those substances are ____________________________ As an animal gets larger, ____________________________ increases more rapidly than ____________________________does o Surface area to volume ratio decreases as animal size increases The relationship between surface area to volume ratio and overall size results in two general patterns: 1. Smaller animals have higher ____________________________ than larger animals, i.e., they use more O2 and produce more CO2 per gram of tissue 2. Larger animals possess adaptations that increase the ____________________________ of surfaces involved in transport of gases, nutrients, or wastes Give three examples of adaptations that increase surface area of a transport surface in animals: Gas Exchange Via Diffusion Animals with very high surface area to volume ratios (e.g., ____________________________) may rely primarily on diffusion for gas exchange o Nearly every cell is in direct contact with the external environment or some internal cavity (e.g., a ____________________________), so no specialised gas exchange organs are needed Animals that undergo gas exchange in this way are restricted to living in wet environments o Gases can only diffuse across a moist surface o Gas exchange surfaces must be ____________________________for diffusion, which makes them more vulnerable to water loss  GAS EXCHANGE AND CIRCULATION Biol 1215, Ch. 39/42 Dr. Kyra Janot Summer Term 2024 Gas Exchange in Air Vs. Water Obtaining O2 from water requires greater efficiency than obtaining O2 from air: o Per unit volume, air has about __________________ more O2 than water o Water is about ___________________ denser than air, so ventilation of water requires more energy Breathing air requires less energy, but animals must have a way of preventing ____________________________ across their gas exchange surfaces Gills of Aquatic Animals Many animals that undergo gas exchange in water use gills to do so, e.g., nudibranchs, marine worms, crustaceans, echinoderms, fish o Number, placement, and overall structure varies Gills are extensions of the body surface made of a thin layer of epithelium o Flattened, and may have several levels of ____________________________ Gills may be external or internal: o External gills are in direct contact with surrounding water o Internal gills are protected by an ____________________________, and water must be driven over them by specialised structures (e.g., limbs, cilia) Gills of Bony Fishes o Gills of bony fishes are generally similar in structure, with gill arches located on both sides of the head (teleosts have four gill arches per side) o Each gill arch has many gill filaments, each filament has many gill lamellae o Gill lamellae are sheet-like structures with ____________________________ List two ways in which the structure of gills matches their function, with respect to maximising rate of gas diffusion: Most fish ventilate gills by opening and closing their ____________________________, creating a pressure gradient that moves water in one direction o Some fast-moving fish will force water across the gills by swimming with their ____________________________ (ram ventilation)  GAS EXCHANGE AND CIRCULATION Biol 1215, Ch. 39/42 Dr. Kyra Janot Summer Term 2024 Countercurrent Flow in Bony Fish Gills Water that flows across the gill lamellae does so in a direction that is ____________________________ to the flow of blood within the capillaries o Each lamella acts as a countercurrent exchanger, i.e., an arrangement in which two adjacent fluids flow in opposite directions to maintain a ____________________________ gradient Briefly describe how countercurrent flow maintains a concentration gradient of O2 so that blood oxygenation is maximised, using concurrent flow as a comparison: Describe one other example of countercurrent flow that occurs in some animals: Tracheal Systems in Insects Insects that breathe air possess a tracheal system which consists of tiny branching tubes that penetrate the body o By having the gas exchange surface located ____________________________, water loss is minimised o Tracheae open to the exterior via spiracles, which can be closed in ____________________________ to further prevent water loss Tracheae are highly branched, and the ends are very tiny, allowing for air to be transported directly to the ____________________________ o In insects, gas exchange occurs directly between the respiratory system and the body tissues Small insects with short tracheae rely on ____________________________ for ventilation o Larger insects contract and relax abdominal and flight muscles, causing tracheae to ____________________________, pushing air out or pulling it in  GAS EXCHANGE AND CIRCULATION Biol 1215, Ch. 39/42 Dr. Kyra Janot Summer Term 2024 Lungs Lungs are ____________________________ that are used for gas exchange in air o As infoldings of the body surface, they minimise water loss in terrestrial environments Found in terrestrial amphibians, reptiles, and mammals, as well as some fish and invertebrates o The ____________________________of lungs generally correlates with an animal’s ____________________________ Unlike tracheal systems, lungs are only involved in gas exchange between the ____________________________ and the ____________________________ Air reaches the lungs via a series of branching ducts Briefly describe the path of air flow through human lungs, starting with the nose/mouth and ending in alveoli: Lung Ventilation in Amphibians Vertebrates actively ventilate their lungs by