Animal Structure and Function: An Introduction (MIDTERM)

39 Animal Structure and Function: An Introduction Animal species are dramatically diverse, with radically different body structures. For example, consider how different the elephant and the bird are, not only in s...

39 Animal Structure and Function: An Introduction Animal species are dramatically diverse, with radically different body structures. For example, consider how different the elephant and the bird are, not only in size but also in body form and lifestyle (see pho- key concepts tograph). Despite their differences, animal groups share many charac- teristics, including their relatively large size. 39.1 Cells make up tissues, various types of tissues make up Why are most animals larger than bacteria, archaea, protists, and organs, and tissues and organs working together make up fungi? The answer may be related to ecological niches—the functional organ systems. The main types of tissues found in animals roles of a species within a community. By the time animals evolved, other are epithelial, connective, muscle, and nervous tissues. organisms already occupied most available ecological niches. For new 39.2 Homeostatic mechanisms are mainly negative feedback species to succeed, they had to displace others from a niche or adapt to a systems that maintain a relatively stable internal new one. Success in a new niche required a new body plan, and new body environment. plans often required larger size. Increased size also provided more opportu- nity for capturing food. Predators are typically larger than their prey. 39.3 Thermoregulation is the process of maintaining To grow larger than their bacterial and protist competitors, ani- homeostasis of body temperature despite changes in mals had to be multicellular. Recall that the size of a single cell is lim- surrounding (or internal) temperature. ited by the ratio of its surface area (plasma membrane) to its volume (see Chapter 4). The plasma membrane needs to be large enough rel- ative to the cell’s volume to permit passage of materials into and out of the cell so that the conditions necessary for life can be maintained. In a multicellular animal, each cell has a large enough ratio of sur- face area to volume to effectively regulate its internal environment. Individual cells live and die, and they are replaced while the organism continues to maintain itself and thrive. The number of cells, not their individual sizes, is mainly responsible for the size of an animal. photo: Larger body size does not mean bigger cells. The cells In unicellular organisms such as bacteria and many protists, the of the elephant mother, her calf, and the bird on the young ele- single cell carries on all the activities necessary for life. Recall that uni- phant’s back are all about the same size. The elephants are larger cellular and small, flat organisms depend on diffusion for many life than the bird because their genes specify that their bodies consist processes, including gas exchange and disposal of metabolic wastes. of a larger number of cells. The cells of the young elephant will One reason they can be small is that they do not require complex continue to multiply until it reaches adult size (African elephant, organ systems like multicellular organisms do. Loxodonta africana). MaggyMeyer/Shutterstock.com 821 Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.  In this chapter we focus on the basic form and function of the as the cavity (lumen) of the intestine. The other surface of an animal body. Anatomy is the study of an organism’s structure. epithelial layer attaches to the underlying tissue by a noncellu- ­Physiology is the study of how the body functions. Remember that in lar basement membrane consisting of tiny fibers and nonliv- biological systems, structures are adapted to function at every level of ing polysaccharide material that the epithelial cells produce. organization. Notice the many examples of this basic principle as we Epithelial tissue forms the outer layer of the skin and the describe the types and functions of tissues and the principal organ sys- tems of animals. In this chapter we also discuss the important concept linings of the digestive, respiratory, excretory, and reproduc- of homeostasis, using regulation of body temperature as an example. In tive tracts. As a result, everything that enters or leaves the the following chapters, we discuss how organ systems work together to body must cross at least one layer of epithelium. Food taken maintain homeostasis as animals carry out their many life processes. into the