USMLE Step 1 Audio Crash Course

USMLE I Complete Test Prep and Review for the United States Medical Licensure Examination Step 1 (USMLE I)

www.AudioLearn.com

Table of Contents Preface............................................................................................................................................ 1 Chapter 1: Biochemistry .............................................................................................................. 3 Amino Acids ............................................................................................................................... 3 Proteins ....................................................................................................................................... 6 Simple Sugars ............................................................................................................................. 7 Types of Sugars........................................................................................................................... 8 Carbohydrates ............................................................................................................................. 9 Fatty Acids .................................................................................................................................. 9 Fatty Acid Synthesis and Breakdown ....................................................................................... 11 Lipids ........................................................................................................................................ 12 Biological Functions of Lipids.................................................................................................. 13 Nucleotides ............................................................................................................................... 14 Nucleotide Structure ................................................................................................................. 14 Deoxyribonucleic Acid or DNA ............................................................................................... 15 Ribonucleic Acid or RNA......................................................................................................... 18 Types of RNA Molecules ......................................................................................................... 20 Biochemistry in Medical Disciplines ........................................................................................ 21 Biochemical Nutrition............................................................................................................... 23 Biochemistry and Pharmacology .............................................................................................. 23 Key Takeaways ......................................................................................................................... 24 Quiz ........................................................................................................................................... 24 Chapter 2: Anatomy ................................................................................................................... 31 Anatomy of the Central Nervous System ................................................................................. 31 Head and Neck Anatomy .......................................................................................................... 33 Cardiovascular Anatomy .......................................................................................................... 39 Respiratory Tract Anatomy....................................................................................................... 42 Gastrointestinal Anatomy ......................................................................................................... 44 Gastrointestinal Structure.......................................................................................................... 45 Parts of the GI Tract.................................................................................................................. 46 Non-Hollow Digestive Organs ................................................................................................. 47 Urinary Tract Anatomy ............................................................................................................. 47 Pelvic Anatomy in Females ...................................................................................................... 48 Reproductive Anatomy in Males .............................................................................................. 50

Upper Extremity Anatomy........................................................................................................ 51 Lower Extremity Anatomy ....................................................................................................... 53 Key Takeaways ......................................................................................................................... 55 Quiz ........................................................................................................................................... 56 Chapter 3: Physiology................................................................................................................. 62 Cellular Physiology................................................................................................................... 62 Cell Membrane.......................................................................................................................... 62 Internal Environment of the Cell .............................................................................................. 65 Nervous System Physiology ..................................................................................................... 68 Cardiovascular Physiology ....................................................................................................... 72 Blood Vessels............................................................................................................................ 74 Respiratory Physiology ............................................................................................................. 75 Respiratory Volumes ................................................................................................................ 76 Respiratory Rate........................................................................................................................ 77 Gas Exchange............................................................................................................................ 78 Renal and Acid-Base Physiology.............................................................................................. 79 Acid-Base Physiology............................................................................................................... 81 Gastrointestinal Physiology ...................................................................................................... 81 Endocrine Physiology ............................................................................................................... 84 Hypothalamic-Pituitary System ................................................................................................ 86 Thyroid Gland ........................................................................................................................... 89 Parathyroid Glands.................................................................................................................... 90 Adrenal Glands ......................................................................................................................... 90 Key Takeaways ......................................................................................................................... 92 Quiz ........................................................................................................................................... 92 Chapter 4: Embryology .............................................................................................................. 98 Female Reproductive Cycle in Early Pregnancy ...................................................................... 98 Follicular phase ......................................................................................................................... 98 Ovulatory Phase ...................................................................................................................... 100 Luteal Phase ............................................................................................................................ 101 Luteal Phase Defect ................................................................................................................ 102 The Process of Meiosis ........................................................................................................... 102 Meiosis I.................................................................................................................................. 104 Meiosis II ................................................................................................................................ 104

Oogenesis ................................................................................................................................ 104 Spermatogenesis ..................................................................................................................... 106 Human Fertilization ................................................................................................................ 108 Blastulation ............................................................................................................................. 110 Gastrulation ............................................................................................................................. 111 The Normal Placenta............................................................................................................... 112 Functions of the Placenta ........................................................................................................ 113 Common Placental Problems .................................................................................................. 115 Others classifications .............................................................................................................. 115 Embryo Development: Week 2............................................................................................... 117 Division of the Blastocyst ....................................................................................................... 120 Abnormalities of Week Two................................................................................................... 121 Embryo Development: Week 3............................................................................................... 122 Embryonic Development: Week 4 .......................................................................................... 124 Fourth Month of Pregnancy .................................................................................................... 125 Fifth Month of Pregnancy ....................................................................................................... 126 Month Six of Pregnancy ......................................................................................................... 126 Miscarriages ............................................................................................................................ 126 Key Takeaways ....................................................................................................................... 127 Quiz ......................................................................................................................................... 128 Chapter 5: Microbiology .......................................................................................................... 134 The Study of Microscopy........................................................................................................ 134 Optical Microscopy................................................................................................................. 134 Electron Microscopy ............................................................................................................... 136 Microbiological Cultures ........................................................................................................ 137 Viral cultures........................................................................................................................... 137 Eukaryotic Cell Cultures ......................................................................................................... 138 Innate Immune System ........................................................................................................... 138 The Barrier System ................................................................................................................. 138 The Inflammatory Response .................................................................................................. 138 The Role of the Complement System ..................................................................................... 139 Cells of the Innate Immune System ........................................................................................ 140 Adaptive Immune System ....................................................................................................... 141 Cells of the Adaptive Immune System .................................................................................. 141

