Contents UNIT ONE UNIT TWO Mechanisms of Disease Alterations in Body Defenses 1 Cell Structure and Function 1 7 Stress and Adaptation 121 Edward W. Carroll Mary Pat Kunert Functional Components of the Cell 2 Homeostasis 122 Cell Metabolism and Energy Sources 7 Stress 123 Cell Membrane Transport, Signal Transduction, Disorders of the Stress Response 128 and Generation of Membrane Potentials 9 8 The Immune Response 134 Body Tissues 14 Cynthia V. Sommer 2 Tissue Adaptation and Injury 24 The Immune System 134 Developmental Aspects of the Immune System 148 Cellular Adaptation 24 Cell Injury and Death 27 9 Inflammation, Tissue Repair, and Fever 150 3 Genetic Control of Cell Function 36 Cynthia V. Sommer, Carol M. Porth Edward W. Carroll The Inflammatory Response 150 Genetic Control of Cell Function 36 Tissue Repair and Wound Healing 157 Chromosomes 41 Temperature Regulation and Fever 161 Patterns of Inheritance 44 Gene Mapping and Technology 46 10 Alterations in the Immune Response 168 4 Genetic and Congenital Disorders 50 Carol M. Porth, Kathleen Sweeney Genetic and Chromosomal Disorders 50 Allergic and Hypersensitivity Disorders 168 Disorders Due to Environmental Influences 58 Transplantation Immunopathology 174 Autoimmune Disorders 175 5 Alterations in Cell Growth Immunodeficiency Disorders 178 and Replication: Neoplasia 64 UNIT THREE Kathryn Ann Caudell Concepts of Cell Growth 64 Alterations in the Hematologic System Characteristics of Benign and Malignant Neoplasms 67 11 Alterations in White Blood Cells 191 Carcinogenesis and Causes of Cancer 72 Kathryn Ann Caudell, Kathryn J. Gaspard Clinical Features 77 Hematopoietic and Lymphoid Tissue 191 Childhood Cancers 81 Non-neoplastic Disorders of White Blood Cells 194 Neoplastic Disorders of Hematopoietic 6 Alterations in Fluids, Electrolytes, and Lymphoid Origin 197 and Acid-Base Balance 84 12 Alterations in Hemostasis Composition and Compartmental Distribution of Body Fluids 84 and Blood Coagulation 205 Sodium and Water Balance 90 Kathryn J. Gaspard Potassium Balance 99 Mechanisms of Hemostasis 205 Calcium and Magnesium Balance 103 Hypercoagulability States 209 Acid-Base Balance 108 Bleeding Disorders 210 xix xx Contents 13 Alterations in Red Blood Cells 216 21 Alterations in Respiratory Function: Kathryn J. Gaspard Disorders of Gas Exchange 376 The Red Blood Cell 216 Disorders of Lung Inflation 376 Anemia 220 Obstructive Airway Disorders 380 Polycythemia 227 Interstitial Lung Diseases 390 Age-Related Changes in Red Blood Cells 227 Pulmonary Vascular Disorders 392 Respiratory Failure 395 UNIT FOUR Alterations in the Cardiovascular System UNIT SIX Alterations in the Urinary System 14 Structure and Function of the Cardiovascular System 231 22 Control of Kidney Function 401 Organization of the Circulatory System 232 Kidney Structure and Function 402 Principles of Blood Flow 233 Tests of Renal Function 412 The Heart as a Pump 236 Blood Vessels and the Peripheral Circulation 246 23 Alterations in Renal Function 415 Neural Control of Circulatory Function 251 Congenital and Hereditary Disorders of the Kidney 415 Obstructive Disorders 417 15 Alterations in Blood Flow 254 Urinary Tract Infections 421 Disorders of the Arterial Circulation 254 Disorders of Glomerular Function 425 Disorders of the Venous Circulation 266 Tubulointerstitial Disorders 429 Disorders of Blood Flow Caused by Neoplasms 430 Extravascular Forces 269 24 Renal Failure 433 16 Alterations in Blood Pressure 274 Acute Renal Failure 433 Control of Blood Pressure 274 Chronic Renal Failure 436 Hypertension 279 Renal Failure in Children and Elderly Persons 443 Orthostatic Hypotension 287 25 Alterations in Urine Elimination 446 17 Alterations in Cardiac Function 291 Control of Urine Elimination 446 Disorders of the Pericardium 291 Alterations in Bladder Function 449 Coronary Heart Disease 294 Cancer of the Bladder 456 Myocardial and Endocardial Disease 302 Valvular Heart Disease 308 UNIT SEVEN Heart Disease in Infants and Children 312 Alterations in the 18 Heart Failure and Circulatory Shock 320 Gastrointestinal System Candace Hennessy, Carol