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Chapter 42 Circulation and Gas Exchange Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Mammalian Heart: A Closer Look • A closer look at the mammalian heart provides a better understanding of how double circulation works Pulmonary artery Aorta Pulmonary artery Left atrium Anterior vena cava Right atrium Pulmonary veins Pulmonary veins Semilunar valve Atrioventricular valve Semilunar valve Atrioventricular valve Posterior Figure 42.6 vena cava Right ventricle Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Left ventricle The human heart • Cone shaped organ located beneath the sternum and has a size of a clinched fist (a hand that is tightly closed). • Surrounded by a sac with a two-layered wall. • Comprised mostly of cardiac muscle tissue. • The two atria have thin walls and function as collection chambers for blood returning to the heart, and pumping only the short distances to the ventricles • The two ventricles have thick, powerful walls that pump blood to the organs. The left ventricle pumps blood to all the body organs. • The heart chambers alternately; contract → pump blood or relax → fill with blood. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The heart contracts and relaxes – In a rhythmic cycle called the cardiac cycle • The contraction, or pumping, phase of the cycle – Is called systole • The relaxation, or filling, phase of the cycle – Is called diastole • The heart rate, also called the pulse – Is the number of beats per minute Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The cardiac cycle 2 Atrial systole; Semilunar valves closed ventricular diastole 0.1 sec 0.4 sec Semilunar valves open 0.3 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 • The volume of blood per minute that the left ventricle pumps into the systemic circuit is called the cardiac output (5.25 liter per minute= the whole blood volume). • The volume of pumped blood depends on; – Heart rate: The number of heart beats per minute. It is 60 beats in humans but also depends on the individual’s activity. Elephants hearts beat 25 per minute while shrew ( one type of mice) beats 600 per minute. – Stroke volume: The amount of blood pumped by the left ventricle each time it contracts (75 ml per beat). Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Cardiac output can increase up to five fold during heavy exercise , this is equivalent to pumping amount of blood equal to 2-3 body weight in 2-3 minutes. There are four valves (flap of connective tissue) in the heart to prevent back flow of blood during systole (dictate a one way flow through the heart): • Atrioventicular valves: found between each atrium and ventricle and keep blood from flowing back to the atria during ventricle contraction. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Semilunar valves: located where the aorta leaves the left ventricle and where the pulmonary artery leaves the right ventricle. They prevent flow of blood back into ventricles when they relax (diastole) • A heart murmur is a defect in ore or more valves that allows back flow of blood. In serious cases, a surgery involves replacing the valves is a must. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Maintaining the Heart’s Rhythmic Beat • Some cardiac muscle cells are self-excitable – Meaning they contract without any signal from the nervous system Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • A region of the heart called the sinoatrial (SA) node, or pacemaker – Sets the rate and timing at which all cardiac muscle cells contract • Impulses from the SA node – Travel to the atrioventricular (AV) node • At the AV node, the impulses are delayed (0.1 sec). – And then travel to the Purkinje fibers that make the ventricles contract Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The impulses that travel during the cardiac cycle produce electrical currents as they pass through cardiac muscle. Can be recorded as an electrocardiogram (ECG or EKG). Because the SA node of the human heart is made up of specialized cells and located within the heart itself, it is called myogenic heart. In contrast, pacemaker of most arthropod hearts originated in motor nerves arising from the outside, it is referred to as a neurogenic heart. 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. 4 Signals spread to heart apex. Throughout ventricles. Heart apex Purkinje fibers Bundle branches AV node ECG Figure 42.8 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings SA node is influenced by variety of physiological cues; two sets of nerves affect the heart rate; – one set speeds up the pacemaker – the other set slows it down SA is also affected by some hormones such as epinephrine (fight–or-flight hormone) which increases the heart rate body temperature is another factor that affect the pacemaker as an increase of 1C in the body temperature increases the heart rate of 10 beats/min. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Concept 42.3: Physical principles govern blood circulation • The same physical principles that govern the movement of water in plumbing systems – Also influence the functioning of animal circulatory systems Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Blood Vessel Structure and Function • The “infrastructure” of the circulatory system – • Is its network of blood vessels The walls of arteries and veins have three similar layers: – An outer layer of connective tissue with elastic fibers that permits stretching and recoil of the vessel. – A middle layer of smooth muscles and elastic fibers. – An inner endothelium of simple squamous epithelium i.e the lining of the vessels. – The middle and outer walls of arteries are thicker than that of veins. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings All blood vessels • Are built of similar tissues – Have three similar layers Artery Vein Basement membrane Endothelium 100 µm Valve Endothelium Endothelium Smooth muscle Smooth muscle Connective tissue Capillary Connective tissue Vein Artery Venule Figure 42.9 Arteriole Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Structural differences in arteries, veins, and capillaries – Correlate with their different functions • Arteries have thicker walls – To accommodate the 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 Blood Flow Velocity • Physical laws governing the movement of fluids through pipes influence blood flow and blood pressure – Blood flows about 30 cm/second in the aorta and about 0.026 cm/second in the capillaries. i.e approximately 1000 time faster. – The velocity decreases in accordance with the Law of Continuity: Fluid will flow faster through narrow portions of a pipe than wider portions if the volume of flow remains constant. – An artery give rise to so many arterioles and then capillaries that the total diameter of vessels is much greater in capillary beds than in the artery, thus blood flow slower. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 50 40 30 20 10 0 Systolic pressure Venae cavae Veins Capillaries Venules Diastolic pressure Arteries 120 100 80 60 40 20 0 Arterioles Figure 42.11 5,000 4,000 3,000 2,000 1,000 0 Aorta Pressure (mm Hg) Velocity (cm/sec) Area (cm2) • The velocity of blood flow varies in the circulatory system Blood Pressure Is the hydrostatic pressure that blood exerts against the wall of a vessel • Pressure is greater in arteries than in veins and is greater during systole. • Peripheral resistance: results from impedance by arterioles; blood enters arteries faster than it can leave. As a consequence of the elasticity of the arteries working against peripheral resistance there is a substantial blood pressure even at diastole. • In veins, pressure is nearly zero. Blood return to the heart by the action of skeletal muscles around the veins. • Veins have valves that allow blood to flow only towards the heart. • The blood pressure of a healthy resting human oscillates between 120 Hg at systole and 70 mm Hg at diastole. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Systolic pressure – Is the pressure in the arteries during ventricular systole – Is the highest pressure in the arteries • Diastolic pressure – Is the pressure in the arteries during diastole – Is lower than systolic pressure Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Blood pressure • Can be easily measured in humans 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 120 Pressure in cuff below 120 Pressure in cuff below 70 120 70 Sounds audible in stethoscope Artery Sounds stop 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. • Blood pressure is determined partly by cardiac output – And partly by peripheral resistance due to variable constriction of the arterioles – Nerve impulses, hormones and other signals (stress) can raise the blood pressure by constricting blood vessels – Cardiac output is adjusted in coordination with changes in peripheral resistance Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Capillary Function • All tissues and organs receive a sufficient supply of blood even though only 5-10% of the capillaries are carrying blood at any given time. • Capillaries in the brain, heart, kidneys and liver usually carry a full load of blood. • During exercise blood is drew from the digestive tract to the skeletal muscles and skin that is why indigestion might occur if some one had a big meal and went directly to play or swim Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mechanism of blood distribution in capillaries • In one mechanism – involves the contraction and relaxation of the smooth muscle layer of the arterioles. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In a second mechanism – Precapillary sphincters control the flow of blood between arterioles and venules Precapillary sphincters (a) Thoroughfare channel Sphincters relaxed increase blood flow Arteriole (b) Sphincters contracted Reduce blood flow Arteriole Venule Capillaries Venule (c) Capillaries and larger vessels (SEM) Figure 42.13 a–c Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 20 m • The critical exchange of substances between the blood and interstitial fluid – Takes place across the thin endothelial walls of the capillaries – About 85% of fluid that leaves the blood at the arterial end of the capillary returns from the interstitial fluid at the venous end while the other 15% returned to the blood through the lymphatic system. – Fluid reenters the circulation directly at the venous end of the capillary bed and indirectly through the lymphatic system – Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The difference between blood pressure and osmotic pressure – Drives fluids out of capillaries at the arteriole end and into capillaries at the venule end Red 15 m blood cell 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. Tissue cell INTERSTITIAL FLUID Capillary Net fluid movement out Net fluid movement in Capillary Figure 42.14 Pressure Direction of blood flow Blood pressure Osmotic pressure Inward flow Outward flow Arterial end of capillary Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Venule end At the venule end of a capillary, blood pressure is less than osmotic pressure, and fluid flows from the interstitial fluid into the capillary. Fluid Return by the Lymphatic System • capillary walls leak fluid about 4 L/day and some blood proteins which return to the blood via the Lymphatic System. Once inside the lymphatic system this fluid (blood and proteins) is called lymph • The lymphatic system returns fluid to the body from the capillary beds • Lymph is a fluid similar in composition to interstitial fluid. • The lymphatic system drains into the circulatory system at two locations near the shoulders. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Lymph nodes are specialized swellings along the system that filter the lymph and attack viruses and bacteria thus participate in the defense system. • Lymph capillaries penetrate small intestine villi and absorb fats, thus transporting it from the digestive system to the circulatory system. • Inside the lymph nodes there is connective tissue filled with white blood cells specialized for defense. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Concept 42.4: Blood is a connective tissue with cells suspended in plasma • Blood has a pH of 7.4 • Humans have 4-6 liters of whole blood (plasma+ cellular elements). • Cellular elements represent about 45% of the blood. • Cellular elements can be separated form plasma by centrifugation Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Blood Composition and Function • Blood consists of several kinds of cells – Suspended in a liquid matrix called plasma • The cellular elements – Occupy about 45% of the volume of blood Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Plasma • Blood plasma is about 90% water • Among its many solutes are – Inorganic salts in the form of dissolved ions, sometimes referred to as electrolytes Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The composition of mammalian plasma Plasma 55% Constituent Water Ions (blood electrolytes) Sodium Potassium Calcium Magnesium Chloride Bicarbonate Major functions Solvent for carrying other substances Osmotic balance pH buffering, and regulation of membrane permeability Separated blood elements Plasma proteins Albumin Fibringen Immunoglobulins (antibodies) 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 • Another important class of solutes is the plasma proteins – Which influence; blood pH, osmotic pressure, and viscosity • Various types of plasma proteins – Function in lipid transport, immunity, and blood clotting • Serum: is the blood plasma that has the clotting factors removed and normally contain the antibodies Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cellular Elements • Suspended in blood plasma are two classes of cells – Red blood cells, which transport oxygen – White blood cells, which function in defense • A third cellular element, platelets – Are fragments of cells that are involved in clotting Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The cellular elements of mammalian blood Cellular elements 45% Cell type Number per L (mm3) of blood Erythrocytes (red blood cells) Separated blood elements 5–6 million Leukocytes 5,000–10,000 (white blood cells) Functions Transport oxygen and help transport carbon dioxide 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 • Each ml of human blood contains 5-6 million RBC and there are about trillion of these cells in the body’s 5 L of blood. • Their main function is the transport of O2 which depends on rapid diffusion of O2 through plasma membrane • Lack nuclei and mitochondria thus keeps all the space for larger amount of the hemoglobin • generates ATP by anaerobic respiration therefore, they do not consume any of the oxygen they carry • Contain hemoglobin, iron-containing trans protein. • There are 250 million molecules of hemoglobin in each RBC, thus an RBC can carry about a billion oxygen molecules. • Erythropoietin is a protein produced in kidneys in response to shortage of O2 in tissues. This protein stimulates the production of RBC. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Leukocytes; Blood contains five types of WBC • function in defense and immunity. • There are 5 types of leukocytes: basophils, eosinophils, neutrophils, lymphocytes and monocytes. • Monocytes and neutrophils are phagocytes • There are usually 5000-10000 WBC in each ml of blood but this number increase temporarily during infection. • Spend most of their time outside the circulatory system in the interstitial fluid and lymphatic system. • Lymphocytes become specialized during an infection and produce the body’s immune response. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Platelets • Fragments of cells, 2-3 um in diameter. • Lack nuclei • Inters blood and function in blood clotting. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Stem Cells and the Replacement of Cellular Elements • The cellular elements of blood wear out and are replaced constantly throughout a person’s life • Erythrocytes circulate the blood for 3-4 months before being destroyed by phagocytic cells. • The Pluripotent Stem Cells give rise to all three types of cellular elements. • These cells are self renewable,found in the red bone marrow and arise in the early embryonic stage. • They produce a number of new blood cells equivalent to the number of dying cells. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Differentiation of blood cells from pluripotent stem cells 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 Stem cells and replacement of cellular elements • Erythrocyte production is controlled by a negative feed back mechanism. • If tissue do not receive enough O2, the kidneys synthesis and secrete a hormone called erythropoietin (EPO) that stimulates production of RBC. The reveres happens if tissues receive more O2 than what they are suppose to have. • EPO is used to treat anemia however, some athletes injects themselves with EPO to increase their RBC levels • This practice is called blood doping and is banned by Olympic committee • Pluripotent cells are used for regenerating the bone marrow after destroying it as a cancer treatment. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Blood Clotting • Blood clotting happened after an injury happens to the endothelium of vessels • After the injury the connective tissue become exposed and the platelets adheres to the fibers • A substance that makes nearby platelets sticky is released • Platelets clump together to for a temporary plug and release clotting factors (12 clotting factors are known). • Clotting factors result in conversion of inactive fibrinogen to active fibrin by the help of thrombin. • Fibrin aggregates into threads that form the clot. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Collagen fibers Platelet releases chemicals that make nearby platelets sticky Platelet plug 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). 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 • Hemophilia is a genetic disorder caused by mutations that affect blood clotting and is characterized by excessive bleeding from even minor cuts. • Spontaneous clotting in the body without injury is inhibited by anti-clotting factors in blood. • Some times platelets clump and fibrin coagulates within blood vessel making what is known as thrombus. • These potentially dangerous clots are likely to form in individuals with cardiovascular diseases. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cardiovascular Disease – Are disorders of the heart and the blood vessels – Account for more than half the deaths in the United States – Tendency to have cardiovascular disease might be inherited however, life style plays a major role, such as smoking, eating habits, lack of exercise, high concentration of cholesterol in the blood. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cholesterol • Normally high concentration of LDLs (low density lipoproteins, bad cholesterol) in the blood correlate with atherosclerosis. • HDLs (high density lipoproteins, good cholesterol) reduce deposition of cholesterol in arterial plaques. • Ratio of LDLs to HDLs is more reliable than total plasma cholesterol as indicator of impending cardiovascular disease • Exercise increase HDLs. Diet also increases HDL example of such diet is the consumption of olive oil which is rich of monounsaturated fatty acids that was found to decrease LDL and increase HDL. • Smoking increase LDL; HDL ratio therefore, increases the risk of cardiovascular disease. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • One type of cardiovascular disease, 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 Atherosclerosis • commonly known as hardening of arteries. Figure 4.18 • Chronic cardiovascular disease characterized by plaques that develop in the inner walls of arteries and narrow the bore of the vessel • Form at sites where smooth muscle layer of artery thickens abnormally and inner walls become rough • Site become infiltrated with fibrus connective tissue and lipids such as cholesterol thus encouges thrombus formation. • embolus more likely trapped in narrow vessels. Sings of Atherosclerosis; • Angina pectoris: chest pain that occur when heart receives insufficient oxygen due to plaques in the arteries. • Hypertension: High blood pressure, increase the risk of atheroseclerosis, heart attack and stroke. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Hypertension • Promotes atherosclerosis by damaging endothelium layer of the blood vessels • Increase risk of heart attack and stroke • Atherosclerosis increase blood pressure by narrowing and reducing their elasticity. • High blood pressure can be controlled by medication, diet, exercise or combination • A diastolic pressure above 90 is a cause for concern Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A heart attack Is the death of cardiac muscle tissue resulting from blockage of one or more coronary arteries thus decreasing O2 supply to the cardiac muscle. A thrombus that causes heart attack/stroke may form; • – In a coronary artery – Artery in the brain – Elsewhere in the circulatory system and reaches the heart. The thrombus occurs due to the accumulation of LDL in arteries triggering an inflammatory reaction similar to that caused by bacterial infection. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Embolus is a moving clot from one place to another. – Cardiac or brain tissue downstream from obstruction may die – If damage in the heart interrupts conduction of electrical impulses through cardiac muscle, heart rate may change dramatically or the heart may stop beating – If cardiopulmonary resuscitation (CPR) within few minutes, person may survive. • A stroke – Is the death of nervous tissue in the brain, usually resulting from rupture or blockage of arteries in the head. Once happened survival depends on damage extent. 