Antigens and their Presentation .............................................................................................. 142 T Lymphocyte Activity ........................................................................................................... 143 B Lymphocyte Activity........................................................................................................... 143 Bacteria Anatomy and Physiology.......................................................................................... 144 Pathogenic Bacteria ................................................................................................................ 146 Anaerobic Infections ............................................................................................................... 147 Viral Anatomy and Physiology............................................................................................... 149 The Epidemiology of Viruses ................................................................................................. 151 Viral Diseases ......................................................................................................................... 151 Clinically-significant Viral Infections in Humans .................................................................. 152 Fungal Anatomy and Physiology ............................................................................................ 155 Pathogenic Fungi .................................................................................................................... 155 Candida Infections .................................................................................................................. 155 Aspergillus Infections in Humans........................................................................................... 156 Cryptococcus Infections.......................................................................................................... 157 Histoplasma Infections............................................................................................................ 157 Pneumocystis Infections ......................................................................................................... 158 Protozoan Infection ................................................................................................................. 159 Giardia Infections.................................................................................................................... 160 Cryptosporidium Infection ...................................................................................................... 161 Amoebiasis (Amoeba Infection) ............................................................................................. 161 Cyclospora Infections ............................................................................................................. 161 Toxoplasmosis ........................................................................................................................ 162 Plasmodium Infections............................................................................................................ 162 Key Takeaways ....................................................................................................................... 163 Quiz ......................................................................................................................................... 163 Chapter 6: Immunology ........................................................................................................... 170 Natural Barriers to Pathogens ................................................................................................. 170 Nonspecific Responses ........................................................................................................... 170 Specific Responses.................................................................................................................. 171 Overview of the Human Immune System............................................................................... 171 The Barrier System ................................................................................................................. 172 Innate Immune System ........................................................................................................... 172 Inflammation ........................................................................................................................... 172

Complement System ............................................................................................................... 174 Cellular Immunity ................................................................................................................... 174 Phagocytosis ........................................................................................................................... 175 Adaptive Immune System ....................................................................................................... 176 Passive Immunity .................................................................................................................... 177 Active Immunity ..................................................................................................................... 177 Antigens .................................................................................................................................. 177 Antibodies ............................................................................................................................... 180 Cell-Mediated Immunity......................................................................................................... 182 T Lymphocytes ....................................................................................................................... 182 T Cell-Related Diseases .......................................................................................................... 183 Humoral Immunity.................................................................................................................. 184 B Lymphocyte......................................................................................................................... 185 B Lymphocyte Diseases.......................................................................................................... 185 Cytokines ................................................................................................................................ 186 Cytokine Receptors ................................................................................................................. 186 Cytokines and Diseases........................................................................................................... 187 Complement System ............................................................................................................... 187 Complement-related Diseases................................................................................................. 188 Hypersensitivity and the Immune System .............................................................................. 188 Allergies .................................................................................................................................. 189 HIV Disease and Immunity .................................................................................................... 190 Severe Combined Immunodeficiency Disease (SCID)........................................................... 191 Leukemia................................................................................................................................. 191 Non-Hodgkin’s Lymphoma .................................................................................................... 192 Hodgkin’s Lymphoma ............................................................................................................ 193 Transplantation and the Immune System................................................................................ 193 The Immunology of Rejection ................................................................................................ 194 Autoimmune Diseases ............................................................................................................ 195 Key Takeaways ....................................................................................................................... 195 Quiz ......................................................................................................................................... 196 Chapter 7: Pharmacology ........................................................................................................ 202 Pharmacokinetics .................................................................................................................... 202 Drugs that affect the Autonomic Nervous System ................................................................. 203