M. Porth Heart Failure 320 26 Structure and Function of Circulatory Failure (Shock) 330 the Gastrointestinal System 459 Heart Failure in Children and the Elderly 336 Structure and Organization of the Gastrointestinal Tract 460 UNIT FIVE Innervation and Motility 463 Alterations in the Respiratory System Hormonal and Secretory Function 466 Digestion and Absorption 468 Anorexia, Nausea, and Vomiting 471 19 Structure and Function of the Respiratory System 339 27 Alterations in Gastrointestinal Structural Organization of the Respiratory System 340 Function 473 Exchange of Gases Between the Atmosphere Disorders of the Esophagus 473 and the Lungs 344 Disorders of the Stomach 476 Exchange and Transport of Gases 351 Disorders of the Small and Large Intestines 480 Control of Breathing 356 20 Alterations in Respiratory Function: Infectious Disorders and Neoplasia 359 Respiratory Tract Infections 359 Cancer of the Lung 367 Respiratory Disorders in Infants and Children 369 Contents xxi 28 Alterations in Hepatobiliary 35 Sexually Transmitted Diseases 627 Function 494 Patricia McCowen Mehring The Liver and Hepatobiliary System 494 Infections of the External Genitalia 627 Disorders of the Liver 500 Vaginal Infections 630 Disorders of the Gallbladder and Extrahepatic Vaginal-Urogenital-Systemic Infections 632 Bile Ducts 510 Disorders of the Exocrine Pancreas 513 UNIT TEN Alterations in the Nervous System 29 Alterations in Body Nutrition 517 Joan Pleuss 36 Organization and Control of Regulation of Food Intake and Energy Metabolism 517 Overnutrition and Obesity 521 the Nervous System 637 Undernutrition 524 Edward W. Carroll, Robin L. Curtis Nervous Tissue Cells 637 Nerve Cell Communication 641 UNIT EIGHT Development and Organization of Alterations in the Endocrine System the Nervous System 644 The Spinal Cord and Brain 651 30 Organization and Control of The Autonomic Nervous System 660 the Endocrine System 529 37 Alterations in Brain Function 667 Glenn Matfin, Safak Guven, Julie A. Kuenzi The Endocrine System 529 Diane Book Brain Injury 668 31 Alterations in Pituitary, Thyroid, Cerebrovascular Disease 679 Parathyroid, and Adrenal Function 538 Infections and Neoplasms 685 Seizure Disorders 688 Glenn Matfin, Safak Guven, Julie A. Kuenzi Dementias 691 General Aspects of Altered Endocrine Function 538 Pituitary and Growth Hormone Disorders 539 38 Alterations in Neuromuscular Thyroid Disorders 545 Parathyroid Hormone Disorders 551 Function 696 Disorders of Adrenal Cortical Function 552 Carol M. Porth, Robin L. Curtis The Organization and Control of Motor Function 696 32 Diabetes Mellitus 560 Skeletal Muscle and Peripheral Nerve Disorders 702 Safak Guven, Julie A. Kuenzi, Glenn Matfin Basal Ganglia and Cerebellum Disorders 709 Energy Metabolism 560 Upper and Lower Motoneuron Disorders 713 Diabetes Mellitus 565 Spinal Cord Injury 716 39 Pain 725 UNIT NINE Elizabeth C. Devine Alterations in the Male and Female Organization and Control of Reproductive Systems Somatosensory Function 725 Pain 731 33 Alterations in the Male Alterations in Pain Sensitivity and Special Types Reproductive System 581 of Pain 739 Headache 741 Physiologic Basis of Male Reproductive Function 581 Pain in Children and Older Adults 744 Disorders of the Penis, the Scrotum and Testes, and the Prostate 587 40 Alterations in Special Sensory Disorders in Childhood and Aging Changes 597 Function 747 34 Alterations in the Female Edward W. Carroll, Susan A. Fontana Reproductive System 602 The Eye and Disorders of Vision 747 The Ear and Disorders of Auditory Function 763 Patricia McCowen Mehring The Vestibular System and Maintenance Structure and Function of the Female of Equilibrium 772 Reproductive System 602 Disorders of the Female Reproductive Organs 607 Menstrual Disorders 619 Disorders of the Breast 622 xxii Contents 44 Alterations in Skin Function UNIT ELEVEN Alterations in the Skeletal and Integrity 835 and Integumentary Systems Gladys Simandl Structure of the Skin 835 Manifestations of Skin Disorders 839 41 Structure and Function of Skin Damage Caused by Ultraviolet Radiation 841 the Skeletal