ASIM'S WEBWORLD View: Main School Main AP Biology Chapter Guides RELATED LINKS Review Questions and Answers		AP BIOLOGY: Chapter Forty-Six Outline INTRODUCTION Heterotrophs Obtain Energy by Oxidizing Carbon Compounds Called aerobic cell respiration Remove electrons from organic compounds Channel electrons along series of proton pumps in mitochondria Generates ATP Electrons (accompanied by protons) donated to oxygen gas to form water Carbon atoms cleaved, released as carbon dioxide Process Consumes Oxygen and Generate Carbon Dioxide and Water Called metabolic water to emphasize its source Provides sole source of water for some desert vertebrates Diluted into body internal water in other organisms Carbon dioxide can lower pH of body fluid and must be eliminated External respiration: uptake of oxygen and release of carbon dioxide THE COMPOSITION OF AIR Composition and Properties of Air All oxygen in the air is a result of photosynthesis Dry air = 78.09% N2 + 20.95% O2 + 0.93% (argon + inert gases) + 0.03 CO2 Amount of air present decreases at high altitudes fig 46.1 At sea level, air pressure measures 760 mm of mercury fig 46.2 Equals the barometric pressure of air Equivalent to one atmosphere of pressure Each gas within the air exerts a partial pressure = 760 x % gas Nitrogen + inert gases = 760 x 79.02% = 600.6 mm Hg Oxygen = 760 x 20.95% = 159.2 mm Hg Carbon dioxide = 760 x 0.03% = 0.2 mm Hg Less air, therefore less oxygen present at high altitudes Barometric pressure above 6000 meters = 380 mm Hg Partial pressure of oxygen (PO2)= 380 x 20.95% = 80 mm Hg Only half the oxygen is available compared to sea level The Diffusion of Gases Across Cell Membranes Cell membranes of terrestrial organisms freely permeable to oxygen Cell membranes cannot exist without a surrounding layer of water Oxygen concentration in cytoplasm lower than liquid surrounding cells Net diffusion of oxygen from environment into cells Net diffusion of carbon dioxide in opposite direction Gases redistributed by circulatory system Fick's Law of Diffusion Diffusion of oxygen into the epithelial aqueous layer is passive Driven by the difference in oxygen concentration between the interior of the organism and the external environment Mathematical relationship called Fick`s Law of Diffusion R = D x A x Δp / d R = rate of diffusion D = diffusion constant A = area over which diffusion takes place Δp = difference in partial pressures on each side d = distance across which diffusion takes place Evolutionary changes optimize R by favoring certain parameters fig 46.3 Increase surface area Decrease distance d Increase concentration difference Δp THE EVOLUTION OF EXTERNAL RESPIRATION fig 46.5 Simple Diffusion Oxygen diffuses too slowly to be efficient over more than 0.5 mm Severely limits size of organisms Protists are small enough to utilize simple diffusion fig 46.3 As size increases, surface area-to volume ratio decreases Surface area proportional to radius squared (r2) Volume proportional to radius cubed (r 3) Surface area-to-volume ratio proportional to r2/r3 or 1/r As the radius increases the ratio decreases Metabolism may be slowed down to compensate Increase in size must be accompanied by facilitation of diffusion of oxygen into organism Creating a Water Current Most primitive phyla possess no special respiratory organs Can obtain oxygen via diffusion by increasing Δp in Fick`s equation Increase difference in O2 concentration by creating a water current Constantly replace water over diffusion surface Δp does not decrease as diffusion proceeds Keep exterior O2 concentration high Results in higher realized value of R, rate of diffusion Increasing the Diffusion Surface Area More advanced invertebrates and vertebrates possess respiratory organs Increase surface area over which diffusion occurs Provides contact between external environment and internal circulating fluids Increase A and decreasing d Aquatic organs (gills) project from body into water Simple gills like papulae of echinoderms fig 46.3c Convoluted gills of fish fig 46.3e Increase in diffusion surface area enables aquatic organisms to extract more oxygen Enclosing the Gills Disadvantage of external gills Difficult to constantly circulate water past diffusion surface Neotenic amphibian larvae physically move gill through water fig 46.4 Inefficient, highly branched gills offer resistance against