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
Sternum Heart Pelvis Testis Fem Skeletal system Endocrine system Spinal Nervous system Respiratory system Lymphatic/Immune syste FIGURE 49.5 Vertebrate organ systems. The 11 principal organ systems of the human body are shown, including both male and female reproductive 986 Part XIlI Animal Form and Function
986 Part XIII Animal Form and Function Skull Sternum Pelvis Femur Brain Spinal cord Nerves Skeletal system Circulatory system Endocrine system Nervous system Respiratory system Lymphatic/Immune system Trachea Lungs Lymph nodes Spleen Lymphatic vessels Testis (male) Ovary (female) Pituitary Thyroid Thymus Adrenal gland Pancreas Arteries Veins Heart FIGURE 49.5 Vertebrate organ systems. The 11 principal organ systems of the human body are shown, including both male and female reproductive systems
Pectoralis Liver Biceps Stomach Kidney Smal stine Ureter abdominus Bladde Sartorius Digestive system Urinary system Muscular system Hair fallopian Vas deferens Testis Uterus P Vair Reproductive system Reproductive system Integumentary system FIGURE 49.5(continued) Chapter 49 Organization of the Animal Body 987
Chapter 49 Organization of the Animal Body 987 Salivary glands Esophagus Liver Stomach Small intestine Large intestine Vas deferens Testis Penis Digestive system Urinary system Muscular system Reproductive system (male) Reproductive system (female) Integumentary system Ovary Fallopian tube Uterus Vagina Hair Skin Fingernails Gastrocnemius Pectoralis major Biceps Rectus abdominus Sartorius Quadriceps Ureter Bladder Urethra Kidney FIGURE 49.5 (continued)
49.2 Epithelial tissue forms membranes and glands Characteristics of Epithelial Tissue capillaries, for example, where the thin, delicate nature of these membranes permits the rapid movement of molecules An epithelial membrane, or epithelium, covers every sur-(such as the diffusion of gases). A simple cuboidal epithelium face of the vertebrate body. Epithelial membranes are de- lines the small ducts of some glands, and a simple columna rived from all three germ layers. The epidermis, derived epithelium is found in the airways of the respiratory tract from ectoderm, constitutes the outer portion of the skin. and in the gastrointestinal The inner surface of the digestive tract is lined by an ep- terspersed among the columnar epithelial cells are numer ithelium derived from endoderm, and the inner surfaces of ous goblet cells, specialized to secrete mucus. The columnar the body cavities are lined with an epithelium derived from epithelial cells of the respiratory airways contain cilia on their apical surface(the surface facing the lumen, or cavity), Because all body surfaces are covered by epithelial mem- which move mucus toward the throat. In the small intes- branes, a substance must pass through an epithelium in tine, the apical surface of the columnar epithelial cells form order to enter or leave the body. Epithelial membranes fingerlike projections called microvilli, that increase the sur- thus provide a barrier that can impede the passage of some face area for the absorption of food. substances while facilitating the passage of others. For Stratified epithelial membranes are several cell layers land-dwelling vertebrates, the relative impermeability of thick and are named according to the features of their up- the surface epithelium(the epidermis) to water offers es- permost layers. For example, the epidermis is a stratified sential protection from dehydration and from airborne squamous epithelium. In terrestrial vertebrates it is further athogens(disease-causing organisms). On the other hand, characterized as a keratinized epithelium, because its upper the epithelial lining of the digestive tract must allow selec- layer consists of dead squamous cells and filled with a tive entry of the products of digestion while providing a water-resistant protein called keratin. The deposition of barrier to toxic substances, and the epithelium of the lungs keratin in the skin can be increased in response to abrasion, must allow for the rapid diffusion of gases producing calluses. The water-resistant property of keratin Some epithelia become modified in the course of em- is evident when the skin is compared with the red portion bryonic development into glands, which are specialized for of the lips, which can easily become dried and chapped be- secretion. A characteristic of all epithelia is that the cells cause it is covered by a nonkeratinized, stratified squamous are tightly bound together, with very little space between epithelium them. As a consequence, blood vessels cannot be interposed The glands of vertebrates are derived from invaginated between adjacent epithelial cells. Therefore, nutrients and epithelium. In exocrine glands, the connection between oxygen must diffuse to the epithelial cells from blood ves- the gland and the epithelial membrane is maintained as a sels in nearby tissues. This places a limit on the thickness of duct. The duct channels the product of the gland to the epithelial membranes; most are only one or a few cell layers surface of the epithelial membrane and thus to the external environment(or to an interior compartment that opens Epithelium possesses remarkable regenerative powers, the exterior, such as the digestive tract). Examples of constantly replacing its cells throughout the life of the ani- ocrine glands include sweat and sebaceous (oil) glands, mal. For example, the liver, a gland formed from epithelial which secrete to the external