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 • The lungs of mammals have a spongy texture and are honeycombed with a moist epithelium that functions as the respiratory surface • Air inters through the nostrils and get filtered by hair, warmed, humidified and sampled for odor then flow through to pharynx then to larynx which works as a voice box that contains the vocal cords which produces the sound by vibrating. • From the larynx air pass through the trachea (windpipe) which branches in two bronchi one leading to each lung. Each bronchus branches into finer tubes called bronchioles. At the air tips the bronchioles dead ends are called alveoli (singular alveolus) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 42.6: Breathing ventilates the lungs • The process that ventilates the lugs is called breathing, a frog ventilates its lungs by positive pressure while mammals ventilate their lungs by negative pressure (which forces air down the trachea). • Negative pressure works like a suction pump pulling air instead of pushing it into the lungs in a process called inhalation. • The alternate inhalation and exhalation of air ventilates the lungs. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings How a Mammal Breathes • Mammals ventilate their lungs – By 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 • Vertebrates ventilate their lungs by Breathing • Maintain a maximumO2 concentration and minimum CO2 concentration in the alveoli. • When a mammal is at rest, most of the shallow inhalation results from contraction of the diaphragm. • When the diaphragm contracts, it pushes down towards the abdomen, enlarging the thoracic cavity. • Contraction of the rib muscles expands the rib cage by pulling the ribs upward and the breastbone upward. This change increase the lung volume and as a result the air pressure in the alveoli become lower than the atmospheric pressure. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Because gas flow from region of higher pressure to the region of lower pressure, air pushes through and inhalation occurs. • During exhalation, the rib muscles and diaphragm relax, lung volume is reduced and the air pressure is increased in the alveoli forcing air up to breathing tubes and out of the trachea to nostrils producing the exhalation. During exercise , contraction of the rib muscles increases lung volume Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Tidal Volume: the amount of air an animal inhales and exhales with each breath during normal breathing. (500 ml in humans). • Vital Capacity: the maximum air volume that can be inhaled and exhaled during forced breathing. (4800 ml in young males, 3400 ml in females.) • Residual Volume: is the amount of air that remains in the lungs even after forced breathing after exhalation. • As lungs lose their resilience (strength) as a result of aging or disease the residual volume increases on the expense of the vital capacity which limits the effectiveness of gas exchange. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Control of Breathing in Humans • The main breathing control centers – Are located in two regions of the brain, the medulla oblongata and the pons. Figure 42.26. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Control of Breathing in Humans Figure 42.26 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. 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 Pons 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. 2 Breathing control centers Medulla oblongata 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 decreasin both if CO2 levels are depressed. Carotid arteries 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. Aorta 3 6 Diaphragm Rib muscles Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. The Control of Breathing • Breathing is an automatic action. We inhale when nerves in the breathing control centers of the medulla oblonga and pons send impulses to the rib muscles or diaphragm, stimulating the muscles to contract. • This occurs every 10-14 time per minute. • The medulla’s control center also monitors blood and cerebrospinal fluid pH, which drops as blood CO2 concentration increase. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Control of Breathing … cont. • When pH is dropped (increase of CO2), the tempo and depth of breathing are increased and the excess CO2 is removed in exhaled air. • O2 concentration in the blood only effects the breathing control centers when it becomes extremely low. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Sensors in the aorta and carotid arteries – Monitor O2 and CO2 concentrations in the blood – Exert secondary control over breathing by signaling the medulla to increase breathing rate. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Concept 42.7: Respiratory pigments bind and transport gases • The metabolic demands of many organisms – Require that the blood transport large quantities of O2 and CO2 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Role of Partial Pressure Gradients • The diffusion of gases , whether in air or water depends on partial pressure. • The partial pressure of gas is the proportion of the total atmospheric pressure (760 mm Hg) contributed by the gas. • Oxygen comprises 21% of the atmosphere: its partial pressure (PO2)= 160 mm, (0.21 x 760). • CO2 comprises about 0.03% of the atmosphere, (PCO2 = 0.23 mm Hg). • Gases diffuse always from areas of high partial pressure to those of low partial pressures. • Blood arriving at the lungs from systemic circulation has a lower PO2 and a higher PCO2 than air in the alveoli. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Thus the blood exchange gases with air in the alveoli and the PO2 of the blood increases while the PCO2 decreases. • In systemic capillaries gradients of partial pressure favor diffusion of O2 out of the blood and diffusion of CO2 into it, since cellular respiration rapidly depletes interstitial fluid of O2 and adds CO2. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • In the lungs and in the tissues – O2 and CO2 diffuse from where their partial pressures are higher to where they are lower Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Inhaled air Exhaled air 1600.2 Alveolar epithelial cells Blood entering alveolar capillaries 120 27 O2CO2 Alveolar spaces O2 CO2 104 40 O2CO2 1 Alveolar capillaries of lung Pulmonary arteries Blood 4 leaving tissue capillaries 40 45 O2 CO2 Heart Tissue O COcapillaries 2 CO2 Tissue cells Figure 42.27 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 2 O2 40 45 O2 CO2 Systemic veins O2 CO2 <40 >45 O2 CO2 O2 Blood leaving alveolar capillaries 104 40 O2 CO2 Pulmonary veins Systemic arteries 2 3 Blood entering tissue capillaries 100 40 O2 CO2 • Like all respiratory pigments – 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 Oxygen Transport • oxygen is carried by respiratory pigments in the blood of most animals since oxygen is not very soluble in water. • Hemoglobin is the oxygen transporting pigment in almost all vertebrates. • Binding of oxygen to hemoglobin is reversible: binding occur in the lungs, release occurs in the tissues. • Binding and release of oxygen depends on cooperation between subunits of hemoglobin in which the binding of O2 to one subunit induces the other subunits to bind O2 with more affinity. • . Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Cooperative O2 binding and release – Is evident in the dissociation curve for hemoglobin • A drop in pH – Lowers the affinity of hemoglobin for O2 thus releases O2 to the tissues Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Bohr’s shift is the lowering of hemoglobin’s affinity for oxygen upon a drop in pH. • This occur in active tissues due to the entrance of CO2 into the blood Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings O2 saturation of hemoglobin (%) (a) PO2 and Hemoglobin Dissociation at 37°C and pH 7.4 100 O2 unloaded from hemoglobin during normal metabolism 80 O2 reserve that can be unloaded from hemoglobin to tissues with high metabolism 60 40 20 0 0 20 40 60 80 100 Tissues during Tissues exercise at rest Lungs (b) pH and Hemoglobin Dissociation Figure 42.29a, b Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings O2 saturation of hemoglobin (%) PO2 (mm Hg) 100 pH 7.4 80 Bohr shift: Additional O2 released from pH 7.2 hemoglobin at lower pH (higher CO2 concentration) 60 40 20 0 0 20 40 60 80 100 PO2 (mm Hg) Carbon Dioxide Transport • Carbon dioxide is transported by the blood in three forms: – dissolved CO2 in the plasma (7%). – Bound to the amino groups of hemoglobin (23%). – As biocarbonate ions in the plasma (70%). • CO2 from cells diffuses into the blood plasma and then into RBC. In the RBCs, CO2 is converted into bicarbonate. • The CO2 reacts with water to form carbonic acid. • Carbonic acid quickly disassociate to bicarbonate and hydrogen ions • Bicarbonate then diffuse out of RBCs to the blood plasma. • The hydrogen ions attach to the hemoglobin and other proteins. • This process is reversed in the lungs. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Carbon dioxide from respiring cells – Diffuses into the blood plasma and then into erythrocytes and is ultimately released in the lungs 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 CO2 produced Some CO2 is picked up and transported by hemoglobin. 7 Most of the HCO3– diffuse into the plasma where it is carried in the bloodstream to the lungs. 8 In the HCO3– diffuse from the plasma red blood cells, combining with H+ released from hemoglobin and forming H2CO3. 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. InterstitialCO 2 fluid 1 Blood plasma CO 2 within capillary Capillary wall 2 CO2 H2O 3 CO2 transport from tissues 3 4 Hemoglobin Red H2CO3 blood Carbonic acid Hb picks up cell CO and H+ 2 5 HCO3– + H+ Bicarbonate 4 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. HCO3– 7 6 To lungs CO2 transport to lungs HCO3– 8 HCO3– + H+ 5 Carbonic acid dissociates into a biocarbonate ion (HCO3–) and a hydrogen ion (H+). H2CO3 Hb 9 11 CO2 Hemoglobin releases CO2 and H+ H2O CO2 6 Hemoglobin binds most of the H+ from H2CO3 preventing the H+ from acidifying the blood and thus preventing the Bohr shift. Figure 42.30 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). End of material requested from this chapter Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Overview: 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 • In unicellular organisms – These exchanges occur directly with the environment • For most of the cells making up multicellular organisms – Direct exchange with the environment is not possible Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The feathery gills projecting from a salmon – Are an example of a specialized exchange system found in animals Figure 42.1 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Concept 42.1: Circulatory systems reflect phylogeny • Transport systems – Functionally connect the organs of exchange with the body cells Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Most complex animals have internal transport systems – That circulate fluid, providing a lifeline between the aqueous environment