breathing, i.e., alternation between inhalation and exhalation of air Positive pressure ventilation is used by some amphibians, e.g., frogs Describe the steps involved in positive pressure ventilation of amphibians:  GAS EXCHANGE AND CIRCULATION Biol 1215, Ch. 39/42 Dr. Kyra Janot Summer Term 2024 Lung Ventilation in Mammals Mammals use negative pressure ventilation: 1. Rib muscles and the diaphragm ____________________________, increasing the ____________________________ of the chest cavity and decreasing _______________________ inside the lungs 2. Air flows from high pressure to low pressure, i.e., into the lungs 3. Rib muscles and the diaphragm ___________________________, the volume of the chest cavity __________________________, and pressure in the lungs ____________________ 4. Air flows from high pressure to low pressure, i.e., out of the lungs and into the external environment Lung Ventilation in Birds Birds have very efficient lungs, with air sacs that function as bellows and maintain ____________________________ Ventilation involves four steps: 1. Inhalation #1 – air flows through the ____________________________ and enters two large air sacs located posterior to the lungs 2. Exhalation #1 – air leaves the posterior sacs and enters tiny branching airways called parabronchi, located in the ____________________________ part of the lungs 3. Inhalation #2 – air moves into ____________________________, and into anterior air sacs 4. Exhalation #2 – air moves out of anterior air sacs, through the ____________________________, and out into the environment Bird lungs are more efficient than mammalian lungs for a couple of reasons: 1. Gas exchange occurs during both inhalation and exhalation, since air is moving across ____________________________ during both events ▪ Gas exchange only takes place during ____________________________ in mammals 2. Capillaries are arranged ____________________________to parabronchi ▪ Less efficient than countercurrent flow in fish, but more efficient than the ____________________________ arrangement of capillaries around mammalian alveoli  GAS EXCHANGE AND CIRCULATION Biol 1215, Ch. 39/42 Dr. Kyra Janot Summer Term 2024 Circulation and Gas Exchange with Body Tissues Blood Composition Blood is the circulatory fluid found in animals with closed circulatory systems ____________________________ tissue consisting of cells within an extensive watery extracellular matrix 1. ____________________________of blood volume is plasma (water ECM) 2. ____________________________of blood volume is formed elements Formed elements include: 1. Platelets – cell fragments involved in____________________________ 2. Leukocytes (white blood cells) – diverse set of cells that act as part of the immune system by ____________________________ 3. Erythrocytes (red blood cells) – transport O2 from the lungs to the body tissues using respiratory pigments Respiratory Pigments O2 is not very soluble in water, so animals have respiratory pigments: o Respiratory pigments are ____________________________ that bind to O2, greatly increasing the amount of O2 that the circulatory fluid can carry Arthropods and many ____________________________ have hemocyanin, which contains ____________________________ as the O2-binding component Most vertebrates and some invertebrates have hemoglobin, which contains ____________________________ as the O2-binding component o Each hemoglobin molecule is composed of ____________________________ and can carry four O2 molecules Hemoglobin’s Affinity for O2 Hemoglobin undergoes cooperative binding: o When one subunit binds to an O2 molecule, it causes a ____________________________ in remaining subunits that increases their affinity for O2 o Conversely, unloading of an O2 molecule makes it easier for additional molecules to be unloaded The O2 dissociation curve shows ____________________________ of hemoglobin at different ____________________________ levels o The sigmoidal shape is due to cooperative binding  GAS EXCHANGE AND CIRCULATION Biol 1215, Ch. 39/42 Dr. Kyra Janot Summer Term 2024 Explain how each part of the O2 dissociation curve is related to the cooperative binding/unbinding of hemoglobin and O2: Cooperative binding results in exercising tissues ____________________________than resting tissues o Without cooperative binding hemoglobin would be less likely to reach ____________________________ at the respiratory surface, and the difference in O2 delivery between resting and exercising tissues would be ____________________________ Explain what the shape of the O2 dissociation curve without cooperative binding indicates regarding binding of hemoglobin and O2:  GAS EXCHANGE AND CIRCULATION Biol 1215, Ch. 39/42 Dr. Kyra Janot Summer Term 2024 Hemoglobin’s affinity for O2 is also impacted by pH and temperature o A ____________________________results in a change to the O2 dissociation curve called the Bohr shift, as lower pH results in hemoglobin having a lower affinity for O2 o ____________________________ also results in hemoglobin having a lower affinity for O2 How does the impact of pH and temperature on hemoglobin’s affinity for O2 ensure that more O2 is delivered to tissues that need it the most? Circulatory Systems of Different Lineages Types of Circulatory Systems Small, flat animals do not need circulatory systems, but all other animals will have a circulatory system that includes: 1. A circulatory fluid that ____________________________ throughout the body 2. One or more hearts that generate the ____________________________ needed for fluid to flow 3. A set of vessels that ____________________________ the flow of fluid Circulatory systems may be open or closed: o In an open circulatory system a single fluid called ____________________________ acts as both circulatory fluid and interstitial fluid, and it is not exclusively confined to the vessels o In a closed circulatory system ____________________________ acts as the circulatory fluid and is distinct from interstitial fluid, as it is always confined to the vessels  GAS EXCHANGE AND CIRCULATION Biol 1215, Ch. 39/42 Dr. Kyra Janot Summer Term 2024 Open Circulatory Systems ____________________________ and most ____________________________ have open circulatory systems Hemolymph is actively pumped throughout the body in a limited system of vessels, and it comes in____________________________ with body tissues o Transports substances that may include gases, nutrients, wastes, hormones, cells, respiratory pigments, clotting agents… One or more hearts contract to pump hemolymph into vessels that empty into ____________________________ o When these hearts relax, pressure inside ____________________________ and hemolymph is sucked back in via openings on the surface o Body movements also help to move hemolymph back to the heart Describe two limitations of open circulatory systems: Closed Circulatory Systems Closed circulatory systems are found in animals that are typically ____________________________, e.g.: o Vertebrates, which are generally large and highly mobile o Cephalopods, which are often active hunters o Annelids, which may be active burrowers or hunters Blood flows continuously through a series of vessels, with pressure generated by a heart o ____________________________ can be maintained at a much higher level than in an open circulatory system o Blood flow can be directed in a more controlled way in response to tissue needs Vertebrate Circulatory Systems: Vessels Vertebrates have closed circulatory systems with three types of vessels: 1. Arteries are tough, thick-walled vessels that take blood ____________________________ ▪ Small arteries are called arterioles 2. Capillaries have walls that are ____________________________, allowing for rapid diffusion of gases and other substances between the blood and tissues 3. Veins are thin-walled vessels that ____________________________ ▪ Small veins are called venules  GAS EXCHANGE AND CIRCULATION Biol 1215, Ch. 39/42 Dr. Kyra Janot Summer Term 2024 Vertebrate Circulatory Systems: the Heart Vertebrate hearts contain two or more chambers o At least one thin-walled atrium, which receives blood from ____________________________ o At least one thick-walled ventricle, which generates the force needed to pump blood through the circulatory system Mammalian hearts have ____________________________ o Atria pump blood to the ventricles below, through atrioventricular (AV) valves o The right ventricle pumps blood to ____________________________ o The left ventricle pumps blood to ____________________________ Evolution of Vertebrate Circulatory Systems  GAS EXCHANGE AND CIRCULATION Biol 1215, Ch. 39/42 Dr. Kyra Janot Summer Term 2024 Fish Circulatory Systems Fish have a two-chambered heart (one atrium, one ventricle) and a ____________________________of blood flow Force generated by the ventricle must be sufficient to push blood through capillary beds of both ________________________________________________________ o Blood pressure drops when blood flows through each capillary bed, due to mechanical resistance o While blood pressure in this system is relatively low, it is sufficient in part because fish live in water, so gravity does not reduce blood flow further Amphibian Circulatory Systems Amphibians have a three-chambered heart (two atria, one ventricle) and double circulation o O2-poor blood flows through the pulmocutaneous circuit to pick up O2 from ____________________________ o O2-rich blood flows through the systemic circuit to deliver O2to body tissues o O2-poor and O2-rich blood mix in the ____________________________ Blood only has to make it through one set of capillaries before returning to the heart, so higher ____________________________can be maintained Why might mixing of blood in the ventricle decrease gas exchange efficiency? (Non-Avian) Reptile Circulatory Systems Turtles, lizards, and snakes have a three-chambered heart(two atria, one ventricle) where the ventricle is partially divided o Partial division of the ventricle results in better____________________________ of O2-rich and O2- poor blood, making gas exchange more efficient overall o Also possess double circulation, and a bypass vessel that shunts blood from the ____________________________ to the ____________________________when the animal is underwater Crocodilians have double circulation, as well as a unique heart that has both a ____________________________and four chambers (two atria and two ventricles) o Separate ventricles associated with the pulmonary and systemic circuits allow for ____________________________of O2-rich and O2-poor blood  GAS EXCHANGE AND CIRCULATION Biol 1215, Ch. 39/42 Dr. Kyra Janot Summer Term 2024 Bird and Mammal Hearts Both mammals and birds have a four-chambered heart with two atria and two ventricles (but no bypass vessel) o The ____________________________of the heart pumps and receives only O2-rich blood o The ____________________________of the heart pumps and receives only O2-poor blood Similarity in heart structure of birds and mammals is the result of