surface of the skin, and acces- tissue, can readily regenerate after substantial portions of it sory digestive glands such as the salivary glands, liver, and have been surgically removed. The epidermis is renewed pancreas, which secrete to the surface of the epithelium lin- every two weeks, and the epithelium inside the stomach is ing the digestive tract. replaced every two to three days. Endocrine glands are ductless glands; their connections There are two general classes of epithelial membranes: with the epithelium from which they were derived are lost simple and stratified. These classes are further subdivided during development. Therefore their secretions, called into squamous, cuboidal, and columnar, based upon the hormones, are not channeled onto an epithelial membrane shape of the cells(table 49.2). Squamous cells are flat, Instead, hormones enter blood capillaries and thus stay cuboidal cells are about as thick as they are tall, and colum- within the body endocrine glands are discussed in more nar cells are taller than they are wide detail in chapter 56 ypes of Epithelial Tissues Epithelial tissues include membranes that cover all Simple epithelial membranes are one cell layer thick. a body surfaces and glands. The epidermis of the skin is simple, squamous epithelium is composed of squamous ep an epithelial membrane specialized for protection, thelial cells that have an irregular, flattened shape with ta- whereas membranes that cover the surfaces of hollow pered edges. Such membranes line the lungs and ble organs are often specialized for transport. 988 Part XIlI Animal Form and Function
Characteristics of Epithelial Tissue An epithelial membrane, or epithelium, covers every surface of the vertebrate body. Epithelial membranes are derived from all three germ layers. The epidermis, derived from ectoderm, constitutes the outer portion of the skin. The inner surface of the digestive tract is lined by an epithelium derived from endoderm, and the inner surfaces of the body cavities are lined with an epithelium derived from mesoderm. Because all body surfaces are covered by epithelial membranes, a substance must pass through an epithelium in order to enter or leave the body. Epithelial membranes thus provide a barrier that can impede the passage of some substances while facilitating the passage of others. For land-dwelling vertebrates, the relative impermeability of the surface epithelium (the epidermis) to water offers essential protection from dehydration and from airborne pathogens (disease-causing organisms). On the other hand, the epithelial lining of the digestive tract must allow selective entry of the products of digestion while providing a barrier to toxic substances, and the epithelium of the lungs must allow for the rapid diffusion of gases. Some epithelia become modified in the course of embryonic development into glands, which are specialized for secretion. A characteristic of all epithelia is that the cells are tightly bound together, with very little space between them. As a consequence, blood vessels cannot be interposed between adjacent epithelial cells. Therefore, nutrients and oxygen must diffuse to the epithelial cells from blood vessels in nearby tissues. This places a limit on the thickness of epithelial membranes; most are only one or a few cell layers thick. Epithelium possesses remarkable regenerative powers, constantly replacing its cells throughout the life of the animal. For example, the liver, a gland formed from epithelial tissue, can readily regenerate after substantial portions of it have been surgically removed. The epidermis is renewed every two weeks, and the epithelium inside the stomach is replaced every two to three days. There are two general classes of epithelial membranes: simple and stratified. These classes are further subdivided into squamous, cuboidal, and columnar, based upon the shape of the cells (table 49.2). Squamous cells are flat, cuboidal cells are about as thick as they are tall, and columnar cells are taller than they are wide. Types of Epithelial Tissues Simple epithelial membranes are one cell layer thick. A simple, squamous epithelium is composed of squamous epithelial cells that have an irregular, flattened shape with tapered edges. Such membranes line the lungs and blood capillaries, for example, where the thin, delicate nature of these membranes permits the rapid movement of molecules (such as the diffusion of gases). A simple cuboidal epithelium lines the small ducts of some glands, and a simple columnar epithelium is found in the airways of the respiratory tract and in the gastrointestinal tract, among other locations. Interspersed among the columnar epithelial cells are numerous goblet cells, specialized to secrete mucus. The columnar epithelial cells of the respiratory airways contain cilia on their apical surface (the surface facing the lumen, or cavity), which move mucus toward the throat. In the small intestine, the apical surface of the columnar epithelial cells form fingerlike projections called microvilli, that increase the surface area for the absorption of food. Stratified epithelial membranes are several cell layers thick and are named according to the features of their uppermost layers. For example, the epidermis is a stratified squamous epithelium. In terrestrial vertebrates it is further characterized as a keratinized epithelium, because its upper layer consists of dead squamous cells and filled with a water-resistant protein called keratin. The deposition of keratin in the skin