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Chapter 42: Circulation and Gas Exchange Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Trading with the Environment • Every organism must exchange materials with its environment – And this exchange ultimately occurs at the cellular level Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Unicellular organisms – Exchanges occur directly with the environment • Multicellular organisms – Direct exchange not possible Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Salmon gills – example of a specialized exchange system Figure 42.1 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Circulatory systems reflect phylogeny • Transport systems connect the organs of exchange with the body cells Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Complex animals have internal transport systems – circulate fluid, lifeline between the aqueous environment of cells and the exchange organs, such as lungs, that exchange chemicals with the outside environment Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Invertebrate Circulation Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Gastrovascular Cavities • Simple animals, e.g. cnidarians are two cells thick • gastrovascular cavity – digestion and distribution of substances throughout the body Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Circular canal Radial canal Mouth 5 cm Figure 42.2 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Open and Closed Circulatory Systems • Found in more complex animals • 3 basic components – circulatory fluid (blood) – set of tubes (blood vessels) – muscular pump (the heart) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Arthropods, and most molluscs – Open circulatory system Heart Hemolymph in sinuses surrounding ograns Anterior vessel Lateral vessels Ostia Tubular heart Figure 42.3a Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings (a) An open circulatory system • Closed circulatory system – Blood is confined to vessels and is distinct from the interstitial fluid efficient Heart Interstitial fluid Small branch vessels in each organ Dorsal vessel (main heart) Auxiliary hearts Figure 42.3b Ventral vessels (b) A closed circulatory system Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Vertebrate Circulation • Vertebrates have a closed circulatory system – called the cardiovascular system • Blood vessels and a 2-4-chambered heart Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Arteries capillaries (sites of chemical exchange)veinsheart Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Fishes • 2 chamber heart – One ventricle and one atrium • Ventricle gills (picks up O2 and disposes of CO2) body atrium Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Amphibians • 3-chambered heart, with two atria and one ventricle • Ventricle pumps blood into a forked artery, splits the ventricle’s output into the pulmocutaneous circuit and the systemic circuit double circulation Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Reptiles (Except Birds) • Double circulation – With a pulmonary circuit (lungs) and a systemic circuit • Turtles, snakes, and lizards – 3-chambered heart Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mammals and Birds • Ventricle is completely divided into separate right and left chambers • The left side of the heart pumps and receives only oxygen-rich blood • While the right side receives and pumps only oxygen-poor blood Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • 4-chambered heart – essential adaptation of the endothermic way of life characteristic of mammals and birds Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Vertebrate circulatory systems, fig. 42.4 AMPHIBIANS REPTILES (EXCEPT BIRDS) MAMMALS AND BIRDS Lung and skin capillaries Lung capillaries Lung capillaries FISHES Gill capillaries Artery Pulmocutaneous circuit Gill circulation Heart: ventricle (V) A Atrium (A) Systemic Vein circulation Systemic capillaries Right systemic aorta Pulmonary circuit A A V Right V Left Right Systemic circuit Systemic capillaries Figure 42.4 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Pulmonary circuit Left Systemic V aorta Left A Systemic capillaries A V Right A V Left Systemic circuit Systemic capillaries Mammalian Circulation: The Pathway • Heart valves – one-way flow of blood through the heart Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Blood begins at right ventricle lungs (blood loads O2 and unloads CO2) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Oxygen-rich blood from the lungs heart at the left atrium left ventricle body heart Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • mammalian cardiovascular system 7 Capillaries of head and forelimbs Anterior vena cava Pulmonary artery Aorta Pulmonary artery 9 6 Capillaries of right lung Capillaries of left lung 2 4 3 Pulmonary vein 5 1 Right atrium 3 11 Left atrium Pulmonary vein 10 Left ventricle Right ventricle Aorta Posterior vena cava 8 Figure 42.5 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Capillaries of abdominal organs and hind limbs The Mammalian Heart: A Closer Look Pulmonary artery Aorta Pulmonary artery Anterior vena cava Right atrium Left atrium Pulmonary veins Pulmonary veins