Seeley's Essentials of Anatomy & Physiology Tenth Edition PDF
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Summary
This is a textbook on human anatomy and physiology. It covers the structure and function of the human body at different levels, including chemical, cellular, tissue, and organ system levels. The book describes systemic and regional approaches to the study of anatomy and how organ systems work together to maintain homeostasis.
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# **Seeley's Essentials of Anatomy & Physiology, Tenth Edition** This International Student Edition is for use outside of the U.S. ## **1.1 Anatomy** **Learning Outcomes:** After reading this section, you should be able to: - Define anatomy and describe the levels at which anatomy can be studied....
# **Seeley's Essentials of Anatomy & Physiology, Tenth Edition** This International Student Edition is for use outside of the U.S. ## **1.1 Anatomy** **Learning Outcomes:** After reading this section, you should be able to: - Define anatomy and describe the levels at which anatomy can be studied. - Explain the importance of the relationship between structure and function. Human anatomy and physiology is the study of the structure and function of the human body. The human body has many intricate parts with coordinated functions maintained by a complex system of checks and balances. The coordinated function of all the parts of the human body allows us to interact with our surroundings by adjusting how the body responds to changes in environmental information. This information comes from inside and outside the body. These changes serve as stimuli. Knowing human anatomy and physiology also provides the basis for understanding disease. The study of human anatomy and physiology is important for students who plan a career in the health sciences because health professionals need a sound knowledge of structure and function in order to perform their duties. In addition, understanding anatomy and physiology helps us to be well prepared to make a decision about our own health care or that of a loved one. It also can allow us to distinguish between useful medical treatments and those that may be harmful. **Anatomy** is the scientific discipline that investigates the structure of the body. The word anatomy means to dissect, or cut apart and separate, the parts of the body for study. Anatomy covers a wide range of studies, including the structure of body parts, their microscopic organization, and the processes by which they develop. In addition, anatomy examines the relationship between the structure of a body part and its function. Just as the structure of a hammer makes it well suited for pounding nails, the structure of body parts allows them to perform specific functions effectively. For example, bones can provide strength and support because bone cells secrete a hard, mineralized substance. Understanding the relationship between structure and function makes it easier to understand and appreciate anatomy. Two basic approaches to the study of anatomy are systemic anatomy and regional anatomy. **Systemic anatomy** is the study of the body by systems, such as the cardiovascular, nervous, skeletal, and muscular systems. It is the approach taken in this and most introductory textbooks. **Regional anatomy** is the study of the organization of the body by areas. Within each region, such as the head, abdomen, or arm, all systems are studied simultaneously. This is the approach taken in most medical and dental schools. Anatomists have two general ways to examine the internal structures of a living person: surface anatomy and anatomical imaging. **Surface anatomy** is the study of external features, such as bony projections, which serve as landmarks for locating deeper structures. **Anatomical imaging** involves the use of x-rays, ultrasound, magnetic resonance imaging, and other technologies to create pictures of internal structures, such as when determining if a bone is broken or a ligament is torn. Both surface anatomy and anatomical imaging provide important information for diagnosing disease. ## **1.2 Physiology** **Learning Outcomes:** After reading this section, you should be able to: - Define physiology. - State two major goals of physiology. **Physiology** is the scientific discipline that deals with the processes or functions of living things. It is important in physiology to recognize structures as dynamic rather than fixed and unchanging. The major goals for studying physiology are: - to understand and predict the body's responses to stimuli - to understand how the body maintains internal conditions within a narrow range of values in the presence of continually changing internal and external environments. **Human physiology** is the study of a specific organism, the human, whereas **cellular physiology** and **systemic physiology** are subdivisions that emphasize specific organizational levels. ## **1.3 Structural and Functional Organization of the Human Body** **Learning Outcomes:** After reading this section, you should be able to: - Describe the six levels of organization of the body, and describe the major characteristics of each level. - List