Infectious diseases can be spread in countless ways: through food, water, insects, or by touching or breathing a contagious element. For instance, microbes can be transmitted in a day care on toys that are handled by many children and caregivers, in a restaurant with unsanitary kitchen tools, or on a public transportation vehicle when one passenger coughs or sneezes. One of the common concerns of public health officials is how to limit the spread of infectious disease by informing, motivating, and providing resources to the general population.
In this Discussion, you analyze factors that impact the spread of an infectious disease. You consider how public health officials could address different methods by which the disease is spread. Also, you identify social and ethical issues that might arise when trying to address the methods and provide recommendations for managing those issues.
To prepare for this Discussion,
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- Review this week’s Learning Resources on communicable diseases and the factors involved in the cycle of infectious diseases.
- Select an infectious disease of interest to you.
- Identify methods by which the disease you selected is spread, and consider how these methods could be limited or addressed.
- Reflect on the social and ethical issues that public health officials might face when trying to address the spread of the disease, and consider how those issues could be managed.
post a brief description of the infectious disease you selected. Describe at least two methods by which your disease could be spread. Then, explain how those methods could be limited or addressed, including any social or ethical issues that might arise. Finally, provide recommendations for public health officials trying to manage those issues or challenges.
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The words organ and system were discussed in Chapter 1 as having special meanings when applied to the body. An organ is a structure made up of two or more kinds of tissues organized in such a way that the tissues can together perform a more complex function than can any tissue alone. A system is a group of organs arranged in such a way that they can together perform a more complex function than can any organ alone. This chapter gives an overview of the 11 major organ systems of the body. In the chapters that follow, the presentation of information on individual organs and an explanation of how they work together to accomplish complex body functions will form the basis for the discussion of each organ system. For example, a detailed description of the skin as the primary organ of the integumentary system will be covered in Chapter 5, and information on the bones of the body as organs of the skeletal system will be presented in Chapter 6. Knowledge of individual organs and how they are organized into groups makes much more meaningful the understanding of how a particular organ system functions as a unit in the body. Recent discoveries coupled with intensive ongoing research efforts have allowed scientists to identify, isolate, and then culture primitive cells called adult and embryonic stem cells in the laboratory. So called adult stem cells are obtained from tissues, such as bone marrow or the cornea of the eye, taken from either a cadaver or living adult donor. STUDY TIPS Chapter 4 is the perfect “big picture” chapter. It is a preview for most of the remaining chapters in the text. 1. Put the name of the system on one side of a fl ash card and the function of that system and its organs on the other side. Notice how each organ contributes to the function of the system. 2. In your study groups, go over the fl ash cards. Discuss how several systems need to be involved in accomplishing one function in the body, such as getting food or oxygen to the cells. 3. Go over the questions in the back of the chapter and discuss possible test questions. 4. Before you begin the chapter dealing with a particular system, it would be helpful to get an overview of that system by reviewing the synopsis of that system in this chapter. 79 80 Chapter 4 Organ Systems of the Body They generally produce cells similar to the tissue type they were isolated from and have only a limited ability to produce other specifi c cell types. Using complex research methods, embryonic stem cells, which are obtained from a developing embryo, can be “directed” to produce many different cell types such as muscle, nerve, and various types of glandular tissue. Stem cell research has produced exciting and complex advances in biology that will have a profound impact on human health. Although many scientifi c and ethical questions remain unanswered, the potential now exists for cell, tissue, and organ “engineering” that may well permit repair or total replacement of diseased or damaged organs in a functioning organ system. When you have completed your study of the major organ systems in the chapters that follow, it will be possible to view the body not as an assembly of individual parts but as an integrated and functioning whole. This chapter names the systems of the body and the major organs that compose them, and it briefl y describes the functions of each system. It is intended to provide a basic “road map” to help you anticipate and prepare for the more detailed information that follows in the remainder of the text. ORGAN SYSTEMS OF THE BODY In contrast to cells, which are the smallest structural units of the body, organ systems are its largest and most complex structural units.