mouth and swallowed is not really “inside” the body until it is absorbed through the epithelium of the digestive tract and enters the blood. To a large extent, the permeabili- ties of the various epithelial tissues regulate the exchange of 39.1 T  issues, Organs, and substances between the different parts of the body as well as Organ Systems between the animal and the external environment. Epithelial tissues perform many functions, including pro- tection, absorption, secretion, and sensation. The epithelial learning objectives layer of the skin, the epidermis, covers the entire body and pro- tects it from mechanical injury, chemicals, bacteria, and fluid 1 Compare the structure and function of the four main kinds loss. The epithelial tissue lining the digestive tract absorbs of animal tissues: epithelial, connective, muscle, and ner- vous tissues. nutrients and water into the body. Some epithelial cells form glands that secrete cell products such as hormones, enzymes, 2 Compare the main types of epithelial tissue and describe their functions. or sweat. Other epithelial cells are sensory receptors that receive information from the environment. For example, epithelial cells 3 Compare the main types of connective tissue and describe their functions. in taste buds and in the nose specialize as chemical receptors. TABLE 39-1 illustrates the main types of epithelial tissue, indi- 4 Contrast the three types of muscle tissue and describe their functions. cates their locations in the body, and describes their functions (pages 824–825). We can distinguish three types of epithelial 5 Relate the structure of the neuron to its function. cells based on their shape. Squamous epithelial cells are thin, 6 Briefly describe the organ systems of a mammal and sum- flat cells shaped like flagstones. Simple squamous epithelium lines marize the functions of each organ system. the blood vessels and the air sacs in the lungs. Cuboidal epithelial cells are short cylinders. When you look at them from the side, In a multicellular organism, cells specialize to perform specific they appear cube-shaped, like dice. Actually, each cuboidal cell tasks. Recall from Chapter 1 that cells organize to form tissues, is typically hexagonal in cross section, making it an eight-sided and tissues associate to form organs such as the heart or stom- polyhedron. Simple cuboidal epithelium lines the kidney tubules. ach. Groups of tissues and organs make up the organ systems of When viewed from the side, columnar epithelial cells look a complex organism. Billions of cells organize to form the tissues, like columns or cylinders. The nucleus is usually located near organs, and organ systems of a lobster, a crocodile, or an elephant. the base of the cell. Viewed from above or in cross section, A tissue consists of a group of closely associated, similar these cells often appear hexagonal. On its free surface, a colum- cells that carry out specific functions. Biologists classify ani- nar epithelial cell may have cilia that beat in a coordinated way, mal tissues as epithelial, connective, muscle, or nervous tissue. moving materials over the tissue surface. Most of the upper Classification of tissues depends on their structure and origin. respiratory tract is lined with ciliated columnar epithelium that Each kind of tissue is composed of specialized cells with spe- moves particles of dust and other foreign material away from cific sizes, shapes, and arrangements. Some tissues are special- the lungs. ized to transport materials, whereas others contract, enabling Epithelial tissue is also classified by number of layers. Simple the animal to move. Still others secrete hormones that regu- epithelium is composed of one layer of cells. It is usually located late metabolic processes. Structure and function are closely where substances are secreted, excreted, or absorbed, or where linked at every level of organization. As we discuss each tissue materials diffuse between compartments. For example, simple type, notice the relationship between its form and its function. squamous epithelium lines the air sacs in the lungs. The structure Notice also how biological systems continuously interact. of this thin tissue allows diffusion of gases in and out of air sacs. Stratified epithelium, which has two or more layers, pro- Epithelial tissues cover the body tects underlying tissues. For example, stratified squamous epithelium, which makes up the outer layer of your skin, is and line its cavities continuously sloughed off during normal wear and tear. It Epithelial tissue (also called epithelium) consists