the eleven organ systems, identify their components, and describe the major functions of each system. The body can be studied at six structural levels: - **Chemical:** Atoms combine to form molecules. - **Cell:** Molecules form organelles which make up cells. - **Tissue:** Similar cells and surrounding materials make up tissues. - **Organ:** Different tissues combine to form organs. - **Organ system:** Organs make up an organ system. - **Organism:** Organ systems make up an organism. The structural and functional characteristics of all organisms are determined by their chemical makeup. The **chemical level** of organization involves how atoms, such as hydrogen and carbon, interact and combine into molecules. This is important because a molecule's structure determines its function. For example, collagen molecules are strong, ropelike fibers that give skin structural strength and flexibility. With old age, the structure of collagen changes, and the skin becomes fragile and more easily torn during everyday activities. A brief overview of chemistry is presented in chapter 2. **Cells** are the basic structural and functional units of organisms. Molecules can combine to form **organelles**, which are the small structures that make up some cells. For example, the nucleus contains the cell's hereditary information, and mitochondria manufacture adenosine triphosphate, a molecule cells use for a source of energy. Although cell types differ in their structure and function, they have many characteristics in common. Knowledge of these characteristics and their variations is essential to a basic understanding of anatomy and physiology. The cell is discussed in chapter 3. A **tissue** is a group of similar cells and the materials surrounding them. The characteristics of the cells and surrounding materials determine the functions of the tissue. The many tissues that make up the body are classified into four primary types: - epithelial - connective - muscle - nervous. Tissues are discussed in chapter 4. An **organ** is composed of two or more tissue types that together perform one or more common functions. Examples of some of our organs include the heart, stomach, liver, and urinary bladder. An **organ system** is a group of organs classified as a unit because of a common function or set of functions. For example, the urinary system consists of the kidneys, ureters, urinary bladder, and urethra. The kidneys produce urine, which is transported by the ureters to the urinary bladder, where it is stored until eliminated from the body by passing through the urethra. In this text, we consider eleven major organ systems: - integumentary - skeletal - muscular - nervous - endocrine - cardiovascular - lymphatic - respiratory - digestive - urinary - reproductive. The coordinated activity of the organ systems is necessary for normal function. For example, the digestive system takes in food, processing it into nutrients that are carried by the blood of the cardiovascular system to the cells of the other systems. These cells use the nutrients and produce waste products that are carried by the blood to the kidneys of the urinary system, which removes waste products from the blood. Because the organ systems are so interrelated, dysfunction in one organ system can have profound effects on other systems. For example, a heart attack can result in inadequate circulation of blood. Consequently, the organs of other systems, such as the brain and kidneys, can malfunction. An **organism** is any living thing considered as a whole, whether composed of one cell, such as a bacterium, or of trillions of cells, such as a human. The human organism is a complex of organ systems that are mutually dependent upon one another. ## **1.4 Characteristics of Life** **Learning Outcome:** After reading this section, you should be able to: - List and define six characteristics of life. Humans are organisms sharing characteristics with other organisms. The most important common feature of all organisms is life. This text recognizes six essential characteristics of life: 1. **Organization:** refers to the specific relationship of the many individual parts of an organism, from cell organelles to organs, interacting and working together. Living things are highly organized. All organisms are composed of one or more cells. Some cells, in turn, are composed of highly specialized organelles, which depend on the precise functions of large molecules. Disruption of this organized state can result in loss of function and death. 2. **Metabolism:** is the ability to use energy to perform vital functions, such as growth, movement, and reproduction. Plants capture energy from sunlight to synthesize sugars (a process called photosynthesis), and humans obtain energy from food. 3. **Responsiveness:** is the ability of an organism to sense changes in the environment and make the adjustments that help maintain its life. Examples of responses are movements toward food or water and away from danger or poor environmental conditions such as extreme cold or heat. Organisms can also make adjustments that maintain their internal environment. For example, if body temperature increases in a hot environment, sweat glands produce sweat, which can lower body temperature down to the normal level. 