movement Special branchial chambers in other organisms pump water past gills Internal mantle cavity of mollusks opens to outside, contains gills Contraction of muscular walls draws water in and expels it Crustacean cavity lies between body and hard exoskeleton Movement of limbs draws water through branchial chamber THE FISH GILL AS AN AQUATIC RESPIRATORY MACHINE Most Successful Branchial Chamber Evolved in Bony Fishes Water passes through mouth into two opercular cavities Gills are located between mouth and entrance to cavity Water then passes out of body after passing over gills and through cavity One-way flow of water over gills Maintains high concentration of oxygen outside gills Continuously swimming fish have nearly immovable gill covers Water constantly forced over gills as fish swim Process is a form of ram ventilation Most bony fish have flexible gill covers fig 46.5 Inhales water into mouth Exhales water over gills and through opercular cavities Effects of Gill Construction on Parameters of Diffusion Structure of gills fig 46.6 Each gill composed of two rows of gill filaments that project into flow of water Filaments divided into thin, disk-like lamellae that lie parallel to water flow Direction of blood circulation runs opposite that of water flow Countercurrent flow maximizes Δp between water and blood Advantage of countercurrent exchange fig 46.7a Least oxygenated blood meets least oxygenated water at back of gill Most oxygenated blood meets most oxygenated water at front of gill Diffusion occurs along entire length of gill If water and blood flowed in the same direction Oxygen-free blood would meet highly oxygenated water Diffusion would initially be high fig 46.7b Oxygenated blood would meet less oxygenated water at back of gill Diffusion would cease, only front part of gill would be functional Fish gills are up to 85% efficient FROM AQUATIC TO ATMOSPHERIC BREATHING More Oxygen Present in Air Than in Water Water = 5-10 ml O2 per 1 liter water Air = 210 ml of O2 per 1 liter air Many aquatic animals use air as their oxygen source Gills Not Adaptable for Terrestrial Use Air is less buoyant than water Lamellae lack structural support, collapse without water buoyancy Collapse reduces diffusion surface area Internal air passages remain open due to structural support Water diffuses into air through evaporation Terrestrial organisms constantly lose water to atmosphere Gills provide an enormous surface area for water loss Evolved two main kinds of terrestrial respiratory organs Both systems sacrifice efficiency to reduce water loss Tracheae of insects fig 46.3d Extensive series of air-filled passages within body Oxygen diffuses directly from trachea to cells, no circulatory intervention Openings close when CO2 levels are below certain point to limit water loss Lungs of terrestrial vertebrates Air enters and exits through one tube, minimizes evaporation Two-way flow of air replaces one-way flow Diffusion surfaces not exposed to pure fresh air Δp is far from maximal, lungs are less efficient than gills Amphibians Low efficiency of lungs offset by high concentration of oxygen Efficiency not a critical problem to early land vertebrates Structure of the amphibian respiratory system fig 46.8 Lung is a simple convoluted sac Connected by trachea (windpipe) to rear of oral cavity (mouth) Opening controlled by glottis, sinuses connect oral cavity to nose Much oxygen obtained by diffusion across moist skin, cutaneous respiration Reptiles More active, greater metabolic need for oxygen Cannot obtain oxygen through watertight skin surface Changes within the reptile respiratory system Lungs possess small air chambers fig 46.8b Larger surface area for diffusion Mammals Metabolic demands even greater due to maintaining constant body temperature Lungs more highly branched with more alveoli clusters fig 46.8c Each alveoli cluster connected to main air passageway by short bronchiole All gas exchange occurs across walls of alveoli fig 46.3f Branching and alveoli vastly increase total surface area Humans have 300 million alveoli in two lungs Area about 42 times the surface area of body Active mammals do not have greater lung mass Have smaller, more numerous alveoli Thinner epithelial layer separates alveoli from blood Birds Metabolism of flying necessitates a more efficient respiratory system Avian lung works like a two-cycle pump