The 11 major organ systems that compose the human body are listed here. 1. Integumentary 2. Skeletal 3. Muscular 4. Nervous 5. Endocrine 6. Cardiovascular (circulatory) 7. Lymphatic 8. Respiratory 9. Digestive 10. Urinary 11. Reproductive a. Male subdivision b. Female subdivision Examine Figure 4-1 to fi nd a diagrammatic listing of the body systems and the major organs in each. In addition to the information contained in Figure 4-1, each system is presented in visual form in Figures 4-2 through 4-13. Visual presentation of material is often useful in gaining an understanding of the interrelationships that are so important in anatomy and physiology. For a brief 3D tour of each of the body’s organ systems, go to AnimationDirect on your CD-ROM. Integumentary System Note in Figure 4-2 that the skin is the largest and most important organ in the integumentary (in-tegyoo-MEN-tar-ee) system. Its weight in most adults is 20 pounds or more, accounting for about 16% of total body weight and making it the body’s heaviest organ. The integumentary system includes the skin and its accessory structures, which include the hair, nails, and specialized sweat- and oil-producing glands. In addition, a number of microscopic and highly specialized sense organs are embedded in the skin. They permit the body to respond to various stimuli such as pain, pressure, touch, and changes in temperature.
The integumentary system is crucial to survival. Its primary function is protection. The skin protects underlying tissue against invasion by harmful bacteria, bars entry of most chemicals, and minimizes the chances of mechanical injury to underlying structures. In addition, the skin regulates body temperature by sweating, synthesizes important chemicals, and functions as a sophisticated sense organ. Skeletal System The sternum or breastbone, the humerus, and the femur shown in Figure 4-3 are examples of the 206 individual organs (bones) found in the skeletal system. The system includes not only bones but also related tissues such as cartilage and ligaments that Chapter 4 Organ Systems of the Body 81 Skin Hair Nails Sense receptors Sweat glands Oil glands Respiratory system Nose Pharynx Larynx Trachea Bronchi Lungs Digestive system PRIMARY ORGANS Mouth Pharynx Esophagus Stomach Small intestine Large intestine Rectum Anal canal ACCESSORY ORGANS Teeth Salivary glands Tongue Liver Gallbladder Pancreas Appendix Skeletal system Bones Joints Muscular system Muscles Cardiovascular system Heart Blood vessels Lymphatic system Lymph nodes Lymph vessels Thymus Spleen Tonsils Nervous system Brain Spinal cord Nerves Urinary system Kidneys Ureters Urinary bladder Urethra Endocrine system Pituitary gland Pineal gland Hypothalamus Thyroid gland Parathyroid Thymus Adrenals Pancreas (islet tissue) Ovaries (female) Testes (male) Reproductive system MALES Gonads Testes Genital ducts Ductus (vas) deferens Urethra Accessory organs Prostate Genitalia Penis Scrotum FEMALES Gonads Ovaries Accessory organs Uterus Uterine (fallopian) tubes Vagina Genitalia Vulva Mammary glands (breasts) Integumentary system FIGURE 4-1 Body systems and their organs. 82 Chapter 4 Organ Systems of the Body FIGURE 4-3 Skeletal system. S L I R Femur Sternum Humerus FIGURE 4-2 Integumentary system. S L I R Nails Hair Skin Chapter 4 Organ Systems of the Body 83 together provide the body with a rigid framework for support and protection. In addition, the skeletal system, through the existence of joints between bones, makes possible the movements of body parts. Without joints, we could make no movements; our bodies would be rigid, immobile hulks. Bones also serve as storage areas for important minerals such as calcium and phosphorus. The formation of blood cells in the red marrow of certain bones is another crucial function of the skeletal system.
Muscular System Individual skeletal muscles are the organs of the muscular system. Muscles not only produce movement and maintain body posture but also generate the heat required for maintaining a constant core body temperature. The skeletal muscles are called voluntary, or striated, muscles because their contractions are under conscious control and their individual cells appear striated when viewed with a microscope. In addition to the skeletal or voluntary muscles that constitute the muscular system, two other important types of muscle tissue are found in the body. Involuntary, or smooth, muscle tissue is found in blood vessel walls, other tubular structures, and in the lining of hollow organs such as the stomach and small intestine. Cardiac muscle is the specialized type of involuntary muscle tissue of the heart. By contracting, it pumps blood into the vessels of the circulatory system. The tendon labeled in Figure 4-4 represents how tendons attach muscles to bones. When stimulated by a nervous impulse, muscle tissue shortens or contracts. Voluntary movement occurs when skeletal muscles contract because of the way muscles are attached to bones and the way bones articulate or join together with one another in joints. Contraction of smooth muscle in blood vessel walls helps maintain blood pressure. In the digestive tube, contraction of smooth muscle propels food through the system and then moves undigested residue from the body. Nervous System The brain, spinal cord, and nerves are the organs of the nervous system. As you can see in Figure 4-5, nerves extend from the brain and spinal cord to every area of the body. The extensive networking FIGURE 4-4 Muscular system. Tendon Muscle S L I R 84 Chapter 4 Organ Systems of the Body of the components of the nervous system makes it possible for this complex system to perform its primary functions. These include the following: 1. Communication between body functions 2. Integration of body functions 3. Control of body functions 4. Recognition of sensory stimuli These functions are accomplished by specialized signals called nerve impulses. In general, the functions of the nervous system result in rapid activity that lasts usually for a short duration. For example, we can chew our food normally, walk, and perform coordinated muscular movements only if our nervous system functions properly. The nerve impulse permits the rapid and precise control of diverse body functions. Other types of nerve impulses cause glands to secrete fl uids. In addition, elements of the nervous system can recognize certain stimuli (STIMyoo-lye), such as heat, light, pressure, or temperature, that affect the body. When stimulated, these specialized components of the nervous system, called sense organs (discussed in Chapter 9), generate nervous impulses that travel to the brain or spinal cord where analysis or relay occurs and, if needed, appropriate action is initiated.
