XIII lizard breathe better than oth Animal form and more efficiently than some of its Function Ing air into Its lungs from the Why Some Lizards Take Deep breath Sometimes, what is intended as a straightforward observa- tional study about an animal turns out instead to uncover an odd fact, something that doesn' t at first seem to make sense Teasing your understanding with the unexpected, this kind of tantalizing finding can be fun and illuminating to investi- you look very carefully at how lizards rur es to light when gate Just such an unexpected puz A lizard runs a bit like a football fullback, swinging his shoulder forward to take a step as the opposite foot pushes off the ground. This produces a lateral undulating gait, the searchers around the country that study the biology of body flexing from side to side with each step This sort of ards. She set out to investigate this puzzle several years gait uses the body to aid the legs in power runni con- ago, first by examining oxygen consumption tracting the chest(intercostal) muscles on the side of the Looking at oxygen consumption seemed a very straig body opposite the swinging shoulder, the lizard literally forward approach. If the axial constraint hypothesis is cor- thrusts itself forward with each flex of its body ect, then running lizards should exhibit a lower oxygen The odd fact, the thing that at first doesn t seem to make onsumption because of lowered breathing efficiency. This sense,is that running lizards should be using these same in- is just what her research team found with green iguanas tercostal chest muscles for something else (Iguana iguana). Studying fast-running iguanas on tread At rest, lizards breathe by expanding their chest, much as mills, oxygen consumption went down as running pro- rou do. The greater volume of the expanded thorax lowers ceeded, as the axial constraint hypothesis predicted the interior air pressure, causing fresh air to be pushed into Unexpectedly, however, another large lizard gave a com- the lungs from outside. You expand your chest by contract- pletely different result. The savannah monitor lizard ing a diaphragm at the bottom of the chest. Lizards do not (Varanus exanthematicus) exhibited elevated oxygen con- Q have a diaphragm. Instead, they expand their chest by con- sumption with increasing speeds of locomotion! This result tracting the intercostal chest muscles on both sides of the iggests that something else is going on in monitor lizards chest simultaneously. This contraction rotates the ribs, Somehow, they seem to have found a way to beat the axial causing the chest to expand Do you see the problem: A running lizard cannot contract How do they do it? Taking a more detailed look at run its chest muscles on both sides simultaneously for effective ng monitor lizards, Dr. Brainerd's research team ran a se- breathing at the same time that it is contracting the same ries of experiments to sort this out. First, they used videora chest muscles alternatively for running. This apparent conflict diography to directly observe lung ventilation in monitor has led to a controversial hypothesis abou out how running lizards while the lizards were running on a treadmill. The lizards breathe.Called the axial constraint hypothesis, it states X-ray negative vided aled the monitor's trick that lizards are subject to a speed-dependent axial constraint the breathing cycle began with an inhalation that did not that prevents effective lung ventilation while they are running. completely fill the lungs, just as the axial constraint hypoth This constraint, if true, would be rather puzzling from esis predicts. But then something else kicks in. The gular n evolutionary perspective, because it suggests that when a cavity located in the throat area also fills with air, and as in- lizard needs more oxygen because it is running, it breathes halation proceeds the gular cavity compresses, forcing this less effectively air into the lu Like an afterburner on a jet, this added air Dr. Elizabeth Brainerd of the University of Massachu contia s the efficiency of breathing, making up for the lost ncrea setts,Amherst, is one of a growing cadre of young re- Ition of the intercostal chest muscles