fig 46.9 With inhalation air passes into posterior air sacs With exhalation air flows into lung With next inhalation, that air passes from lung to anterior air sacs Air flows out of the body with next exhalation Air flow is unidirectional from posterior to anterior Birds have no "dead volume" of air remaining in lungs as do mammals Air at the diffusing surface of the lung is fully oxygenated Direction of air flow is different from the flow of blood fig 46.10 Flow of air and blood are at 90% angles to one another Called cross-current flow Less efficient than fish, more efficient than mammals Birds can survive in much higher altitudes than mammals Birds increase Δp value in Fick`s equation THE STRUCTURE AND MECHANICS OF THE HUMAN RESPIRATORY SYSTEM Structure of the Respiratory Tree Air normally enters through nostrils Lined with hairs to filter out dust Extensive array of cilia further cleans and moistens air fig 46.11 Air passes through glottis Slit in larynx (voice box) Enters trachea, branches into two bronchi one for each lung fig 46.12 Bronchi further branch into smaller tubes, narrowest called bronchioles Trachea and bronchi reinforced with cartilaginous rings Bronchioles have only smooth muscle in walls Smooth muscle lining adjusts size of passageway Contraction stimulated by parasympathetic division of the nervous system Decrease in diameter by half increases resistance sixteen fold Sympathetic division relaxes smooth muscle, causes bronchodilation, decreases resistance Bronchodilation also caused by epinephrine Drug used to treat symptoms of asthma triggered by release of histamine The Structure of the Lung Terminal bronchioles deliver air to respiratory bronchioles Contain alveoli where gas exchange occurs Alveoli are outpouchings surrounded by capillaries Lines by epithelium only one cell layer thick Outside of lungs covered by visceral pleural membrane Inner wall of thoracic cavity lined by parietal pleural membrane Space between membranes called the pleural cavity Normally small and filled with fluid Fluid links membranes together like water film holds two sheets of cellophane together Lungs held tight to thoracic cavity Each lung has own pleural cavity, if one punctured other lung functional Air Flow in the Lung Human lung functions as one-cycle pump During inhalation or inspiration Rib external intercostal muscles contract raising the ribs fig 46.13 Diaphragm contracts, lowers and flattens Increases volume of thorax Due to coupling of pleural membranes, volume of lungs also increases Pressure of air in lungs decreases, air drawn into lungs fig 46.14 During exhalation or expiration Diaphragm and external intercostal muscles relax Structures of thorax return to previous condition Volume of thorax and lungs decreases Increases pressure of air in lungs, air forced out Extra air can be forced out of lungs Contraction of internal intercostal muscles lowers ribs Diaphragm pushed further up into thoracic cavity fig 46.13b Air volumes of human lungs Tidal volume: volume inspired and expired in a single breath About 500 ml of air Anatomical dead space: 150 ml within air passages Can be increased to 3000 ml during exercise Diffusion surface of lungs exposed to mixture of fresh and oxygen-depleted air Functional residual capacity (FRC): volume in lung after normal resting expiration Residual volume: volume in lung after maximal expiration Vital capacity: amount of air expired after forceful, maximum inspiration Emphysema reduces vital capacity Alveoli destroyed by cigarette smoking Respiratory rate: number of breaths per unit time Minute respiratory volume (MRV) Equals tidal volume x respiratory rate per minute Air entering and leaving lung per minute Normally 5 liters/minute, can be as high as 130 liters/minute Conditions associated with abnormal P CO2 Hyperventilation MRV extremely high CO2 removed from blood by ventilation faster than its produced by tissues Hypoventilation MRV unusually low Elevated P CO2 level Hyperpnea High MRV, high metabolic rate Normal blood P CO2 level GAS TRANSPORT AND EXCHANGE Association of Respiratory and Circulatory Systems Transport of oxygen extremely slow if only by diffusion Transported through circulatory system via carrier Blood plasma holds maximum of 3 ml O2/liter Whole blood is able to carry 200 ml O2/liter Hemoglobin: oxygen carrier protein within the blood of most animals