Sympathetic Drugs .................................................................................................................. 204 Parasympathetic Drugs ........................................................................................................... 204 Analgesic Drugs ...................................................................................................................... 205 Sedative and Anti-Anxiety Drugs ........................................................................................... 205 Antidepressants ....................................................................................................................... 205 Antipsychotic Drugs ............................................................................................................... 205 Drugs for Parkinson’s Disease ................................................................................................ 206 Cardiovascular System Drugs ................................................................................................. 206 Corticosteroid Drugs ............................................................................................................... 207 Drugs for Diabetes Mellitus .................................................................................................... 207 Thyroid Drugs ......................................................................................................................... 208 Pituitary Gland Drugs ............................................................................................................. 208 Respiratory System Drugs ...................................................................................................... 209 Drugs for Nausea .................................................................................................................... 210 Antacid Drugs ......................................................................................................................... 210 Anti-Ulcer Drugs .................................................................................................................... 211 Anti-diarrheal Drugs ............................................................................................................... 211 Laxatives ................................................................................................................................. 211 Motility Stimulants and Antispasmodic Drugs ....................................................................... 212 Antibiotics ............................................................................................................................... 212 Classes of Antibiotics ............................................................................................................. 213 Antiviral Drugs ....................................................................................................................... 216 Antifungal Drugs .................................................................................................................... 218 Female Sex Hormones ............................................................................................................ 219 Androgens ............................................................................................................................... 219 Penile Erectile Dysfunction Drugs.......................................................................................... 219 Disease Modifying Anti-Rheumatic Drugs (DMARDs) ........................................................ 220 Chemotherapy Drugs .............................................................................................................. 220 Key Takeaways ....................................................................................................................... 220 Quiz ......................................................................................................................................... 220 Chapter 8: Toxicology .............................................................................................................. 227 Toxic Exposures...................................................................................................................... 227 Emergency Treatment of a Toxic Exposure ........................................................................... 228 Toxicology Testing ................................................................................................................. 229

Central Nervous System Toxicity ........................................................................................... 230 Hepatic Toxicity...................................................................................................................... 233 Nephrotoxicity ........................................................................................................................ 233 Lung Toxicity.......................................................................................................................... 233 Cardiac Toxicity...................................................................................................................... 234 Ototoxicity .............................................................................................................................. 235 Teratogens ............................................................................................................................... 235 Key Takeaways ....................................................................................................................... 236 Quiz ......................................................................................................................................... 236 Chapter 9: Endocrinology ........................................................................................................ 243 Hypothalamus and Pituitary Gland Function and Disorders .................................................. 243 Hypothalamus ......................................................................................................................... 243 Hypophyseal Portal System .................................................................................................... 245 Pituitary Gland ........................................................................................................................ 245 Thyroid Gland Disorders ........................................................................................................ 247 Thyroid Diseases..................................................................................................................... 247 Adrenal Gland Function and Disorders .................................................................................. 248 Adrenal Gland Diseases .......................................................................................................... 248 Pineal Gland Function and Disorders ..................................................................................... 249 Diabetes insipidus ................................................................................................................... 249 Syndrome of Inappropriate ADH Secretion ........................................................................... 250 Pancreatic Endocrine Function ............................................................................................... 251 Pancreatic Diseases ................................................................................................................. 252 Parathyroid Gland Function and Disorders............................................................................. 252 Parathyroid Gland Diseases .................................................................................................... 252 Reproductive Endocrinology .................................................................................................. 253 Ovarian Function .................................................................................................................... 253 Ovarian Diseases..................................................................................................................... 253 The Male Testes ...................................................................................................................... 254 Testicular Disorders ................................................................................................................ 254 Key Takeaways ....................................................................................................................... 254 Quiz ......................................................................................................................................... 255 Chapter 10: Musculoskeletal Diseases .................................................................................... 261 Spinal Diseases ....................................................................................................................... 261

Scoliosis .................................................................................................................................. 263 Bone cancer............................................................................................................................. 264 Fractures of the Bones ............................................................................................................ 266 Osteoarthritis ........................................................................................................................... 267 Rheumatoid Arthritis .............................................................................................................. 268 Myopathies.............................................................................................................................. 270 Fibromyalgia ........................................................................................................................... 271 Neuromuscular diseases .......................................................................................................... 271 Musculoskeletal Sports Injuries .............................................................................................. 273 Total Joint Replacement ......................................................................................................... 274 Key Takeaways ....................................................................................................................... 276 Quiz ......................................................................................................................................... 276 Chapter 11: Neurology ............................................................................................................. 283 The Neuron ............................................................................................................................. 283 Classification of Neurons........................................................................................................ 285 Neurotransmitter Production Classification Systems ............................................................. 285 Glial Cells ............................................................................................................................... 285 The Synapse ............................................................................................................................ 287 The Somatosensory System .................................................................................................... 290 Somatic Pathways ................................................................................................................... 290 The Medial lemniscal pathway ............................................................................................... 290 Organization of Somatosensory Systems................................................................................ 291 Sensory Transduction.............................................................................................................. 291 Types of Somatosensory Receptors ........................................................................................ 292 Pathophysiology of the Somatosensory System ..................................................................... 293 Upper Motor Neurons ............................................................................................................. 293 Upper Motor Neuron Injuries ................................................................................................. 294 Lower Motor Neurons............................................................................................................. 294 Lower Motor Neuron Injury ................................................................................................... 295 Pyramidal Motor System ........................................................................................................ 295 Peripheral Nervous System ..................................................................................................... 296 Autonomic Nervous System ................................................................................................... 297 Cardiovascular Regulation by the ANS .................................................................................. 298 Thermoregulation by the Autonomic Nervous System .......................................................... 299