Endocrine System The endocrine system is composed of specialized glands and cells that secrete chemicals known as hormones directly into the blood. Sometimes called ductless glands, the organs of the endocrine system perform the same general functions as the nervous system: communication, integration, and control. The nervous system provides rapid, brief control by way of fast-traveling nerve impulses. The endocrine system provides slower but longer-lasting control by hormone secretion; for example, secretion of growth hormone controls the rate of development over long periods of gradual growth. In addition to controlling growth, hormones are the main regulators of metabolism, reproduction, and other body activities. They play important roles in fl uid and electrolyte balance, acid-base balance, and energy metabolism. As you can see in Figure 4-6, the endocrine glands are widely distributed throughout the body. The pituitary (pi-TOO-i-tair-ee) gland, pineal (PINee-al) gland, and hypothalamus (hye-poh-THALah-muss) are located in the skull. The thyroid (THYFIGURE 4-5 Nervous system. S L I R Nerves Brain Spinal cord Chapter 4 Organ Systems of the Body 85 QUICK royd) and parathyroid (PAIR-ah-THY-royd) glands are in the neck, and the thymus (THY-muss) gland is in the thoracic cavity, specifi cally in the mediastinum (see Figure 1-4, p. 8). The adrenal (ah-DREEnal) glands and pancreas (PAN-kree-as), which also serves as an accessory organ of digestion, are found in the abdominal cavity. Note in Figure 4-6 that the ovaries in the female and the testes in the male also function as endocrine glands. They secrete the sex hormones that stimulate the development of the secondary sexual characteristics, including the beard in men and maturation of breasts in adolescent girls.
Cardiovascular (Circulatory) System The cardiovascular, or circulatory, system consists of the heart, which is a muscular pumping device as shown in Figure 4-7, and a closed system of blood vessels made up of arteries, veins, and capillaries. As the name implies, blood contained in this system is pumped by the heart around a closed circle or circuit of vessels as it passes through the body. The primary function of the circulatory system is transportation. The need for an effi cient transportation system in the body is critical. Transportation needs include continuous movement of oxygen and carbon dioxide, nutrients, hormones, and other important substances. Wastes produced by the cells are released into the bloodstream on an ongoing basis and are transported by the blood to the excretory organs. The circulatory system also helps regulate body temperature by distributing heat throughout the body and by assisting in retaining or releasing heat from the body by regulating blood fl ow near the body surface. Certain cells of the circulatory system also can become involved in the defense of the body or immunity.