of cells fit- must also continuously regenerate. The cells of p­ seudostratified ted tightly together to form a continuous layer, or sheet, of epithelium appear layered, but they are not. Although all its cells. One surface of the sheet is typically exposed because it cells rest on a basement membrane, not every cell extends to covers the body (outer layer of the skin) or lines a cavity, such the exposed surface of the tissue. This arrangement gives the 822 / Chapter 39 Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. impression of two or more cell layers. Some of the respira- tory passageways are lined with pseudostratified epithelium Unicellular glands (goblet cells) equipped with cilia. The lining of blood and lymph vessels is called endothe- lium. Endothelial cells have a different embryonic origin from “true” epithelium. However, these cells are structurally simi- lar to squamous epithelial cells and can be included in that category. Glands are made of epithelial cells Basement A gland consists of one or more epithelial cells specialized to pro- membrane duce and secrete a product such as sweat, milk, mucus, wax, saliva, hormones, or enzymes (FIG. 39-1). Epithelial tissue lining the cavi- (a) Goblet cells. These unicellular glands ties and passageways of the body typically has some specialized secrete mucus. mucus-secreting cells called goblet cells. The mucus lubricates these surfaces, offers protection, and facilitates the movement of materials. Glands are classified as exocrine or endocrine. E ­ xocrine glands, like goblet cells and sweat glands, secrete their products onto a free epithelial surface, typically through a duct (tube). Endocrine glands lack ducts. These glands release their prod- ucts, called hormones, into the interstitial fluid (tissue fluid) or blood. Hormones are typically transported by the cardiovas- cular system. (Endocrine glands are discussed in Chapter 49.) Epithelial cells form membranes (b) Sweat gland. This (c) Parotid salivary An epithelial membrane consists of a sheet of epithelial tissue simple gland consists of gland. Compound and a layer of underlying connective tissue. Types of epithe- a coiled tube. Its wall is glands, like the parotid, constructed of simple have branched ducts. lial membranes include mucous m ­ embranes and serous mem- cuboidal epithelium. branes. A mucous membrane, or mucosa, lines a body cavity that opens to the outside of the body, such as the digestive Figure 39-1 Glands tract or respiratory tract. Goblet cells in the epithelial layer A gland consists of one or more epithelial cells. secrete mucus that lubricates the tissue and protects it from drying. A serous membrane lines a body cavity that does not open to the outside of the body. It consists of simple squa- Connective tissue typically contains three types of fibers: mous epithelium over a thin layer of loose connective tis- collagen, elastic, and reticular. Collagen fibers, the most sue. This type of membrane secretes fluid into the cavity it numerous type, are made of collagens, a group of fibrous pro- lines. Examples of serous membranes are the pleural mem- teins found in all animals (see Fig. 3-23b). Collagens are the branes lining the pleural cavities around the lungs and the most abundant proteins in mammals, accounting for about pericardial membranes lining the pericardial cavity around 25% of their total protein mass. Collagen is very tough (meat the heart. is tough because of its collagen content). The tensile strength (ability to stretch without tearing) of collagen fibers is com- Connective tissues support other parable to that of steel. Collagen fibers are wavy and flexible, allowing them to remain intact when tissue is stretched. body structures Elastic fibers branch and fuse to form networks. They Almost every organ in the body has a framework of ­connective can be stretched by a force and then (like a stretched rubber tissue that supports and cushions it. Compared with epithelial band) return to their original size and shape when the force is tissues, connective tissues contain relatively few cells. Con- removed. Elastic fibers, composed of the protein elastin, are nective tissue cells are embedded in an extensive intercellular an important component of structures that must stretch. substance consisting of threadlike, microscopic fibers scat- Reticular fibers are very thin, branched fibers that form tered throughout a matrix, a thin gel of polysaccharides that delicate networks joining connective tissues to neighboring tis- the cells secrete. The structure and properties of the inter- sues. Reticular fibers consist of collagen and some glycoprotein. cellular substance help determine the nature and function of The cells of various kinds of connective tissues differ in each kind of connective tissue. their shapes and structures and in the kinds of fibers and Animal Structure and Function: An Introduction / 823 Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.  