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CAMPBELL BIOLOGY IN FOCUS Urry • Cain • Wasserman • Minorsky • Jackson • Reece 34 Circulation and Gas Exchange Lecture Presentations by Kathleen Fitzpatrick and Nicole Tunbridge © 2014 Pearson Education, Inc. Describe the function of the respiratory system. © 2014 Pearson Education, Inc. Concept 34.5: Gas exchange occurs across specialized respiratory surfaces Gas exchange is the uptake of molecular O2 from the environment and the discharge of CO2 to the environment © 2014 Pearson Education, Inc. Gases hate to be in mixtures (e.g. gas mixtures, dissolved in liquids, etc.). © 2014 Pearson Education, Inc. Partial Pressure Gradients in Gas Exchange Partial pressure is the pressure exerted by a particular gas in a mixture of gases For example, the atmosphere is 21% O2, by volume, so the partial pressure of O2 (PO2) is 0.21 the atmospheric pressure © 2014 Pearson Education, Inc. Partial pressures also apply to gases dissolved in liquid, such as water When water is exposed to air, an equilibrium is reached in which the partial pressure of each gas is the same in the water and the air A gas always undergoes net diffusion from a region of higher partial pressure to a region of lower partial pressure © 2014 Pearson Education, Inc. There are 4 requirements a respiratory surface must meet in order to be efficient at gas exchange: 1. Moist 2. Thin membrane 3. Increased surface area 4. Connection to a circulatory system © 2014 Pearson Education, Inc. As we review the evolution and physiology of the respiratory system, validate the claim made on the last slide. -Where is the respiratory surface? -How does habitat affect the respiratory structure? © 2014 Pearson Education, Inc. Respiratory Media O2 is plentiful in air, and breathing air is relatively easy In a given volume, there is less O2 available in water than in air Obtaining O2 from water requires greater energy expenditure than air breathing Aquatic animals have a variety of adaptations to improve efficiency in gas exchange © 2014 Pearson Education, Inc. Figure 34.17 Coelom Gills Parapodium (functions as gill) (a) Marine worm © 2014 Pearson Education, Inc. Tube foot (b) Sea star Respiratory Surfaces Gas exchange across respiratory surfaces takes place by diffusion Respiratory surfaces tend to be large and thin and are always moist Respiratory surfaces vary by animal and can include the skin, gills, tracheae, and lungs © 2014 Pearson Education, Inc. Gills in Aquatic Animals Gills are outfoldings of the body that create a large surface area for gas exchange Ventilation is the movement of the respiratory medium over the respiratory surface Ventilation maintains the necessary partial pressure gradients of O2 and CO2 across the gills © 2014 Pearson Education, Inc. Aquatic animals move through water or move water over their gills for ventilation Fish gills use a countercurrent exchange system, where blood flows in the opposite direction to water passing over the gills Blood is always less saturated with O2 than the water it meets Countercurrent exchange mechanisms are remarkably efficient © 2014 Pearson Education, Inc. Figure 34.18 O2-poor blood Gill arch Lamella O2-rich blood Blood vessels Gill arch Water Operculum flow Water flow Blood flow Countercurrent exchange PO2 (mm Hg) in water Gill filaments © 2014 Pearson Education, Inc. Net diffusion of O2 150 120 90 60 30 140 110 80 50 30 PO2 (mm Hg) in blood © 2014 Pearson Education, Inc. Tracheal Systems in Insects The tracheal system of insects consists of a network of air tubes that branch throughout the body The tracheal system can transport O2 and CO2 without the participation of the animal’s open circulatory system Larger insects must ventilate their tracheal system to meet O2 demands © 2014 Pearson Education, Inc. Figure 34.19 Muscle fiber 2.5 m Tracheoles Mitochondria Tracheae Air sacs Body cell Tracheole Air sac Trachea External opening © 2014 Pearson Education, Inc. Air Figure 34.19a Muscle fiber 2.5 m Tracheoles Mitochondria © 2014 Pearson Education, Inc. Lungs Lungs are an infolding of the body surface, usually divided into numerous pockets The circulatory system (open and closed) transports gases between the lungs and the rest of the body The use of lungs for gas exchange varies among vertebrates that lack gills © 2014 Pearson Education, Inc. Considering the mammalian system, trace the flow of air from the nasal orifice to the alveoli. © 2014 Pearson Education, Inc. Mammalian Respiratory Systems: A Closer Look A system of