organ systems - ck-12 foundationresourcesdev.ck12.org/ddf0f23a2654d92e1d67e3de605336aa.pdf · 2010....
TRANSCRIPT
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Contents
1 The Human Body 5
1.1 Lesson 1 Organization of the Human Body . . . . . . . . . . . . . . . . . . . 5
1.2 Lesson 35.2: Homeostasis and Regulation . . . . . . . . . . . . . . . . . . . . 15
2 Skin, Bones, and Muscles 27
2.1 The Skeletal System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.2 The Muscular System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
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Chapter 1
The Human Body
Welcome to the Organ Systems Unit! We will be embarkingon a study of the human body and all the systems that allowit to function so successfully. First we’ll get a quick look atwhat an organ system is and what different systems thereare in the human body.
Here is your task: Copy the ”Levels of Organization” graphic organizer into the Notes sectionof your journal.
Then use the following section to find and fill in the appropriate information. You will havea quiz on this information next week. The section ends when you see the Stop Sign.
1.1 Lesson 1 Organization of the Human Body
Lesson Objectives
• Describe the levels of organization of the human body.• Outline the role of a specialized cell.• Identify the four tissue types found in the human body.• Summarize how tissues and organs relate to each other.• Name two body systems that work together for a common purpose.
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Introduction
In most multicellular organisms, not all cells are alike. For example, the cells that make upyour skin are different from cells that make up your liver, your blood, or your eyes. Yet,all these specialized cells develop from one single fertilized egg which means all of your cellshave the same DNA. But liver, blood, and eye cells are very different from each other in formand function. While these cells are specialized for a specific job, there are other cells in thebody that remain unspecialized. These cells multiply continuously to replace the millions ofdifferent body cells that die and need to be replaced every day.
Cells
Cells are the most basic units of life in your body. Each specialized cell has a specificfunction in the body. For example, nerve cells transmit electrical messages around the body,and white blood cells patrol the body and attack invading bacteria. Other cells includespecialized cells in the kidney (such as kidney glomerulus parietal cell), brain cells (such asastrocytes), stomach cells (such as parietal cells), and muscle cells (such as red and whiteskeletal muscle fibers). Cells group together in tissues to carry out a specific function, anddifferent tissues work together to form organs. This grouping of cells and tissues is referredto as levels of organization. Complex multicellular organisms, which include flatworms andhumans, have different levels of organization.
Differentiation
Every cell in the body originated from a single fertilized egg, which is called a zygote. Thezygote divides many times to produce an embryo. These embryonic cells differentiate intomany different cell types which in time give rise to all the cells types present in the body of allhumans (and other mammals), from a new-born baby to an elderly adult. Differentiation isthe process by which an unspecialized cell (such as a fertilized egg cell), divides many times toproduce specialized cells that work together and make up the body. During differentiation,certain genes are turned on, or become activated, while other genes are switched off, orinactivated. This process is regulated by the cell. A differentiated cell will develop specificstructures and perform certain functions.
Tissues
A tissue is a group of connected cells that have a similar function within an organism.The simplest living multicellular organisms, sponges, are made of many specialized types ofcells that work together for a common goal. Such cell types include digestive cells, tubularpore cells, and epidermal cells. Though the different cell types create a large organized,
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multicellular structure—the visible sponge—they are not organized into true tissues. If asponge is broken up by passing it through a sieve, the sponge will reform on the other side.
More complex organisms such as jellyfish, coral, and sea anemones have a tissue level oforganization. For example, jellyfish have tissues that have separate protective, digestive,and sensory functions. There are four basic types of tissue in the body of all animals,including the human body. These make up all the organs, structures and other contents ofthe body. Figure 1.2 shows an example of each tissue type.
The four basic types of tissue are:
• Epithelial tissue is made up of layers of tightly packed cells that line the surfacesof the body for protection, secretion, and absorption. Examples of epithelial tissueinclude the skin, the lining of the mouth and nose, and the lining of the digestivesystem.
• Muscle tissue is made up of cells contain contractile filaments that move past eachother and change the size of the cell. There are three types of muscle tissue: smoothmuscle which is found in the inner linings of organs; skeletal muscle, which is attachedto bone and moves the body; and cardiac muscle which is found only in the heart.
• Nervous tissue is made up of the nerve cells (neurons) that together form the nervoussystem, including the brain and spinal cord.
• Connective tissue is made up of many different types of cells that are all involved instructure and support of the body. Bone, blood, fat, and cartilage are all connectivetissues. Connective tissue can be densely packed together, as bone cells are, or looselypacked, as adipose tissue (fat cells) are.
Figure 1.1
•
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Figure 1.2: (a) Scanning electron micrograph (SEM) image of lung trachea epithelial tis-sue, (b) Transmission electron micrograph (TEM) image of skeletal muscle tissue, (c) Lightmicroscope image of neurons of nervous tissue, (d) red blood cells, a connective tissue.
Organs and Organ SystemsOrgans are the next level of organization in the body. An organ is a structure made of twoor more tissues that work together for a common purpose. Skin, the largest organ in thebody, is shown in one of the Figures 1.4. The human body has many different organs, suchas the heart, the kidneys, the pancreas, and the skin. Two or all of the tissue types can befound in an organ. Organs inside the body are called internal organs.
The most complex organisms have organ systems. An organ system is a group of organsthat act together to carry out complex interrelated functions, with each organ focusing on apart of the task. An example of an organ system is the human digestive system in which themouth and esophagus ingests food, the stomach crushes and liquefies it, the pancreas andgall bladder make and release digestive enzymes, and the intestines absorb nutrients intothe blood. An organ can be part of more than one organ system. For example the ovariesproduce hormones which make them a part of the endocrine system. The ovaries also makeeggs which makes them part of the reproductive system.
The different organ systems of the body are shown in Table 1.1. Sometimes the cardiovas-
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Figure 1.3: The image above shows some of the internal organs in a human.
Figure 1.4: Your skin is the largest organ in your body. In this cross section image of skin,the four different tissue types (epithelial, connective, nervous, and muscle tissues) can beseen working together.
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cular system and the lymphatic system are grouped together into one single system calledthe circulatory system.
Table 1.1: Major Organ Systems of the Human Body
Organ System Function Organs, Tissues, and Struc-tures Involved
Cardiovascular Transporting oxygen, nutri-ents and other substances tothe body cells, and wastes,carbon dioxide, and othersubstances away from cells;it can also help stabilizebody temperature and pH
Heart, blood, blood vessels
Lymphatic Defense against infectionand disease, transfer oflymph between tissues andthe blood stream
Lymph, lymph nodes,lymph vessels
Digestive Processing of foods and ab-sorption of nutrients, miner-als, vitamins, and water
Salivary glands, esophagus,stomach, liver, gallbladder,pancreas, small intestine,large intestine
Endocrine Communication within thebody with hormones; di-recting long-term changeover other organ systems tomaintain homeostasis
Among many, the pituitarygland, pineal gland, thyroid,parathyroid gland, adrenalglands, testes, and ovaries
Integumentary Protection from injury andfluid loss; physical defenseagainst infection by microor-ganisms; temperature con-trol
Skin, hair, and nails
Muscular Movement, support, heatproduction
Skeletal, cardiac, andsmooth muscles, tendons
Nervous Collecting, transferring andprocessing information; di-recting short-term changeover other organ systems inorder to maintain homeosta-sis
Brain, spinal cord, nerves,and sense organs (eyes, ears,tongue, skin, nose)
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Table 1.1: (continued)
Organ System Function Organs, Tissues, and Struc-tures Involved
Reproductive Production of gametes (sexcells) and sex hormones;production of offspring
Fallopian tubes, uterus,vagina, ovaries, mammaryglands, testes, vas deferens,seminal vesicles, prostate,and penis
Respiratory Delivery of air to sites wheregas exchange can occur be-tween the blood and cells(around body) or blood andair (lungs)
Mouth, nose, pharynx, lar-ynx, trachea, bronchi, lungs,and diaphragm
Skeletal Support and protection ofsoft tissues of body; move-ment at joints; production ofblood cells; mineral storage
Bones, cartilage, ligaments
Urinary Removal of excess water,salts, and waste productsfrom blood and body; con-trol of pH
Kidneys, ureters, urinarybladder, and urethra
Immune Defending against microbialpathogens (disease-causingagents) and other diseases
Leukocytes, tonsils, ade-noids, thymus, and spleen
Lesson Summary
• Not all cells are alike in a multicellular organism, but all of the cells in a multicellularorganism have the same DNA.