can be increased in response to abrasion, producing calluses. The water-resistant property of keratin is evident when the skin is compared with the red portion of the lips, which can easily become dried and chapped because it is covered by a nonkeratinized, stratified squamous epithelium. The glands of vertebrates are derived from invaginated epithelium. In exocrine glands, the connection between the gland and the epithelial membrane is maintained as a duct. The duct channels the product of the gland to the surface of the epithelial membrane and thus to the external environment (or to an interior compartment that opens to the exterior, such as the digestive tract). Examples of exocrine glands include sweat and sebaceous (oil) glands, which secrete to the external surface of the skin, and accessory digestive glands such as the salivary glands, liver, and pancreas, which secrete to the surface of the epithelium lining the digestive tract. Endocrine glands are ductless glands; their connections with the epithelium from which they were derived are lost during development. Therefore, their secretions, called hormones, are not channeled onto an epithelial membrane. Instead, hormones enter blood capillaries and thus stay within the body. Endocrine glands are discussed in more detail in chapter 56. Epithelial tissues include membranes that cover all body surfaces and glands. The epidermis of the skin is an epithelial membrane specialized for protection, whereas membranes that cover the surfaces of hollow organs are often specialized for transport. 988 Part XIII Animal Form and Function 49.2 Epithelial tissue forms membranes and glands
Table 49.2 Epithelial Tissue Simple epithelium SQUAMOUS Cuboidal Typical Location Lining of lungs, capillary walls, and blood vessels Function Cells very thin; provides thin layer across which diffusion can readily occur Characteristic Cell Types Epithelial cells CUBOIDAL Columna Typical Location epithelial Lining of some glands and kidney tubules; covering of ovaries Nucleus Cells rich in specific transport channels; functions in secretion and absorption Characteristic Cell Types Goblet cell Gland cells COLUMNAR Surface lining of stomach, intestines, and parts of respiratory tract Function Thicker cell layer; provides protection and functions in secretion and Characteristic Cell Types Epithelial cells Stratified Epithelium columnar 就心武 Tough layer of cells; provide Goblet cell Characteristic Cell Types epitheli PSEUDOSTRATIFIED COLUMNAR Typical location helial Secretes mucus: dense with cilia that aid in movement of Characteristic Cell T7 Gland cells; ciliated epithelial cells Nucleus Chapter 49 Organization of the Animal Body 989
Chapter 49 Organization of the Animal Body 989 Table 49.2 Epithelial Tissue Simple Epithelium SQUAMOUS Typical Location Lining of lungs, capillary walls, and blood vessels Function Cells very thin; provides thin layer across which diffusion can readily occur Characteristic Cell Types Epithelial cells CUBOIDAL Typical Location Lining of some glands and kidney tubules; covering of ovaries Function Cells rich in specific transport channels; functions in secretion and absorption Characteristic Cell Types Gland cells COLUMNAR Typical Location Surface lining of stomach, intestines, and parts of respiratory tract Function Thicker cell layer; provides protection and functions in secretion and absorption Characteristic Cell Types Epithelial cells Stratified Epithelium SQUAMOUS Typical Location Outer layer of skin; lining of mouth Function Tough layer of cells; provides protection Characteristic Cell Types Epithelial cells PSEUDOSTRATIFIED COLUMNAR Typical Location Lining parts of the respiratory tract Function Secretes mucus; dense with cilia that aid in movement of mucus; provides protection Characteristic Cell Types Gland cells; ciliated epithelial cells Cuboidal epithelial cells Nucleus Cytoplasm Cilia Pseudo– stratified columnar cell Goblet cell Simple squamous epithelial cell Nucleus Columnar epithelial cells Nucleus Goblet cell Nuclei
49.3 Connective tissues contain abundant extracellular material Connective Tissue Proper Connective tissues are derived from embryonic meso- derm and occur in many different forms(table 49.3) These various forms are divided into two major classes connective tissue proper, which is further divided into loose and dense connective tissues; and special connec tive tissues that include cartilage, bone. and blood. At first glance, it may seem odd that such diverse tissues are placed in the same category. Yet all connective tissues do share a common structural feature: they all have abun ant extracellular material because their cells are spaced widely apart. This extracellular material is generically known as the matrix of the tissue. In bone. the extracel lular matrix contains crystals that make the bones hard in blood, the extracellular matrix is plasma, the fluid por- tion of the blood Loose connective tissue consists of cells scattered FIGURE 49.6 within an amorphous mass of proteins that form a ground Collagen fibers. Each fiber is composed of many individual substance. This gelatinous material is stre ed by loose scattering of protein fibers such as collagen(figure 49.6), elastin, which makes the tissue elastic, and reticulin which supports the tissue by forming a collagenous mesh work. The flavored gelatin we eat for dessert consists of the extracellular material from loose connective tissues. The ells that secrete collagen and other fibrous proteins are known as fibroblasts Loose