Ophthalmologic Autonomic Nervous System Regulation...................................................... 299 Genitourinary Autonomic Nervous System Regulation ......................................................... 299 Gastrointestinal Autonomic Nervous System Regulation ...................................................... 299 Neurotransmitter Activity in the Autonomic Nervous System ............................................... 300 Autonomic Nervous System Disorders................................................................................... 300 The Senses .............................................................................................................................. 300 The Traditional Senses............................................................................................................ 301 Sensory Diseases ..................................................................................................................... 302 The Human Brain.................................................................................................................... 303 Cerebrum................................................................................................................................. 303 Cerebellum .............................................................................................................................. 304 Brainstem ................................................................................................................................ 304 Blood Supply in the Brain....................................................................................................... 304 Brain Function ........................................................................................................................ 305 Diseases of the Spinal Cord .................................................................................................... 306 The Limbic System ................................................................................................................. 307 The Hypothalamus .................................................................................................................. 308 The Amygdala......................................................................................................................... 309 The Hippocampus ................................................................................................................... 309 The Limbic Cortex .................................................................................................................. 309 Limbic System Function ......................................................................................................... 310 The Cranial Nerves ................................................................................................................. 311 Neurotransmitter Mechanisms ................................................................................................ 313 Types of Neurotransmitters..................................................................................................... 314 Actions of Neurotransmitters .................................................................................................. 314 Common Neurotransmitters in the Nervous System .............................................................. 315 Drug Activity and the Neurotransmitters................................................................................ 316 Learning .................................................................................................................................. 316 Types of Learning ................................................................................................................... 317 Factors that affect Learning .................................................................................................... 317 Dementia ................................................................................................................................. 318 Incidence and Prevalence ........................................................................................................ 318 Predisposing Factors ............................................................................................................... 319 Signs and Symptoms ............................................................................................................... 319

Clinical Presentation ............................................................................................................... 319 Etiology ................................................................................................................................... 320 Pathology ................................................................................................................................ 320 Treatment and Management ................................................................................................... 321 Complications ......................................................................................................................... 321 Key Takeaways ....................................................................................................................... 322 Quiz ......................................................................................................................................... 322 Chapter 12: Psychiatry ............................................................................................................. 328 Amnestic Disorders................................................................................................................. 328 Signs and Symptoms of Amnestic Disorders.......................................................................... 328 Clinical Presentation of Amnestic Disorders .......................................................................... 329 Etiology of Amnestic Disorders.............................................................................................. 329 Bipolar Disorder...................................................................................................................... 330 Signs and Symptoms of Bipolar Disorder .............................................................................. 330 Etiology ................................................................................................................................... 331 Treatment and Management of Bipolar Disorder ................................................................... 331 Delirium .................................................................................................................................. 332 Signs and Symptoms of Delirium ........................................................................................... 332 Treatment and Management of Delirium................................................................................ 333 Dissociative Disorders ............................................................................................................ 333 Signs and Symptoms of Dissociative Disorders ..................................................................... 333 Clinical Presentation ............................................................................................................... 334 Treatment and Management of Dissociative Disorders .......................................................... 335 Dysthymia ............................................................................................................................... 335 Signs and Symptoms of Dysthymia ........................................................................................ 335 Treatment and Management of Dysthymia............................................................................. 336 Complications of Dysthymia .................................................................................................. 336 Eating Disorders...................................................................................................................... 336 Incidence and Prevalence of Eating Disorders ....................................................................... 337 Signs and Symptoms of Eating Disorders .............................................................................. 337 Treatment of Eating Disorders ................................................................................................ 338 Generalized Anxiety Disorder ................................................................................................ 338 Signs and Symptoms of Generalized Anxiety Disorder ......................................................... 339 Treatment and Management of GAD ..................................................................................... 339