• Each specialized cell has a specific function in the body. Specialized cells group togetherto carry out a specific function.
• Every cell in the body originated from a single zygote. The unspecialized zygotedifferentiates to produce specialized cells that work together and make up the body.
• A tissue is a group of connected cells that have a similar function within an organism.There are four basic types of tissue in the body of all animals: connective, muscle,nervous, and epithelial.
• An organ is a structure made of two or more different types of tissue that work togetherfor a common purpose.
• An organ system is a group of organs that act together to carry out complex relatedfunctions, with each organ focusing on a part of the task.
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Figure 1.5: There are 4 levels of organization in the human body starting with cells (themost simple) and gradually increasing in complexity until it reaches an organ system.
Review Questions
1. Give three examples of specialized cells.2. List the four tissue types that are found in the human body, and give an example ofeach type.
3. These cells form the lining of the trachea. Identify the cells and the type of tissue ofwhich the ciliated cells in Figure 1.6 are a part.
4. Summarize the relationship between tissues and organs.5. Identify an organ that is part of two body systems.6. A classmate says that the lymphatic system should not be an organ system in its ownright, and is a part of the cardiovascular system. Do you agree or disagree with yourclassmate? Explain your answer by using your knowledge of organ systems.
Further Reading / Supplemental Links
• Human Anatomy ©2003 by Fredric H. Martini, Inc. and Michael J.Timmons. Pub-lished by Pearson Education, Inc.
• http://web.jjay.cuny.edu/˜acarpi/NSC/14-anatomy.htm• http://en.wikipedia.org
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Vocabularyadult stem cells Undifferentiated cells that are found within the body and that divide to
replace dying cells and damaged tissues.
cell The most basic unit of life; basic unit of structure and function in living organisms.
differentiation The process by which an unspecialized cell (such as a fertilized egg cell),divides many times to produce specialized cells that work together and make up thebody.
embryonic stem cells Stem cells found in embryos that can divide indefinitely, and spe-cialize into any cell type.
organ A structure made of two or more tissues that work together for a common purpose.
organ system A group of organs that act together to carry out complex interrelated func-tions, with each organ focusing on a part of the task.
tissue A group of connected cells that have a similar function within an organism.
Points to Consider• The smallest unit capable of carrying out life processes in your body is a single cell.Cells organize into tissues, which organize into organs. Groups of organs work togetheras organ systems. Consider how the last meal you consumed is interacting with eachlevel of organization in your body.
• Think about the advantages and disadvantages of having a body composed of manysmall cells as opposed to a single large cell.
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Figure 1.7: Lesson 1 ends here. Great work!
1.2 Lesson 35.2: Homeostasis and Regulation
Lesson Objectives
• Identify the process by which body systems are kept within certain limits.• Explain the role of feedback mechanisms in homeostasis.• Distinguish negative feedback from positive feedback.• Identify and example of two organ systems working together to maintain homeostasis.• Summarize the role of the endocrine system in homeostasis.• Outline the result of a disturbance in homeostasis of a body system.
Introduction
The human body is made up of trillions of cells that all work together for the maintenanceof the entire organism. While cells, tissues, and organs may perform very different functions,all the cells in the body are similar in their metabolic needs. Maintaining a constant internalenvironment by providing the cells with what they need to survive (oxygen, nutrients, andremoval of waste) is necessary for the well-being of individual cells and of the entire body.The many processes by which the body controls its internal environment are collectivelycalled homeostasis.
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Homeostasis
Homeostasis refers to stability, balance, or equilibrium within a cell or the body. It is anorganism’s ability to keep a constant internal environment. Homeostasis is an importantcharacteristic of living things. Keeping a stable internal environment requires constant ad-justments as conditions change inside and outside the cell. The adjusting of systems withina cell is called homeostatic regulation. Because the internal and external environments ofa cell are constantly changing, adjustments must be made continuously to stay at or nearthe set point (the normal level or range). Homeostasis can be thought of as a dynamicequilibrium rather than a constant, unchanging state.
Feedback Regulation Loops
The endocrine system plays an important role in homeostasis because hormones regulate theactivity of body cells. The release of hormones into the blood is controlled by a stimulus.For example, the stimulus either causes an increase or a decrease in the amount of hormonesecreted. Then, the response to a stimulus changes the internal conditions and may itselfbecome a new stimulus. This self-adjusting mechanism is called feedback regulation.
Feedback regulation occurs when the response to a stimulus has an effect of some kind on theoriginal stimulus. The type of response determines what the feedback is called. Negativefeedback occurs when the response to a stimulus reduces the original stimulus. Positivefeedback occurs when the response to a stimulus increases the original stimulus.
Thermoregulation: A Negative Feedback Loop
Negative feedback is the most common feedback loop in biological systems. The systemacts to reverse the direction of change. Since this tends to keep things constant, it allowsthe maintenance of homeostatic balance. For instance, when the concentration of carbondioxide in the human body increases, the lungs are signaled to increase their activity andexhale more carbon dioxide, (your breathing rate increases). Thermoregulation is anotherexample of negative feedback. When body temperature rises, receptors in the skin and thehypothalamus sense the temperature change. The temperature change (stimulus) triggersa command from the brain. This command, causes a response (the skin makes sweat andblood vessels near the skin surface dilate), which helps decrease body temperature. Figure1.8 shows how the response to a stimulus reduces the original stimulus in another of thebody’s negative feedback mechanisms.
Positive feedback is less common in biological systems. Positive feedback acts to speed up
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Figure 1.8: Control of blood glucose level is an example of negative feedback. Blood glucoseconcentration rises after a meal (the stimulus). The hormone insulin is released by thepancreas, and it speeds up the transport of glucose from the blood and into selected tissues(the response). Blood glucose concentrations then decrease, which then decreases the originalstimulus. The secretion of insulin into the blood is then decreased.
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the direction of change. An example of positive feedback is lactation (milk production). Asthe baby suckles, nerve messages from the mammary glands cause the hormone prolactin,to be secreted by the pituitary gland. The more the baby suckles, the more prolactin isreleased, which stimulates further milk production.
Not many feedback mechanisms in the body are based on positive feedback. Positive feedbackspeeds up the direction of change, which leads to increasing hormone concentration, a statethat moves further away from homeostasis.