System 779 Primary Disorders of the Skin 842 Characteristics of Skeletal Tissue 779 Nevi and Skin Cancers 853 Skeletal Structures 785 Age-Related Skin Manifestations 857 42 Alterations in the Skeletal System: Trauma, Infection, and Glossary 863 Developmental Disorders 789 APPENDIX A: Lab Values 873 Kathleen E. Gunta Injury and Trauma of Musculoskeletal Structures 789 Bone Infections 799 APPENDIX B: Weblinks 875 Neoplasms 802 Index 879 Disorders of Skeletal Growth and Development in Children 805 43 Alterations in the Skeletal System: Metabolic and Rheumatoid Disorders 814 Debra Bancroft Rizzo, Kathleen E. Gunta Metabolic Bone Disease 814 Rheumatic Disorders 820 Rheumatic Diseases in Children and the Elderly 832 UNIT One Mechanisms of Disease CHAPTER 1 Cell Structure and Function Signal Transduction and Cell Communication Functional Components of the Cell Cell Membrane Receptors The Nucleus Messenger-Mediated Control of Nuclear Function The Cytoplasm and Its Organelles Membrane Potentials Ribosomes Electrical Potentials Endoplasmic Reticulum Action Potentials Golgi Complex Body Tissues Lysosomes and Peroxisomes Cell Differentiation Mitochondria Embryonic Origin of Tissue Types The Cytoskeleton Epithelial Tissue Microtubules Simple Epithelium Microfilaments Stratified and Pseudostratified Epithelium The Cell Membrane Glandular Epithelium Cell Metabolism and Energy Sources Connective or Supportive Tissues Anaerobic Metabolism Loose Connective Tissue Aerobic Metabolism Dense Connective Tissue Cell Membrane Transport, Signal Transduction, Muscle Tissue and Generation of Membrane Potentials Skeletal Muscle Movement Across the Cell Membrane Smooth Muscle Passive Movement Cell Junctions and Cell-to-Cell Adhesion Active Transport and Cotransport Endocytosis and Exocytosis Ion Channels The cell is the smallest functional unit that an organism can be divided into and retain the characteristics neces- sary for life. Cells with similar embryonic origin or func- tion are often organized into larger functional units called tis- sues.These tissues in turn combine to form the various body structures and organs. Although the cells of different tissues 1 2 Unit One: Mechanisms of Disease and organs vary in structure and function, certain characteris- proteins, glycoproteins, and lipoproteins. Lipids comprise tics are common to all cells. Cells are remarkably similar in 2% to 3% of most cells. The most important lipids are the their ability to exchange materials with their immediate envi- phospholipids and cholesterol, which are mainly insoluble in ronment, obtaining energy from organic nutrients, synthesiz- water; they combine with proteins to form the cell membrane ing complex molecules, and replicating themselves. Because and the membranous barriers that separate different cell com- most disease processes are initiated at the cellular level, an un- partments. Some cells also contain large quantities of triglyc- derstanding of cell function is crucial to understanding the dis- erides. In the fat cells, triglycerides can constitute up to 95% of ease process. Some diseases affect the cells of a single organ, the total cell mass. The fat stored in these cells represents stored others affect the cells of a particular tissue type, and still others energy, which can be mobilized and used wherever it is needed affect the cells of the entire organism. in the body. Few carbohydrates are found in the cell, and these are used primarily for fuel. Potassium, magnesium, phosphate, sulfate, and bicarbonate ions are the major intracellular elec- FUNCTIONAL COMPONENTS trolytes. Small quantities of sodium, chloride, and calcium OF THE CELL ions are also present in the cell. These electrolytes facilitate the generation and transmission of electrochemical impulses in Although diverse in their organization, all eukaryotic cells nerve and muscle cells. Intracellular electrolytes participate in (cells with a true nucleus) have in common structures that per- reactions that are necessary for cellular metabolism. form unique functions. When seen under a light microscope, three major