981 Why Some Lizards Take a Deep Breath Sometimes, what is intended as a straightforward observational study about an animal turns out instead to uncover an odd fact, something that doesn’t at first seem to make sense. Teasing your understanding with the unexpected, this kind of tantalizing finding can be fun and illuminating to investigate. Just such an unexpected puzzle comes to light when you look very carefully at how lizards run. A lizard runs a bit like a football fullback, swinging his shoulder forward to take a step as the opposite foot pushes off the ground. This produces a lateral undulating gait, the body flexing from side to side with each step. This sort of gait uses the body to aid the legs in power running. By contracting the chest (intercostal) muscles on the side of the body opposite the swinging shoulder, the lizard literally thrusts itself forward with each flex of its body. The odd fact, the thing that at first doesn’t seem to make sense, is that running lizards should be using these same intercostal chest muscles for something else. At rest, lizards breathe by expanding their chest, much as you do. The greater volume of the expanded thorax lowers the interior air pressure, causing fresh air to be pushed into the lungs from outside. You expand your chest by contracting a diaphragm at the bottom of the chest. Lizards do not have a diaphragm. Instead, they expand their chest by contracting the intercostal chest muscles on both sides of the chest simultaneously. This contraction rotates the ribs, causing the chest to expand. Do you see the problem? A running lizard cannot contract its chest muscles on both sides simultaneously for effective breathing at the same time that it is contracting the same chest muscles alternatively for running. This apparent conflict has led to a controversial hypothesis about how running lizards breathe. Called the axial constraint hypothesis, it states that lizards are subject to a speed-dependent axial constraint that prevents effective lung ventilation while they are running. This constraint, if true, would be rather puzzling from an evolutionary perspective, because it suggests that when a lizard needs more oxygen because it is running, it breathes less effectively. Dr. Elizabeth Brainerd of the University of Massachusetts, Amherst, is one of a growing cadre of young researchers around the country that study the biology of lizards. She set out to investigate this puzzle several years ago, first by examining oxygen consumption. Looking at oxygen consumption seemed a very straightforward approach. If the axial constraint hypothesis is correct, then running lizards should exhibit a lower oxygen consumption because of lowered breathing efficiency. This is just what her research team found with green iguanas (Iguana iguana). Studying fast-running iguanas on treadmills, oxygen consumption went down as running proceeded, as the axial constraint hypothesis predicted. Unexpectedly, however, another large lizard gave a completely different result. The savannah monitor lizard (Varanus exanthematicus) exhibited elevated oxygen consumption with increasing speeds of locomotion! This result suggests that something else is going on in monitor lizards. Somehow, they seem to have found a way to beat the axial constraint. How do they do it? Taking a more detailed look at running monitor lizards, Dr. Brainerd’s research team ran a series of experiments to sort this out. First, they used videoradiography to directly observe lung ventilation in monitor lizards while the lizards were running on a treadmill. The X-ray negative video images revealed the monitor’s trick: the breathing cycle began with an inhalation that did not completely fill the lungs, just as the axial constraint hypothesis predicts. But then something else kicks in. The gular cavity located in the throat area also fills with air, and as inhalation proceeds the gular cavity compresses, forcing this air into the lungs. Like an afterburner on a jet, this added air increases the efficiency of breathing, making up for the lost contribution of the intercostal chest muscles. Part XIII Animal Form and Function Some species of lizard breathe better than others. The savannah monitor lizard Varanus exanthematicus breathes more efficiently than some of its relatives by pumping air into its lungs from the gular folds over its throat. Real People Doing Real Science
No axial constraint Gular pumping 800 Axial constraint EE 600 Gular pumpin disabled 0 Speed (km/h) → Recovery Effects of gular pumping in lizards. (a)THEORY: The axial constraint hypothesis predicts that, above a threshold speed, ventilation, measured by expired gas volume (VE), will decrease with increasing speed, and only reach a maximum during the recovery period after lo- comotion ceases. Without axial constraint, ventilation should reach its maximum during locomotion. ()EXPERIMENT: Monitor lizards typically show no axial constraint while running. Axial constraint is evident, however, if gular pumping of air is disabled. So, it seems that ome species of monitor lizards are able to use gular pumping to overcome the axial constraint on ventilation The Experiment value up to a