Impulse Control Disorders ...................................................................................................... 340 Signs and Symptoms of Impulse Control Disorders ............................................................... 340 Treatment and Management of Impulsive Control Disorders ................................................ 341 Major Depression .................................................................................................................... 342 Signs and Symptoms of Major Depression............................................................................. 342 Treatment and Management of Major Depression ................................................................. 343 Obsessive-Compulsive Disorder............................................................................................. 343 Signs and Symptoms of OCD ................................................................................................. 344 Treatment and Management of OCD...................................................................................... 344 Personality Disorders .............................................................................................................. 345 Clinical Presentation of Personality Disorders ....................................................................... 345 Phobias .................................................................................................................................... 346 Signs and Symptoms of Phobias ............................................................................................. 347 Treatment and Management of Phobias ................................................................................. 347 Posttraumatic Stress Disorder ................................................................................................. 348 Signs and Symptoms of PTSD................................................................................................ 349 Treatment and Management of PTSD .................................................................................... 349 Psychotic Disorders ................................................................................................................ 350 Signs and Symptoms of Psychotic Disorders ......................................................................... 351 Treatment and Management of Psychotic Disorders .............................................................. 351 Schizophrenia.......................................................................................................................... 351 Signs and Symptoms of Schizophrenia................................................................................... 352 Treatment and Management of Schizophrenia ....................................................................... 352 Somatoform Disorders ............................................................................................................ 353 Signs and Symptoms of Somatoform Disorders ..................................................................... 353 Treatment and Management of Somatoform Disorders.......................................................... 354 Substance Use Disorders......................................................................................................... 355 Signs and Symptoms of Substance Use Disorders ................................................................. 355 Treatment and Management of Substance Use Disorders ...................................................... 356 Key Takeaways ....................................................................................................................... 356 Quiz ......................................................................................................................................... 357 Chapter 13: Reproductive system ........................................................................................... 363 Gynecological Care of the Well Woman ................................................................................ 363 The Breast Examination.......................................................................................................... 363

The Pelvic Exam ..................................................................................................................... 363 The Pap Test ........................................................................................................................... 363 HPV Testing............................................................................................................................ 364 Mammograms ......................................................................................................................... 364 Abnormal Uterine Bleeding .................................................................................................... 365 Signs and Symptoms of Abnormal Uterine Bleeding ............................................................. 365 Treatment and Management of Abnormal Uterine Bleeding ................................................. 365 Contraception and Sterilization............................................................................................... 366 Birth Control Pills ................................................................................................................... 366 Cervical Cap............................................................................................................................ 367 Condoms ................................................................................................................................. 367 Contraceptive Film.................................................................................................................. 367 Contraceptive Foam ................................................................................................................ 367 Contraceptive Implant............................................................................................................. 367 Contraceptive Sponge ............................................................................................................. 368 Contraceptive Suppository ...................................................................................................... 368 Diaphragm............................................................................................................................... 368 Emergency Contraception....................................................................................................... 368 Female Condom ...................................................................................................................... 368 Injectable Contraceptive ......................................................................................................... 369 Intrauterine Contraception ...................................................................................................... 369 The Contraceptive Patch ......................................................................................................... 369 The Contraceptive Ring .......................................................................................................... 369 The Contraceptive Shield........................................................................................................ 370 Female Sterilization ................................................................................................................ 370 Gynecological Infections ........................................................................................................ 370 Signs and Symptoms of pelvic inflammatory disease and bacterial vaginosis....................... 370 Etiology of PID ....................................................................................................................... 371 Treatment and Management of pelvic inflammatory disease and bacterial vaginosis ........... 371 Sexually Transmitted Infections of the Female ...................................................................... 372 Signs and Symptoms of Sexually Transmitted Infections ...................................................... 372 Clinical Presentation of Sexually Transmitted Infections ...................................................... 373 Treatment and Management of Sexually Transmitted Ifections ............................................. 373 Endometriosis ......................................................................................................................... 374

Signs and Symptoms of Endometriosis .................................................................................. 374 Treatment and Management of Endometriosis ....................................................................... 375 Pelvic Masses in Women ........................................................................................................ 375 Clinical Presentation of a Pelvic Mass.................................................................................... 376 Treatment and Management of Ovarian Cancer ..................................................................... 376 Treatment and Management of Uterine Fibroids .................................................................... 376 Polycystic Ovarian Syndrome................................................................................................. 377 Clinical Presentation of Polycystic Ovarian Syndrome .......................................................... 377 Treatment and Management of Polycystic Ovarian Syndrome .............................................. 377 Breast Diseases in Women...................................................................................................... 378 Incidence and Prevalence of Breast Diseases ......................................................................... 378 Signs and Symptoms of Breasts Diseases............................................................................... 378 Clinical Presentation of Breasts Diseases ............................................................................... 379 Treatment and Management of Breast Diseases ..................................................................... 379 Menopause .............................................................................................................................. 379 Early Menopause .................................................................................................................... 380 Perimenopause ........................................................................................................................ 381 Postmenopause ........................................................................................................................ 381 Treatment of Menopause ........................................................................................................ 381 Urinary Incontinence in Women............................................................................................. 382 Signs and Symptoms of Urinary Incontinence ....................................................................... 382 Treatment and Management of Incontinence ......................................................................... 383 Uterine Prolapse ...................................................................................................................... 384 Treatment and Management of Uterine Prolapse ................................................................... 384 Gynecological Oncology ........................................................................................................ 385 Treatment and Management Gynecological Cancers ............................................................. 385 Genitourinary Issues of the Male ............................................................................................ 386 Prostatitis................................................................................................................................. 386 Prostate Cancer ....................................................................................................................... 387 Erectile Dysfunction (ED) ...................................................................................................... 388 Key Takeaways ....................................................................................................................... 388 Quiz ......................................................................................................................................... 388 Chapter 14: Dermatology ......................................................................................................... 395 Normal Skin Structure and Function ...................................................................................... 395