System InteractionsEach body system contributes to the homeostasis of other systems and of the entire organism.No system of the body works in isolation and the well-being of the person depends upon thewell-being of all the interacting body systems. A disruption within one system generally hasconsequences for several additional body systems. Most of these organ systems are controlledby hormones secreted from the pituitary gland, a part of the endocrine system. Table 1.2summarizes how various body systems work together to maintain homeostasis.
Main examples of homeostasis in mammals are as follows:
• The regulation of the amounts of water and minerals in the body. This is known asosmoregulation. This happens primarily in the kidneys.
• The removal of metabolic waste. This is known as excretion. This is done by theexcretory organs such as the kidneys and lungs.
• The regulation of body temperature. This is mainly done by the skin.• The regulation of blood glucose level. This is mainly done by the liver and the insulinand glucagon secreted by the pancreas in the body.
Table 1.2: Types of Homeostatic Regulation in the Body
Homeostatic Pro-cesses
Hormones andOther Messengers
Tissues, Organs andOrgan Systems In-volved
Osmoregula-tion (also calledexcretion)
Excess water, salts,and urea expelledfrom body
Antidiuretic hor-mone (ADH),aldosterone, an-giotensin II, carbondioxide
Kidneys, urinarybladder, ureters,urethra (urinarysystem), pituitarygland (endocrinesystem), lungs(respiratory system)
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Table 1.2: (continued)
Homeostatic Pro-cesses
Hormones andOther Messengers
Tissues, Organs andOrgan Systems In-volved
Thermoregulation Sweating, shivering,dilation/constrictionof blood vessels atskin surface, insu-lation by adiposetissue, breakdownof adipose tissue toproduce heat
Nerve impulses Skeletal muscle(muscular system),nerves (nervoussystem), bloodvessels (cardiovas-cular system), skinand adipose tissue(integumentary sys-tem), hypothalamus(endocrine system)
Chemical Regu-lation (includingglucoregulation)
Release of insulinand glucagon intothe blood in re-sponse to rising andfalling blood glucoselevels, respectively;increase in breathingrate in response toincreases carbondioxide levels in theblood, and release ofcarbon dioxide intoexhaled air fromlungs, secretion oferythropoietin bykidneys to stimulateformation of redblood cells
Insulin, glucagon,cortisol, carbondioxide, nerveimpulses, erythro-poietin (EPO)
Pancreas (endocrinesystem), liver (di-gestive system);adrenal glands (en-docrine system)lungs (respiratorysystem), brain(nervous system),kidneys (urinarysystem)
Endocrine System
The endocrine system, shown in Figure 1.9, includes glands which secrete hormones into thebloodstream. Hormones are chemical messenger molecules that are made by cells in one partof the body and cause changes in cells in another part of the body. The endocrine systemregulates the metabolism and development of most body cells and body systems throughfeedback mechanisms. For example, Thyrotropin-Releasing Hormone (TRH) and Thyroid
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Stimulating Hormone (TSH) are controlled by a number of negative feedback mechanisms.The endocrine glands also release hormones that affect skin and hair color, appetite, andsecondary sex characteristics of males and females.
Figure 1.9: The endocrine system controls almost every other body system through feedbackmechanisms. Most of the mechanisms of the endocrine system are negative feedback.
The endocrine system has a regulatory effect on other organ systems in the human body. Inthe muscular system, hormones adjust muscle metabolism, energy production, and growth.In the nervous system, hormones affect neural metabolism, regulate fluid and ion concentra-tion and help with reproductive hormones that influence brain development.
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Urinary System
Toxic wastes build up in the blood as proteins and nucleic acids are broken down and usedby the body. The urinary system rids the body of these wastes. The urinary system is alsodirectly involved in maintaining proper blood volume. The kidneys also play an importantrole in maintaining the correct salt and water content of the body. External changes, such as awarm weather, that lead to excess fluid loss trigger feedback mechanisms that act to maintainthe body’s fluid content by inhibiting fluid loss. The kidneys also produce a hormone callederythropoietin, also known as EPO, which stimulates red blood cell production.
Reproductive System
The reproductive system does little for the homeostasis of the organism. The reproductivesystem relates instead to the maintenance of the species. However, sex hormones do havean effect on other body systems, and an imbalance in sex hormones can lead to variousdisorders. For example, a woman whose ovaries are removed early in life is at higher risk ofdeveloping osteoporosis, a disorder in which bones are thin and break easily. The hormoneestrogen, produced by the ovaries, is important for bone growth. Therefore, a woman whodoes not produce estrogen will have impaired bone development.
Disruption of HomeostasisMany homeostatic mechanisms keep the internal environment within certain limits (or setpoints). When the cells in your body do not work correctly, homeostatic balance is disrupted.Homeostatic imbalance may lead to a state of disease. Disease and cellular malfunction canbe caused in two basic ways: by deficiency (cells not getting all they need) or toxicity (cellsbeing poisoned by things they do not need). When homeostasis is interrupted, your body cancorrect or worsen the problem, based on certain influences. In addition to inherited (genetic)influences, there are external influences that are based on lifestyle choices and environmentalexposure. These factors together influence the body’s ability to maintain homeostatic bal-ance. The endocrine system of a person with diabetes has difficulty maintaining the correctblood glucose level. A diabetic needs to check their blood glucose levels many times duringthe day, as shown in Figure 1.10, and monitor daily sugar intake.
Internal Influences: Heredity
Genetics: Genes are sometimes turned off or on due to external factors which we have somecontrol over. Other times, little can be done to prevent the development of certain genetic
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Figure 1.10: A person with diabetes has to monitor their blood glucose carefully. Thisglucose meter analyses only a small drop of blood. For an animation of diabetes (), see
diseases and disorders. In such cases, medicines can help a person’s body regain homeostasis.An example is the metabolic disorder Type 1 diabetes, which is a disorder where the pancreasis no longer producing adequate amounts of insulin to respond to changes in a person’s bloodglucose level. Insulin replacement therapy, in conjunction with carbohydrate counting andcareful monitoring of blood glucose concentration, is a way to bring the body’s handlingof glucose back into balance. Cancer can be genetically inherited or be due to a mutationcaused by exposure to toxin such as radiation or harmful drugs. A person may also inherita predisposition to develop a disease such as heart disease. Such diseases can be delayedor prevented if the person eats nutritious food, has regular physical activity, and does notsmoke.
External Influences: Lifestyle
Nutrition: If your diet lacks certain vitamins or minerals your cells will function poorly, andyou may be at risk to develop a disease. For example, a menstruating woman with inadequatedietary intake of iron will become anemic. Hemoglobin, the molecule that enables red bloodcells to transport oxygen, requires iron. Therefore, the blood of an anemic woman will havereduced oxygen-carrying capacity. In mild cases symptoms may be vague (e.g. fatigue), butif the anemia is severe the body will try to compensate by increasing cardiac output, leadingto weakness, irregular heartbeats and in serious cases, heart failure.
Physical Activity: Physical activity is essential for proper functioning of our cells andbodies. Adequate rest and regular physical activity are examples of activities that influence
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homeostasis. Lack of sleep is related to a number of health problems such as irregularheartbeat, fatigue, anxiety, and headaches. Being overweight and obesity, two conditionsthat are related to poor nutrition and lack of physical activity greatly affect many organsystems and their homeostatic mechanisms. Being overweight or obese increases a person’srisk of developing heart disease, Type 2 diabetes, and certain forms of cancer. Staying fit byregularly taking part in aerobic activities such as walking, shown in Figure 1.11, has beenshown to help prevent many of these diseases.