Lymphatic System The lymphatic system is composed of lymph nodes, lymphatic vessels, and specialized lymphatic organs such as the tonsils, thymus, and spleen. Note that the thymus in Figure 4-8 functions as an endocrine gland and as a lymphatic gland. Instead of containing blood, the lymphatic vessels are fi lled with lymph, a whitish, watery fl uid that contains lymphocytes, proteins, and some fatty molecules. No red blood cells are present. The lymph is formed from the fl uid around the body cells and diffuses into the lymph vessels. However, unlike blood, lymph does not circulate repeatedly through a closed circuit or loop of vessels. Instead, lymph fl owing through lymphatic vessels eventually enters the circulatory system by passing through large ducts, including the thoracic duct shown in Figure 4-8, which in turn connect with veins in the upper area of the thoracic cavity. Collections of lymph nodes can be seen in the axillary (armpit) and in the inguinal (groin) areas of the body in Figure 4-8. The formation and movement of lymph are discussed in Chapter 13. The functions of the lymphatic system include movement of fl uids and certain large molecules from the tissue spaces around the cells and movement of fat-related nutrients from the digestive tract back to the blood. The lymphatic system is also involved in the functioning of the immune system, which plays a critical role in the defense mechanism of the body against disease. Respiratory System The organs of the respiratory system include the nose, pharynx (FAIR-inks), larynx (LAIR-inks), trachea (TRAY-kee-ah), bronchi (BRONG-kye), and lungs (Figure 4-9). Together these organs permit the movement of air into the tiny, thinwalled sacs of the lungs called alveoli (al-VEEoh-lye). In the alveoli, oxygen from the air is exchanged for the waste product carbon dioxide, which is carried to the lungs by the blood so that it can be eliminated from the body. The organs of the respiratory system perform a number of functions in addition to permitting movement of air into the alveoli. For example, if you live in a cold or dry environment, incoming air can be warmed and humidifi ed as it passes over the linFIGURE 4-7 Cardiovascular (circulatory) system. S L I R Veins Heart Arteries Chapter 4 Organ Systems of the Body 87 FIGURE 4-8 Lymphatic system. S L I R Spleen Thymus Thoracic duct Lymph vessels Bone marrow Lymph node FIGURE 4-9 Respiratory system. S L I R Bronchi Trachea (wind pipe) Lungs Pharynx (throat) Oral cavity Nasal cavity Larynx (voice box) 88 Chapter 4 Organ Systems of the Body ing of the respiratory air passages. In addition, inhaled irritants such as pollen or dust passing through the respiratory tubes can be trapped in the sticky mucus that covers the lining of many respiratory passages and then eliminated from the body. The respiratory system is also involved in regulating the acid-base balance of the body— a function that is discussed in Chapter 19.
Digestive System The organs of the digestive system (Figure 4-10) are often separated into two groups: the primary organs and the secondary or accessory organs (see Figure 4-1). They work together to ensure proper digestion and absorption of nutrients. The primary organs include the mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anal canal. The accessory organs of digestion include the teeth, salivary glands, tongue, liver, gallbladder, pancreas, and appendix . The primary organs of the digestive system form a tube, open at both ends, called the gastrointestinal (GAS-troh-in-TESS-tih-nul) or GI tract. Food that enters the tract is digested, its nutrients are absorbed, and the undigested residue is eliminated from the body as waste material called feces (FEE-seez). The accessory organs assist in the mechanical or chemical breakdown of ingested food. The appendix, although classifi ed as an accessory organ of digestion and physically attached to the digestive tube, is not functionally important in the digestive process. However, in- fl ammation of the appendix, called appendicitis (ah-pen-di-SYE-tis) is a very serious clinical condition and often requires surgery.
Urinary System The organs of the urinary system include the kidneys, ureters (YOOR-eh-terz), bladder, and urethra (yoo-REE-thrah). The kidneys (Figure 4-11) “clear” or clean the blood of the waste products continually produced by the metabolism of nutrients in the body cells. The kidneys also play an important role in maintaining the electrolyte, water, and acid-base balances in the body.
Reproductive Systems The normal function of the reproductive system is different from the normal function of other organ systems of the body. The proper functioning of the reproductive systems ensures survival, not of the individual but of the species—the human race. In addition, production of the hormones that permit the development of sexual characteristics occurs as a result of normal reproductive system activity. Male Reproductive System The male reproductive structures shown in Figure 4-12 include the gonads (GO-nadz), called testes (TES-teez), which produce the sex cells or sperm; one of the important genital ducts, called the vas deferens (vas DEF-er-enz); and the prostate (PROSStayt), which is classifi ed as an accessory organ in the male. The penis (PEE-nis) and scrotum (SKROHtum) are supporting structures and together are known as the genitalia (jen-i-TAIL-yah). The urethra, which is identifi ed in Figure 4-11 as part of the urinary system, passes through the penis. It serves as a genital duct that carries sperm to the exterior and also as a passageway for the elimination of urine. Functioning together, these structures produce, transfer, and ultimately introduce sperm into the female reproductive tract, where fertilization can occur. Sperm produced by the testes travel through a number of genital ducts, including the vas deferens, to exit the body. The prostate and other accessory organs, which add fl uid and nutrients to the sex cells as they pass through the ducts and the supporting structures (especially the penis), permit transfer of sex cells into the female reproductive tract. Female Reproductive System The female gonads are the ovaries. The accessory organs shown in Figure 4-13 include the uterus (YOO-ter-us), uterine (YOO-ter-in), or fallopian, tubes, and the vagina (vah-JYE-nah). In the female the term vulva (VUL-vah) is used to describe the external genitalia. The breasts, or mammary glands, are also classifi ed as external accessory sex organs in the female. The reproductive organs in the female produce the sex cells, known as ova; receive the male sex cells (sperm); transfer the sex cells to the uterus; permit fertilization; and allow for the development, birth, and nourishment of offspring