Acrochordon ........................................................................................................................... 397 Pyogenic Granuloma............................................................................................................... 398 Cutaneous Horn ...................................................................................................................... 399 Nevus Sebaceous of Jadassohn ............................................................................................... 399 Seborrheic Keratosis ............................................................................................................... 400 Verruca vulgaris ...................................................................................................................... 401 Bullous Diseases of the Skin................................................................................................... 401 Bullous pemphigoid ................................................................................................................ 401 Dermatitis Herpetiformis ........................................................................................................ 402 Linear IgA Disease ................................................................................................................. 403 Genetic Diseases of the Skin................................................................................................... 403 Neurofibromatosis 1................................................................................................................ 404 Legius Syndrome .................................................................................................................... 404 Tuberous Sclerosis .................................................................................................................. 404 Sturge-Weber Syndrome......................................................................................................... 405 Pigment Disorders of the Skin ................................................................................................ 405 Melasma .................................................................................................................................. 405 Post-Inflammatory Hyperpigmentation .................................................................................. 407 Vitiligo and Focal Hypopigmentation .................................................................................... 407 Albinism.................................................................................................................................. 408 Acne and Related Disorders of the Skin ................................................................................. 409 Acne Vulgaris ......................................................................................................................... 409 Rosacea ................................................................................................................................... 410 Connective Tissue Diseases of the Skin ................................................................................. 412 Systemic Sclerosis .................................................................................................................. 412 Ehlers-Danlos Syndrome ........................................................................................................ 412 Pseudoxanthoma Elasticum .................................................................................................... 413 Cutis Laxa ............................................................................................................................... 413 Granulomatous Diseases of the Skin ...................................................................................... 414 Granuloma Annulare............................................................................................................... 414 Granulomatous Dermatitis ...................................................................................................... 416 Palisading Neutrophilic Granulomatous Dermatitis ............................................................... 416 Papulosquamous and Eczematous Diseases of the Skin ......................................................... 416 Psoriasis .................................................................................................................................. 416

Seborrheic Dermatitis ............................................................................................................. 417 Lichen Planus .......................................................................................................................... 419 Atopic Eczema ........................................................................................................................ 419 Skin Cancers ........................................................................................................................... 420 Basal Cell Cancer.................................................................................................................... 420 Squamous Cell Carcinoma of the Skin ................................................................................... 421 Malignant Melanoma .............................................................................................................. 421 Predisposing Factors for Skin Cancer ..................................................................................... 422 Treatment and Management of Skin Cancer .......................................................................... 422 Infections of the Skin .............................................................................................................. 423 Cellulitis .................................................................................................................................. 423 Erysipelas ................................................................................................................................ 424 Impetigo .................................................................................................................................. 425 Key Takeaways ....................................................................................................................... 426 Quiz ......................................................................................................................................... 427 Summary .................................................................................................................................... 433 Course Questions and Answers ............................................................................................... 435

Preface Welcome to Audiolearn’s United States Medical Licensing Examination Part 1 Course, Presented by AudioLearn.

The United States Medical Licensing Association (USMLE) is sponsored by the Federation of State Medical Boards and administered by the National Board of Medical Examiners. According to them the USMLE assesses the physician’s ability to apply knowledge, concepts and principles and to demonstrate fundamental patient centered skills that are important in health and disease and that constitute the basis of safe and effective patient care.

The goal of this course is to offer a broad base of knowledge regarding the modern practice of medicine, focusing on the diseases encountered most commonly by the primary care health care practitioner.

Diseases can be inherited or congenital, in which they are present from birth or acquired disorders discovered in adults or older children after some type of external or internal trigger.

The first chapter this course is intended to be a thorough discussion of basic biochemistry principles.

This will include a discussion of the major proteins, carbohydrates, and lipids (including their precursor molecules). The main biochemical reactions occurring in the cell and in the human body will also be discussed as part of this chapter.

The second chapter delves into the anatomy of the human body. Anatomy, strictly speaking, involves the major structures of the body, from the brain through the head and neck, into the thorax and abdomen including the pelvic structures. The anatomy of the extremities is also covered as part of this course.

Chapter three in the course examines physiology of the human body. Unlike the structural aspects of the human body in anatomy, physiology covers the function of the body. Human physiology can be approach on a molecular, microscopic, or macroscopic level. Each of the body parts involved in physiology operate partially independent of each other body, but mostly work together as an interconnected physiological system.

The fourth chapter will cover the topic of embryology. This will begin with a discussion of the male and female reproductive aspects of embryology and the process fertilization or the union of egg and sperm.

The early days and weeks of embryological development are covered in this chapter as well as the later development of the fetus. Disorders related to embryological development will also be discussed.

The fifth chapter of this course will be a thorough discussion of microbiology, in particular, medical microbiology. Diseases caused by bacteria, viruses, fungi, and protozoal organisms will be a major part of the discussion in this chapter. The unique microbiology of these organisms will be covered including the most communicable diseases and their pathogens.

