《生物学》课程参考书籍文献（英文版，Chapter 49 - Chapter 60）Part XIII Animal Form and Function、Part XIV Regulating the Animal Body.pdf_P11-P15

pecial Connective Tissues The special connective tissues--carti- lage, bone, and blood-each have unique cells and extracellular matrices that allow them to perform their specialized func- tons Cartil 他 Cartilage(figure 49.8)is a specialized Larynx connective tissue in which the ground substance is formed from a characteristic Perichondrium ype of glycoprotein, and the collagen fibers are laid down along the lines of stress in long, parallel arrays. The result is a firm and flexible tissue that does not Lacunae stretch, is far tougher than loose or dense connective tissue, and has great tensile strength. Cartilage makes up theTrachea entire skeletal system of the modern a Chondrocytes nathans and cartilaginous fishes(see chapter 48), replacing the bony skeletons hat were characteristic of the ancestors of these vertebrate groups. In most adult vertebrates, however, cartilage is re- FIGURE 49.8 stricted to the articular goint) surfaces of Cartilage is a strong, flexible tissue that makes up the larynx(voice box)and and to other specific locations. In hu- microscope in(6), where the cartilage cells, or chondrocytes, are visible within cavities, or mans, for example, the tip of the nose, lacunae, in the matrix(extracellular material)of the cartilage. This is diagrammed in(c) the pinna (outer ear flap), the interverte- bral discs of the backbone, the larynx (voice box)and a few other structures are composed of car cytes extend cytoplasmic processes toward neighboring os tilage teocytes through tiny canals, or canaliculi(figure 49.9). Os- Chondrocytes, the cells of the cartilage, live within teocytes communicate with the blood vessels in the central spaces called lacunae within the cartilage ground substance. canal through this cytoplasmic network. These cells remain alive, even though there are no blood It should be noted here that some bones such as those vessels within the cartilage matrix, because they receive of the cranium, are not formed first as cartilage models oxygen and nutrients by diffusion through the cartilage These bones instead develop within a membrane of dense ground substance from surrounding blood vessels. This dif- irregular connective tissue. The structure and formation of fusion can only occur because the cartilage matrix is not bone are discussed in chapter 50 calcified. as is bone Bor Blood is classified as a connective tissue because it contains In the course of fetal development, the bones of vertebrate abundant extracellular material, the fluid plasma. The cells fins, arms, and legs, among others, are first "modeled"in of blood are erythrocytes, or red blood cells, and leuko cartilage. The cartilage matrix then calcifies at particular cytes, or white blood cells(figure 49.10). Blood also con locations, so that the chondrocytes are no longer able to tains platelets, or thrombocytes, which are fragments of a obtain oxygen and nutrients by diffusion through the ma- type of bone marrow cell trix. The dying and degenerating cartilage is then replaced Erythrocytes are the most common blood cells; there are by living bone. Bone cells, or osteocytes, can remain alive about 5 billion in every milliliter of blood. During their mat even though the extracellular matrix becomes hardened uration in mammals, they lose their nucleus, mitochondria, t th crystals of calcium phosphate. This is because blood and endoplasmic reticulum. As a result, mammalian erythro- ssels travel through central canals into the bone. Osteo cytes are relatively inactive metab Each erythrocyte 992 Part XIlI Animal Form and Function