speed of 1 km/hr. The value began to decrease Brainerd set out to test this gular pumping hypothesis. gular between 1 and 2 km/hr indicating that there was constraint pumping occurs after the initial inhalation because the lizard on ventilation. During the recovery period, VE increased as closes its mouth, sealing shut internal nares(nostril-like struc- predicted by the axial constraint hypothesis, because there was no longer constraint on the intercostal muscles. Ve in- tures).Air is thus trapped in the gular cavity. By contracting creased to pay back an oxygen debt that occurred durin the lungs. This process can be disrupted by propping the period of time when anaerobic metabolism took over g the muscles that compress the gular cavity, this air is forced into mouth open so that, when the gular cavity is compressed, its Comparing the VE measurements under control and ex- perimental conditions, the researchers concluded that moni- air escapes back out of the mouth. The lizards were trained tor lizards are indeed subject to speed-dependent axial con to run on a treadmill. A Plastic mask was placed over the ani- straint just as theory had predicted, but can circumvent this mal's mouth and nostrils and air was drawn through the mask The mask permitted the measurement of oxygen and Co constraint when running by using an accessory gular pump levels as a means of monitoring gas consumption. The ex- to enhance ventilation. When the gular pump was experi- pired gas volume (Ve was measured in the last minutes of lo- mentally disrupted, the speed-dependent axial constraint comotion and the first minute of recovery at each speed. The condition became apparent. Although the researchers have not conducted a more speeds ranged from 0 km/hr to 2 km/hr. The maximum run- complete comparative analysis using the methods shown To disable gular pumping, the animals mouth was here, they have found correlations between gular pumpin ind increased locomotor activity. Six highly active species propped open with a retainer made of plastic tubing. In exhibited gular pumping while six less active species did not parallel exper riments that allow gular pumping, the same exhibit gular pumping in lung ventilation. It is interesting animals wore the masks, but no retainer was used to disrupt the oral seal necessary for gular pumping to speculate that gular pumping evolved in lizards as a neans of enhancing breathing to allow greater locomotor endurance. The gular pumping seen in lizards is similar to The results the breathing mechanism found in amphibians and ai Parallel experiments were conducted on monitor lizards breathing fish. In these animals, the air first enters a cavity with and without gular pumpin close and the buccal cavity collapses, forcing air into the pumping alloz en t lar pumping lungs. The similarities in these two mechanisms suggest mechanism was not obstructed, the VE increased to a maxi- that one might have arisen from the oth mum at a speed of 2 km/hr and decreased during the recov- ery period(see blue line in graph b above). This result is predicted under conditions where there is no axial con- straint on the animal(see graph a above). To explore this experiment furthe er. go to 2. Gular pumping disabled. When the gular pumping tualLabatwww.mhhe.com/raven6/vlab13.mhtml mechanism is obstructed, VE increased above the resting
The Experiment Brainerd set out to test this gular pumping hypothesis. Gular pumping occurs after the initial inhalation because the lizard closes its mouth, sealing shut internal nares (nostril-like structures). Air is thus trapped in the gular cavity. By contracting muscles that compress the gular cavity, this air is forced into the lungs. This process can be disrupted by propping the mouth open so that, when the gular cavity is compressed, its air escapes back out of the mouth. The lizards were trained to run on a treadmill. A plastic mask was placed over the animal’s mouth and nostrils and air was drawn through the mask. The mask permitted the measurement of oxygen and CO2 levels as a means of monitoring gas consumption. The expired gas volume (VE) was measured in the last minutes of locomotion and the first minute of recovery at each speed. The speeds ranged from 0 km/hr to 2 km/hr. The maximum running speed of these lizards on a treadmill is 6.6 km/hr. To disable gular pumping, the animal’s mouth was propped open with a retainer made of plastic tubing. In parallel experiments that allow gular pumping, the same animals wore the masks, but no retainer was used to disrupt the oral seal necessary for gular pumping. The Results Parallel experiments were conducted on monitor lizards with and without gular pumping: 1. Gular pumping allowed. When the gular pumping mechanism was not obstructed, the VE increased to a maximum at a speed of 2 km/hr and decreased during the recovery period (see blue line in graph b above). This result is predicted under conditions where there is no axial constraint on the animal (see graph a above). 