The sixth chapter of this course will cover immunology. Medical immunology includes the innate and acquired immune system. Both aspects of the immune system have humoral and cell-mediated

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components, which will also be covered. The basic disorders of the immune functions are also discussed in this chapter.

The seventh chapter of this course is a thorough discussion of pharmacology. There are hundreds of different drugs used in humans that are effective against numerous disorders. The pharmaceutical interventions that will be covered are based on the major classifications of the different drugs and will include a discussion of the various mechanisms of actions.

The eighth chapter in this course will mainly include the topic of toxicology, including toxicology screening and the various toxic substances a person can come in contact with. Toxicology testing includes testing for substances of abuse, which will also be covered as part of this chapter.

The ninth chapter of the course is a thorough discussion of endocrinology. Diseases of the endocrine system can affect children, such as type 1 diabetes. Other disorders of the endocrine system affect mainly adults. The various endocrine diseases covered include diabetes, thyroid disorders, pituitary gland disorders, hypothalamic disorders, and dieseases of the adrenal glands.

The tenth chapter of the course will cover musculoskeletal diseases. This includes disorders of the bones, the spinal column, the muscles, and the joints. Both inherited and acquired diseases of the musculoskeletal system will be covered, including different treatments for musculoskeletal disorders.

The eleventh chapter of the course is intended to be a discussion of neurology. Neurological diseases start with diseases of the neurons, which are the main cells of the nervous system. Normal neurological function will be covered, including the sensory nervous system and the motor nervous system. The autonomic nervous system is covered along with the various diseases affecting the central and peripheral nervous system.

The twelfth chapter of the course is a comprehensive discussion of psychiatric disorders. The major focus of the chapter is on disorders affecting adults; however, some of the course discussion will be on psychiatric diseases stemming from childhood experiences. Most psychiatric diseases have a psychological origin but some are organic in nature.

The thirteenth chapter of the course will be a thorough discussion of the reproductive system. Both the structure and function of male and female reproductive anatomy and physiology will be covered. The many diseases of the female reproductive tract and male reproductive tract are also discussed in this chapter.

The focus of the fourteenth chapter will be the topic of dermatology and the disorders of the skin. There are numerous skin disorders that can be inherited, acquired, or congenital. Each type of skin disorder has a characteristic clinical finding, specific pathological findings on biopsy, and treatments designed either to cure the disorder or to decrease the symptoms of the disease. Each of these components will be covered as part of this chapter.

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Chapter 1: Biochemistry The basis of all human diseases and cellular processes can be explained by the biochemistry of the cell.

Knowledge of biochemistry requires a thorough understanding of amino acids, fatty acids, carbohydrates, and nucleic acids. It also requires knowledge of how these molecules are synthesized and metabolized. All of these topics are discussed in this first chapter.

Amino Acids Most amino acids are considered the building blocks of proteins in the body, although not all amino acids make proteins. The primary components of an amino acid is the amine group (-NH3 group), a carboxyl group (a -COOH group), and a different side chain that defines the amino acid. In humans, there are twenty-one different amino acids that are the building blocks of proteins in the body. Each has a unique shape based on the presents of a pH of 7.4, which is the normal pH of the human body.

Figure 1 shows the basic structure of an amino acid:

Figure 1 The basic molecules nitrogen, hydrogen, oxygen, and carbon compose amino acids, but other atomic particles (such as sulfur) can be in the side chain. While five hundred amino acids are present in natural

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substances, humans have slightly more than twenty that are in use in protein building or in the synthesis of neurotransmitters. L-tryptophan, for example, is an amino acid used to make serotonin. For this reason, some providers will give L-tryptophan to depressed patients to build serotonin levels.

Proteins and amino acids are the second largest molecular substance found in the human body. They can be classified according to their side chain, which can be aliphatic, acrylic, aromatic, or hydroxyl. Each side chain has a specific polarity that affects its solubility in aqueous solutions. The generic formulation of amino acids in humans is H2NCHRCOOH, where “R” refers to the side chain. All proteinogenic amino acids in humans are of the L-isomer type.

There are twenty standard amino acids that are coded for by at least one gene (there can be more than one gene for a protein). There are two non-standard amino acids with no gene that codes for them which are synthesize in other ways. Selenocysteine, for example, is encoded by a stop codon and an SECIS segment, not a gene. Pyrrolysine is another example of a non-standard amino acid.

Figure 2 shows the standard amino acids seen in nature:

Figure 2 Essential amino acids are not produced by the human body and must be consumed. There are nine of them and they include histidine, leucine, isoleucine, lysine, phenylalanine, methionine, threonine, valine, and tryptophan. Those that can be produced by the human body, including arginine, cysteine,

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glutamine, glycine, proline, tyrosine, alanine, asparagine, aspartic acid, glutamic acid, and selenocysteine.