Semilunar valve Semilunar valve Atrioventricular valve Atrioventricular valve Posterior vena cava Right ventricle Figure 42.6 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Left ventricle Cardiac cycle • Contraction, or pumping, phase of the cycle – Is called systole • Relaxation, or filling, phase of the cycle – Is called diastole Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The cardiac cycle (~ 0.8 sec.) 2 Atrial systole; Semilunar valves closed ventricular diastole 0.1 sec Semilunar valves open 0.3 sec 0.4 sec AV valves open 1 Atrial and ventricular diastole Figure 42.7 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings AV valves closed 3 Ventricular systole; atrial diastole • Heart rate, also called the pulse – number of beats per minute • Cardiac output – volume of blood pumped Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Maintaining the Heart’s Rhythmic Beat • Cardiac muscle cells are self-excitable – contract without any signal from the nervous system Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Sinoatrial (SA) node, or pacemaker – Sets the rate and timing • Impulses from the SA node – Travel to the atrioventricular (AV) node • At the AV node, the impulses are delayed – And then travel to the Purkinje fibers ventricles contract Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Impulses recorded as an electrocardiogram (ECG or EKG) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The control of heart rhythm 1 Pacemaker generates wave of signals to contract. SA node (pacemaker) 2 Signals are delayed 3 Signals pass at AV node. to heart apex. 4 Signals spread Throughout ventricles. Bundle branches AV node Heart apex ECG Figure 42.8 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Purkinje fibers Blood Vessel Structure and Function • The “infrastructure” of the circulatory system Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • All blood vessels – Have three similar layers Vein Artery Basement membrane Endothelium 100 µm Valve Endothelium Smooth muscle Connective tissue Endothelium Smooth muscle Capillary Connective tissue Artery Vein Venule Figure 42.9 Arteriole Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Arteries have thicker walls – high pressure of blood pumped from the heart Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • In the thinner-walled veins – Blood flows back to the heart mainly as a result of muscle action Direction of blood flow in vein (toward heart) Valve (open) Skeletal muscle Valve (closed) Figure 42.10 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • velocity of blood flow slowest in the capillary beds Systolic pressure Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Veins Venules Venae cavae Figure 42.11 Capillaries Diastolic pressure Arterioles 120 100 80 60 40 20 0 Arteries 50 40 30 20 10 0 Aorta Velocity ( 5,000 4,000 3,000 2,000 1,000 0 Pressure Area as a result of the high resistance and large total cross-sectional area • Systolic pressure – pressure in the arteries during ventricular systole • Diastolic pressure – pressure in the arteries during diastole – lower than systolic pressure Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Blood pressure measurement 1 A typical blood pressure reading for a 20-year-old is 120/70. The units for these numbers are mm of mercury (Hg); a blood pressure of 120 is a force that can support a column of mercury 120 mm high. 4 The cuff is loosened further until the blood flows freely through the artery and the sounds below the cuff disappear. The pressure at this point is the diastolic pressure remaining in the artery when the heart is relaxed. Blood pressure reading: 120/70 Pressure in cuff above 120 Rubber cuff inflated with air Pressure in cuff below 120 120 Pressure in cuff below 70 120 70 Sounds audible in stethoscope Artery Artery closed 2 A sphygmomanometer, an inflatable cuff attached to a pressure gauge, measures blood pressure in an artery. The cuff is wrapped around the upper arm and inflated until the pressure closes the artery, so that no blood flows past the cuff. When this occurs, the pressure exerted by the cuff exceeds the pressure in the artery. Figure 42.12 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 3 A stethoscope is used to listen for sounds of blood flow below the cuff. If the artery is closed, there is no pulse below the cuff. The cuff is gradually deflated until blood begins to flow into the forearm, and sounds from blood pulsing into the artery below the cuff can be heard with the stethoscope. This occurs when the blood pressure is greater than the pressure exerted by the cuff. The pressure at this point is the systolic pressure. Sounds stop Capillaries Precapillary sphincters Thoroughfare channel (a) Sphincters relaxed Venule Arteriole Capillaries (b) Sphincters contracted Arteriole Venule (c) Capillaries and larger vessels (SEM) Figure 42.13 a–c Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 20 m • The difference between blood pressure and osmotic pressure – Drives fluids out of capillaries at the arteriole end and into capillaries at the venule end Tissue cell INTERSTITIAL FLUID Net fluid Net fluid Capillary Red blood cell out movement in 15 m At the arterial end of a capillary, blood