of living 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 • The wide range of invertebrate body size and form – Is paralleled by a great diversity in circulatory systems Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Gastrovascular Cavities • Simple animals, such as cnidarians – Have a body wall only two cells thick that encloses a gastrovascular cavity • The gastrovascular cavity – Functions in both digestion and distribution of substances throughout the body Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Some cnidarians, such as jellies – Have elaborate gastrovascular cavities Circular canal Mouth Radial canal 5 cm Figure 42.2 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Open and Closed Circulatory Systems • More complex animals – Have one of two types of circulatory systems: open or closed • Both of these types of systems have three basic components – A circulatory fluid (blood) – A set of tubes (blood vessels) – A muscular pump (the heart) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • In insects, other arthropods, and most molluscs – Blood bathes the organs directly in an open circulatory system Heart Hemolymph in sinuses surrounding ograns Anterior vessel Figure 42.3a Lateral vessels Ostia Tubular heart (a) An open circulatory system Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • In a closed circulatory system – Blood is confined to vessels and is distinct from the interstitial fluid 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 • Closed systems – Are more efficient at transporting circulatory fluids to tissues and cells Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Survey of Vertebrate Circulation • Humans and other vertebrates have a closed circulatory system – Often called the cardiovascular system • Blood flows in a closed cardiovascular system – Consisting of blood vessels and a two- to fourchambered heart Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Arteries carry blood to capillaries – The sites of chemical exchange between the blood and interstitial fluid • Veins – Return blood from capillaries to the heart Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Fishes • A fish heart has two main chambers – One ventricle and one atrium • Blood pumped from the ventricle – Travels to the gills, where it picks up O2 and disposes of CO2 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Amphibians • Frogs and other amphibians – Have a three-chambered heart, with two atria and one ventricle • The ventricle pumps blood into a forked artery – That splits the ventricle’s output into the pulmocutaneous circuit and the systemic circuit Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Reptiles (Except Birds) • Reptiles have double circulation – With a pulmonary circuit (lungs) and a systemic circuit • Turtles, snakes, and lizards – Have a three-chambered heart Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mammals and Birds • In all mammals and birds – The 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 • A powerful four-chambered heart – Was an 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 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 • Concept 42.2: Double circulation in mammals depends on the anatomy and pumping cycle of the heart • The structure and function of the human circulatory system – Can serve as a model for exploring mammalian circulation in general Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mammalian Circulation: The Pathway • Heart valves – Dictate a one-way flow of blood through the heart Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Blood begins its flow – With the right ventricle pumping blood to the lungs • In the lungs – The blood loads O2 and unloads CO2 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Oxygen-rich blood from the lungs – Enters the heart at the left atrium and is pumped to the body tissues by the left ventricle • Blood returns to the heart – Through the right atrium Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The 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 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 Elite Animal Athletes • Migratory and diving mammals – Have evolutionary adaptations that allow them to perform extraordinary feats Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Ultimate Endurance Runner • The extreme O2 consumption of the antelopelike pronghorn – Underlies its ability to run at high speed over long distances Figure 42.31 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Diving Mammals • Deep-diving air breathers – Stockpile O2 and deplete it slowly Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Concept 42.5: Gas exchange occurs across specialized respiratory surfaces • Gas exchange – 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 Cellular respiration Figure 42.19 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 • Gills are outfoldings of the body surface – Specialized for gas exchange Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • In some invertebrates – The 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 • The effectiveness of gas exchange in some gills, including those of fishes – Is increased by ventilation and countercurrent flow of blood and water Oxygen-poor blood Gill arch Gill arch Water flow Blood vessel Oxygen-rich blood Lamella Operculum O2 Figure 42.21 Water flow over lamellae showing % O2 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 – Consists of 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