Special Connective Tissues The special connective tissues—cartilage, bone, and blood—each have unique cells and extracellular matrices that allow them to perform their specialized functions. Cartilage Cartilage (figure 49.8) is a specialized connective tissue in which the ground substance is formed from a characteristic type of glycoprotein, and the collagen fibers are laid down along the lines of stress in long, parallel arrays. The result is a firm and flexible tissue that does not stretch, is far tougher than loose or dense connective tissue, and has great tensile strength. Cartilage makes up the entire skeletal system of the modern agnathans and cartilaginous fishes (see chapter 48), replacing the bony skeletons that were characteristic of the ancestors of these vertebrate groups. In most adult vertebrates, however, cartilage is restricted to the articular (joint) surfaces of bones that form freely movable joints and to other specific locations. In humans, for example, the tip of the nose, the pinna (outer ear flap), the intervertebral discs of the backbone, the larynx (voice box) and a few other structures are composed of cartilage. Chondrocytes, the cells of the cartilage, live within spaces called lacunae within the cartilage ground substance. These cells remain alive, even though there are no blood vessels within the cartilage matrix, because they receive oxygen and nutrients by diffusion through the cartilage ground substance from surrounding blood vessels. This diffusion can only occur because the cartilage matrix is not calcified, as is bone. Bone In the course of fetal development, the bones of vertebrate fins, arms, and legs, among others, are first “modeled” in cartilage. The cartilage matrix then calcifies at particular locations, so that the chondrocytes are no longer able to obtain oxygen and nutrients by diffusion through the matrix. The dying and degenerating cartilage is then replaced by living bone. Bone cells, or osteocytes, can remain alive even though the extracellular matrix becomes hardened with crystals of calcium phosphate. This is because blood vessels travel through central canals into the bone. Osteocytes extend cytoplasmic processes toward neighboring osteocytes through tiny canals, or canaliculi (figure 49.9). Osteocytes communicate with the blood vessels in the central canal through this cytoplasmic network. It should be noted here that some bones, such as those of the cranium, are not formed first as cartilage models. These bones instead develop within a membrane of dense, irregular connective tissue. The structure and formation of bone are discussed in chapter 50. Blood Blood is classified as a connective tissue because it contains abundant extracellular material, the fluid plasma. The cells of blood are erythrocytes, or red blood cells, and leukocytes, or white blood cells (figure 49.10). Blood also contains platelets, or thrombocytes, which are fragments of a type of bone marrow cell. Erythrocytes are the most common blood cells; there are about 5 billion in every milliliter of blood. During their maturation in mammals, they lose their nucleus, mitochondria, and endoplasmic reticulum. As a result, mammalian erythrocytes are relatively inactive metabolically. Each erythrocyte 992 Part XIII Animal Form and Function Larynx Trachea FIGURE 49.8 Cartilage is a strong, flexible tissue that makes up the larynx (voice box) and several other structures in the human body. The larynx (a) is seen under the light microscope in (b), where the cartilage cells, or chondrocytes, are visible within cavities, or lacunae, in the matrix (extracellular material) of the cartilage. This is diagrammed in (c). Perichondrium Lacunae Chondrocytes

contains about 300 million molecules of the iron-containing protein benoglobn the principal carrier of oxygen in verte- brates and in many other groups of nimals There are several types of leukocytes but tog sandth as numerous as erythrocytes Unlike mammalian erythrocytes, leuko- cytes have nuclei and mitochondria but lack the red pigment hemoglobin These cells are therefore hard to see under a microscope without special staining. The names neutrop bils eosinophils, and basophils distinguish three types of leukocytes on the basis of their staining properties; other leuko- cytes include lympbocytes and monocytes. These different types of leukocytes play critical roles in immunity as will be de- Blood vessels ribed in chapter 57 The blood plasma is the"commons Central canal of the body; it (or a derivative of it) travels to and from every cell in the Osteocyte body. As the plasma circulates, it car ries nourishment, waste products, heat, and regulatory molecules. Practically every substance used by cells, includin sugars, lipids, and amino acids, is deliv ered by the plasma to the body cells Waste products from the cells are car- FIGURE 49.9 ried by the plasma to the kidneys, liver, The structure of bone. A photomicrograph(a)and diagram (6)of the structure of bone, and lungs or gills for disposal, and reg showing the bone cells, or osteocytes, within their lacunae(cavities) in the bone matrix. Igh the bone matrix is ulatory molecules(hormones) that en- nourished by blood vessels in the central cavity Nourishment is carried between the docrine gland cells secrete are carried osteocytes through a network of cytoplasmic processes extending through tiny canals, or by the plasma to regulate the activities canaliculi. of most organs of the body. The plasma also contains sodium calcium. and other inorganic ions that all cells need, as well as numerous proteins. Plasm GURE 49.10 White and red proteins include fibrinogen, produced by the liver, which helps blood to clot; al blood cells (500x). White bumin, also produced by the liver blood cells. or which exerts an osmotic force needed for fluid balance; and antibodies pro- hly spherical duced by lymphocytes and needed for nd have irregula Special connective tissues each have Red blood cel a unique extracellular matrix between cells. The matrix of cartilage is composed of organic spheres, typically material, whereas that of bone with a depressed npregnated with calcium phosphate center, forming rystals. The matrix of blood is fluid biconcave discs the plasma Chapter 49 Organization of the Animal Body 993