Figure 1.11: Adding physical activity to your routine can be as simple as walking for a totalof 60 minutes a day, five times a week.
Mental Health: Your physical health and mental health are inseparable. Our emotionscause chemical changes in our bodies that have various effects on our thoughts and feelings.Negative stress (also called distress) can negatively affect mental health. Regular physicalactivity has been shown to improve mental and physical wellbeing, and helps people to copewith distress. Among other things, regular physical activity increases the ability of thecardiovascular system to deliver oxygen to body cells, including the brain cells. Medicationsthat may help balance the amount of certain mood-altering chemicals within the brain areoften prescribed to people who have mental and mood disorders. This is an example ofmedical help in stabilizing a disruption in homeostasis.
Environmental Exposure
Any substance that interferes with cellular function and causes cellular malfunction is acellular toxin. There are many different sources of toxins, for example, natural or synthetic
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drugs, plants, and animal bites. Air pollution, another form of environmental exposure totoxins is shown in Figure 1.12. A commonly seen example of an exposure to cellular toxinsis by a drug overdose. When a person takes too much of a drug that affects the centralnervous system, basic life functions such as breathing and heartbeat are disrupted. Suchdisruptions can results in coma, brain damage, and even death.
Figure 1.12: Air pollution can cause environmental exposure to cellular toxins such as mer-cury.
The six factors described above have their effects at the cellular level. A deficiency orlack of beneficial pathways, whether caused by an internal or external influence, will almostalways result in a harmful change in homeostasis. Too much toxicity also causes homeostaticimbalance, resulting in cellular malfunction. By removing negative health influences andproviding adequate positive health influences, your body is better able to self-regulate andself-repair, which maintains homeostasis.
Lesson Summary
• Homeostasis is an organism’s ability to maintain a stable internal environment. Home-ostasis is an important characteristic of living things. Keeping a stable internal en-vironment requires constant adjustments as conditions change inside and outside thecell.
• Feedback regulation mechanisms are important to homeostasis. Feedback regulationoccurs when the response to a stimulus has an effect of some kind on the original
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stimulus. The type of response (increase or decrease in the stimulus) determines whatthe feedback is called.
• Negative feedback occurs when the response to a stimulus reduces the original stimulus.Positive feedback occurs when the response to a stimulus increases the original stimulus.
• No system of the body works in isolation, and the well-being of a person depends uponthe well-being of all the interacting body systems. A disruption within one systemgenerally has consequences for several additional body systems.
• The homeostatic balance of most organs and organ systems is controlled by hormonessecreted from the pituitary gland, a part of the endocrine system.
• When the cells in your body do not work correctly, homeostatic balance is disrupted.Homeostatic imbalance may lead to a state of disease. Type 2 diabetes is a disease inwhich homeostasis of the blood glucose level is disturbed, leading to an imbalance thataffect many other body systems, including the cardiovascular system.
Review Questions
1. Outline the importance of homeostasis to an organism.2. How do feedback mechanisms help maintain homeostasis?3. What is the difference between negative and positive feedback?4. Identify and give an example of two organ systems working together to maintain home-ostasis.
5. Summarize the role of the endocrine system in homeostasis.6. Name two diseases that can result from an imbalance in body homeostasis.7. Why is positive feedback not an effective way of controlling hormone levels?
Further Reading / Supplemental Links
• Ostrom, K.M., Department of Nutritional Sciences, University of Connecticut, Storrs.• A review of the hormone prolactin during lactation.Prog Food Nutr Sci. 1990; 14(1):1-43.
• Anatomy and Physiology © 2002 by Elaine N. Marieb. Published by Benjamin Cum-mings.
• http://www.medscape.com/medline/abstract/2092340• http://www.cotc.edu/ebrisker/PDF%20files/49%206%20endocrine%20LECTURE.pdf• http://en.wikibooks.org/wiki/Human_Physiology• http://www.ncbi.nlm.nih.gov/About/primer/genetics_cell.html• http://www.health.gov/dietaryguidelines/• http://en.wikipedia.org
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Vocabularyhomeostasis Stability, balance, or equilibrium within the cell or a body; an organism’s
ability to keep a constant internal environment.
negative feedback Occurs when the response to a stimulus reduces the original stimulus.
positive feedback Occurs when the response to a stimulus increases the original stimulus.
Points to Consider• Negative feedback is most common feedback loop in biological systems. The systemacts to reverse the direction of change. Positive feedback is less common in biologicalsystems. The system acts to speed up the direction of change. Consider how yoursocial interactions with teachers, parents and other students may be classified as eitherpositive or negative feedback.
• When homeostasis is interrupted, your body can correct or worsen the problem, basedon certain influences. In addition to genetic influences, there are external influencesthat are based on lifestyle choices and environmental exposures. Describe how yourlifestyle may positively or negatively affect your body’s ability to maintain homeostasis
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Chapter 2
Skin, Bones, and Muscles
2.1 The Skeletal System
Welcome to our study of the SKELETAL SYSTEM. Please read the following section, definethe key terms and and answer the questions listed at the end of the section. This assignmentis due Tuesday, March 2nd. You may answer in the Notes section of your Quick WriteJournal.
Lesson Objectives
• Identify the main tissues and organs of the skeletal system.• List four functions of the skeletal system.• Describe three movable joints.• Identify two nutrients that are important for a healthy skeletal system.• Describe two skeletal system injuries.
Check Your Understanding
• What is an organ system?• What is connective tissue?
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IntroductionHow important is your skeleton? Can you imaging your body without it? You would bea wobbly pile of muscle and internal organs, and you would not be able to move aroundmuch. You will learn about these functions in this lesson. Your skeleton is important formany different things. Bones are the main organs of the skeletal system. They are madeup of living tissue. If you think you have broken a bone it’s important to visit a healthcareprofessional. A broken bone may not heal properly by itself. A sprain can be bandaged upproperly to reduce swelling and discomfort. A doctor or other healthcare professional canalso give you advice on how to manage such an injury at home.
Your SkeletonHumans are vertebrates, which are animals that have a backbone. The sturdy scaffolding ofbones and cartilage that is found inside vertebrates is called a skeleton. The adult humanskeleton has about 206 bones, some of which are named in Figure 2.1. The skeletons ofbabies and children have many more bones and more cartilage than adults have. As a childgrows, these “extra” bones grow into each other, and cartilage gradually hardens to becomebone tissue.
You may think that bones are dry and lifeless, but they are very much alive. The white, hardbones that you might see in a museum or science book, are only the hard mineral remains ofthe bone tissue. Living bones are full of life. They contain many different types of tissues.
Cartilage is found at the end of bones and is made of tough protein fibers called collagen.Cartilage creates smooth surfaces for the movement of bones that are next to each other,like the bones of the knee. Ligaments are made of tough protein fibers and connect bonesto each other. Your bones, cartilage, and ligaments make up your skeletal system.
Functions of BonesYour skeletal system gives shape and form to your body, but it is also important in otherhomeostatic functions. The main functions of the skeletal system are:
• Support The skeleton supports the body against the pull of gravity. The large bonesof the lower limbs support the trunk when standing.
• Protection The skeleton provides a framework that supports and protects the softorgans of the body. For example, the skull surrounds the brain to protect it frominjury. The bones of the rib cage help protect the heart and lungs.