4. **Growth:** refers to an increase in size of all or part of the organism. It can result from an increase in cell number, cell size, or the amount of substance surrounding cells. For example, bones grow when the number of bone cells increases and the bone cells become surrounded by bone matrix. 5. **Development:** includes the changes an organism undergoes through time. Human development begins when the egg is fertilized by the sperm and ends with death. The greatest developmental changes occur before birth, but many changes continue after birth, and some continue throughout life. Development usually involves growth, but it also involves differentiation. **Differentiation** is change in cell structure and function from generalized to specialized. For example, following fertilization, cells start to specialize to become different cell types, such as skin, bone, muscle, or nerve cells. These differentiated cells form tissues and organs. 6. **Reproduction:** is the formation of new cells or new organisms. Without reproduction of cells, growth and tissue repair are impossible. Without reproduction of the organism, the species becomes extinct. ## **1.5 Homeostasis** **Learning Outcomes:** After reading this section, you should be able to: - Define homeostasis, and explain why it is important for proper body function. - Describe a negative-feedback mechanism and give an example. - Describe a positive-feedback mechanism and give an example. **Homeostasis** is the existence and maintenance of a relatively constant environment within the body despite fluctuations in either the external environment or the internal environment. Most body cells are surrounded by a small amount of fluid, and normal cell functions depend on the maintenance of the cells' fluid environment within a narrow range of conditions, including temperature, volume, and chemical content. These conditions are called **variables** because their values can change. One familiar variable is body temperature, which can increase when the environment is hot or decrease when the environment is cold. **Homeostatic mechanisms**, such as sweating or shivering, normally maintain body temperature near an average normal value, or **set point**. Most homeostatic mechanisms are governed by the nervous system or the endocrine system. Note that homeostatic mechanisms are not able to maintain body temperature precisely at the set point. Instead, body temperature increases and decreases slightly around the set point, producing a **normal range** of values. As long as body temperatures remain within this normal range, homeostasis is maintained. These changes are actually fairly minimal. Note that the normal body temperature range is not more than 1°F above or below normal. Our average body temperature is 98.6°F. The organ systems help control the internal environment so that it remains relatively constant. For example, the digestive, respiratory, cardiovascular, and urinary systems function together so that each cell in the body receives adequate oxygen and nutrients and so that waste products do not accumulate to a toxic level. If the fluid surrounding cells deviates from homeostasis, the cells do not function normally and may even die. Disease disrupts homeostasis and sometimes results in death. Modern medicine attempts to understand disturbances in homeostasis and works to reestablish a normal range of values. ## **Negative Feedback** Most systems of the body are regulated by **negative-feedback mechanisms**, which maintain homeostasis. In everyday terms, the word negative is used to mean "bad" or "undesirable." In this context, negative means "to decrease." Negative feedback is when any deviation from the set point is made smaller or is resisted. Negative feedback does not prevent variation but maintains variation within a normal range. The maintenance of normal body temperature is an example of a negative-feedback mechanism. Normal body temperature is important because it allows molecules and enzymes to keep their normal shape so they can function optimally. An optimal body temperature prevents molecules from being permanently destroyed. Picture the change in appearance of egg whites as they are cooked; a similar phenomenon can happen to molecules in our body if the temperature becomes too high. Thus, normal body temperature is required to ensure that tissue homeostasis is maintained. Most negative-feedback mechanisms, such as the one that maintains normal body temperature, have three components: 1. A **receptor** monitors the value of a variable, such as body temperature, by detecting stimuli. 2. A **control center**, such as part of the brain, determines the set point for the variable and receives input from the receptor about the variable. 3. An **effector** can change the value of the variable when directed by the control center. A changed variable is a stimulus because it initiates a homeostatic mechanism. Normal body temperature depends on the coordination of multiple structures, which are regulated by the control center, or hypothalamus, in the brain. If body temperature rises, sweat glands (the effectors) produce sweat and the body cools. If body temperature falls, sweat glands do not produce sweat. The stepwise process that regulates body temperature involves the interaction of receptors, the control center, and effectors. Often, there is more than one effector and the control center must integrate them. In the case of elevated body temperature, thermoreceptors in the skin and hypothalamus detect the increase in temperature and send the information to the hypothalamus control center. In turn, the hypothalamus stimulates blood vessels in the skin to relax and sweat glands to produce sweat, which sends more blood to the body's surface for radiation of heat away from the body. The sweat glands and skin blood vessels are the effectors in this scenario. Once body temperature returns to normal, the control center signals the sweat glands to reduce sweat production and the blood vessels constrict to their normal diameter. On the other hand, if body temperature drops, the control center does not stimulate the sweat glands. Instead, the skin blood vessels constrict more than normal and blood is directed to deeper regions of the body, conserving heat in the interior of the body. In addition, the hypothalamus stimulates shivering, quick cycles of skeletal muscle contractions, which generates a great amount of heat. Again, once the body temperature returns to normal, the effectors stop. In both cases, the effectors do not produce their responses indefinitely and are controlled by negative feedback. Negative feedback acts to return the variable to its normal range. ## **Positive Feedback** Positive-feedback mechanisms occur when the initial stimulus further stimulates the response. In other words, positive means that the deviation from the set point becomes even greater. In this case, the word "positive" indicates an increase. At times, this type of response is required to re-achieve homeostasis. For example, during blood loss, a chemical responsible for clot formation stimulates production of itself. In this way, a disruption in homeostasis is resolved through a positive-feedback mechanism. What prevents the entire vascular system from clotting? The clot formation process is self-limiting. Eventually, the components needed to form a clot will be depleted in the damaged area and more clot material cannot be formed. Birth is another example of a normally occurring positive-feedback mechanism. Near the end of pregnancy, the uterus is stretched by the baby's large size. This stretching, especially around the opening of the uterus, stimulates contractions of the uterine muscles. The uterine contractions push the baby against the opening of the uterus, stretching it further. This stimulates additional contractions, which result in additional stretching. This positive-feedback sequence ends when the baby is delivered from the uterus and the stretching stimulus is eliminated. On the other hand, occasionally a positive-feedback mechanism can be detrimental instead of helpful. One example of a detrimental positive-feedback mechanism is inadequate delivery of blood to cardiac muscle. Contraction of cardiac muscle generates blood pressure and moves blood through the blood vessels to the tissues. A system of blood vessels on the outside of the heart provides cardiac muscle with a blood supply sufficient to allow normal contractions to occur. In effect, the heart pumps blood to itself. Just as with other tissues, blood pressure must be maintained to ensure adequate delivery of blood to the cardiac muscle. Following extreme blood loss, blood pressure decreases to the point that the delivery of blood to cardiac muscle is inadequate. As a result, cardiac muscle homeostasis is disrupted, and cardiac muscle does not function normally. The heart pumps less blood, which causes the blood pressure to drop even lower. The additional decrease in blood pressure further reduces blood delivery to cardiac muscle, and the heart pumps even less blood, which again decreases the blood pressure. The process continues until the blood pressure is too low to sustain the cardiac muscle, the heart stops beating, and death results. Following a moderate amount of blood loss (e.g., after donating a pint of blood), negative-feedback mechanisms result in an increase in heart rate that restores blood pressure. However, if blood loss is severe, negative-feedback mechanisms may not be able to maintain homeostasis, and the positive-feedback effect of an ever-decreasing blood pressure can develop. A basic principle to remember is that many disease states result from the failure of negative-feedback mechanisms to maintain homeostasis. The purpose of medical therapy is to overcome illness by aiding negative-feedback mechanisms. For example, a transfusion can reverse a constantly decreasing blood pressure and restore homeostasis. ## **1.6 Terminology and the Body Plan** **Learning Outcomes:** After reading this section, you should be able to: - Describe a person in anatomical position. - Define the directional terms for the human body, and use them to locate specific body structures. - Know the terms for the parts and regions of the body. - Name and describe the three major