Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Circulation and gas exchange Overview Circulation Gas exchange

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Overview 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 Circulation Overview Circulatory systems – Open and closed Open and closed – Circulation in invertebrates Circulation in invertebrates – Circulation in vertebrates Circulation in vertebrates Mammalian circulation system – The Pathway The Pathway – The Pumping The Pumping – The Movement The Movement – The Exchange The Exchange

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Circulation Diffusion alone is not adequate for transporting substances over long distances in animals – Time for a substance to diffuse is proportional to the square of the distance 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 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 Figure 42.2 Circular canal Radial canal 5 cm Mouth

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 Tubular heart Lateral vessels Ostia (a) An open circulatory system Figure 42.3a

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 Figure 42.3b Interstitial fluid Heart Small branch vessels in each organ Dorsal vessel (main heart) Ventral vessels Auxiliary hearts (b) A closed circulatory system

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Open systems – Less energetically costly – Can function as a hydrostatic skeleton 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 four- chambered 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 AMPHIBIANSREPTILES (EXCEPT BIRDS)MAMMALS AND BIRDS Systemic capillaries Lung capillaries Lung and skin capillariesGill capillaries Right Left RightLeft Right Left Systemic circuit Pulmocutaneous circuit Pulmonary circuit Systemic circulation Vein Atrium (A) Heart: ventricle (V) Artery Gill circulation A V V VVV A A A AA Left Systemic aorta Right systemic aorta Figure 42.4 Vertebrate circulatory systems

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 O 2 and disposes of CO 2

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 Mammalian Circulation: The Pathway The mammalian cardiovascular system Pulmonary vein Right atrium Right ventricle Posterior vena cava Capillaries of abdominal organs and hind limbs Aorta Left ventricle Left atrium Pulmonary vein Pulmonary artery Capillaries of left lung Capillaries of head and forelimbs Anterior vena cava Pulmonary artery Capillaries of right lung Aorta Figure

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Heart valves – Dictate a one-way flow of blood through the heart Blood begins its flow – With the right ventricle pumping blood to the lungs In the lungs – The blood loads O 2 and unloads CO 2

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 Mammalian Circulation: The Pumping 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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The heart rate, also called the pulse – Is the number of beats per minute The cardiac output – Is the volume of blood pumped into the systemic circulation per minute It depends on the heart rate and stroke volume

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Some cardiac muscle cells are self-excitable – Meaning they contract without any signal from the nervous system A region of the heart called the sinoatrial (SA) node, or pacemaker – Sets the rate and timing at which all cardiac muscle cells contract

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The SA node generates electrical impulses that spread rapidly through the wall of the atria Purkinje fibers conduct the signals to the apex of the heart and throughout ventricular walls This stimulates the ventricles to contract from the apex toward the atria, driving blood to the arteries

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The pacemaker is influenced by – Nerves, hormones, body temperature, and exercise

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mammalian Circulation: The Movement 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 The “infrastructure” of the circulatory system – Is its network of blood vessels

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings All blood vessels – Are built of similar tissues – Have three similar layers Figure 42.9 Artery Vein 100 µm ArteryVein Arteriole Venule Connective tissue Smooth muscle Endothelium Connective tissue Smooth muscle Endothelium Valve Endothelium Basement membrane Capillary

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Structural differences in arteries, veins, and capillaries – Correlate with their different functions Capillaries have very thin walls – To enhance exchange 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 Figure Direction of blood flow in vein (toward heart) Valve (open) Skeletal muscle Valve (closed)

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 travels over a thousand times faster in the aorta than in capillaries Law of continuity – Fluid flows through narrower segments of the pipe faster than it flows through wider segments

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The velocity of blood flow varies in the circulatory system – And is slowest in the capillary beds as a result of the large total cross-sectional area Figure ,000 4,000 3,000 2,000 1,000 0 Aorta Arteries Arterioles Capillaries Venules Veins Venae cavae Pressure (mm Hg) Velocity (cm/sec) Area (cm 2 ) Systolic pressure Diastolic pressure

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Blood Pressure Fluids exert a force called hydrostatic pressure – Fluids flow from areas of high to low pressure Blood pressure – Is the hydrostatic pressure that blood exerts against the wall of a vessel; it is much greater in the arteries when the heart contracts during systole

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Surge of pressure felt during pulse is due to narrow openings of arterioles impeding the exit of blood from arteries, the peripheral resistance

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 control the arteriole wall muscles – Stress, both physical and emotional can raise blood pressure by triggering nervous and hormonal responses that will constrict blood vessels

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cardiac output is adjusted in concert with changes in peripheral resistance – During heavy exercise, arterioles in working muscles dilate admitting greater flow of oxygen and decreasing peripheral resistance – At the same time cardiac output increases

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Capillary Function Capillaries in major organs are usually filled to capacity – But in many other sites, the blood supply varies

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Two mechanisms – Regulate the distribution of blood in capillary beds In one mechanism – Contraction of the smooth muscle layer in the wall of an arteriole constricts the vessel

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In a second mechanism – Precapillary sphincters control the flow of blood between arterioles and venules Figure a–c Precapillary sphincters Thoroughfare channel Arteriole Capillaries Venule (a) Sphincters relaxed (b) Sphincters contracted Venule Arteriole (c) Capillaries and larger vessels (SEM) 20  m

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mammalian Circulation: The Exchange The critical exchange of substances between the blood and interstitial fluid – Takes place across the thin endothelial walls of the capillaries

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 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. Capillary Red blood cell 15  m Tissue cell INTERSTITIAL FLUID Capillary Net fluid movement out Net fluid movement in Direction of blood flow Blood pressure Osmotic pressure Inward flow Outward flow Pressure Arterial end of capillary 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. Figure 42.14

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Fluid Return by the Lymphatic System 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 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 Gas exchange Respiratory surfaces Respiratory adaptations for aquatic animals Respiratory adaptations for terrestrial animals Breathing across vertebrates Diffusion of gases

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Gas exchange occurs across specialized respiratory surfaces Gas exchange – Supplies oxygen for cellular respiration and disposes of carbon dioxide Figure Organismal level Cellular level Circulatory system Cellular respiration ATP Energy-rich molecules from food Respiratory surface Respiratory medium (air of water) O2O2 CO 2

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 For simple animals, plasma membrane of every cell is close enough to outside environment for gases to diffuse in and out Most animals, the bulk of the body lacks direct access to the respiratory medium – Some animals like earthworms and amphibians use entire outer skin as a respiratory organ, how?

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 Tube foot Coelom Figure 42.20a

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Many segmented worms have flaplike gills – That extend from each segment of their body Figure 42.20b (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. Gill Parapodia

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 Figure 42.20c, d (d) Crayfish. Crayfish and other crustaceans have long, feathery gills covered by the exoskeleton. Specialized body appendages drive water over the gill surfaces. (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. Gills

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 Countercurrent exchange Figure Gill arch Water flow Operculum Gill arch Blood vessel Gill filaments Oxygen-poor blood Oxygen-rich blood Water flow over lamellae showing % O 2 Blood flow through capillaries in lamellae showing % O 2 Lamella 100% 40% 70% 15% 90% 60% 30% 5% O2O2

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 42.22a Tracheae Air sacs 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 O 2, most of the fluid is withdrawn into the body. This increases the surface area of air in contact with cells. Tracheal Systems in Insects The tracheal system of insects – Consists of tiny branching tubes that penetrate the body

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The tracheal tubes – Supply O 2 directly to body cells Air sac Body cell Trachea Tracheole Tracheoles Mitochondria Myofibrils Body wall (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 2.5 µm Air

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 vein (oxygen-rich blood) Terminal bronchiole Branch from the pulmonary artery (oxygen-poor blood) Alveoli Colorized SEM SEM 50 µm Heart Left lung Nasal cavity Pharynx Larynx Diaphragm Bronchiole Bronchus Right lung Trachea Esophagus Figure 42.23

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Breathing ventilates the lungs The process that ventilates the lungs is breathing – The alternate inhalation and exhalation of air

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings How an Amphibian Breathes An amphibian such as a frog – 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 Mammals ventilate their lungs – By negative pressure breathing, which pulls air into the lungs Air inhaledAir exhaled INHALATION Diaphragm contracts (moves down) EXHALATION Diaphragm relaxes (moves up) Diaphragm Lung Rib cage expands as rib muscles contract Rib cage gets smaller as rib muscles relax Figure 42.24

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 INHALATION Air sacs fill EXHALATION Air sacs empty; lungs fill Anterior air sacs Trachea Lungs Posterior air sacs Air 1 mm Air tubes (parabronchi) in lung Figure 42.25

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Air passes through the lungs – In one direction only Every exhalation – Completely renews the air in the lungs

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Role of Partial Pressure Gradients Gases diffuse down pressure gradients – In the lungs and other organs Diffusion of a gas – Depends on differences in a quantity called partial pressure

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A gas always diffuses from a region of higher partial pressure – To a region of lower partial pressure

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In the lungs and in the tissues – O 2 and CO 2 diffuse from where their partial pressures are higher to where they are lower

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Inhaled airExhaled air O2O2 CO 2 O2O2 O2O2 O2O2 O2O2 O2O2 O2O2 O2O CO 2 O2O2 Alveolar epithelial cells Pulmonary arteries Blood entering alveolar capillaries Blood leaving tissue capillaries Blood entering tissue capillaries Blood leaving alveolar capillaries CO 2 O2O2 Tissue capillaries Heart Alveolar capillaries of lung 45 Tissue cells Pulmonary veins Systemic arteries Systemic veins O2O2 CO 2 O2O2 Alveolar spaces Figure 42.27