Four polypeptide subunit protein Each subunit combines with iron containing heme group fig 46.15 Hemoglobin picks up oxygen in lungs Bright red color when bound with oxygen Called oxyhemoglobin Hemoglobin releases oxygen at tissues Called deoxyhemoglobin Dark red color, looks blue under skin Hemoglobin widely distributed oxygen carrier protein throughout animal kingdom Hemocyanin: second carrier protein found in many invertebrates Uses copper instead of iron Does not occur within blood cells, exists free in hemolymph Oxygen Transport At P O2 of 100 mm Hg, 97% bound to hemoglobin in red blood cells Percent saturation in arterial blood is 97% at sea level Extracellular fluid surrounding tissues has lower P O2 Oxygen diffuses from capillaries into tissues P O2 of venous blood is 40 mm hg, percent saturation is 75% Graphical representation is an oxyhemoglobin dissociation curve fig 46.16a At rest, 22% (97-75) of the oxyhemoglobin releases oxygen to tissues One fifth of oxygen unloaded in tissues, four-fifths in blood as reserve Blood can additionally supply oxygen needs at exercise If venous blood P O2 is 20 mm Hg, saturation is 35% fig 46.16b Amount unloaded now 62% (97-35) Blood contains reserves for 4-5 minutes without breathing Presence of CO2 at metabolizing tissues Combines with water to form carbonic acid, lowers pH of blood Occurs in red blood cells, hemoglobin has less affinity for oxygen Hemoglobin releases oxygen more readily Dissociation curve shifted to right, called Bohr effect fig 46.17 2,3 diphosphoglycerate (DPG) also shifts curve to right fig 46.17 Also augments unloading of oxygen Production inhibited by oxyhemoglobin Anything that reduces oxyhemoglobin causes production of DPG Example: high altitudes Low P O2 of air lowers level of oxyhemoglobin Immediately causes rapid fatigue Red cells produce DPG after a few days, shifts curve to right Stimulates unloading of oxygen, lessens fatigue After a few weeks, kidneys produce erythropoietin Stimulates bone marrow to produce more red cells Hemoglobin binds to carbon monoxide (CO) Binding to CO more efficient than to O2 CO not readily dissociated; small amounts cause respiratory failure Carbon Dioxide Transport As red blood cells unload oxygen, blood absorbs CO2 from tissues 20% binds to hemoglobin, 8% dissolved in plasma, 72% binds to red cell cytoplasm Carbonic anhydrase catalyzes formation of carbonic acid Carbonic acid dissociates to form bicarbonate and hydrogen ions CO2 removed from plasma, allows loading of greater amounts Blood carry CO2 back to lungs Lower concentration of CO2 in alveoli Carbonic anhydrase reaction proceeds in reverse Gaseous CO2 released, diffuses into alveoli Leaves body with next exhalation fig 46.18 HOW THE BRAIN CONTROLS BREATHING Breathing Initiated by Respiratory Center in Brain Sends nerve signals to diaphragm and intercostal muscles Expansion of chest causes inspiration Expiration proceeds when neurons stop producing impulses Breathing muscles are skeletal, but are under involuntary control Can be voluntarily over-ridden in hypo- or hyperventilation Reflex Pathway Prevents Life Threatening Alterations in Breathing No breathing causes increase in blood P CO2 Causes increase in carbonic acid, lowers blood pH Peripheral chemoreceptors in aortic and carotid bodies are sensitive to pH Send impulses to respiratory control center to reinitiate breathing Central chemoreceptors detect changes in pH of cerebrospinal fluid (CSF) fig 46.19 Peripheral chemoreceptors are responsible for immediate changes Central chemoreceptors are responsible for sustained changes Indefinite hyperventilation also prevented by chemoreceptors THE EVOLUTION OF CIRCULATORY SYSTEMS All Organisms Must Capture Nutrients and Gases from the Environment Simple organisms transport materials across membrane of each cell fig 46.20a Interior of large organisms cannot communicate with environment Fluids within body cavity facilitate movement of materials fig 46.20b Circulation: transport of materials through an internal fluid Types of Circulatory Systems Closed system: blood enclosed within vessels Circulating fluid does not mix with other body fluids Materials pass across by diffusion through walls of vessels Annelids have a closed system fig 46.20c Movement of fluid in vessels assisted by muscle contraction All vertebrates have closed circulatory system Open system: no distinction between circulating fluid and body fluid Arthropods have an open system fig 46.20d Muscular tube in body cavity pumps fluid through network of channels Fluid drains back into central cavity Advantage of closed systems Can change diameter of individual muscle-encased vessels Regulate fluid flow in specific parts of body independently THE FUNCTIONS OF VERTEBRATE CIRCULATORY SYSTEMS Nutrient and Waste Transport Nutrients enter blood through wall of small intestine Carried to liver for storage or metabolism Dissolved glucose and metabolites carried to all body cells Metabolizing cells release wastes into blood Wastes carried to kidney for removal Constitutes metabolic circuit or systemic circulation Oxygen and Carbon Dioxide Transport Oxygen diffuses into blood through gills or lungs Oxygen accumulates in hemoglobin of red blood cells fig 46.21 Oxygen released at metabolizing cells Carbon dioxide, a metabolic product, is released by cells into blood Waste carbon dioxide carried back to gills or lungs and released Constitutes respiratory circuit or pulmonary circulation Temperature Regulation Most vertebrates are poikilotherms, body temperature varies with environmental temperature Mammals and birds are homeotherms, maintain constant body temperature Heat distributed by circulating blood Temperature adjusted by directing flow to interior or extremities Decrease body temperature by dissipating heat to environment fig 46.22 Retain heat by directing blood from extremities to interior Some animals use countercurrent heat exchange system fig 46.23 Hormone Circulation Body activities coordinated by hormones produced in endocrine glands Hormones transported to target tissues throughout body Hormones persist only a short time, are destroyed by body enzymes THE CARDIOVASCULAR SYSTEM Three Elements in a Vertebrate Closed Circulatory System Heart: muscular pump Blood vessels: tubes located through the body Blood: fluid circulating within vessels Heart and blood vessels comprise cardiovascular system Arteries: direct blood away from heart Arterioles: large network of smaller vessels, lead away from heart Capillaries: exchange with cells occurs across this fine network Venules: small vessels that collect blood from capillaries Veins: large vessels carry blood back to heart Anatomy of a Blood Vessel Similar structures found in arteries, arterioles, veins and venules fig 46.24 Walls are composed of four layers of tissue Innermost endothelium: epithelial sheet of cells Thick layer of elastic fibers Layer of smooth muscle Encased in connective tissue Walls too thick to permit exchange of materials Exchange occurs in capillaries, have only endothelium Arteries and Arterioles Carry Blood Away from the Heart Elastic fibers allow large artery to expand and recoil when receiving blood from heart Smaller arteries and arterioles are less elastic, but have thicker smooth muscle Network of small vessels provides flow resistance Inversely proportional to radius of the tube to the fourth power Small diameter arteries and arterioles cause greatest resistance to blood flow Contraction of smooth muscle causes vasoconstriction Increases resistance Decreases flow Relaxation of smooth muscle causes vasodilation Decreases resistance Increases flow Blood around some organs regulated by precapillary sphincters fig 46.25 Rings of smooth muscle around arterioles where they empty into capillaries Close off specific capillary beds to all blood flow Exchange Takes Place in the Capillaries Heart provides sufficient pressure to pump against resistance of arterial tree and into capillaries Every cell within 100 µm of a capillary Average capillary 1 mm long, 8 µm wide, just larger than red blood cell fig 46.7 Capillaries have greatest cross-sectional area of all types of vessels Blood velocity decreases in capillary beds fig 46.27 Provides greater time for exchange of materials with extracellular fluid Blood releases oxygen and nutrients, picks up carbon dioxide and wastes Blood pressure greatly reduced when blood enters veins Veins and Venules Return Blood to the Heart Two main veins return systemic blood to heart Four veins return pulmonary blood back to heart (two from each lung) Veins and venules have thinner layer of smooth muscle than arteries fig 46.28 Pressure one-tenth that of arteries Most blood in body held in veins Can expand to hold