Table 39-1 Epithelial Tissues Nuclei of squamous epithelial cells Simple Squamous Epithelium Main Locations Air sacs of lungs; lining of blood vessels Functions Passage of materials where little or no protection is needed and where diffusion is major form of transport Description and Comments Cells are flat and arranged as single layer Ed Reschke/Getty Images 25 mm LM of simple squamous epithelium. Nuclei of cuboidal epithelial cells Lumen of tubule Simple Cuboidal Epithelium Main Locations Linings of kidney tubules; gland ducts Functions Secretion and absorption Description and Comments Single layer of cells; LM shows cross section through tubules; from the side each cell looks like a short ­cylinder; some have microvilli for absorption Ed Reschke/Peter Arnold/Getty Images 25 mm LM of simple cuboidal epithelium. Goblet cell Nuclei of columnar cells Simple Columnar Epithelium Main Locations Linings of much of digestive tract and upper part of respiratory tract Functions Secretion, especially of mucus; absorption; protection; moves layer of mucus Description and Comments Single layer of columnar cells; highly developed Golgi complex; often ciliated; goblet cells secrete mucus Ed Reschke/Getty Images 25 mm LM of simple columnar epithelium. Continued 824 / Chapter 39 Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.  Table 39-1 Epithelial Tissues (continued) Stratified Squamous Epithelium Main Locations Skin; mouth lining; vaginal lining Functions Protection only; little or no absorption or transit of mate- rials; outer layer continuously sloughed off and replaced from below Description and Comments Several layers of cells, with only the lower ones columnar and metabolically active; division of lower cells causes older ones to be pushed upward toward surface, ­becoming flatter as they move Nuclei Ed Reschke/Getty Images 50 mm LM of stratified squamous epithelium. Pseudostratified Epithelium Main Locations Some respiratory passages; ducts of many glands Cilia Functions Secretion; protection; moves layer of mucus Epithelial cells Description and Comments Ciliated, mucus-secreting, or with microvilli; comparable in many ways to columnar epithelium except that not all cells are the same height; so, although all cells con- tact the same basement membrane, the tissue appears Nuclei stratified Basement membrane Ed Reschke/Getty Images 25 mm LM of pseudostratified columnar epithelium, ciliated. matrices they secrete. Fibroblasts are connective tissue cells through connective tissues, cleaning up cell debris and phago- that produce the fibers, as well as the protein and carbohy- cytosing foreign matter, including bacteria. drate complexes, of the matrix. Fibroblasts release protein Some of the main types of connective tissue are (1) loose components that become arranged to form the characteristic and dense connective tissues; (2) elastic connective tissue; fibers. These cells are especially active in developing tissues (3) reticular connective tissue; (4) adipose tissue; (5) cartilage; and are important in healing wounds. As tissues mature, the (6) bone; and (7) blood, lymph, and tissues that produce blood number of fibroblasts decreases, and they become less active. cells. These tissues vary widely in their structural details and Macrophages, the body’s scavenger cells, commonly wander in the functions they perform (TABLE 39-2). Animal Structure and Function: An Introduction / 825 Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.  Table 39-2 Connective Tissues Collagen fibers Nuclei of fibroblasts Loose Connective Tissue Elastic fibers Main Locations Everywhere that support must be combined with elasticity, such as sub­ cutaneous tissue (the layer of tissue beneath the dermis of the skin) Functions Support; reservoir for fluid and salts Description and Comments Ed Reschke/Getty Images Fibers produced by fibroblast cells embedded in semifluid matrix; other types of cells, e.g., macrophages, present 50 mm LM of loose connective tissue. Dense Connective Tissue Main Locations Nucleus of Tendons; many ligaments; dermis of skin fibroblast Functions Support; transmits mechanical forces Collagen fibers Ed Reschke/Getty Images Description and Comments