contains about 300 million molecules of the iron-containing protein hemoglobin, the principal carrier of oxygen in vertebrates and in many other groups of animals. There are several types of leukocytes, but together they are only one-thousandth as numerous as erythrocytes. Unlike mammalian erythrocytes, leukocytes have nuclei and mitochondria but lack the red pigment hemoglobin. These cells are therefore hard to see under a microscope without special staining. The names neutrophils, eosinophils, and basophils distinguish three types of leukocytes on the basis of their staining properties; other leukocytes include lymphocytes and monocytes. These different types of leukocytes play critical roles in immunity, as will be described in chapter 57. The blood plasma is the “commons” of the body; it (or a derivative of it) travels to and from every cell in the body. As the plasma circulates, it carries nourishment, waste products, heat, and regulatory molecules. Practically every substance used by cells, including sugars, lipids, and amino acids, is delivered by the plasma to the body cells. Waste products from the cells are carried by the plasma to the kidneys, liver, and lungs or gills for disposal, and regulatory molecules (hormones) that endocrine gland cells secrete are carried by the plasma to regulate the activities of most organs of the body. The plasma also contains sodium, calcium, and other inorganic ions that all cells need, as well as numerous proteins. Plasma proteins include fibrinogen, produced by the liver, which helps blood to clot; albumin, also produced by the liver, which exerts an osmotic force needed for fluid balance; and antibodies produced by lymphocytes and needed for immunity. Special connective tissues each have a unique extracellular matrix between cells. The matrix of cartilage is composed of organic material, whereas that of bone is impregnated with calcium phosphate crystals. The matrix of blood is fluid, the plasma. Chapter 49 Organization of the Animal Body 993 FIGURE 49.9 The structure of bone. A photomicrograph (a) and diagram (b) of the structure of bone, showing the bone cells, or osteocytes, within their lacunae (cavities) in the bone matrix. Though the bone matrix is calcified, the osteocytes remain alive because they can be nourished by blood vessels in the central cavity. Nourishment is carried between the osteocytes through a network of cytoplasmic processes extending through tiny canals, or canaliculi. FIGURE 49.10 White and red blood cells (500×). White blood cells, or leukocytes, are roughly spherical and have irregular surfaces with numerous extending pili. Red blood cells, or erythrocytes, are flattened spheres, typically with a depressed center, forming biconcave discs. Blood vessels Central canal Osteocyte within a lacuna Canaliculi

49.4 Muscle tissue provides for movement, and nerve tissue provides for control Muscle tissue stimulated by a nerve, and then all of the cells in the sheet contract as a unit. In vertebrates, muscles of this type line Muscle cells are the motors of the vertebrate body. The the walls of many blood vessels and make up the iris of the characteristic that makes them unique is the relative abun- eye. In other smooth muscle tissues, such as those in the dance and organization of actin and myosin filaments wall of the gut, the muscle cells themselves may sponta- within them. Although these filaments form a fine network neously initiate electric impulses and contract, leading to a in all eukaryotic cells, where they contribute to cellular slow, steady contraction of the tissue. Nerves regulate, movements, they are far more common in muscle cells, rather than cause, this activity which are specialized for contraction. Vertebrates possess three kinds of muscle: smooth, skeletal, and cardiac(table Skeletal muscle ated muscles because their cells have transverse stripes Skeletal muscles are usually attached by tendons to bones when viewed in longitudinal section under the microscope. so that, when the muscles contract, they cause the bones to The contraction of each skeletal muscle is under voluntar move at their joints. a skeletal muscle is made up of numer control, whereas the contraction of cardiac and smooth ous, very long muscle cells, called muscle fibers, which lie muscles is generally involuntary. Muscles are described in parallel to each other within the muscle and insert into the more detail in chapter 50 tendons on the ends of the muscle. each skeletal muscle fiber is stimulated to contract by a nerve fiber; therefore, a Smooth muscle stronger muscle contraction will result when more of the muscle fibers are stimulated by nerve fibers to contract. In Smooth muscle was the earliest form of muscle to evolve, this way, the nervous system can vary the strength of skele- ind it is found throughout the animal kingdom. In verte- tal muscle contraction. Each muscle fiber contracts by brates, smooth muscle is found in the organs of the internal means of substructures called myofibrils(figure 49. 11)that environment, or viscera, and is sometimes known as visceral contain highly ordered arrays of actin and myosin myofil muscle. Smooth muscle tissue is organized into sheets of aments, that, when aligned, give the muscle fiber its striated long, spindle-shaped cells, each cell containing a single nu- appearance. Skeletal muscle fibers are produced during de- cleus. In some tissues, the cells contract only when they are velopment by the fusion of several cells, end to end. This sarcoplasmic reticulum Myofibrils Nucleus Myofilaments of FIGURE 49.11 A muscle fiber, or muscle cell. Each muscle fiber is composed of numerous myofibrils, which, in turn, are composed of actin and myosin filaments. Each muscle fiber is multinucleate as a result of its embryological development from the fusion of smaller cells. Muscle cells have a modified endoplasmic reticulum called the sarcoplasmic reticulum. 994 Part XIlI Animal Form and Function