greater quantities Venous pressure not sufficient to return blood to heart from feet and legs Aided by contraction of skeletal muscles One-way venous valves direct flow toward heart fig 46.29 The Lymphatic System Recovers Lost Fluid Circulatory system open to diffusion through capillary walls Filtration driven by pressure of blood, supplies cells with oxygen and nutrients Most fluid returned by osmosis due to concentration of protein in blood fig 46.30 Open lymphatic system collects rest of fluid and returns it to blood fig 46.31 Composed of lymphatic capillaries, lymphatic vessels, lymph nodes and lymphatic organs like spleen and thymus Fluid in tissues drains into open-ended lymph capillaries Lymph passes into progressively larger vessels Lymphatic vessels contain vein-like one-way valves fig 46.32 Right lymphatic duct and thoracic duct drain into veins on side of neck Blockage of lymphatic systems leads to edema Lymph fluid movement assisted by movement of muscles Some lymph vessels contract rhythmically Some animals have lymph hearts Lymph modified by phagocytic cells in nodes and lymphatic organs Contain germinal centers for production of lymphocytes Thymus plays central role in immune system BLOOD The Plasma Is the Blood`s Fluid Blood plasma is a complex solution of three major components in water Metabolites and wastes Dissolved within are glucose, amino acids, vitamins Also includes wastes and hormones Ions Plasma is a dilute salt solution Primarily sodium, chloride and bicarbonate Trace amounts of calcium, magnesium and metallic ions Proteins Liver produces most plasma proteins, including albumin Alpha and beta globin proteins are carriers of lipids and steroid hormones Fibrinogen associated with blood clotting Serum is blood fluid minus the fibrinogen Plasma protein concentration maintain osmotic balance Erythrocytes Transport Oxygen Each milliliter of blood contains 5 billion erythrocytes or red blood cells Hematocrit: volume of blood composed of red blood cells, 45% of blood volume Each cell is a flat disk with a central depression fig 46.34 Collection of polysaccharides on outer membrane identify blood groups Mature mammal cells lack nuclei and protein-synthesis machinery Can not repair selves, have short life span of four months Removed by spleen, bone marrow, liver Cells produced in bone marrow during erythropoiesis Leukocytes Defend the Body Less than 1% of total blood cells Larger than red cells, contain no hemoglobin, virtually colorless Circulate in blood, present in interstitial fluid Function to defend body against microbes and foreign substances Granular leukocytes include neutrophils, basophils, eosinophils Nongranular leukocytes include monocytes and lymphocytes Role in inflammatory response Injured cells release histamine Dilation of arterioles increases blood flow, makes area red and warm Neutrophils leave capillaries, accumulate at site of injury Joined by monocytes which are converted into macrophages Neutrophil and macrophages entrap microorganisms and foreign particles Lymphocytes play key role in antibody production Eosinophils may help defend against parasitic infections Platelets Help Blood to Clot Platelets are cell fragments that pinch off from megakaryocytes, no nuclei Play important role in blood clotting Ruptured vessel constricts due to contraction of smooth muscle in wall Platelets accumulate and form plug with tissues Fibrin protein glues platelets together Plug of platelets, fibrin and trapped red cells constitutes a blood clot Injury to tissues causes inactive clotting proteins in blood to become active Activated proteins are called clotting factors Cause cascade of reactions that produces thrombin from prothrombin Thrombin catalyzes conversion of fibrinogen to fibrin fig 46.35 THE EVOLUTION OF THE VERTEBRATE HEART Reflects Two Transitions in History of Vertebrates Shift from filter feeding to active capture of prey Invasion of land Evolved new breathing apparatus Decrease of pressure from sea to air Development of homeothermy The Early Chordate Heart Was a Peristaltic Pump Peristaltic contractions of muscular wall of ventral artery Pumps blood in both directions, greater flow in direction of wave The Fish Heart Is a One-Cycle Chamber Pump Four consecutive chambers fig 46.36 Two collection chambers: sinus venosus and atrium Two pumping chambers: ventricle and conus arteriosus