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Figure 2.1: The skeletal system is made up of bones, cartilage, and ligaments. The skeletalsystem has many important functions in your body.
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• Movement Bones work together with muscles as simple mechanical lever systems tomove the body.
• Making Blood Cells Blood cells are made mostly inside certain types of bones.• Storage Bones store calcium. They contain more calcium than any other organ does.Calcium is released by the bones when blood levels of calcium drop too low. Themineral phosphorus is also stored in bones.
Structure of BonesBones are organs. Recall that organs are made up of two or more types of tissues. Bonescome in many different shapes and sizes, but they are all made of the same materials. Thetwo main types of bone tissue are compact bone and spongy bone. Compact bone makesup the dense outer layer of bones. Spongy bone is lighter and less dense than compactbone, and is found toward the center of the bone. The tough, shiny, white membrane thatcovers all surfaces of bones is called the periosteum.
Many bones also contain a soft connective tissue called bone marrow. There are twotypes of bone marrow: red marrow and yellow marrow. Red marrow makes red blood cells,platelets, and most of the white blood cells for the body (discussed in the Diseases and theBody’s Defenses chapter). Yellow marrow makes white blood cells. The bones of newbornbabies contain only red marrow. As children get older, their red marrow is replaced byyellow marrow. In adults, red marrow is found mostly in the bones of the skull, the ribs, andpelvic bones. Bone come in four main shapes. They can be long, short, flat, or irregular.Identifying a bone as long, short, flat, or irregular is based on the shape of the bone not thesize of the bone. For example, both small and large bones can be classified as long bones.The small bones in your fingers and the largest bone in your body, the femur, are long bones.The structure of a long bone is shown in Figure 2.2.
How Bones Develop and GrowYour skeleton began growing very early in your development. After only eight weeks ofgrowth from a fertilized egg, your skeleton was formed by cartilage and other connectivetissues. At this point your skeleton was quite bendy and flexible. After a few more weeksof growth, the cells that form hard bone began growing in the cartilage, and your skeletonbegan to harden. However, not all of the cartilage is replaced by bone. Cartilage remainsin many places in your body including your joints, your rib cage, your ears, and the tip of
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Figure 2.3: This diagram shows a simplified view of the Compact, Spongy and Yellow Marrowlayers of a bone. In reality, there would be blood vessels flowing through these layers as well.
your nose.
A baby is born with zones of cartilage in its bones that allow growth of the bones. Theseareas, called growth plates, allow the bones to grow longer as the child grows. When the childreaches an age of about 18 to 25 years, all of the cartilage in the growth plate is replaced bybone. This stops the bone from growing any longer.
Even though bones stop growing in length in early adulthood, they can continue to increasein thickness throughout life. This thickening can be in response to stress from increasedmuscle activity or to weight-bearing exercise.
Joints and How They Move
A joint is a point at which two or more bones meet. There are three types of joints in thebody: fixed, partly movable, and movable. Fixed joints do not allow any bone movement.Many of the joints in your skull are fixed (Figure 2.4). Partly movable joints allow only alittle movement. Your backbone has partly movable joints between the vertebrae (Figure2.5). Movable joints allow movement and provide mechanical support for the body. Jointsare a type of lever, which is a rigid object that is used to increase the mechanical force thatcan be applied to another object. Can openers and scissors are examples of levers. Jointsreduce the amount of energy that is spent moving the body around. Just imagine howdifficult it would be to walk about if you did not have knees!
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Figure 2.4: The skull has fused joints. Fused joints do not allow any movement of the bones,which protects the brain from injury.
Figure 2.5: The joints between your vertebrae (b) are partially movable.
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Movable JointsMovable joints are the most mobile joints of all. They are also the most common type ofjoint in your body. Your fingers, toes, hips, elbows, and knees all have movable joints. Thesurfaces of bones at movable joints are covered with a smooth layer of cartilage. The spacebetween the bones in a movable joint is filled with a liquid called synovial fluid. Synovialfluid is a thick, stringy fluid that looks a lot like egg white. The fluid lubricates and cushionsthe bones when they move at the joint. There are many different types of movable joints,and many different examples. Four types of movable joints are shown in Figures 2.6, 2.7and 2.8.
In a ball and socket joint the ball-shaped surface of one bone fits into the cuplike shapeof another. Examples of a ball and socket joint include the hip, shown in Figure 2.6, andthe shoulder.
Figure 2.6: Your hip joint is a ball and socket joint. The ball end of one bone fits into thesocket of another bone. These joints can move in many different directions.
In a hinge joint, the ends of the bones are shaped in a way that allows motion only in twodirections, forward and backward. Examples of hinge joints are the knees and elbows. Aknee joint is shown in Figure 2.7.
The pivot joint is formed by a process that rotates within a ring, the ring being formedpartly of bone, and partly of ligament. An example of a pivot joint is the joint between theradius and ulna that allows you to turn the palm of your hand up and down. A pivot jointis shown in Figure 2.8.
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Figure 2.7: The knee joint is a hinge joint. Like a door hinge, a hinge joint allows backwardand forward movement.
A gliding joint is a joint which allows only gliding movement. The gliding joint allows onebone to slide over the other. The gliding joint in your wrist allows you to flex your wrist.It also allows you to make very small side-to-side motions. There are also gliding joints inyour ankles.
Figure 2.8: Pivot Joint The joint at which the radius and ulna meet is a pivot joint. Move-ment at this joint allows you to flip your palm over without moving your elbow joint.
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Figure 2.9: The examples of the types of movable joints. What type of joint is the knee?Hip?
Keeping Bones and Joints HealthyJust like a houseplant depends on you taking good care of it by watering it and giving itplant food, so too does your body depend on you! You can help keep your bones and skeletalsystem healthy by eating well and getting enough exercise. Weight-bearing exercises helpkeep bones strong. Weight-bearing exercises work against gravity; such activities includebasketball, tennis, gymnastics, karate, running, and walking. When the body is exercisedregularly by doing a weight-bearing activity, bones respond by adding more bone cells makingthe bones denser.
Eating WellDid you know that what you eat now, as a teenager, can affect how healthy your skeletalsystem will be in 30, 40, and even 50 years from now? Calcium and vitamin D are twoof the most important nutrients for a healthy skeletal system. Your bones need calcium togrow properly. If you do not get enough calcium in your diet as a teenager, your bones maybecome weak and break easily later in life. Osteoporosis is a disease in which bones becomelighter and more porous than they should be. Light and porous bones are more likely tobreak, which can cause pain and prevent a person from walking. Being immobile can causemore bone loss which can make the disease worse.
Older women are most likely to develop osteoporosis because it is linked to the decreasein production of sex hormones. However, poor nutrition, especially diets that are low incalcium and vitamin D, increase the risk of osteoporosis in later life. Not doing regular
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weight-bearing exercises is also linked to having thinner, weaker bones. Two of the easiestways to prevent osteoporosis is to eat a healthful diet that has the right amount of calciumand vitamin D, and to do weight-bearing exercise day.
Foods that are a good source of calcium include: milk, yogurt, and cheese. Non-dairy sourcesof calcium include Chinese cabbage, kale, and broccoli. Many fruit juices, fruit drinks, tofu,and cereals have calcium added into them. These foods are also an important source ofcalcium.
Teenagers are recommended to get 1300 mg of calcium every day. One cup of milk providesabout 300 mg of calcium, which about 30% of your daily requirement for calcium. Othersources of calcium are shown in Figure ??.