Collagen fibers may be regularly or irregularly arranged 25 mm LM of dense connective tissue. Elastic fibers Elastic Connective Tissue Main Locations Structures that must both expand and return to their original size, such as lung tissue and large arteries Function Confers elasticity Description and Comments Ed Reschke/Getty Images Branching elastic fibers interspersed with fibroblasts 50 mm LM of elastic connective tissue. Reticular fibers Reticular Connective Tissue Main Locations Framework of liver; lymph nodes; spleen Function Support Description and Comments Ed Reschke/Getty Images Consists of interlacing reticular fibers 50 mm LM of reticular connective tissue. Continued 826 / Chapter 39 Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.  Table 39-2 Connective Tissues (continued) Adipose Tissue Main Locations Subcutaneous layer; forms protective pads around certain internal organs Cells filled with Functions fat deposits Stores fat; insulation; supports organs such as mammary glands, kidneys Description and Comments Nuclei Fat cells are star shaped at first; fat droplets accumulate until typical ­ring-shaped cells are produced 50 mm LM of adipose tissue. Intercellular Chondrocytes Lacuna substance Cartilage Main Locations Supporting skeletons in sharks and rays; ends of bones in mammals and some other vertebrates; supporting rings in wall of trachea; tip of nose; external ear Function Flexible support Ed Reschke/Getty Images Description and Comments Cells (chondrocytes) separated from one another by intercellular sub- stance; cells occupy lacunae 50 mm LM of cartilage. Lacunae Haversian canal Matrix Bone Main Locations Forms skeletal structure in most vertebrates Functions Supports and protects internal organs; calcium reservoir; skeletal muscles attach to bones Description and Comments Cells (osteocytes) in lacunae; in compact bone lacunae embedded in lamellae, concentric circles of matrix surrounding Haversian canals 50 mm LM of bone. Red blood cells White blood cells Blood Main Locations Within heart and blood vessels of circulatory system Functions Transports oxygen, nutrients, wastes, and other materials; white blood cells defend against disease organisms Ed Reschke/Getty Images Description and Comments Consists of red blood cells, white blood cells, and platelets dispersed in fluid matrix (plasma) 25 mm LM of blood. Animal Structure and Function: An Introduction / 827 Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.  Loose connective tissue is the most widely distributed con- a large, central marrow cavity that contains a spongy tissue nective tissue in the vertebrate body. Together with adipose tissue, called marrow. Yellow marrow consists mainly of fat. Red loose connective tissue forms the subcutaneous (below the skin) marrow is the connective tissue in which blood cells are pro- layer that attaches skin to the muscles and other structures beneath. duced. We discuss bone in more detail in Chapter 40. Nerves, blood vessels, and muscles are wrapped in loose connec- Blood is a circulating tissue that helps other parts of the tive tissue. This tissue also forms a thin filling between body parts body communicate and interact. Like other connective tissues, and serves as a reservoir for fluid and salts. Loose connective tis- blood consists of specialized cells dispersed in an intercellu- sue consists of fibers running in all directions through a semifluid lar substance. In mammals blood consists of red blood cells, matrix. Its flexibility permits the parts it connects to move. white blood cells, and platelets, all suspended within plasma, Dense connective tissue, found in the dermis (lower layer) the liquid, noncellular part of the blood. In humans and other of the skin, is very strong, but is somewhat less flexible than loose vertebrates, red blood cells contain the respiratory pigment that connective tissue. Collagen fibers predominate. Tendons, the transports oxygen. White blood cells defend the body against cords that connect muscles to bones, and ligaments, the cables disease-causing microorganisms (discussed in Chapter 45). that connect bones to one another, consist of dense connective Platelets, small fragments broken off from large cells in the tissue in which collagen bundles are arranged in a definite pattern. bone marrow, play a key role in blood clotting. Plasma consists Elastic connective tissue consists mainly of bundles of par- of water, proteins, salts, and a variety of soluble chemical mes- allel elastic fibers. This tissue is found in structures that must sengers such as hormones that it