pressure is greater than osmotic pressure, and fluid flows out of the capillary into the interstitial fluid. At the venule end of a capillary, blood pressure is less than osmotic pressure, and fluid flows from the interstitial fluid into the capillary. Direction of blood flow Pressure Capillary movement Figure 42.14 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Blood pressure Osmotic pressure Inward flow Outward flow Arterial end of capillary Venule end Fluid Return by the Lymphatic System • Returns fluid to the body from the capillary beds • Aids in body defense Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Blood is a connective tissue with cells suspended in plasma (matrix) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Blood Composition and Function • The cellular elements – Occupy about 45% of the volume of blood Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Plasma • 90% water • Also, dissolved ions, sometimes referred to as electrolytes Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • mammalian plasma Plasma 55% Constituent Major functions Water Solvent for carrying other substances Icons (blood electrolytes Sodium Potassium Calcium Magnesium Chloride Bicarbonate Plasma proteins Albumin Fibringen Immunoglobulins (antibodies) Osmotic balance pH buffering, and regulation of membrane permeability Separated blood elements Osmotic balance, pH buffering Clotting Defense Substances transported by blood Nutrients (such as glucose, fatty acids, vitamins) Waste products of metabolism Respiratory gases (O2 and CO2) Hormones Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 42.15 Cellular Elements • Red blood cells, which transport oxygen • White blood cells, which function in defense • Platelets – (fragments of cells that are involved in clotting) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • cellular elements of mammalian blood, fig. 42.15 Cellular elements 45% Cell type Separated blood elements Number per L (mm3) of blood Functions Erythrocytes (red blood cells) 5–6 million Transport oxygen and help transport carbon dioxide Leukocytes (white blood cells) 5,000–10,000 Defense and immunity Lymphocyte Basophil Eosinophil Neutrophil Monocyte Platelets Figure 42.15 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 250,000 400,000 Blood clotting Erythrocytes (red blood cells) • Most numerous blood cells – Transport oxygen Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Leukocytes • 5 types of white blood cells, or leukocytes – Monocytes, neutrophils, basophils, eosinophils, and lymphocytes, which function in defense by phagocytizing bacteria and debris or by producing antibodies Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Platelets • blood clotting Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Erythrocytes, leukocytes, and platelets all develop from a common source – pluripotent stem cells in the red marrow of bones Pluripotent stem cells (in bone marrow) Lymphoid stem cells Myeloid stem cells Basophils B cells T cells Lymphocytes Eosinophils Neutrophils Erythrocytes Figure 42.16 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Platelets Monocytes Blood clotting • A cascade of complex reactions – Converts fibrinogen to fibrin, forming a clot 1 The clotting process begins when the endothelium of a vessel is damaged, exposing connective tissue in the vessel wall to blood. Platelets adhere to collagen fibers in the connective tissue and release a substance that makes nearby platelets sticky. 2 The platelets form a plug that provides emergency protection against blood loss. 3 This seal is reinforced by a clot of fibrin when vessel damage is severe. Fibrin is formed via a multistep process: Clotting factors released from the clumped platelets or damaged cells mix with clotting factors in the plasma, forming an activation cascade that converts a plasma protein called prothrombin to its active form, thrombin. Thrombin itself is an enzyme that catalyzes the final step of the clotting process, the conversion of fibrinogen to fibrin. The threads of fibrin become interwoven into a patch (see colorized SEM). Collagen fibers Platelet plug Platelet releases chemicals that make nearby platelets sticky Fibrin clot Clotting factors from: Platelets Damaged cells Plasma (factors include calcium, vitamin K) Prothrombin Figure 42.17 Thrombin Fibrinogen Fibrin Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 5 µm Red blood cell Cardiovascular Disease • more than half the deaths in the United States Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • atherosclerosis – Is caused by the buildup of cholesterol within arteries Connective tissue Smooth muscle Plaque Endothelium (a) Normal artery 50 µm (b) Partly clogged artery Figure 42.18a, b Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 250 µm • Hypertension, or high blood pressure – Promotes atherosclerosis and increases the risk of heart attack and stroke • A heart attack – Is the death of cardiac muscle tissue resulting from blockage of one or more coronary arteries • A stroke – Is the death of nervous tissue in the brain, usually resulting from rupture or blockage of arteries in the head Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Gas Exchange • Across