Figure 2.10
Your skin makes vitamin D when exposed to sunlight. The pigment melanin in the skin actslike a filter that can prevent the skin from making vitamin D. As a result, people with darkerskin need more time in the sun than people with lighter skin to make the same amount ofvitamin D.
Fish is naturally rich in vitamin D. Vitamin D is added to other foods including milk, soymilk and breakfast cereals. Teenagers are recommended to get 5 micrograms (200 IU/day)of vitamin D every day. A 3 &frac;12; ounce portion of cooked salmon provides 360 IU ofvitamin D.
Lack of vitamin D, or deficiency, can be caused by two different things: not enough sunlightexposure, and lack of vitamin D in the diet. Vitamin D deficiency results in problems withbone growth and hardening. This leads to bone softening diseases such as rickets in childrenand osteomalacia in adults. Osteomalacia is a bone disease in which the bones do not hardenproperly and they can break easily. Rickets is a type of osteomalacia. An X-ray of a child thathas rickets is shown in Figure 2.11. Lack of vitamin D may also be related to osteoporosis.
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Figure 2.11: Rickets is a softening of the bones in children that may cause fractures andbending of the bones, especially of the legs. The bones have not hardened properly becauseof lack of vitamin D, and bend under the weight of the body.
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Bone FracturesEven though they are very strong, bones can fracture, or break. Fractures can happen atdifferent places on a bone. They are usually due to excess bending stress on the bone.Bending stress is what causes a pencil to break if you were to bend it too far. Soon after afracture, the body begins to repair the break. The area becomes swollen and sore. Withina few days bone cells travel to the break site and begin to rebuild the bone. It takes about2 to 3 months before compact and spongy bone form at the break site.
Sometimes the body needs extra help in repairing a broken bone. In such a case a surgeonwill piece a broken bone together with metal pins. Moving the broken pieces together willhelp keep the bone from moving, and give the body a chance to repair the break. A brokenulna has been repaired with pins in Figure 2.12.
Figure 2.12: The upper part of the ulna, at the elbow is broken, as you can see in the X-rayat left. The x-ray at right was taken after a surgeon inserted pins into the joint to keep thetwo pieces of the ulna together. The two pieces of bone were reattached with metal pins.The line of staples is closing the skin wound.
Cartilage InjuriesOsteoarthritis is a condition in which the cartilage at the ends of the bones breaks down.The break down of the cartilage leads to pain and stiffness in the joint. Decreased movementof the joint because of the pain may lead to muscles that are attached to the joint to become
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weaker, and ligaments may become looser. Osteoarthritis is the most common form ofarthritis. It has many causes, some of the more common causes include old age, sportinjuries to the joint, bone fractures, and overweight and obesity. Total hip replacement is acommon treatment for osteoarthritis.
Ligament InjuriesRecall that a ligament is a short band of tough connective tissue that connects bones togetherto form a joint. Ligaments can get injured when a joint gets twisted or bends too far. Theprotein fibers that make up a ligament can get strained or torn, causing swelling and pain.Injuries to ligaments are called sprains. Ankle sprains are a common type of sprain. Asmall ligament in the knee, called the anterior cruciform ligament (ACL), is a common siteof injury in athletes. Ligament injuries can take a long time to heal. Treatment of the injuryincludes rest and special exercises that are developed by a physical therapist.
Preventing InjuriesPreventing injuries to your bones and ligaments is easier and much less painful than treatingan injury. Wearing the correct safety equipment when doing activities that require safetyequipment can help prevent many common injuries. For example, wearing a bicycle helmetcan help prevent a skull injury if you fall. Warming up and cooling down properly can helpprevent ligament and muscle injuries. Torn ligaments and fractured bones are common sportinjuries. Such injuries need to be treated by a doctor. Overuse injuries such as ligamentstrains and tears are common injuries for teenage athletes. Correct conditioning and enoughrest can help prevent overuse injuries.
Stretching after activity may help prevent injuries. Regular stretching improves the flexibilityof muscles and tendons. It also improves the range of mobility of your joints. Stretchingcan also improve your posture, and may help prevent some aches and pains caused by tightmuscles.
Lesson Summary• Bones, cartilage, and ligaments make up the skeletal system. The skeleton supportsthe body against the pull of gravity. The skeleton provides a framework that supportsand protects the soft organs of the body. Bones work together with muscles as simplemechanical lever systems to move the body. Blood cells are made mostly inside thebone marrow. Bones store calcium.
• There are three types of joints in the body: fixed, partly movable, and movable. Fixedjoints do not allow any bone movement. Partly movable joints allow only a littlemovement. Movable joints allow movement and provide mechanical support for the
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body. Joints are a type of lever, which is a rigid object that is used to increase themechanical force that can be applied to another object. Joints reduce the amount ofenergy that is spent moving the body around. Calcium and vitamin D are two of themost important nutrients for a healthy skeletal system.
• Bones need calcium to grow properly. Vitamin D deficiency results in problems withbone growth and hardening. Osteoporosis is a disease in which bones become lighterand more porous than they should be. Light and porous bones are more likely to breakthan dense bones. Osteomalacia is a bone disease in which the bones do not hardenproperly and they can break easily. Osteoarthritis is a condition in which the cartilageat the ends of the bones breaks down. The break down of the cartilage leads to painand stiffness in the joint. A sprain is an injury to a ligament. A fracture is a break orcrack in a bone.
Review Questions1. What are the organs of the skeletal system?2. Name one tissue of the skeletal system.3. List four functions of the skeletal system.4. Name three types of movable joints and tell where they can be found in the body.5. “All joints in the body are movable.” Do you agree with this statement? Explain whyor why not. (Intermediate
6. How are the joints in your body similar to levers?7. Why is calcium important for a healthy skeletal system?8. The recommended daily amount of calcium for teenagers is 1300 mg. If a persongets only 1000 mg a day, what percentage of the recommended daily amount are theygetting?
9. Name two things you can do to keep your skeletal system healthy.10. What part of the skeletal system does osteoarthritis affect?11. Why might a doctor need to insert pins into a broken bone?
Further Reading / Supplemental Links• http://www.girlshealth.gov/bones• [http://www.cdc.gov/nccdphp/dnpa/nutrition/nutrition_for_everyone/basics/calcium.htmhttp://www.cdc.gov/nccdphp/dnpa/nutrition/nutrition_for_everyone/basics/calcium.htm
• http://en.wikipedia.org/wiki
Vocabularyball and socket joint Joint structure in which the ball-shaped surface of one bone fits
into the cuplike depression in another bone; examples include the shoulder and hip
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joints.
bone marrow Soft connective tissue found inside many bones; site of blood cell formation.
cartilage Smooth covering found at the end of bones; made of tough collagen proteinfibers; creates smooth surfaces for the easy movement of bones against each other.
compact bone The dense, hard outer layer of a bone.
fracture Bone injury, often called a ”break;” usually caused by excess bending stress onbone.
gliding joint Joint structure that allows one bone to slide over the other; examples includesthe joints in the wrists and ankles.
hinge joint Joint structure in which the ends of bones are shaped in a way that allowsmotion in two directions only (forward and backward); examples include the knees andelbows.
joint Point at which two or more bones meet.
ligaments Fibrous tissue that connects bones to other bones; made of tough collagen fibers.
movable joint Most mobile type of joint; the most common type of joint in the body.
osteoarthritis A condition in which the cartilage at the ends of the bones breaks down.
osteoporosis Disease in which bones become lighter and more porous than normal.
periosteum Tough, shiny, white membrane that covers all surfaces of bones.
pivot joint Joint structure in which the end on one bone rotates within a ring-type struc-ture which can be made partly of bone and partly of ligament; example includes thejoint between the radius and ulna.
spongy bone Lighter and less dense than compact bone; found toward the center of thebone.
sprain A ligament injury; usually caused by the sudden overstretching of a joint whichcauses tearing.