components of the eukaryotic cell become evident: The Nucleus the nucleus, the cytoplasm, and the cell membrane (Fig. 1-1). The internal matrix of the cell is called protoplasm. Proto- The nucleus of the cell appears as a rounded or elongated struc- plasm is composed of water, proteins, lipids, carbohydrates, ture situated near the center of the cell (see Fig. 1-1). It is en- and electrolytes. Water makes up 70% to 85% of the cell’s closed in a nuclear membrane and contains chromatin and a protoplasm. The second most abundant constituents (10% to distinct region called the nucleolus.All eukaryotic cells have at 20%) of protoplasm are the cell proteins, which form cell struc- least one nucleus (prokaryotic cells, such as bacteria, lack a nu- tures and the enzymes necessary for cellular reactions. Proteins cleus and nuclear membrane). The nucleus is the control cen- can also be found complexed to other compounds as nucleo- ter for the cell. It contains deoxyribonucleic acid (DNA) that is Cilia Microvilli Secretory vesicles Nuclear pores Mitochondrion Golgi apparatus Nucleolus Free Nuclear envelope ribosomes surrounding nucleus Peroxisome Rough endoplasmic Microtubule reticulum Lysosome Cell membrane ■FIGURE 1-1■ Composite cell Chromatin designed to show in one cell all of Smooth the various components of the endoplasmic reticulum nucleus and cytoplasm. Chapter 1: Cell Structure and Function 3 membrane contains many structurally complex circular pores KEY CONCEPTS where the two membranes fuse to form a gap. Many classes of THE FUNCTIONAL ORGANIZATION molecules, including fluids, electrolytes, RNA, some proteins, OF THE CELL and perhaps some hormones, can move in both directions through the nuclear pores. ■ Cells are the smallest functional unit of the body. They contain structures that are strikingly similar to The Cytoplasm and Its Organelles those needed to maintain total body function. The cytoplasm surrounds the nucleus, and it is in the cyto- ■ The nucleus is the control center for the cell. It also plasm that the work of the cell takes place. Cytoplasm is es- contains most of the hereditary material. sentially a colloidal solution that contains water, electrolytes, suspended proteins, neutral fats, and glycogen molecules. ■ The organelles, which are analogous to the organs Although they do not contribute to the cell’s function, pig- of the body, are contained in the cytoplasm. They ments may also accumulate in the cytoplasm. Some pigments, include the mitochondria, which supply the energy such as melanin, which gives skin its color, are normal con- needs of the cell; the ribosomes, which synthesize stituents of the cell. proteins and other materials needed for cell func- Embedded in the cytoplasm are various organelles, which tion; and the lysosomes, which function as the cell’s function as the organs of the cell. These organelles include the digestive system. ribosomes, endoplasmic reticulum, Golgi complex, lysosomes and peroxisomes, and mitochondria. ■ The cell membrane encloses the cell and provides for intracellular and intercellular communication, trans- Ribosomes port of materials into and out of the cell, and main- The ribosomes serve as sites of protein synthesis in the cell. tenance of the electrical activities that power cell They are small particles of nucleoproteins (rRNA and pro- function. teins) that can be found attached to the wall of the endoplas- mic reticulum or as free ribosomes (Fig. 1-2). Free ribosomes are scattered singly in the cytoplasm or joined by strands of mRNA to form functional units called polyribosomes.Free ribo- somes are involved in the synthesis of proteins, mainly as essential to the cell because its genes contain the information intracellular enzymes. necessary for the synthesis of proteins that the cell must pro- duce to stay alive. These proteins include structural proteins Endoplasmic Reticulum and enzymes used to synthesize other substances, including The endoplasmic reticulum (ER) is an extensive system of carbohydrates and lipids. The genes also represent the individ- paired membranes and flat