2. Gular pumping disabled. When the gular pumping mechanism is obstructed, VE increased above the resting value up to a speed of 1 km/hr. The value began to decrease between 1 and 2 km/hr indicating that there was constraint on ventilation. During the recovery period, VE increased as predicted by the axial constraint hypothesis, because there was no longer constraint on the intercostal muscles. VE increased to pay back an oxygen debt that occurred during the period of time when anaerobic metabolism took over. Comparing the VE measurements under control and experimental conditions, the researchers concluded that monitor lizards are indeed subject to speed-dependent axial constraint, just as theory had predicted, but can circumvent this constraint when running by using an accessory gular pump to enhance ventilation. When the gular pump was experimentally disrupted, the speed-dependent axial constraint condition became apparent. Although the researchers have not conducted a more complete comparative analysis using the methods shown here, they have found correlations between gular pumping and increased locomotor activity. Six highly active species exhibited gular pumping while six less active species did not exhibit gular pumping in lung ventilation. It is interesting to speculate that gular pumping evolved in lizards as a means of enhancing breathing to allow greater locomotor endurance. The gular pumping seen in lizards is similar to the breathing mechanism found in amphibians and airbreathing fish. In these animals, the air first enters a cavity in the mouth called the buccal cavity. The mouth and nares close and the buccal cavity collapses, forcing air into the lungs. The similarities in these two mechanisms suggest that one might have arisen from the other. Speed (km/h) Axial constraint No axial constraint VE max VE max Recovery Speed (km/h) Recovery Expired gas volume (VE) VE (ml/min/kg) 1000 800 600 400 200 0 0 1 Gular pumping allowed Gular pumping disabled 2 (a) (b) Effects of gular pumping in lizards. (a) THEORY: The axial constraint hypothesis predicts that, above a threshold speed, ventilation, measured by expired gas volume (VE), will decrease with increasing speed, and only reach a maximum during the recovery period after locomotion ceases. Without axial constraint, ventilation should reach its maximum during locomotion. (b) EXPERIMENT: Monitor lizards typically show no axial constraint while running. Axial constraint is evident, however, if gular pumping of air is disabled. So, it seems that some species of monitor lizards are able to use gular pumping to overcome the axial constraint on ventilation. To explore this experiment further, go to the Virtual Lab at www.mhhe.com/raven6/vlab13.mhtml
490 Organization of the 0 Animal body Concept outline 49.1 The bodies of vertebrates are organized into Do. M Organization of the Body. Cells are organized into tissues, and tissues are organized into organs. Several organs can cooperate to form organ systems 49.2 Epithelial tissue forms membranes and glands Characteristics of Epithelial Tissue. Epithelial membranes cover all body surfaces, and thus can serve for protection or for transport of materials. Glands are also epithelial tissue. Epithelial membranes may be composed of one layer or many 49.3 Connective tissues contain abundant extracellular mate Connective Tissue Proper. Connective tissues have abundant extracellular material In connective tissue proper, this material consists of protein fibers within an amorphous ground substance FIGURE 49.1 Special Connective Tissues. These tissues include Bone. Like most of the tissues in the vertebrate body, bone is a cartilage,bone, and blood, each with their own unique form dynamic structure constantly renewing itself. of extracellular material 49.4 Muscle tissue provides for movement, and nerve tissue provides for control. Then most people think of animals, they think of their Muscle Tissue. Muscle tissue contains the filaments D③d也m由hem actin and myosin, which enable the muscles to contrac When they think about the diversity of animals, they may There are three types of muscle: smooth, cardiac, ane think of the differences between the predatory lions and skeletal tigers and the herbivorous deer and antelope, between a fe- Nerve Tissue. Nerve cells, or neurons, have specialized ocious-looking shark and a playful dolphin. Despite the regions that produce and conduct electrical impulses Neuroglia cells support neurons but do not conduct differences among these animals, they are all vertebrates All vertebrates share the same basic body plan, with the same sorts of organs operating in much the same way. In this chapter, we will begin a detailed consideration of the biology of vertebrates and of the fascinating structure and function of their bodies(figure 49.1)