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Figure 2.13: Reading for the Skeletal System Lesson Stops Here! Great Job!
Points to Consider• How does your skeletal system interact with your muscular system?• How might a broken bone affect the functioning of the muscular system?• How do tendons differ from ligaments? How are they similar?
2.2 The Muscular System
It’s time to pump up your knowledge on muscles! Please read through this section andcomplete the Review Questions at the end in the Notes section of your Quick Write Journal.This assignment will be due on Wednesday, March 10th at the beginning of the period.
Lesson Objectives• Identify the three muscle types in the body.• Describe how skeletal muscles and bones work together to move the body.• Describe how exercise affects the muscular system.• Identify two types of injuries to the muscular system.
Check Your Understanding• What is muscle tissue?• What is the function of the muscular system?
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Introduction
The muscular system is the body system that allows us to move. You depend on manymuscles to keep you alive. Your heart, which is mostly muscle, pumps blood around yourbody. Muscles are always moving in your body. Certain muscle movements happen withoutyou thinking about them, while you can control other muscle movements. In this lesson youwill learn about the different types of muscles in your body and how your muscular systemworks with the other body systems to keep you alive and healthy. You will also learn howand why regular physical activity is important for good health.
Types of Muscles
Each muscle in the body is made up of cells called muscle fibers. Muscle fibers are long,thin cells that can do something that other cells cannot do—they are able to get shorter.Shortening of muscle fibers is called contraction. Nearly all movement in thebody is the result of muscle contraction.
You are aware of and can control certain muscle movements. Other muscle movements youare not aware of and cannot control. Muscles that you can control are called voluntarymuscles. Muscles that you cannot control are called involuntary muscles. There are threedifferent types of muscles in the body (Figure ??): skeletal, smooth, and cardiac muscle.Skeletal muscle is voluntary muscle. Smooth muscle and cardiac muscle are involuntarymuscles.
• Skeletal muscle is usually attached to the skeleton. Skeletal muscles move the body.They usually contract voluntarily, but they can contract involuntarily by reflexes. Forexample, you can choose to move your arms, but your arm would move automaticallyif you were to burn your finger on a stove top.
• Smooth muscle is found within the walls of organs and structures such as the esoph-agus, stomach, intestines, and blood vessels. Unlike skeletal muscle, smooth muscle isinvoluntary muscle which means it not under your control.
• Cardiac muscle is also an involuntary muscle but is a specialized kind of musclefound only in the heart.
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Figure 2.14: The three types of muscle are cardiac, smooth, and skeletal. Can you list whereeach is found?
Muscles, Bones, and MovementSkeletal muscles are attached to the skeleton by tendons. A tendon is a tough band ofconnective tissue that connects a muscle to a bone. (See the example of the Achilles tendonconnecting to the calf muscle in the figure below)Tendons are similar to ligaments exceptthat ligaments join bone to each other.
Figure 2.15
Muscles move the body by contracting against the skeleton. When muscles contract theyget shorter, when they relax, they get longer. By contracting and relaxing, muscles pull onbones and allow the body to move. Muscles work together in pairs. Each muscle in the pairworks against the other to move bones at the joints of the body. The muscle that contractsto cause a joint to bend is called the flexor. The muscle that contracts to cause the jointto straighten is called the extensor.
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Figure 2.16: See the difference between tendons and ligaments in this image. Be sure toknow the difference between the two.
Figure 2.17
For example, the biceps and triceps muscles work together to allow you to bend and straightenyour elbow. Your biceps muscle, shown in Figure 2.18, contracts, and at the same time thetriceps muscle relaxes. The contracting biceps pull on the radius bone and the elbow bends.To straighten the arm, the biceps muscle relaxes and the triceps on the opposite side of theelbow joint contracts. The biceps is the flexor and the triceps is the extensor of your elbowjoint. In this way the joints of your body act like levers. This lever action of your jointsreduces the amount of energy you have to spend to make large body movements.
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Figure 2.18: The biceps and triceps act against one another to bend and straighten the elbowjoint. To bend the elbow, the biceps contract and the triceps relax. To straighten the elbow,the triceps contract and the biceps relax.
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Muscles and the Nervous SystemMuscles are controlled by the nervous system (see the Controlling the Body chapter). Nervessend messages to the muscular system from the brain. Nerves also send messages to the brainfrom the muscles. Remember that smooth and cardiac muscles are involuntary muscles. Thismeans that you cannot control the nerve messages that get sent to and from these muscles.For example, you cannot make your heart muscle stop beating. Likewise, you cannot makefood stop moving through your intestines. You can however control the movement of yourskeletal muscle. When you want to move your foot, electrical messages called impulses movealong nerve cells from your brain to the muscles of your foot. At the point at which thenerve cell and muscle cells meet, the electrical message is converted to a chemical message.The muscle cells receive the chemical message, which causes tiny protein fibers inside themuscle cells to get shorter. The muscles contract, pulling on the bones, and your foot moves.
Figure 2.19: The connection between a nerve cell (neuron) and a muscle fiber.
Muscles and Exercise
Physical exercise is any activity that maintains or improves physical fitness and overallhealth. Regular physical exercise is important in preventing lifestyle diseases such as heartdisease, cardiovascular disease, Type 2 diabetes, and obesity.
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Regular exercise improves the health of the muscular system. Muscles that are exercised arebigger and stronger than muscles that are not exercised. Exercise improves both muscularstrength and muscular endurance. Muscular strength is the ability of a muscle to exertforce during a contraction. Muscular endurance is the ability of a muscle to continue tocontract over a long time without getting tired. Two types of exercises help improve thefitness of muscles, anaerobic exercise and aerobic exercise.
Exercises are grouped into three types depending on the effect they have on the body:
• Aerobic exercises such as cycling, walking, and running, increase muscular en-durance.
• Anaerobic exercises such as weight training, or sprinting increase muscle strength.• Flexibility exercises such as stretching, improve the range of motion of muscles andjoints. Regular stretching helps avoid activity-related injuries.
Anaerobic Exercise and Muscular Strength
Anaerobic exercises cause muscles to get bigger and stronger. Anaerobic exercises use aresistance against which the muscle has to work to lift or push away. The resistance can bea weight or a person’s own body weight, as shown in Figure 2.20. As a result of repeatedmuscle contractions, muscle fibers build up larger energy stores and the muscle tissue getsbigger. The larger a muscle is the greater the force it can apply to lift a weight or move abody joint. The muscles of weight lifters are large, and are therefore strong.
Figure 2.20: Anaerobic exercises involve the muscles working against resistance. In this casethe resistance is the persons own body weight.
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Aerobic Exercise and Muscular Endurance
Aerobic exercises are exercises that cause your heart to beat faster and allow your musclesto use oxygen to contract. Aerobic exercise causes many different changes in skeletal muscle.Muscle energy stores are increased, the ability to use oxygen improves, and more capillariessurround the muscle fibers. These changes result in the ability of the muscle to avoid gettingtired, and to use oxygen and food more efficiently. Aerobic exercise also helps improvecardiac muscle. It results in the heart being able to pump a larger volume of blood witheach beat due to an increase in the size of the heart’s ventricles. Examples of an aerobicexercise are shown in Figure 2.21.