transports from one part of expand and then return to their original size, such as lung the body to another. We discuss blood in Chapter 44. tissue and the walls of large arteries. Lymph tissue, which is important in immune functions, Reticular connective tissue is composed mainly of interlac- is a type of connective tissue with large numbers of lympho- ing reticular fibers. It forms a supporting internal framework cytes, a type of white blood cell. Lymph tissue organizes to in many organs, including the liver, spleen, and lymph nodes. form small masses of tissue called lymph nodes and larger The cells of adipose tissue store fat and release it when fuel organs, including the tonsils and spleen. We discuss lymph is needed for cellular respiration. Adipose tissue is found in the tissue further in Chapters 44 and 45. subcutaneous layer and in tissue that cushions internal organs. The supporting skeleton of a vertebrate is made of cartilage or of both cartilage and bone. Cartilage is the supporting skeleton in Muscle tissue is specialized to contract the embryonic stages of all vertebrates. In most vertebrates bone Most animals move by contracting the long, cylindrical or spindle- replaces cartilage during development. However, cartilage remains shaped cells of muscle tissue. Muscle cells are called muscle fibers in some supporting structures. In humans, for example, cartilage because of their length. Each muscle fiber contains many thin, is found in the external ear, the supporting rings in the walls of longitudinal, parallel contractile units called myofibrils. Two pro- the respiratory passageways, the tip of the nose, the ends of some teins, myosin and actin, are the chief components of myofibrils. bones, and the discs that serve as cushions between the vertebrae. Myosin and actin play a key role in contraction of muscle fibers. Cartilage is firm yet elastic. Its cells, called chondrocytes, Many invertebrates have skeletal and smooth muscle. secrete a hard, rubbery matrix that surrounds them. They ­Vertebrates have three types of muscle tissue: skeletal, cardiac, also secrete collagen fibers, which become embedded in the and smooth (TABLE 39-3 on page 830). Skeletal muscle makes matrix and strengthen it. Chondrocytes eventually come to up the large muscle masses attached to the bones of the body. lie, singly or in groups of two or four, in small cavities in the Skeletal muscle fibers are very long, and each fiber has many matrix called lacunae. These cells remain alive and are nour- nuclei. The nuclei of skeletal muscle fibers lie just under the ished by nutrients and oxygen that diffuse through the matrix. plasma membrane, which frees the entire central part of the Cartilage tissue lacks nerves, lymph vessels, and blood vessels. skeletal muscle fiber for the myofibrils. This adaptation appears Bone, the main vertebrate skeletal tissue, is like cartilage to increase the efficiency of contraction. When skeletal muscles in that it consists mostly of matrix material. The bone cells, contract, they move parts of the body. Skeletal muscle fibers are called osteocytes, are contained within lacunae. Osteocytes generally under voluntary control. In contrast, you do not nor- secrete and maintain the matrix (FIG. 39-2). Unlike cartilage, mally contract your cardiac and smooth muscle fibers at will. however, bone is a highly vascular tissue, with a substantial Light microscopy shows that both skeletal and cardiac fibers blood supply. Osteocytes communicate with one another by have alternating light and dark transverse stripes, or striations, means of their long cytoplasmic extensions. that change their relative sizes during contraction. Striated mus- A typical bone has an outer layer of compact bone surround- cle fibers contract rapidly but cannot remain contracted for a ing a filling of spongy bone. Compact bone consists of spindle- long period. They must relax and rest momentarily before con- shaped units called osteons. Within each osteon, osteocytes are tracting again. (Muscle contraction is discussed in Chapter 40.) arranged in concentric layers of matrix called lamellae. In turn, Cardiac muscle is the main tissue of the heart. When car- the lamellae surround central microscopic channels known as diac muscle contracts, the heart pumps the blood. The fibers of Haversian canals, through which capillaries and nerves pass. cardiac muscle join end to end, and they branch and rejoin to Bones are amazingly light and strong. Calcium salts of form complex networks. One or two nuclei lie within each fiber. bone render the matrix very hard, and collagen prevents A characteristic feature of cardiac muscle tissue is the presence the bony matrix from being overly brittle. Most bones have of intercalated discs, specialized junctions where the fibers join. 828 / Chapter 39 Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.  