983 49 Organization of the Animal Body Concept Outline 49.1 The bodies of vertebrates are organized into functional systems. Organization of the Body. Cells are organized into tissues, and tissues are organized into organs. Several organs can cooperate to form organ systems. 49.2 Epithelial tissue forms membranes and glands. Characteristics of Epithelial Tissue. Epithelial membranes cover all body surfaces, and thus can serve for protection or for transport of materials. Glands are also epithelial tissue. Epithelial membranes may be composed of one layer or many. 49.3 Connective tissues contain abundant extracellular material. Connective Tissue Proper. Connective tissues have abundant extracellular material. In connective tissue proper, this material consists of protein fibers within an amorphous ground substance. Special Connective Tissues. These tissues include cartilage, bone, and blood, each with their own unique form of extracellular material. 49.4 Muscle tissue provides for movement, and nerve tissue provides for control. Muscle Tissue. Muscle tissue contains the filaments actin and myosin, which enable the muscles to contract. There are three types of muscle: smooth, cardiac, and skeletal. Nerve Tissue. Nerve cells, or neurons, have specialized regions that produce and conduct electrical impulses. Neuroglia cells support neurons but do not conduct electrical impulses. When most people think of animals, they think of their pet dogs and cats and the animals that they’ve seen in a zoo, on a farm, in an aquarium, or out in the wild. When they think about the diversity of animals, they may think of the differences between the predatory lions and tigers and the herbivorous deer and antelope, between a ferocious-looking shark and a playful dolphin. Despite the differences among these animals, they are all vertebrates. All vertebrates share the same basic body plan, with the same sorts of organs operating in much the same way. In this chapter, we will begin a detailed consideration of the biology of vertebrates and of the fascinating structure and function of their bodies (figure 49.1). FIGURE 49.1 Bone. Like most of the tissues in the vertebrate body, bone is a dynamic structure, constantly renewing itself
49.1 The bodies of vertebrates are organized into functional systems Organization of the bod Brain Spinal cord The bodies of all mammals have the same general archi Vertebrae tecture(figure 49.2), and are Peritoneal body plan of other vertebrate groups. This body plan is basically a tube suspended within a tube. Starting from the inside, it is composed of the digestive tract, a lor be that travels from one end of the body to the other mouth to anus). This tube is suspended within an inter- pleural cavtiy nal body cavity, the coelom. In fishes, amphibians, and most reptiles, the coelom is subdivided into two cavities Thoracic one housing the heart and the other the liver stomach and intestines. In mammals and some reptiles, a sheet of muscle, the diaphragm, separates the peritoneal cavity, which contains the stomach, intestines, and liver, from the thoracic cavity; the thoracic cavity is further subdi FIGURE 49.2 Architecture of the vertebrate body. All vertebrates have a vided into the pericardial cavity, which contains the heart, dorsal central nervous system. In mammals and some reptiles, a ind pleural cavities, which contain the lungs. All verte muscular diaphragm divides the coelom into the thoracic cavity brate bodies are supported by an internal skeleton made and the peritoneal cavity of jointed bones or cartilage blocks that grow as the body grows. A b skull surrounds the brain and a col Epithelial Nerve tissue Connective umn of bones. the vertebrae. sur sue rounds the dorsal nerve cord, or spin There are four levels of organizatie in the vertebrate body:(1)cells,(2)tis sues,()organs, and (4)organ systems Like those of all animals. the bodies of Stratified epithelium vertebrates are composed of different ell types. In adult vertebrates, there ning stomepithelium are between 50 and several hundred different kinds of cells ssues Groups of cells similar in structure and ol function are organized into tissues. Early in development, the cells of the Cuboidal epithelium growing embryo differentiate(special kidney