planes of the body and the body organs. - Describe the major trunk cavities and their divisions. - Describe the serous membranes, their locations, and their functions. When you begin to study anatomy and physiology, the number of new words may seem overwhelming. Learning is easier and more interesting if you pay attention to the origin, or **etymology**, of new words. Most of the terms are derived from Latin or Greek. For example, anterior in Latin means "to go before." Therefore, the anterior surface of the body is the one that "goes before" when we are walking. Words are often modified by adding a prefix or suffix. For example, the suffix -itis means an inflammation, so appendicitis is an inflammation of the appendix. As new terms are introduced in this text, their meanings are often explained. The glossary and the list of word roots, prefixes, and suffixes also provide additional information about the new terms. ### **Body Positions** The **anatomical position** refers to a person standing upright with the face directed forward, the upper limbs hanging to the sides, and the palms of the hands facing forward A person is **supine** when lying face upward and **prone** when lying face downward. The position of the body can affect the description of body parts relative to each other. In the anatomical position, the elbow is above the hand, but in the supine or prone position, the elbow and hand are at the same level. To avoid confusion, relational descriptions are always based on the anatomical position, no matter the actual position of the body. ### **Directional Terms** Directional terms describe parts of the body relative to each other. It is important to become familiar with these directional terms as soon as possible because you will see them repeatedly throughout the text. * **Right** and **Left** are used as directional terms in anatomical terminology. * **Superior** is used for above, or up, and **inferior** is used for below, or down. * **Anterior** is used for front, and **posterior** is used for back. * **Dorsal** means toward the back (synonymous with posterior) * **Ventral** means toward the belly (synonymous with anterior) * **Proximal** means closer to a point of attachment * **Distal** means farther from a point of attachment * **Lateral** means away from the midline of the body * **Medial** means toward the middle or midline of the body * **Superficial** means toward or on the surface * **Deep** means away from the surface, internal ### **Body Parts and Regions** Health professionals use a number of terms when referring to different regions or parts of the body. The central region of the body consists of the head, neck, and trunk. The trunk can be divided into the **thorax** (chest), **abdomen** (belly), and **pelvis** (hips). The **upper limb** is divided into the **arm**, **forearm**, **wrist**, and **hand**. The arm extends from the shoulder to the elbow, and the forearm extends from the elbow to the wrist. The **lower limb** is divided into the **thigh**, **leg**, **ankle**, and **foot**. The thigh extends from the hip to the knee, and the leg extends from the knee to the ankle. Note that, contrary to popular usage, the terms arm and leg refer to only a part of the respective limb. The **abdomen** is often subdivided superficially into four sections, or **quadrants**, by two imaginary lines-one horizontal and one vertical-that intersect at the navel The quadrants formed are the right-upper, left-upper, right-lower, and left-lower quadrants. In addition to these quadrants, the abdomen is sometimes subdivided into **regions** by four imaginary lines - two horizontal and two vertical. - These four lines create an imaginary tic-tac-toe figure on the abdomen, resulting in nine regions: - epigastric (ep-i-gas'trik) - right and left hypochondriac (hi-pō-kon'drē-ak) - umbilical (ŭm-bil'i-kål) - right and left lumbar (lŭm'bar) - hypogastric (hī-pō-gas'trik) - right and left iliac (il'e-ak) Clinicians use the quadrants or regions as reference points for locating the underlying organs. For example, the appendix is in the right-lower quadrant, and the pain of an acute appendicitis is usually felt there. Pain in the epigastric region is sometimes due to gastroesophageal reflux disease (GERD), in which stomach acid improperly moves into the esophagus, damaging and irritating its lining. Epigastric pain, however, can have many causes and should be evaluated by a physician. For example, gallstones, stomach or small intestine ulcers, inflammation of the pancreas, and heart disease can also cause epigastric pain. ### **Planes** At times, it is conceptually useful to discuss the body in reference to a series of planes (imaginary flat surfaces) passing through it. Sectioning the body is a way to "look inside" and observe the body's structures. A **sagittal plane** runs vertically through the body and separates it into right and left parts. The word sagittal literally means the flight of an arrow and refers to the way the body would be split by an arrow passing anteriorly to posteriorly. A **median plane** is a sagittal plane that passes through the midline of the body, dividing it into equal right and left halves. A **transverse