Spongy (a) The human skeleton (b) A bone cut open to bone Compact consists mainly of bone. expose its internal structure. bone Haversian Blood canal vessel (c) Blood vessels and Cytoplasmic nerves run through the Lacuna extensions Haversian canal within each osteon of compact bone. Osteon Matrix Cytoplasmic Osteocyte extensions (d) The bone matrix is rigid and hard. Osteocytes become trapped within lacunae but communicate with one another by way of cytoplasmic extensions that extend through tiny canals. Figure 39-2 Bone Smooth muscle occurs in the walls of the digestive tract, Nervous tissue controls muscles uterus, blood vessels, and many other internal organs. Contrac- and glands tion of smooth muscle is necessary for these organs to perform certain functions. For example, smooth muscle contraction in Nervous tissue consists of neurons and glial cells. Neurons the wall of the stomach and intestine moves food through the are specialized for receiving and transmitting signals. Glial digestive tract. When smooth muscle in the walls of arterioles cells support and nourish the neurons, destroy pathogens, (small arteries) contracts, these blood vessels constrict, rais- and modulate transmission of impulses (FIG. 39-3). ing blood pressure. Each s­ pindle-shaped smooth muscle fiber A typical neuron has a cell body containing the nucleus contains a single, central nucleus. as well as two types of cytoplasmic extensions (discussed in ­Chapter 41). Dendrites are cytoplasmic extensions specialized Animal Structure and Function: An Introduction / 829 Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.  Table 39-3 Muscle Tissues Skeletal Cardiac Smooth Location Attached to skeleton Walls of heart Walls of stomach, ­intestines, blood vessels, uterus Type of control Voluntary Involuntary Involuntary Shape of fibers Elongated, cylindrical, blunt ends Elongated, cylindrical, fibers that Elongated, spindle shaped, branch and fuse pointed ends Striations Present Present Absent Number of nuclei per fiber Many One or two One Position of nuclei Peripheral Central Central Speed of contraction Most rapid Intermediate (varies) Slowest Resistance to fatigue Least Intermediate Greatest (with repetitive contraction) Nuclei Striations Nuclei Nuclei Intercalated discs Skeletal muscle fibers Cardiac muscle fibers Smooth muscle fibers for receiving signals and transmitting them to the cell body. Still others transmit signals from the brain and spinal cord to The single axon transmits signals, called nerve impulses, away the muscles and glands. Neurons communicate at junctions from the cell body. Axons range in length from 1 or 2 mm called synapses. A nerve consists of a great many neurons to more than a meter. Those extending from the spinal cord bound together by connective tissue. down the arm or leg in a human, for example, may be a meter In this chapter we have focused on normal tissues. For or more in length. a discussion of some abnormal tissues, see Inquiring About: Certain neurons receive signals from the external or Unwelcome Tissues: Cancers. internal environment and transmit them to the spinal cord and brain. Other neurons relay, process, or store information. Tissues and organs make up the organ systems of the body Axon Tissues associate to form organs. Although an animal organ Nuclei of may be composed mainly of one type of tissue, other types are glial needed to support, protect, provide a blood supply, and trans- cells mit information. For example, the heart is mainly cardiac mus- Neurons cle tissue, but its chambers are lined with endothelium, and its walls contain blood vessels made of endothelium, smooth Dendrite muscle, and connective tissue. The heart also has nerves that transmit information and help regulate the rate and strength of its contractions. Ed Reschke/Getty Images An organized group of tissues and organs that together per- form a specialized set of functions make up an organ ­system. Working together in a very coordinated way, organ systems perform the functions required by the organism. We can iden- tify 11 major organ systems that work together to carry out the 100 mm physiological processes of a ­mammal: i­ ntegumentary system, skeletal system, muscular ­system, nervous ­system, ­endocrine Figure 39-3 LM of nervous tissue system, cardiovascular ­system, lymphatic ­system (which Neurons transmit information in the form of electrical and chemi- functions as the immune ­system), respiratory ­system, cal signals. Glial cells support, protect, and nourish neurons. They ­digestive system, urinary ­system, and ­reproductive system. also communicate and help regulate neural function. FIGURE 39-4 summarizes the principal organs and functions of each organ system. 