Figure 2.21: When done regularly, aerobic activities such as cycling, make the heart stronger.
Both aerobic and anaerobic exercises also improve the ability of the heart to pump bloodaround the body. Aerobic exercise causes the heart to get bigger, and anaerobic exercisecauses the walls of the heart to get thicker. These changes allow the heart to push moreblood throughout the body with every heartbeat.
Keeping Muscles Healthy
Being physically active for 60 minutes a day for at least five days a week improves yourphysical fitness. Being physically active can also help you to reduce your risk of developingdiseases such as cardiovascular disease, Type 2 diabetes, obesity, and certain forms of cancer.Being physically active does not mean you have to do boring workouts. You do not haveto join a gym or be in a sports team to be physically active. Physical activities can includeeveryday things such as walking your dog, vacuuming or sweeping, cycling to school, skating,or climbing a flight of stairs (Figure 2.22).
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Figure 2.22: Adding more physical activity in your daily life does not mean boring or ex-pensive activities, it can be fun! Local and community pools often run swim classes that donot cost a lot, and are designed for beginners.
Muscle InjuriesSometimes muscles and tendons get injured when a person starts doing an activity beforethey have warmed up properly. A warm up is a slow increase in the intensity of a physicalactivity that prepares muscles for an activity. Warming up increases the blood flow to themuscles and increases the heart rate. Warmed-up muscles and tendons are less likely to getinjured. For example, before running or playing soccer, a person might jog slowly to warmmuscles and increase their heart rate. It is important that warm ups prepare the musclesthat are to be used in the activity. Even elite athletes need to warm up, as shown in Figure2.23. Some injuries are caused by overuse. An overuse injury happens if the muscle or jointis not rested enough between activities.
A strain is an injury to a muscle in which the muscle fibers tear because the muscle contractstoo much or contracts before the muscle is warmed up. Strains are also known as pulledmuscles. Overuse injuries often involve tendons. Overuse of tendons can cause tiny tearswithin the protein fibers of the tendon, which gradually weakens the tissue. These tiny tearslead to swelling, pain, and stiffness; a condition called tendinitis. Tendinitis can affect anytendon that is overused. Strains and tendinitis are usually treated with rest, cold compresses,and stretching exercises that a physical therapist designs for each patient.
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Figure 2.23: Warming up before the game helps the players avoid injuries. Some warm-upsmay include stretching exercises. Some researchers believe stretching before activities mayhelp prevent injury.
Proper rest and recovery are also as important to health as exercise is. If you do not getenough rest, your body will become injured and will not improve or react well to exercise.It is important to remember to allow enough recovery time for muscles and tendons to restbetween exercise sessions. You can rest muscles by doing a different activity to what younormally do. For example, if you run, you can rest your running muscles and joints byswimming. This type of rest is called active rest.
Anabolic steroids are hormones that cause the body to build up more protein in its cells.Muscle cells, which contain a lot of protein, get bigger when exposed to anabolic steroids.Your body naturally makes small amounts of anabolic steroids. They help your body repairfrom injury, and help to build bones and muscles. Anabolic steroids are used as medicines totreat people that have illnesses that affect muscle and bone growth. However, some peoplewho do not need anabolic steroid as medicine try to increase their muscle size by taking thesesteroids. When taken in this way, anabolic steroids can have long-term affects other bodysystems. They can damage the person’s kidneys, heart, liver, and reproductive system. Iftaken by adolescents, anabolic steroids can cause bones to stop growing, resulting in stuntedgrowth. (Want to learn more about the effects of steroid use?? Check out this article fromKidsHealth.org ”Are Steroids Worth the Risk?”
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Lesson Summary
• The body has three types of muscle tissue: skeletal, cardiac, and smooth. Musclesmove the body by contracting against the skeleton. Muscles are controlled by thenervous system.
• Nerves send messages to the muscular system from the brain. Nerves also send messagesto the brain from the muscles. Regular exercise improves the health of the muscularsystem. Muscles that are exercised are bigger and stronger than muscles that are notexercised.
• Exercise improves both muscular strength and muscular endurance. Muscular strengthis the ability of a muscle to exert force during a contraction. Muscular endurance isthe ability of a muscle to continue to contract over a long time without getting tired.Identify two types of injuries to the muscular system.
• A strain is an injury to a muscle in which the muscle fibers tear because the musclecontracts too much or contracts before the muscle is warmed up. Tiny tears andswelling in a tendon results in tendinitis.
Review Questions
1. Name the three types of muscle tissue in the body.2. Which of the three types of muscles in the body are voluntary?3. What is another name for muscle cells?4. Describe how skeletal muscles and bones work together to move the body. (Be sure touse the terms flexor and extensor)
5. What is a tendon?6. How does aerobic exercise affect the heart?7. How does aerobic exercise affect skeletal muscle?8. How does anaerobic exercise affect skeletal muscle?9. What is a muscle strain?10. Why is warming up before exercise a good idea?11. Why are taking anabolic steroids a dangerous way to try to build up muscles?
Further Reading / Supplemental Links
• http://www.hmc.psu.edu/healthinfo/m/musclestrain.htm• http://www.cdc.gov/nccdphp/dnpa/physical/everyone/index.htm• http://en.wiki.org
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Vocabularyaerobic exercises Types of exercises that cause the heart to beat faster and allow the
muscles to obtain energy to contract by using oxygen.
anabolic steroids Hormones that cause the body to build up more protein in its cells.
anaerobic exercise Types of exercises that involve short bursts of high-intensity activity;forces the muscles to obtain energy to contract without using oxygen.
cardiac muscle An involuntary and specialized kind of muscle found only in the heart.
contraction Shortening of muscle fibers.
extensor The muscle that contracts to cause a joint to straighten.
flexibility exercises Stretching exercises that improve the range of motion of muscles andjoints.
flexor The muscle that contracts to cause a joint to bend.
involuntary muscle A muscle that a person cannot consciously control; cardiac muscleand smooth muscle are involuntary.
muscle cells Long, thin cells that can contract; also called muscle fibers.
muscle fibers Long, thin cells that can contract; also called muscle cells.
muscular endurance The ability of a muscle to continue to contract over a long timewithout getting tired.
muscular strength The ability of a muscle to exert force during a contraction.
muscular system The body system that allows movement.
physical exercise Any activity that maintains or improves physical fitness and overallhealth.
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physical fitness The ability of your body to carry out your daily activities without gettingout of breath, sore, or overly tired.
skeletal muscle The muscle that is usually attached to the skeleton.
smooth muscle Involuntary muscle found within the walls of organs and structures suchas the esophagus, stomach, intestines, and blood vessels.
strain An injury to a muscle in which the muscle fibers tear because the muscle contractstoo much or contracts before the muscle is warmed up.
tendinitis A condition in which tiny tears form in the protein fibers of the tendon andgradually weaken the tissue.
tendon A tough band of connective tissue that connects a muscle to a bone.
voluntary muscle A muscle that a person can consciously control; skeletal muscle is vol-untary.
warm-up A slow increase in the intensity of a physical activity that prepares muscles foran activity.
Points to Consider• How does your muscular system depend on your digestive system?• How does what you choose to eat affect your muscular system and your skeletal system?
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