specialized respiratory surfaces • Supplies oxygen for cellular respiration and disposes of carbon dioxide Respiratory medium (air of water) O2 CO2 Respiratory surface Organismal level Circulatory system Cellular level Energy-rich molecules from food Figure 42.19 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cellular respiration ATP • Animals require large, moist respiratory surfaces for the adequate diffusion of respiratory gases – Between their cells and the respiratory medium, either air or water Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Gills in Aquatic Animals • Outfoldings of the body surface – Specialized for gas exchange Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Some invertebrates – gills have a simple shape and are distributed over much of the body (a) Sea star. The gills of a sea star are simple tubular projections of the skin. The hollow core of each gill is an extension of the coelom (body cavity). Gas exchange occurs by diffusion across the gill surfaces, and fluid in the coelom circulates in and out of the gills, aiding gas transport. The surfaces of a sea star’s tube feet also function in gas exchange. Gills Coelom Figure 42.20a Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Tube foot • Many segmented worms have flaplike gills – That extend from each segment of their body (b) Marine worm. Many polychaetes (marine worms of the phylum Annelida) have a pair of flattened appendages called parapodia on each body segment. The parapodia serve as gills and also function in crawling and swimming. Parapodia Figure 42.20b Gill Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The gills of clams, crayfish, and many other animals – Are restricted to a local body region (c) Scallop. The gills of a scallop are long, flattened plates that project from the main body mass inside the hard shell. Cilia on the gills circulate water around the gill surfaces. (d) Crayfish. Crayfish and other crustaceans have long, feathery gills covered by the exoskeleton. Specialized body appendages drive water over the gill surfaces. Gills Gills Figure 42.20c, d Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Effectiveness of gills is increased by ventilation and countercurrent flow of blood and water Oxygen-poor blood Gill arch Oxygen-rich blood Lamella Blood vessel Gill arch Water flow Operculum O2 Water flow over lamellae showing % O2 Figure 42.21 Gill filaments Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Blood flow through capillaries in lamellae showing % O2 Countercurrent exchange Tracheal Systems in Insects • The tracheal system of insects – tiny branching tubes that penetrate the body Air sacs Tracheae Spiracle (a) The respiratory system of an insect consists of branched internal tubes that deliver air directly to body cells. Rings of chitin reinforce the largest tubes, called tracheae, keeping them from collapsing. Enlarged portions of tracheae form air sacs near organs that require a large supply of oxygen. Air enters the tracheae through openings called spiracles on the insect’s body surface and passes into smaller tubes called tracheoles. The tracheoles are closed and contain fluid (blue-gray). When the animal is active and is using more O2, most of the fluid is withdrawn into the body. This increases the surface area of air in contact with cells. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 42.22a • The tracheal tubes – Supply O2 directly to body cells Body cell Air sac Tracheole Trachea Air Tracheoles Mitochondria Body wall Myofibrils (b) This micrograph shows cross sections of tracheoles in a tiny piece of insect flight muscle (TEM). Each of the numerous mitochondria in the muscle cells lies within about 5 µm of a tracheole. Figure 42.22b Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 2.5 µm Lungs • Spiders, land snails, and most terrestrial vertebrates have internal lungs Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mammalian Respiratory Systems: A Closer Look • A system of branching ducts – Conveys air to the lungs Branch from the pulmonary artery (oxygen-poor blood) Branch from the pulmonary vein (oxygen-rich blood) Terminal bronchiole Nasal cavity Pharynx Left lung Alveoli 50 µm 50 µm Larynx Esophagus Trachea Right lung Bronchus Bronchiole Diaphragm SEM Heart Figure 42.23 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Colorized SEM • Air inhaled through the nostrils pharynx trachea bronchi bronchioles alveoli, where gas exchange occurs Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings How an Amphibian Breathes • Ventilates its lungs by positive pressure breathing, which forces air down the trachea Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings How a Mammal Breathes • Negative pressure breathing, which pulls air into the lungs Rib cage expands as rib muscles contract Air inhaled Rib cage gets smaller as rib muscles relax Air exhaled Lung Diaphragm INHALATION Diaphragm contracts (moves down) Figure 42.24 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings EXHALATION Diaphragm relaxes (moves up) • Lung volume increases – As the rib muscles and diaphragm contract Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings How a Bird Breathes • Besides lungs, bird have eight or