connective tissue contains other cells as well. in- cluding mast cells that produce histamine(a blood vessel lator)and heparin(an anticoagulant) and macrophages, the immune systems first defense against invading organisms as will be described in detail in chapter 57 Adipose cells are found in loose connective tissue, usually in large groups that form what is referred adipose tissue(figure 49.7). Each adipose cell contains a droplet of fat (triglycerides) within a storage vesicle When that fat is needed for energy, the adipose cell hy- drolyzes its stored triglyceride and secretes fatty acids into the blood for oxidation by the cells of the muscles, liver, and other organs. The number of adipose cells in FIGURE 49.7 an adult is generally fixed. When a person gains weight, Adipose tissue. Fat is stored in globules of adipose tissue, a type the cells become larger, and when weight is lost, the cells of loose connective tissue. As a person gains or loses weight, the size of the fat globules increases or decreases. A person cannot Dense connective tissue contains tightly packed colla- decrease the number of fat cells by losing weight. gen fibers, making it stronger than loose connective tis- sue. It consists of two types: regular and irregular. The collagen fibers of dense regular connective tissue are the capsules of the kidneys and adrenal glands. It also cow lined up in parallel, like the strands of a rope. This is the ers muscle as epimysium, nerves as perineurium, and bones structure of tendons, which bind muscle to bone, and liga as periosteum. ments. which bind bone to bone. In contrast the collagen fibers of dense irregular connective tissue have many Connective tissues are characterized by abundant different orientations. This type of connective tissue pro- extracellular materials in the matrix between cells duces the tough coverings that package organs, such as Connective tissue proper may be either loose or dense 990 Part XIlI Animal Form and Function
Connective Tissue Proper Connective tissues are derived from embryonic mesoderm and occur in many different forms (table 49.3). These various forms are divided into two major classes: connective tissue proper, which is further divided into loose and dense connective tissues; and special connective tissues that include cartilage, bone, and blood. At first glance, it may seem odd that such diverse tissues are placed in the same category. Yet all connective tissues do share a common structural feature: they all have abundant extracellular material because their cells are spaced widely apart. This extracellular material is generically known as the matrix of the tissue. In bone, the extracellular matrix contains crystals that make the bones hard; in blood, the extracellular matrix is plasma, the fluid portion of the blood. Loose connective tissue consists of cells scattered within an amorphous mass of proteins that form a ground substance. This gelatinous material is strengthened by a loose scattering of protein fibers such as collagen (figure 49.6), elastin, which makes the tissue elastic, and reticulin, which supports the tissue by forming a collagenous meshwork. The flavored gelatin we eat for dessert consists of the extracellular material from loose connective tissues. The cells that secrete collagen and other fibrous proteins are known as fibroblasts. Loose connective tissue contains other cells as well, including mast cells that produce histamine (a blood vessel dilator) and heparin (an anticoagulant) and macrophages, the immune system’s first defense against invading organisms, as will be described in detail in chapter 57. Adipose cells are found in loose connective tissue, usually in large groups that form what is referred to as adipose tissue (figure 49.7). Each adipose cell contains a droplet of fat (triglycerides) within a storage vesicle. When that fat is needed for energy, the adipose cell hydrolyzes its stored triglyceride and secretes fatty acids into the blood for oxidation by the cells of the muscles, liver, and other organs. The number of adipose cells in an adult is generally fixed. When a person gains weight, the cells become larger, and when weight is lost, the cells shrink. Dense connective tissue contains tightly packed collagen fibers, making it stronger than loose connective tissue. It consists of two types: regular and irregular. The collagen fibers of dense regular connective tissue are lined up in parallel, like the strands of a rope. This is the structure of tendons, which bind muscle to bone, and ligaments, which bind bone to bone. In contrast, the collagen fibers of dense irregular connective tissue have many different orientations. This type of connective tissue produces the tough coverings that package organs, such as the capsules of the kidneys and adrenal glands. It also covers muscle as epimysium, nerves as perineurium, and bones as periosteum. Connective tissues are characterized by abundant extracellular materials in the matrix between cells. Connective tissue proper may be either loose or dense. 990 Part XIII Animal Form and Function 49.3 Connective tissues contain abundant extracellular material. FIGURE 49.6 Collagen fibers. Each fiber is composed of many individual collagen strands and can be very strong under tension. FIGURE 49.7 Adipose tissue. Fat is stored in globules of adipose tissue, a type of loose connective tissue. As a person gains or loses weight, the size of the fat globules increases or decreases. A person cannot decrease the number of fat cells by losing weight