tubules ize)into three fundamental embryonic Muscle Tissues tissues,called germ layers. From inner most to outermost layers, these are the endoderm. mesoderm, and ecto derm. These germ layers, in turn, dif- ferentiate into the scores of different cell types and tissues that are character istic of the vertebrate body In adult vertebrates, there are four principal Smooth muscle in intestinal wall voluntary muscles hear c muscle in kinds of tissues, or primary tissues: ep- helial, connective, muscle, and nerve FIGURE 49.3 (figure 49.3), each discussed in separate vertebrate tissue types. Epithelial tissues are indicated by blue arrows, connective tissues sections of this chapter. by green arrows, muscle tissues by red arrows, and nerve tissue by a yellow arrow 984 Part XIlI Animal Form and Function
984 Part XIII Animal Form and Function Organization of the Body The bodies of all mammals have the same general architecture (figure 49.2), and are very similar to the general body plan of other vertebrate groups. This body plan is basically a tube suspended within a tube. Starting from the inside, it is composed of the digestive tract, a long tube that travels from one end of the body to the other (mouth to anus). This tube is suspended within an internal body cavity, the coelom. In fishes, amphibians, and most reptiles, the coelom is subdivided into two cavities, one housing the heart and the other the liver stomach, and intestines. In mammals and some reptiles, a sheet of muscle, the diaphragm, separates the peritoneal cavity, which contains the stomach, intestines, and liver, from the thoracic cavity; the thoracic cavity is further subdivided into the pericardial cavity, which contains the heart, and pleural cavities, which contain the lungs. All vertebrate bodies are supported by an internal skeleton made of jointed bones or cartilage blocks that grow as the body grows. A bony skull surrounds the brain, and a column of bones, the vertebrae, surrounds the dorsal nerve cord, or spinal cord. There are four levels of organization in the vertebrate body: (1) cells, (2) tissues, (3) organs, and (4) organ systems. Like those of all animals, the bodies of vertebrates are composed of different cell types. In adult vertebrates, there are between 50 and several hundred different kinds of cells. Tissues Groups of cells similar in structure and function are organized into tissues. Early in development, the cells of the growing embryo differentiate (specialize) into three fundamental embryonic tissues, called germ layers. From innermost to outermost layers, these are the endoderm, mesoderm, and ectoderm. These germ layers, in turn, differentiate into the scores of different cell types and tissues that are characteristic of the vertebrate body. In adult vertebrates, there are four principal kinds of tissues, or primary tissues: epithelial, connective, muscle, and nerve (figure 49.3), each discussed in separate sections of this chapter. 49.1 The bodies of vertebrates are organized into functional systems. Cranial cavity Brain Thoracic cavity Diaphragm Peritoneal cavity Vertebrae Spinal cord Pericardial cavity Right pleural cavtiy FIGURE 49.2 Architecture of the vertebrate body. All vertebrates have a dorsal central nervous system. In mammals and some reptiles, a muscular diaphragm divides the coelom into the thoracic cavity and the peritoneal cavity. Epithelial Tissues Bone Blood Loose connective tissue Muscle Tissues Smooth muscle in intestinal wall Cuboidal epithelium in kidney tubules Columnar epithelium lining stomach Stratified epithelium in epidermis Skeletal muscle in voluntary muscles Cardiac muscle in heart Nerve Tissue Connective Tissues FIGURE 49.3 Vertebrate tissue types. Epithelial tissues are indicated by blue arrows, connective tissues by green arrows, muscle tissues by red arrows, and nerve tissue by a yellow arrow
Organs are body structures composed of several different tissues that form structural and functional unit(figure 49.4). One example is the heart, which contains cardiac muscle. connective tissue, and epithelial tissue and is laced with that helps reg ulate the heartbeat. An organ system is a group of organs that function to- gether to carry out the major activities of the body. For example, the diges- tive system is composed of the diges tive tract, liver, gallbladder, and pan creas. These organs cooperate in the digestion of food and the absorpti of digestion products into the body The vertebrate body contains 11 prin- cipal organ systems(table 49.1 and Cardiac muscle cell The bodies of humans and other mammals contain a cavity divided Organ system Tissue Cell by the diaphragm into thoracic and abdominal cavities. The body s