nine air sacs – That function as bellows that keep air flowing through the lungs Air Air Anterior air sacs Trachea Posterior air sacs Lungs Lungs Air tubes (parabronchi) in lung EXHALATION Air sacs empty; lungs fill INHALATION Air sacs fill Figure 42.25 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 1 mm Control of Breathing in Humans • 2 regions of the brain, the medulla oblongata and the pons Cerebrospinal fluid 1 The control center in the medulla sets the basic rhythm, and a control center in the pons moderates it, smoothing out the transitions between inhalations and exhalations. Pons 2 Nerve impulses trigger muscle contraction. Nerves from a breathing control center in the medulla oblongata of the brain send impulses to the diaphragm and rib muscles, stimulating them to contract and causing inhalation. Breathing control centers Medulla oblongata 4 The medulla’s control center also helps regulate blood CO2 level. Sensors in the medulla detect changes in the pH (reflecting CO2 concentration) of the blood and cerebrospinal fluid bathing the surface of the brain. 5 Nerve impulses relay changes in CO2 and O2 concentrations. Other sensors in the walls of the aorta and carotid arteries in the neck detect changes in blood pH and send nerve impulses to the medulla. In response, the medulla’s breathing control center alters the rate and depth of breathing, increasing both to dispose of excess CO2 or decreasing both if CO2 levels are depressed. Carotid arteries Aorta Figure 42.26 3 In a person at rest, these nerve impulses result in about 10 to 14 inhalations per minute. Between inhalations, the muscles relax and the person exhales. Diaphragm Rib muscles Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 6 The sensors in the aorta and carotid arteries also detect changes in O2 levels in the blood and signal the medulla to increase the breathing rate when levels become very low. • Sensors in the aorta and carotid arteries – Monitor O2 and CO2 concentrations in the blood – Exert secondary control over breathing Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Inhaled air Exhaled air 160 0.2 O2 CO2 120 27 Alveolar spaces O2 CO2 104 Alveolar epithelial cells 40 O2 CO2 Blood entering alveolar capillaries 40 O2 CO2 2 1 O2 Alveolar capillaries of lung 45 O2 CO2 104 Pulmonary veins Systemic arteries Systemic veins CO2 40 40 O2 CO2 Pulmonary arteries Blood leaving tissue capillaries Blood leaving alveolar capillaries Heart Tissue capillaries O2 3 4 45 O2 CO2 Tissue cells Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 100 40 O2 CO2 O2 CO2 Figure 42.27 Blood entering tissue capillaries <40 >45 O2 CO2 Respiratory Pigments • Proteins that transport oxygen – Greatly increase the amount of oxygen that blood can carry Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Oxygen Transport • Respiratory pigment of vertebrates is hemoglobin, contained in the erythrocytes Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Hemoglobin must reversibly bind O2, loading O2 in the lungs and unloading it in other parts of the body Heme group Iron atom O2 loaded in lungs O2 unloaded In tissues Figure 42.28 Polypeptide chain Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings O2 O2 Carbon Dioxide Transport • Hemoglobin also helps transport CO2 – And assists in buffering Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 1 2 Carbon dioxide produced by body tissues diffuses into the interstitial fluid and the plasma. Over 90% of the CO2 diffuses into red blood cells, leaving only 7% in the plasma as dissolved CO2. Tissue cell Some CO2 is picked up and transported by hemoglobin. 1 Blood plasma CO 2 within capillary Capillary wall 2 CO2 Carbonic acid dissociates into a biocarbonate ion (HCO3–) and a hydrogen ion (H+). HCO3– 7 Hemoglobin binds most of the H+ from H2CO3 preventing the H+ from acidifying the blood and thus preventing the Bohr shift. Figure 42.30 9 Carbonic acid is converted back into CO2 and water. 10 CO2 formed from H2CO3 is unloaded from hemoglobin and diffuses into the interstitial fluid. To lungs CO2 transport to lungs HCO3– 8 H2CO3 Hb 9 11 CO2 Hemoglobin releases CO2 and H+ H2O CO2 6 In the HCO3– diffuse from the plasma red blood cells, combining with H+ released from hemoglobin and forming H2CO3. 6 HCO3– + H+ 5 8 Red Hemoglobin H2CO3 blood Carbonic acid Hb picks up cell CO2 and H+ 5 + H+ Bicarbonate However, most CO2 reacts with water in red blood cells, forming carbonic acid (H2CO3), a reaction catalyzed by carbonic anhydrase contained. Within red blood cells. Most of the HCO3– diffuse into the plasma where it is carried in the bloodstream to the lungs. 3 4 HCO3– 4 7 Interstitial CO 2 fluid H2O 3 CO2 transport from tissues CO2 produced CO2 CO2 10 CO2 11 Alveolar space in lung Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings diffuses into the alveolar space, from which it is expelled during exhalation. The reduction of CO2 concentration in the plasma drives the breakdown of H2CO3 Into CO2 and water in the red blood cells (see step 9), a reversal of the reaction that occurs in the tissues (see step 4). Diving Mammals • Deep-diving air breathers – Stockpile O2 and deplete it slowly – Myoglobin Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings