CHAPTER 26 Circulation and Gas Exchange
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INTRODUCTION Every organism must exchange materials with its environment Exchanges ultimately occur at the cellular level In unicellular organisms, these exchanges occur directly with the environment For multicellular organisms, direct exchange with the environment is not possible So they develop special internal transport and gas exchange mechanisms to carry out this process
Transport System in Invertebrates Sponges circulate water from external environment through their body cavity, spongeocoel Cnidarians have a body wall that is only two cells thick and that encloses a gastrovascular cavity
Transport System in Invertebrates Flatworms have a complex gastrovascular cavity that branches to have a large surface area to volume ratio Earthworms have a closed circulatory system, separating blood from body fluids
Transport System in Invertebrates More complex animals have either open or closed circulatory systems Both systems have three basic components: A circulatory fluid (blood or hemolymph) Circulating blood cells (hemocytes) A set of tubes (blood vessels) A muscular pump (the heart)
In insects, other arthropods, and most molluscs, blood bathes the organs directly in an open circulatory system In an open circulatory system, there is no distinction between blood and interstitial fluid, and this general body fluid is more correctly called hemolymph In a closed circulatory system, blood is confined to vessels and is distinct from the interstitial fluid Closed systems are more efficient at transporting circulatory fluids to tissues and cells
Transport System in Vertebrates Humans and other vertebrates have a closed circulatory system, often called the cardiovascular system The three main types of blood vessels are arteries, veins, and capillaries Exchange between the blood and the extracellular fluid occurs at capillary level
Blood and Blood Cells Blood consists of a fluid component plasma and cellular elements Its functions are: i) Transports oxygen, carbon dioxide and nutrients ii) Defends against harmful microorganisms, cells and viruses iii) Prevents blood loss by coagulation iv) Regulates body temperature and ph
Blood and Blood Cells Plasma consists of proteins - albumin, fibrinogen and globulin Cells consists of : i) Red blood cells ii) White blood cells iii) Platelets
Figure 26.02
Red Blood Cells in Different Vertebrates
Blood Vessels The three main types of blood vessels are arteries, veins, and capillaries Arteries are elastic, branch into arterioles and carry blood to capillaries Networks of capillaries called capillary beds are the sites of chemical exchange between the blood and interstitial fluid Venules converge into veins which are inelastic and return blood from capillaries to the heart
Figure 26.05
The hearts and Ciirculatory systems of Vertebrates
Figure 26.07
Single Circulation Bony fishes, rays, and sharks have single circulation with a two-chambered heart In single circulation, blood leaving the heart passes through two capillary beds before returning Double Circulation Amphibian, reptiles, and mammals have double circulation Oxygen-poor and oxygen-rich blood are pumped separately from the right and left sides of the heart
In reptiles and mammals, oxygen-poor blood flows through the pulmonary circuit to pick up oxygen through the lungs In amphibians, oxygen-poor blood flows through a pulmocutaneous circuit to pick up oxygen through the lungs and skin Oxygen-rich blood delivers oxygen through the systemic circuit Double circulation maintains higher blood pressure in the organs than does single circulation
Amphibians Frogs and other amphibians have a threechambered heart: 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 When underwater, blood flow to the lungs is nearly shut off
Reptiles Turtles, snakes, and lizards have a threechambered heart: two atria and one ventricle In alligators, caimans, and other crocodilians a septum divides the ventricle Reptiles have double circulation, with a pulmonary circuit (lungs) and a systemic circuit
Birds and Mammals Mammals and birds have a four-chambered heart with two atria and two ventricles The left side of the heart pumps and receives only oxygen-rich blood, while the right side receives and pumps only oxygen-poor blood Mammals and birds are endotherms and require more O 2 than ectotherms
Figure 26.08
Figure 26.09
Figure 26.10
Mammalian Heart and Circulation 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 Oxygen-rich blood from the lungs enters the heart at the left atrium and is pumped through the aorta to the body tissues by the left ventricle The aorta provides blood to the heart through the coronary arteries
Mammalian Heart and Circulation Blood returns to the heart through the superior vena cava (blood from head, neck, and forelimbs) and inferior vena cava (blood from trunk and hind limbs) The superior vena cava and inferior vena cava flow into the right atrium
Mammalian Heart and Circulation The heart contracts and relaxes in a rhythmic cycle called the cardiac cycle The contraction, or pumping, phase is called systole The relaxation, or filling, phase is called diastole
Mammalian Heart and Circulation The heart rate, also called the pulse, is the number of beats per minute The stroke volume is the amount of blood pumped in a single contraction The cardiac output is the volume of blood pumped into the systemic circulation per minute and depends on both the heart rate and stroke volume
Mammalian Heart and Circulation Four valves prevent backflow of blood in the heart The atrioventricular (AV) valves separate each atrium and ventricle The semilunar valves control blood flow to the aorta and the pulmonary artery The lub-dup sound of a heart beat is caused by the recoil of blood against the AV valves (lub) then against the semilunar (dup) valves Backflow of blood through a defective valve causes a heart murmur
Mammalian Heart and Circulation Some cardiac muscle cells are self-excitable, meaning they contract without any signal from the nervous system The sinoatrial (SA) node, or pacemaker, sets the rate and timing at which cardiac muscle cells contract Impulses that travel during the cardiac cycle can be recorded as an electrocardiogram (ECG or EKG) The pacemaker is also regulated by hormones and temperature
Mammalian Heart and Circulation Impulses from the SA node travel to the atrioventricular (AV) node At the AV node, the impulses are delayed and then travel to the Purkinje fibers that make the ventricles contract
Mammalian Heart and Circulation Blood flows from areas of higher pressure to areas of lower pressure Blood pressure is the pressure that blood exerts against the wall of a vessel Systolic pressure is the pressure in the arteries during ventricular systole; it is the highest pressure in the arteries Diastolic pressure is the pressure in the arteries during diastole; it is lower than systolic pressure A pulse is the rhythmic bulging of artery walls with each heartbeat
The Lymphatic System The lymphatic system returns fluid that leaks out from the capillary beds Fluid, called lymph, reenters the circulation directly at the venous end of the capillary bed and indirectly through the lymphatic system The lymphatic system drains into veins in the neck Valves in lymph vessels prevent the backflow of fluid Lymph nodes are organs that filter lymph and play an important role in the body s defense
Gas Exchange Gas exchange supplies O 2 for cellular respiration and disposes of CO 2 Animals require large, moist respiratory surfaces for exchange of gases between their cells and the respiratory medium, either air or water Respiratory surfaces vary by animal and can include the outer surface, skin, gills, tracheae, and lungs
Respiratory Surfaces Respiratory surfaces vary by animal and so are the respiratory systems 1) Plasma Membrane 2) Trachea 3) Integument 4) Gills 5) Lungs
Invertebrate Respiratory Surfaces 1) Plasma Membrane, Protozoans 2) Trachea, Insects 3) Integument, Annelids 4) Gills, Crusteceans 5) Lungs, Arachnids
Invertebrate Respiration Diffusion through body surfaces Tracheal System
Invertebrate Respiration Lungs Book Lung in Spider Mantle cavity as Lung in Snail
Vertebrate Respiratory Surfaces 1) Integument, Amphibians 2) Gills, Fishes 3) Lungs, Terrestrial Vertebrates (Birds, Mammals)
Vertebrate Respiration: Lungs Amphibians Reptiles Birds Mammals
Lung Ventilation Is movement of air in the lungs (into and out) Involves several physiological principles in steps i) Air moves into the lungs ii) O 2 diffuses from alveoli into the pulmonary capillaries and CO 2 diffuses out of the pulmonary capillaries iii) At the systemic capillaries, oxygen and CO 2 diffuse between the blood and the interstitial fluid in response to concentration gradient iv) O 2 and CO 2 diffuse between interstitial fluid and cells
Lung Ventilation Ventilation takes place two different ways 1) Positive Pressure, Amphibians, some Reptiles 2) Negative Pressure, Reptiles, Birds, Mammals
Figure 26.20
Figure 26.21
Figure 26.22
Figure 26.23
Respiratory Pigments Are organic compounds with the metallic elements iron or copper Pigments combine with O 2 in high O 2 concentrations while, release it in low O 2 concentrations Four common respiratory pigments are: 1) Hemoglobin (many invertebrates and vertebrates) 2) Hemocyanin (Molluscs and some Crustaceans) 3) Hemerythrin (Brachiopods and some Polychaets) 4) Chlorocruorin ( Polychaets)