convergent evolution, not homology o Both birds and mammals are endotherms, and require more O2 than ectotherms Homeostasis of Gas Exchange and Circulation General Principles of Homeostasis Homeostasis is the stability in ____________________________conditions within a cell, tissue, or organ o Important because most processes in an organism can only occur optimally within a narrow range of conditions (e.g., temperature, pH, salinity) Organisms often have homeostatic mechanisms that allow them to regulate internal conditions o Fluctuations in the ____________________________ are minimised, even when larger fluctuations are occurring in the ____________________________ Regulation Vs. Conformation Different organisms regulate different conditions to different degrees 1. E.g., a dog spends energy either ____________________________ to maintain a consistent body temperature, but ____________________________allow their body temperature to vary with the external environment While regulation requires the use of ____________________________, conforming often comes with trade-offs 1. E.g., a fish that does not regulate body temperature may not be able to maintain high activity levels in cold waters Regulation and conformation are two extremes of an overall continuum, with most animals falling somewhere in between Negative Feedback Loops Most animals achieve homeostasis via regulatory systems that _________________________ internal conditions, and trigger negative feedback mechanisms that _________________________excess change in either direction A negative feedback loop involves three general components: 1. A sensor, i.e., a structure that ____________________________ in some condition 2. An integrator, i.e., a structure that ____________________________ and compares it to some set point to determine if a response is needed 3. An effector, i.e., a structure or structures that ____________________________ to restore the monitored condition back to the set point  GAS EXCHANGE AND CIRCULATION Biol 1215, Ch. 39/42 Dr. Kyra Janot Summer Term 2024 Homeostatic Control of Ventilation An animal needs to maintain appropriate levels of blood PO2 and PCO2 in order for ____________________________during both rest and high levels of activity At rest, breathing rate is set by the medullary respiratory centre o This centre stimulates rib and diaphragm muscles to contract ____________________________ in humans During exercise, muscles take up more O2 from the blood and release more CO2, so blood PO2 ____________________________ and blood PCO2 ____________________________, triggering a negative feedback loop Describe or illustrate the negative feedback loop that is involved in bringing O2 levels back up and CO2 levels back down during exercise – make sure to clearly indicate a) what is being sensed, b) the sensors, c) the integrator, d) the effectors, and e) the response enacted by the effectors. Homeostatic Control of Blood Pressure An animal needs to maintain blood pressure at a level that is high enough to sustain sufficient ____________________________ for transport of various substances, but that is not so high that it ____________________________ If blood pressure increases or decreases too much, baroreceptors in the walls of the ____________________________ sense the change o Baroreceptors signal to the brain o The brain sends nervous and hormonal to multiple effectors, including the sinoatrial node (pacemaker) of the heart, cardiac muscles, and blood vessels Describe or illustrate the negative feedback loops that are involved in bringing blood pressure back to a set point if it either increases or decreases too much – make sure to clearly indicate a) what is being sensed, b) the sensors, c) the integrator, d) the effectors, and e) the response enacted by the effectors.  GAS EXCHANGE AND CIRCULATION Biol 1215, Ch. 39/42 Dr. Kyra Janot Summer Term 2024 Learning Outcomes 1. Describe the general characteristics that are necessary for efficient gas exchange a) Discuss the advantages and disadvantages of water and air as respiratory media 2. Explain how surface area to volume ratio scales with size, and two general patterns that arise from this relationship 3. Characterise the major types of gas exchange structures found in animals (skin, gills, tracheal systems, lungs) a) Explain how form matches function for each 4. Explain how ventilation occurs in fish, amphibians, mammals, and birds a) Distinguish between concurrent and countercurrent exchange b) Differentiate between positive pressure breathing and negative pressure breathing c) Compare and explain the efficiency of ventilation in mammals and birds 5. For mammals, describe the exchange of gases in the lungs and in tissues a) Explain the importance of respiratory pigments b) Describe what cooperative binding is, and explain how it impacts the shape of the oxygen dissociation curve c) Explain how heat and pH impact hemoglobin to ensure more oxygen is unloaded to tissues with the greatest need 6. Compare and contrast open and closed circulatory systems 7. Compare and contrast the circulatory systems of the major groups of vertebrates a) Distinguish between pulmonary and systemic circuits and explain the function of each 8. Define homeostasis, and explain the importance of homeostatic mechanisms in animals a) Identify the sensor, integrator, and effector(s) in negative feedback mechanisms b) Briefly describe the negative feedback mechanisms involved in maintaining homeostasis of ventilation and blood pressure in humans