Heartbeat sequence: sinus venosus, atrium, ventricle, conus arteriosus Blood delivered to body tissues is fully oxygenated Flow: heart 9 gills 9 tissues 9 heart fig 46.37a, 38a Circulation to body is sluggish due to resistance in gill capillaries Amphibian and Reptile Hearts Reflect the Evolution of Pulmonary Circulation Evolution of large veins from lungs called pulmonary veins Altered blood flow: blood from lungs returns to heart for repumping Advantage: blood pumped to tissues at higher pressure Disadvantage: oxygenated blood mixed with unoxygenated blood Structure of the amphibian heart fig 46.38b Atrium divided into right and left chambers Conus arteriosus partially separated by a septum Imperfect separation of blood flow into pulmonary and systemic circulations Deficiency partly compensated for by cutaneous respiration Structure of the reptile heart fig 46.38c Ventricle partially divided by a septum Conus arteriosus absent, fully subdivided into arteries leaving heart Greater separation of aerated/nonaerated blood, greater efficiency Complete separation in crocodiles Mammal and Bird Hearts Are True Two-Cycle Pumps Independent evolution in birds and mammals Advent of a double circulatory system Ventricular septum prevents mixing of aerated/nonaerated blood fig 46.17d Left side of heart pumps oxygenated blood to body tissues Right side of heart pumps unoxygenated blood to lungs Evolution related to development of endothermy Same volume of blood moves through each circuit Left ventricle pumps blood through higher resistance pathway than right Left ventricle is more muscular and generates more pressure than right one The Pacemaker of Mammalian and Bird Hearts is a Remnant of the Sinus Venosus Sinus venosus served as collection chamber and pacemaker in early vertebrates Remaining tissue is site of origin of the heartbeat in mammals Located in wall of right atrium Called sinoatrial node (SA node) THE HUMAN HEART Double Pump System Operates Within a Single Organ Right side sends blood to lungs Left side sends blood to rest of body fig 46.39 Circulation Through the Heart fig 46.21 Cardiac cycle: complete journey of blood through body and heart Oxygenated blood from lungs carried through pulmonary veins to left atrium Blood flows from atrium to opening in left ventricle Movement occurs while ventricle is relaxing Period called ventricular diastole Ventricle about 80% full Contraction of right atrium produces final 20 % of blood volume to ventricle Ventricle contracts, called ventricular systole Blood forced out of left ventricle Bicuspid or mitral valve prevents backflow Blood moves one-way through aortic valve to aorta Backpressure of aorta closes aortic valve Prevents blood from reentering ventricle Aorta branches into systemic arteries fig 46.40 Carry oxygen-rich blood to all parts of body Heart receives blood via coronary arteries, not through ventricle Blood from body returns to heart via systemic veins The superior and inferior vena cava are collecting vessels Empty oxygen-depleted blood into right atrium Blood moves from right atrium through tricuspid valve to right ventricle Blood moves out of contracting right ventricle through pulmonary valve Blood pumped to lungs through pulmonary arteries Blood returns from lungs to left side of heart to complete cycle How the Heart Is Stimulated to Contract fig 46.22 Contraction stimulated by membrane depolarization, reversal of electrical polarity Contraction triggered by SA node fig 46.41 SA node is pacemaker Membrane of cells depolarize spontaneously with regular rhythm Depolarization passes from one cardiac muscle cell to another Spreads because cardiac cells are electrically coupled by gap junctions Ventricular wave of depolarization delayed by nearly 0.1 second Atria and ventricles separated by connective tissue Connective tissue cannot propagate depolarization Wave passes via atrioventricular node (AV node) Delay permits atria to completely empty before ventricles contract Depolarization conducted over both ventricles via bundle of His Transmitted by Purkinje fibers that stimulate ventricle myocardial cells Right and left ventricles contract almost simultaneously Monitoring the Heart`s Performance Monitor heart sounds caused by closing of heart valves First (lub): closing of mitral and tricuspid valves at start of ventricular systole Second (dub): closing of pulmonary