vesicles that connects various parts ual units of inheritance that transmit information from one gen- of the inner cell (see Fig. 1-2). The fluid-filled space, called the eration to another. The nucleus is also the site of ribonucleic acid (RNA) synthesis. There are three types of RNA: messenger RNA (mRNA), which copies and carries the DNA instructions for protein synthesis to the cytoplasm; ribosomal RNA (rRNA), Rough ER which moves to the cytoplasm, and becomes the site of protein Ribosomes synthesis; and transfer RNA (tRNA), which also moves into the cytoplasm, where it transports amino acids to the elongating protein as it is being synthesized (see Chapter 3). The complex structure of DNA and DNA-associated proteins dispersed in the nuclear matrix is called chromatin.Each DNA molecule is made up of two extremely long, double-stranded Matrix helical chains containing variable sequences of four nitroge- nous bases. These bases form the genetic code. In cells that are about to divide, the DNA must be replicated before mitosis,or cell division, occurs. During replication, complementary pairs Tubular elements of DNA are generated such that each daughter cell receives an of the ER identical set of genes. The nucleus also contains the darkly stained round body Free called the nucleolus.The rRNA is transcribed exclusively in the ribosomes nucleolus. Nucleoli are structures composed of regions from five different chromosomes, each with a part of the genetic Smooth code needed for the synthesis of rRNA. Cells that are actively ER synthesizing proteins can be recognized because their nu- Vesicular elements cleoli are large and prominent and the nucleus as a whole is of the ER euchromatic. ■FIGURE 1-2■Three-dimensional view of the rough endoplas- Surrounding the nucleus is a doubled-layered membrane mic reticulum (ER) with its attached ribosomal RNA and the called the nuclear envelope or nuclear membrane. The nuclear smooth endoplasmic reticulum. 4 Unit One: Mechanisms of Disease matrix,between the paired ER membrane layers is connected with the space between the two membranes of the double- layered nuclear membrane, the cell membrane, and various cytoplasmic organelles. It functions as a tubular communica- tion system through which substances can be transported from one part of the cell to another. A large surface area and multiple enzyme systems attached to the ER membranes also provide the machinery for a major share of the metabolic Endoplasmic functions of the cell. reticulum (ER) Two forms of ER exist in cells: rough and smooth. Rough ER is studded with ribosomes attached to specific binding sites on Transfer vesicles Secretory Golgi the membrane. The ribosomes, with the accompanying strand granules apparatus of mRNA, synthesize proteins. Proteins produced by the rough ER are usually destined for incorporation into cell membranes ■FIGURE 1-3■Hormone synthesis and secretion.In hormone se- cretion, the hormone is synthesized by the ribosomes attached to and lysosomal enzymes or for exportation from the cell. The the rough endoplasmic reticulum. It moves from the rough ER to rough ER segregates these proteins from other components of the Golgi complex, where it is stored in the form of secretory gran- the cytoplasm and modifies their structure for a specific func- ules. These leave the Golgi complex and are stored within the cyto- tion. For example, the production of plasma protein by liver plasm until released from the cell in response to an appropriate cells take place in the rough ER. All cells require a rough ER for signal. the synthesis of lysosomal enzymes. The smooth ER is free of ribosomes and is continuous with the rough ER. It does not participate in protein synthesis; in- enzymes are acid hydrolases, which means that they require an stead, its enzymes are involved in the synthesis of lipid mole- acid environment. The lysosomes provide this environment by cules, regulation of intracellular calcium, and metabolism and maintaining a pH of approximately 5 in their interior. The pH detoxification of certain hormones and drugs. It is the site