cells FIGURE 49.4 are organized into tissues, which vels of organization within the body. Similar cell types operate together and form are, in turn, organized into organs tissues. Tissues functioning together form organs. Several organs working together to carry out a function for the body are called an organ system. The circulatory system is an example of an organ system. Table 49.1 The Major Vertebrate Organ Systems Detailed System Functions Components Treatment Circulatory Transports cells, respiratory gases, and Heart, blood vessels, lymph, and lymph Ch chemical compounds throughout the body structures Digestive Captures soluble nutrients from ingested louth, esophagus, stomach, intestines, liver, and Chapter 51 pancreas Endocrine Coordinates and integrates the activities of Pituitary, adrenal, thyroid, and other ductless Chapter 56 Integumentary Covers and protects the body Skin, hair, nails, scales, feathers, and sweat glands Chapter 57 Lymphatic/ Vessels transport extracellular fluid and Lymphatic vessels, lymph nodes, thymus, Chapter 57 fat to circulatory system; lymph nodes tonsils, spl and lymphatic organs provide defenses to microbial infection and cancer Muscular Produces body movement Skeletal muscle, cardiac muscle and smooth Chapter 50 muscle Nervous Receives stimuli, integrates information Nerves, sense organs, brain, and spinal cord Chapters 54,55 and directs the body Reproductive Carries out reproduction Testes, ovaries, and associated reproductive Chapter 59 structures Respiratory Captures oxygen and exchanges gases Lungs, trachea, gills, and other air passageways Chapter 53 Skeletal Protects the body and provides support for Bones, cartilage, and ligaments Ur Removes metabolic wastes from the Kidney, bladder, and associated ducts Chapter 58 Chapter 49 Organization of the Animal Body 985
Organs and Organ Systems Organs are body structures composed of several different tissues that form a structural and functional unit (figure 49.4). One example is the heart, which contains cardiac muscle, connective tissue, and epithelial tissue and is laced with nerve tissue that helps regulate the heartbeat. An organ system is a group of organs that function together to carry out the major activities of the body. For example, the digestive system is composed of the digestive tract, liver, gallbladder, and pancreas. These organs cooperate in the digestion of food and the absorption of digestion products into the body. The vertebrate body contains 11 principal organ systems (table 49.1 and figure 49.5). The bodies of humans and other mammals contain a cavity divided by the diaphragm into thoracic and abdominal cavities. The body’s cells are organized into tissues, which are, in turn, organized into organs and organ systems. Chapter 49 Organization of the Animal Body 985 Table 49.1 The Major Vertebrate Organ Systems Detailed System Functions Components Treatment Circulatory Digestive Endocrine Integumentary Lymphatic/ Immune Muscular Nervous Reproductive Respiratory Skeletal Urinary Transports cells, respiratory gases, and chemical compounds throughout the body Captures soluble nutrients from ingested food Coordinates and integrates the activities of the body Covers and protects the body Vessels transport extracellular fluid and fat to circulatory system; lymph nodes and lymphatic organs provide defenses to microbial infection and cancer Produces body movement Receives stimuli, integrates information, and directs the body Carries out reproduction Captures oxygen and exchanges gases Protects the body and provides support for locomotion and movement Removes metabolic wastes from the bloodstream Heart, blood vessels, lymph, and lymph structures Mouth, esophagus, stomach, intestines, liver, and pancreas Pituitary, adrenal, thyroid, and other ductless glands Skin, hair, nails, scales, feathers, and sweat glands Lymphatic vessels, lymph nodes, thymus, tonsils, spleen Skeletal muscle, cardiac muscle, and smooth muscle Nerves, sense organs, brain, and spinal cord Testes, ovaries, and associated reproductive structures Lungs, trachea, gills, and other air passageways Bones, cartilage, and ligaments Kidney, bladder, and associated ducts Chapter 52 Chapter 51 Chapter 56 Chapter 57 Chapter 57 Chapter 50 Chapters 54, 55 Chapter 59 Chapter 53 Chapter 50 Chapter 58 Circulatory system Heart Cardiac muscle Cardiac muscle cell Organ system Organ Tissue Cell FIGURE 49.4 Levels of organization within the body. Similar cell types operate together and form tissues. Tissues functioning together form organs. Several organs working together to carry out a function for the body are called an organ system. The circulatory system is an example of an organ system