and aortic valves at start of ventricular diastole Turbulence from improper closing of valve causes heart murmur Can also monitor changes in blood pressure Ventricles are relaxed during diastole Pressure in arteries at lowest Called diastolic pressure Contraction of ventricle during systole Pressure in arteries at highest Called systolic pressure Normal values: diastolic/systolic = 70-90 mm Hg/110-130 mm Hg Monitor electrocardiogram that records waves of depolarization Human body conducts electricity quite well Depolarization in heart generates electrical signals that spread throughout body Recording of signals called electrocardiogram fig 46.42 First deflection (P wave): depolarization associated with atrial contraction Second deflection (QRS): depolarization of ventricles Last deflection (T wave): ventricular repolarization Cardiac Output Output is the volume pumped by each ventricle per minute Calculated by: rate of heart beat x volume of blood ejected (stroke volume) Cardiac output is increased with exercise Heart rate increases: SA node is less inhibited by parasympathetic nervous system Sympathetic division stimulates heart rate to increase further Skeletal muscles squeeze on veins,returning blood to heart more rapidly Increases rate at which heart fills and ejects blood Sympathetic division and epinephrine make ventricles contract more strongly Ventricles empty more completely REGULATION OF BLOOD FLOW, PRESSURE AND VOLUME Two Factors Control Arteriolar Smooth Muscle Tension Extrinsic control by autonomic nervous system Intrinsic control, autoregulation Each organ gets enough blood for its own activities Increases blow flow to heart and skeletal muscles during exercise Ensures brain has continuous supply of blood Baroreceptor Reflex Baroreceptors located in walls of carotic artery and aortic arch fig 46.43 Respond to changes in systemic arterial blood pressure Connected to cardiovascular control center in medulla Firing rate decreases when blood pressure falls Stimulates sympathetic activity, inhibits parasympathetic activity Results in increased rate and force of heart contraction Restores normal pressure and cardiac output Baroreceptors act to maintain blood flow to brain with rapid standing Changes venous pressure in lower body, reduces pressure above heart Increases volume of blood in lower body Pressure in veins at right side of heart decreased Decreases cardiac output and blood flow to brain = fainting Reflex rapidly increases heart rate, constricts arterioles Maintains normal blood pressure values Effects of hemorrhage Severe blood loss reduces venous return, cardiac output gets dangerously low Reflex causes faster heart rate, vasoconstriction in skin and viscera Diverts blood to heart and brain Reverse action of baroreceptor reflex Rise in blood pressure promotes slowing of heart and vasodilation Lowers blood pressure toward normal values Volume Receptors Blood pressure depends partly on blood volume Higher blood volume means higher blood pressure Volume regulation via three homeostatic systems fig 46.44 Antidiuretic hormone (ADH) system ADH secreted by posterior pituitary with increased osmotic concentration of blood plasma Example: dehydration decreases volume, increases plasma concentration Stimulated thirst and ADH secretion ADH stimulates kidneys to reduce amount of water lost in urine Renin-angiotensin-aldosterone (RAA) system Secretion of aldosterone controlled by cascade that begins in kidney When blood flow through kidney is decreased, endocrine cells secrete renin Renin initiates conversion of plasma proteins to angiotensin I Converted to angiotensin II by enzyme in walls of blood vessels Angiotensin II has two effects Promotes vasoconstriction (raises blood pressure) Stimulates production of aldosterone by adrenal cortex Aldosterone increases total body Na+, reduces water loss Atrial natriuretic hormone (ANH) system Responds to need to excrete Na+ and lower blood volume Inhibits aldosterone secretion ANH secreted by endocrine cells in atrial walls when atrium is stretched by high blood volume Inhibits secretion of renin by kidney, inhibits aldosterone release More Na+ excreted in urine, water follows, blood volume lowered THE CENTRAL IMPORTANCE OF CIRCULATION Ability to Circulate Materials to All Cells in the Body Other Body Systems Depend on Circulatory Systems to Integrate Activities