plane**, or **horizontal plane**, runs parallel to the surface of the ground, dividing the body into superior and inferior parts. A **frontal plane**, or **coronal plane**, runs vertically from right to left and divides the body into anterior and posterior parts. Organs are often sectioned to reveal their internal structure. A cut along the length of the organ is a **longitudinal section**. A **transverse section**, or **cross section**, cuts completely through an organ, similar to cutting a hot dog or banana into round pieces. If a cut is made diagonally across the long axis, it is called an **oblique section**. ### **Body Cavities** The body contains many cavities. Some of these cavities, such as the nasal cavity, open to the outside of the body, and some do not. The trunk contains three large cavities that do not open to the outside of the body: - the **thoracic cavity** - the **abdominal cavity** - the **pelvic cavity** The **thoracic cavity** is surrounded by the rib cage and is separated from the abdominal cavity by the muscular diaphragm. It is divided into right and left parts by a center structure called the **mediastinum**. The mediastinum is a section that houses the heart, the thymus, the trachea, the esophagus, and other structures. The mediastinum is between the two lungs, which are located on each side of the thoracic cavity. The **abdominal cavity** is bounded primarily by the abdominal muscles and contains the stomach, the intestines, the liver, the spleen, the pancreas, and the kidneys. The **pelvic cavity** is a small space enclosed by the bones of the pelvis and contains the urinary bladder, part of the large intestine, and the internal reproductive organs. The abdominal and pelvic cavities are not physically separated and sometimes are called the **abdominopelvic cavity**. ### **Serous Membranes** Serous membranes line the trunk cavities and cover the organs of these cavities. To understand the relationship between serous membranes and an organ, imagine your fist as an organ. Now imagine pushing your fist into an inflated balloon, which represents the cavity membranes. The part of the balloon in contact with your fist (the inner balloon wall) represents the **visceral** (organ) serous membrane, and the outer part of the balloon wall represents the **parietal** (wall) serous membrane. The cavity, or space, between the visceral and parietal serous membranes is normally filled with a thin, lubricating film of serous fluid produced by the membranes. As an organ rubs against another organ or against the body wall, the serous fluid and smooth serous membranes reduce friction. The thoracic cavity contains three serous membrane-lined cavities: - a **pericardial cavity** - two **pleural cavities** The **pericardial cavity** surrounds the heart. The **visceral pericardium** covers the heart. The **parietal pericardium** forms the outer layer of the sac around the heart. The fluid-filled pericardial cavity is the space between the visceral pericardium and the parietal pericardium. The fluid filling the pericardial cavity is called **pericardial fluid**. A **pleural cavity** surrounds each lung. Each lung is covered by **visceral pleura**. **Parietal pleura** lines the inner surface of the thoracic wall, the lateral surfaces of the mediastinum, and the superior surface of the diaphragm. The pleural cavity is located between the visceral pleura and the parietal pleura and contains **pleural fluid**. The abdominopelvic cavity contains a serous membrane-lined cavity called the **peritoneal cavity**. **Visceral peritoneum** covers many of the organs of the abdominopelvic cavity. **Parietal peritoneum** lines the wall of the abdominopelvic cavity and the inferior surface of the diaphragm. The peritoneal cavity is located between the visceral peritoneum and the parietal peritoneum and contains **peritoneal fluid**. The serous membranes can become inflamed-usually as a result of an infection. **Pericarditis** is inflammation of the pericardium, **pleurisy** is inflammation of the pleura, and **peritonitis** is inflammation of the peritoneum. One form of peritonitis occurs when the appendix ruptures as a result of appendicitis. Appendicitis is an inflammation of the appendix that is usually caused by a bacterial infection. The appendix is a small sac attached to the large intestine with a layer of visceral peritoneum. An infection of the appendix can rupture its wall, releasing bacteria into the peritoneal cavity and causing peritonitis. **Mesenteries**, which consist of two layers of peritoneum fused together, connect the visceral peritoneum of some abdominopelvic organs to the parietal peritoneum on the body wall or to the visceral peritoneum of other abdominopelvic organs. The mesenteries anchor the organs to the body wall and provide a pathway for nerves and blood vessels to reach the organs. Other abdominopelvic organs are more closely attached to the body wall and do not have mesenteries. Parietal peritoneum covers these other organs, which are said to be **retroperitoneal**. Retroperitoneal organs include the kidneys, the adrenal glands, a portion of the pancreas, parts of the intestines, and the urinary bladder.