Muscle Tissue Muscle cells are the motors of the vertebrate body. The characteristic that makes them unique is the relative abundance and organization of actin and myosin filaments within them. Although these filaments form a fine network in all eukaryotic cells, where they contribute to cellular movements, they are far more common in muscle cells, which are specialized for contraction. Vertebrates possess three kinds of muscle: smooth, skeletal, and cardiac (table 49.4). Skeletal and cardiac muscles are also known as striated muscles because their cells have transverse stripes when viewed in longitudinal section under the microscope. The contraction of each skeletal muscle is under voluntary control, whereas the contraction of cardiac and smooth muscles is generally involuntary. Muscles are described in more detail in chapter 50. Smooth Muscle Smooth muscle was the earliest form of muscle to evolve, and it is found throughout the animal kingdom. In vertebrates, smooth muscle is found in the organs of the internal environment, or viscera, and is sometimes known as visceral muscle. Smooth muscle tissue is organized into sheets of long, spindle-shaped cells, each cell containing a single nucleus. In some tissues, the cells contract only when they are stimulated by a nerve, and then all of the cells in the sheet contract as a unit. In vertebrates, muscles of this type line the walls of many blood vessels and make up the iris of the eye. In other smooth muscle tissues, such as those in the wall of the gut, the muscle cells themselves may spontaneously initiate electric impulses and contract, leading to a slow, steady contraction of the tissue. Nerves regulate, rather than cause, this activity. Skeletal Muscle Skeletal muscles are usually attached by tendons to bones, so that, when the muscles contract, they cause the bones to move at their joints. A skeletal muscle is made up of numerous, very long muscle cells, called muscle fibers, which lie parallel to each other within the muscle and insert into the tendons on the ends of the muscle. Each skeletal muscle fiber is stimulated to contract by a nerve fiber; therefore, a stronger muscle contraction will result when more of the muscle fibers are stimulated by nerve fibers to contract. In this way, the nervous system can vary the strength of skeletal muscle contraction. Each muscle fiber contracts by means of substructures called myofibrils (figure 49.11) that contain highly ordered arrays of actin and myosin myofilaments, that, when aligned, give the muscle fiber its striated appearance. Skeletal muscle fibers are produced during development by the fusion of several cells, end to end. This 994 Part XIII Animal Form and Function 49.4 Muscle tissue provides for movement, and nerve tissue provides for control. Striations Nucleus Myofilaments of actin and myosin Myofibrils Sarcoplasmic reticulum Mitochondria FIGURE 49.11 A muscle fiber, or muscle cell. Each muscle fiber is composed of numerous myofibrils, which, in turn, are composed of actin and myosin filaments. Each muscle fiber is multinucleate as a result of its embryological development from the fusion of smaller cells. Muscle cells have a modified endoplasmic reticulum called the sarcoplasmic reticulum

embryological development explains why a mature muscle fiber contains many nuclei. The structure and function of skeletal muscle is explained in more detail in chapter 50. Cardiac Muscle The hearts of vertebrates are composed of striated muscle cells arranged very differently from the fibers of skeletal muscle. Instead of having very long, multinucleate cells running the length of the muscle, cardiac muscle is composed of smaller, interconnected cells, each with a single nucleus. The interconnections between adjacent cells appear under the microscope as dark lines called intercalated discs. In reality, these lines are regions where adjacent cells are linked by gap junctions. As we noted in chapter 7, gap junctions have openings that permit the movement of small substances and electric charges from one cell to another. These interconnections enable the cardiac muscle cells to form a single, functioning unit known as a myocardium. Certain cardiac muscle cells generate electric impulses spontaneously, and these impulses spread across the gap junctions from cell to cell, causing all of the cells in the myocardium to contract. We will describe this process more fully in chapter 52. Skeletal muscles enable the vertebrate body to move. Cardiac muscle powers the heartbeat, while smooth muscles provide a variety of visceral functions. Chapter 49 Organization of the Animal Body 995 Table 49.4 Muscle Tissue Nuclei Nuclei Nuclei Intercalated discs SMOOTH MUSCLE Typical Location Walls of blood vessels, stomach, and intestines Function Powers rhythmic, involuntary contractions commanded by the central nervous system Characteristic Cell Types Smooth muscle cells SKELETAL MUSCLE Typical Location Voluntary muscles Function Powers walking, lifting, talking, and all other voluntary movement Characteristic Cell Types Skeletal muscle cells CARDIAC Typical Location Walls of heart Function Highly interconnected cells; promotes rapid spread of signal initiating contraction Characteristic Cell Types Cardiac muscle cells