830 / Chapter 39 Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Inquiring About Unwelcome Tissues: Cancers A neoplasm (“new growth”), or tumor, is an called carcinomas. This group includes breast, your risk of developing cancer by following abnormal growth of cells. A neoplasm may prostate, colon, lung cancer, and most ovarian these recommendations: be benign (“kind”) or malignant (cancerous). cancers. Cancers that develop from connective tissues or muscle are referred to as sarcomas. 1. Do not smoke or use tobacco. Smoking is A benign neoplasm tends to grow slowly, and its Death from cancer typically results from responsible for more than 80% of lung can- cells stay together. Because benign tumors form metastasis, migration of cancer cells through cer cases, and it increases the risk for many masses with distinct borders, they can typically other cancers. be removed surgically. A malignant (“wicked”) blood or lymph channels to other parts of the neoplasm, or cancer, typically grows much body. Once there, cancer cells multiply, form- 2. Avoid prolonged exposure to the sun. When more rapidly and invasively than a benign tumor. ing new malignant neoplasms that interfere in the sun, use sunscreen or sunblock. Expo- In Chapter 17 you learned that cancer with the normal functions of the tissues being sure to the sun is responsible for almost all results from abnormal expression of specific invaded. Cancer often spreads so rapidly and of the more than two million cases of skin genes critical for cell division (see Fig. 17-20). extensively that surgeons cannot locate or cancer reported each year in the United Most cancer cells divide rapidly and in an remove all the malignant masses. States alone. uncontrolled way. Unlike normal cells, which Solid tumors, which account for more than 3. Eat a healthy diet, including fresh, unpro- respect one another’s boundaries and form tis- 85% of cancer deaths, require blood vessels cessed fruits, vegetables, and grains. Limit sues in an orderly, organized manner, cancer to ensure delivery of nourishment and oxy- intake of red meat. Avoid smoked, salt- cells multiply chaotically and infiltrate normal gen. Some tumors grow to several millimeters cured, and nitrite-cured foods. Limit intake tissues. They no longer receive or respond in diameter and then enter a dormant stage, of alcoholic beverages. Reduce intake of appropriately to signals from surrounding cells; which may last for months or even years. Even- foods and drinks that contribute to weight communication is lacking (see figure). tually, cancer cells release a chemical substance gain. Obesity increases the risk of cancer. that stimulates nearby blood vessels to develop 4. Exercise. Physical inactivity has been linked new capillaries. These blood vessels grow into with increased risk of colon, breast, and the abnormal mass of cells. Nourished by its other cancers. new blood supply, the neoplasm may grow 5. Avoid unnecessary exposure to X-rays. Moredun Animal Health Ltd/Science Source rapidly. Newly formed blood vessels have 6. Self-examination and screening can lead to leaky walls that provide a route for metastasis. early diagnosis. Beginning at age 50, both Malignant cells enter the blood through these men and women should be screened for walls and are transported to new sites. colorectal cancer. Detection and removal of Worldwide, cancer causes more than seven polyps (benign growths that can become million deaths each year. In the United States, malignant) can prevent cancer. cancer is the second leading cause of death. 7. Self-examination and screening for women One in three people in the United States devel- includes examining their breasts each ops cancer at some time in his or her life. More month and having regular mammograms than 1.7 million new cancer cases are diag- after age 40. Cervical cancer can be pre- 50 mm vented with regular screening tests, such as nosed each year. Currently, the key to survival is early diagnosis and treatment with some the Papanicolaou (Pap) and human papil- combination of surgery, hormonal treatment, loma virus (HPV) tests. Certain HPV strains When cancer cells multiply, they invade