branching ducts conveys air to the lungs Air inhaled through the nostrils is warmed, humidified, and sampled for odors The pharynx directs air to the lungs and food to the stomach Swallowing tips the epiglottis over the glottis in the pharynx to prevent food from entering the trachea © 2014 Pearson Education, Inc. Air passes through the pharynx, larynx, trachea, bronchi, and bronchioles to the alveoli, where gas exchange occurs Exhaled air passes over the vocal cords in the larynx to create sounds Cilia and mucus line the epithelium of the air ducts and move particles up to the pharynx This “mucus escalator” cleans the respiratory system and allows particles to be swallowed into the esophagus © 2014 Pearson Education, Inc. Gas exchange takes place in alveoli, air sacs at the tips of bronchioles Oxygen diffuses through the moist film of the epithelium and into capillaries Carbon dioxide diffuses from the capillaries across the epithelium and into the air space Animation: Gas Exchange © 2014 Pearson Education, Inc. Figure 34.20a Nasal cavity Pharynx Left lung Larynx (Esophagus) Trachea Right lung Bronchus Bronchiole Diaphragm (Heart) © 2014 Pearson Education, Inc. Figure 34.20b Branch of pulmonary vein (oxygen-rich blood) Branch of pulmonary artery (oxygen-poor blood) Terminal bronchiole Alveoli Capillaries © 2014 Pearson Education, Inc. Figure 34.20c 50 m Dense capillary bed enveloping alveoli (SEM) © 2014 Pearson Education, Inc. Alveoli lack cilia and are susceptible to contamination Secretions called surfactants coat the surface of the alveoli Preterm babies lack surfactant and are vulnerable to respiratory distress syndrome; treatment is provided by artificial surfactants © 2014 Pearson Education, Inc. Figure 34.21 Surface tension (dynes/cm) Results 40 30 20 10 RDS deaths 0 Deaths from other causes (n 9) (n 0) <1,200 g (n 29) (n 9) >1,200 g Body mass of infant © 2014 Pearson Education, Inc. Breathing is an example of respiration, but not all respiration is described as breathing! Figure that one out… © 2014 Pearson Education, Inc. Concept 34.6: Breathing ventilates the lungs The process that ventilates the lungs is breathing, the alternate inhalation and exhalation of air © 2014 Pearson Education, Inc. An amphibian such as a frog ventilates its lungs by positive pressure breathing, which forces air down the trachea Birds have eight or nine air sacs that function as bellows that keep air flowing through the lungs Air passes through the lungs of birds in one direction only Passage of air through the entire system—lungs and air sacs—requires two cycles in inhalation and exhalation © 2014 Pearson Education, Inc. How a Mammal Breathes Mammals ventilate their lungs by negative pressure breathing, which pulls air into the lungs Lung volume increases as the rib muscles and diaphragm contract The tidal volume is the volume of air inhaled with each breath Animation: Gas Exchange © 2014 Pearson Education, Inc. Figure 34.22 Rib cage expands as rib muscles contract. Air inhaled. Rib cage gets smaller as rib muscles relax. Air exhaled. Lung Diaphragm 1 Inhalation: Diaphragm contracts (moves down). © 2014 Pearson Education, Inc. 2 Exhalation: Diaphragm relaxes (moves up). The maximum tidal volume is the vital capacity After exhalation, a residual volume of air remains in the lungs Each inhalation mixes fresh air with oxygen-depleted residual air As a result, the maximum PO2 in alveoli is considerably less than in the atmosphere ***Making the inhalation of oxygen in air ALWAYS favorable © 2014 Pearson Education, Inc. How long can you hold your breath? Is it possible to hold it indefinitely? Why? © 2014 Pearson Education, Inc. Control of Breathing in Humans In humans, the main breathing control center consists of neural circuits in the medulla oblongata, near the base of the brain The medulla regulates the rate and depth of breathing in response to pH changes in the cerebrospinal fluid The medulla adjusts breathing rate and depth to match metabolic demands © 2014 Pearson Education, Inc. Figure 34.23-1 Homeostasis: Blood pH of about 7.4 Stimulus: Rising level of CO2 in tissues lowers blood pH. © 2014 Pearson Education, Inc. Figure 34.23-2 Homeostasis: Blood pH of about 7.4 Stimulus: Rising level of CO2 in tissues lowers blood pH. Carotid arteries Sensor/control center: Cerebrospinal fluid Medulla oblongata © 2014 Pearson Education, Inc. Aorta Figure 34.23-3 Homeostasis: Blood pH of about 7.4 Response: Signals from medulla to rib muscles and diaphragm increase rate and depth of ventilation. Stimulus: Rising level of CO2 in tissues lowers blood pH. Carotid arteries Sensor/control center: Cerebrospinal fluid Medulla oblongata © 2014 Pearson Education, Inc. Aorta Figure 34.23-4 Homeostasis: Blood pH of about 7.4 CO2 level decreases. Response: Signals from medulla to rib muscles and diaphragm increase rate and depth of ventilation. Stimulus: Rising level of CO2 in tissues lowers blood pH. Carotid arteries Sensor/control center: Cerebrospinal fluid Medulla oblongata © 2014 Pearson Education, Inc. Aorta Sensors in the aorta and carotid arteries monitor O2 and CO2 concentrations in the blood These sensors exert secondary control over breathing © 2014 Pearson Education, Inc. Concept 34.7: Adaptations for gas exchange include pigments that bind and transport gases The metabolic demands of many organisms require that the blood transport large quantities of O2 and CO2 © 2014 Pearson Education, Inc. Coordination of Circulation and Gas Exchange Blood arriving in the lungs has a low PO2 and a high PCO2 relative to air in the alveoli In the alveoli, O2 diffuses into the blood and CO2 diffuses into the air In tissue capillaries, partial pressure gradients favor diffusion of O2 into the interstitial fluids and CO2 into the blood Specialized carrier proteins play a vital role in this process © 2014 Pearson Education, Inc. Animation: CO2 Blood to Lungs Animation: CO2 Tissues to Blood Animation: O2 Blood to Tissues Animation: O2 Lungs to Blood © 2014 Pearson Education, Inc. Figure 34.24 120 27 Inhaled air Exhaled air 160 0.2 O2 CO2 O2 CO2 Alveolar epithelial cells CO2 O2 Alveolar spaces Alveolar capillaries Pulmonary veins Pulmonary arteries 40 45 104 40 O2 CO2 O2 CO2 Systemic veins Systemic arteries Systemic capillaries Heart CO2 O2 <40 >45 O2 CO2 Body tissue cells © 2014 Pearson Education, Inc. Respiratory Pigments Respiratory pigments circulate in blood or hemolymph and greatly increase the amount of oxygen that is transported A variety of respiratory pigments have evolved among animals These mainly consist of a metal bound to a protein © 2014 Pearson Education, Inc. The respiratory pigment of almost all vertebrates and many invertebrates is hemoglobin A single hemoglobin molecule can carry four molecules of O2, one molecule for each ironcontaining heme group Hemoglobin binds oxygen reversibly, loading it in the gills or lungs and releasing it in other parts of the body © 2014 Pearson Education, Inc. Figure 34.UN01 Iron Heme Hemoglobin © 2014 Pearson Education, Inc. Hemoglobin binds O2 cooperatively When O2 binds one subunit, the others change shape slightly, resulting in their increased affinity for oxygen When one subunit releases O2, the others release their bound O2 more readily Cooperativity can be demonstrated by the dissociation curve for hemoglobin © 2014 Pearson Education, Inc. O2 saturation of hemoglobin (%) Figure 34.25a 100 O2 unloaded to tissues at rest 80 O2 unloaded to tissues during exercise 60 40 20 0 0 20 Tissues during exercise 40 60 Tissues at rest PO2 (mm Hg) 80 100 Lungs (a) PO2 and hemoglobin dissociation at pH 7.4 © 2014 Pearson Education, Inc. CO2 produced during cellular respiration lowers blood pH and decreases the affinity of hemoglobin for O2; this is called the Bohr shift Hemoglobin also assists in preventing harmful changes in blood pH and plays a minor role in CO2 transport © 2014 Pearson Education, Inc. O2 saturation of hemoglobin (%) Figure 34.25b 100 pH 7.4 80 pH 7.2 60 Hemoglobin retains less O2 at lower pH (higher CO2 concentration 40 20 0 0 20 40 60 80 PO2 (mm Hg) (b) pH and hemoglobin dissociation © 2014 Pearson Education, Inc. 100 Carbon Dioxide Transport Most of the CO2 from respiring cells diffuses into the blood and is transported in blood plasma, bound to hemoglobin or as bicarbonate ions (HCO3–) © 2014 Pearson Education, Inc. Respiratory Adaptations of Diving Mammals Diving mammals have evolutionary adaptations that allow them to perform extraordinary feats For example, Weddell seals in Antarctica can remain underwater for 20 minutes to an hour For example, elephant seals can dive to 1,500 m and remain underwater for 2 hours These animals have a high blood to body volume ratio © 2014 Pearson Education, Inc. Deep-diving air breathers can store large amounts of O2 Oxygen can be stored in their muscles in myoglobin proteins Diving mammals also conserve oxygen by Changing their buoyancy to glide passively Decreasing blood supply to muscles Deriving ATP in muscles from fermentation once oxygen is depleted © 2014 Pearson Education, Inc.