of of the cytoplasm is approximately 7.2, which protects other cel- lipid, lipoprotein, and steroid hormone synthesis. The sar- lular structures from this acidity. coplasmic reticulum of skeletal and cardiac muscle cells is a Lysosomal enzymes are synthesized in the rough ER and form of smooth ER. Calcium ions needed for muscle contrac- then transported to the Golgi apparatus, where they are bio- tion are stored and released from cisternae of the sarcoplasmic chemically modified and packaged as lysosomes. Unlike those reticulum. Smooth ER of the liver is involved in glycogen stor- of other organelles, the sizes and functions of lysosomes vary age and metabolism of lipid-soluble drugs. considerably from one cell to another. The type of enzyme packaged in the lysosome by the Golgi complex determines Golgi Complex this diversity. Although enzymes in the secondary lysosomes The Golgi apparatus, sometimes called the Golgi complex,con- can break down most proteins, carbohydrates, and lipids to sists of stacks of thin, flattened vesicles or sacs. These Golgi their basic constituents, some materials remain undigested. bodies are found near the nucleus and function in association These undigested materials may remain in the cytoplasm as with the ER. Substances produced in the ER are carried to the residual bodiesor be extruded from the cell. In some long-lived Golgi complex in small, membrane-covered transfer vesicles. cells, such as neurons and heart muscle cells, large quantities of Many cells synthesize proteins that are larger than the active residual bodies accumulate as lipofuscin granules or age pig- product. Insulin, for example, is synthesized as a large, inactive ment. Other indigestible pigments, such as inhaled carbon par- proinsulin molecule that is cut apart to produce a smaller, ac- ticles and tattoo pigments, also accumulate and may persist in tive insulin molecule within the Golgi complex of the beta cells residual bodies for decades. of the pancreas. The Golgi complex modifies these substances Lysosomes play an important role in the normal metabo- and packages them into secretory granules or vesicles. Enzymes lism of certain substances in the body. In some inherited dis- destined for export from the cell are packaged in secretory vesi- eases known as lysosomal storage diseases,a specific lysosomal cles. After appropriate signals, the secretory vesicles move out enzyme is absent or inactive, in which case the digestion of cer- of the Golgi complex into the cytoplasm and fuse to the inner tain cellular substances does not occur. As a result, these sub- side of the plasma membrane, where they release their contents stances accumulate in the cell. In Tay-Sachs disease, an auto- into the extracellular fluid. Figure 1-3 is a diagram of the syn- somal recessive disorder, the lysosomal enzyme needed for thesis and movement of a hormone through the rough ER and degrading the GM ganglioside found in nerve cell membranes 2 Golgi complex. In addition to its function in producing secre- is deficient (see Chapter 4). Although GM ganglioside accu- 2 tory granules, the Golgi complex is thought to produce large mulates in many tissues, such as the heart, liver, and spleen, carbohydrate molecules that combine with proteins produced its accumulation in the nervous system and retina of the eye by the rough ER to form glycoproteins. causes the most damage. Smaller than lysosomes, spherical membrane-bound or- Lysosomes and Peroxisomes ganelles called peroxisomes contain a special enzyme that de- The lysosomes can be viewed as the digestive system of the cell. grades peroxides (e.g.,hydrogen peroxide). Peroxisomes func- They consist of small, membrane-enclosed sacs containing hy- tion in the control of free radicals (see Chapter 2). Unless drolytic enzymes capable of breaking down worn-out cell parts degraded, these highly unstable chemical compounds would so they can be recycled. They also break down foreign sub- otherwise damage other cytoplasmic molecules. For example, stances such as bacteria taken into the cell. All of the lysosomal catalase degrades toxic hydrogen peroxide molecules to water. Chapter 1: Cell Structure and Function 5 Peroxisomes also contain the enzymes needed for breaking mitochondria. Although mitochondrial DNA directs the syn- down very–long-chain fatty acids, which are ineffectively de- thesis of 13 of the proteins required for mitochondrial func- graded by mitochondrial enzymes. In liver cells, peroxisomal tion, the DNA of the nucleus encodes the structural proteins enzymes are involved in the formation of the bile acids. of the mitochondria and other proteins needed to carry out cel- lular respiration. Mitochondria Mitochondrial DNA is inherited matrilineally (i.e.,from the The mitochondria are literally the “power plants” of the cell be- mother) and provides a basis for familial lineage studies. cause they transform organic compounds into energy that is Mutations have been found in each of the mitochondrial easily accessible to the cell. Energy is not made here but is ex- genes, and an understanding of the role of mitochondrial DNA tracted from organic compounds. Mitochondria contain the in certain diseases is beginning to emerge. Most tissues in the enzymes needed for capturing most of the energy in foodstuffs body depend to some extent on oxidative metabolism and can and converting it into cellular energy. This multistep process re- therefore be affected by mitochondrial DNA mutations. quires oxygen and is often referred to as aerobic metabolism. Much of this energy is stored in the high-energy phosphate The Cytoskeleton bonds of compounds such as adenosine triphosphate (ATP), which powers the various cellular activities. In addition to its organelles, the cytoplasm contains a network Mitochondria are found close to the site of energy con- of microtubules, microfilaments, intermediate filaments, and sumption in the cell (e.g.,near the myofibrils in muscle cells). thick filaments (Fig. 1-5). Because they control cell shape The number of mitochondria in a given cell type is largely de- and movement, these structures are a major component of the termined by the type of activity the cell performs and how structural elements called the cytoskeleton. much energy is needed to undertake this activity. For example, large increases in mitochondria have been observed in skeletal Microtubules muscle that has been repeatedly stimulated to contract. The microtubules are slender tubular structures composed The mitochondria are composed of two membranes: an of globular proteins called tubulin.Microtubules function in outer membrane that encloses the periphery of the mitochon- many ways, including the development and maintenance of drion and an inner membrane that forms shelflike projections, calledcristae(Fig. 1-4). The outer and inner membranes form two spaces: an outer intramembranous space and an inner ma- Cell membrane trix that is filled with a gel-like material. The outer membrane Mitochondrion is involved in lipid synthesis and fatty acid metabolism. The Microtubule inner membrane contains the respiratory chain enzymes and Rough transport proteins needed for the synthesis of ATP. endoplasmic Mitochondria contain their own DNA and ribosomes and reticulum are self-replicating. The DNA is found in the mitochondrial matrix and is distinct from the chromosomal DNA found in the nucleus. Mitochondrial DNA, known as the “other human genome,” is a double-stranded, circular molecule that encodes the rRNA and tRNA required for intramitochrondial synthesis of proteins needed for the energy-generating function of the Outer limiting membrane Cristae Matrix space Nucleus Microfilament Ribosomes Inner limiting Intermediate membrane filaments ■FIGURE 1-4■Mitochondrion. The inner membrane forms ■FIGURE 1-5■Microtubes and microfilaments of the cell.The transverse folds called cristae, where the enzymes needed for the microfilaments associate with the inner surface of the cell and aid final step in adenosine triphosphate (ATP) production (i.e.,oxida- in cell motility. The microtubules form the cytoskeleton and main- tive phosphorylation) are located. tain the position of the organelles.