Besides tryptophan, there are two non-proteinogenic amino acids worth mentioning. Glutamic acid and GABA (gamma-amino-butyric acid) are neurotransmitters. Glutamic acid is the major excitatory amino acid in the central nervous system, while gamma-amino-butyric acid (GABA) is the main inhibitory amino acid in the central nervous system. Two other non-standard amino acids include glycine (which makes porphyrins in the body) and carnitine (which is necessary for lipid transport).

Amino acids have different structures that determine their solubility. The aromatic amino acids are phenylalanine, tyrosine, and tryptophan. The acidic amino acids are glutamic acid and aspartic acid.

Glycine and alanine are considered “small amino acids” because of their short side chains. Basic amino acids include histidine, lysine, and arginine. Hydrophobic amino acids include valine, leucine, isoleucine, proline, and methionine. These do not dissolve well in water and are found on the inside of proteins— away from an aqueous environment. As in all of chemistry, slightly basic amino acids are attracted to slightly acidic amino acids. All of these side chains determine the protein shape.

Amino acids are crucial to protein synthesis. Peptides are short proteins that have different functions in the body. Longer chains of amino acids are called proteins. There are some peptides that are useful to know about in medicine. Insulin, vasopressin, human growth hormone, and gonadotropin releasing hormone are all well-established pharmaceutical-grade peptides used to treat different diseases. The most commonly prescribed peptide in medicine today is insulin. All therapeutic peptides must be given by non-oral means as they are degraded in the acidic environment of the stomach.

The process of converting amino acids into usable proteins or peptides in the body is called translation. On a cellular level this occurs in the ribosomes through the action of RNA (ribonucleic acid), which is translated from genes in the DNA of the nucleus. Transfer RNA or tRNA is the ribonucleic acid that puts the amino acids one-by-one on the terminal end of the peptide chain. This is where pyrrolysine and selenocysteine are made as they aren’t directly encoded for by a gene.

There are some ribosomal diseases caused by genetic defects that cause ineffective translation. These are rare syndromes that have varying phenotypes. Treacher-Collins syndrome is the most common “ribosomopathy”, leading to craniofacial abnormalities. Other known ribosomopathies are cartilage hair hypoplasia (anemia, dwarfism, hypoplastic hair), Schwachman-Diamond syndrome (neutropenia, pancreatic insufficiency, and short stature), 5q- Syndrome (macrocytic anemia and hypolobulated micromegakaryocytes), and Diamond Blackfan anemia (anemia, craniofacial abnormalities, short stature, and thumb abnormalities).

Non-proteinogenic amino acids are nearly as important clinically as proteinogenic amino acids. The main amino acids that are important in medicine that are non-proteinogenic include triiodothyronine, GABA, tryptophan, and L-dopa. Most of these are not directly encoded for by the DNA of the cell’s nucleus but are made by post-translational modification of existing amino acids. A few are made in the ribosomes themselves, while others are made by non-ribosomal peptide synthetases outside of the actual ribosome.

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Proteins After water, proteins are the most abundant substance in the body. Made in the ribosomes, proteintypes number by the thousands and are synthesized one amino acid at a time through instructions from messenger RNA and the one-by-one placement of the correct amino acid by the transfer RNA. The shape of the protein is almost exclusively a result of the different attractions and repulsions of amino acids in relation to each other and to the aqueous solutions in which they exists. A protein can be made by one polypeptide or by several different polypeptides that are attracted to one another. Some posttranslational modification unrelated to amino acid structure can take place but this is less commonly the case. Hydrogen bonding is another common way in which proteins get their shape.

The average protein lasts one to two days in the human body although many have the capacity to remain intact for many years. Abnormal or misfolded proteins are degraded within seconds, while enzymes can last just a few minutes. The makeup and shape of a protein is what gives the protein its half-life. As helpful molecules in the body, proteins serve many functions. Myosin and actin for example are muscle proteins that are responsible for the contraction of muscles. Small peptides are used as neurotransmitters and in other cell-signaling jobs, in the immune response (such as cytokines), and in the activity of the cell cycle. All peptides and proteins used by the body are made directly by the body. All proteins consumed are broken down into amino acids before being absorbed and other amino acids are synthesized from even smaller molecules.

Each peptide has a distinct end. The amino terminus or N-terminus has the amino group at the end of it, while the carboxyl terminus or the C-terminus has the carboxyl end on it. While they are completely linear, as mentioned, rarely is their shape linear in nature. A peptide or oligopeptide is defined as any peptide chain that is shorter than about 30 amino acids. Anything longer than that is called a polypeptide or protein. There are one to three billion different proteins per cell in the human body that can number just a few of each or millions of copies of the same protein.

The DNA message is located in the nucleus of the cell. There are triplet codons (which will be described later) of nucleic acids that each encode for a specific amino acid. Because there are sixty-four possible combinations of triplet codons, there is some redundancy so that more than one triplet codon will encode for the same amino acid. RNA polymerase is the enzyme in the nucleus that causes the transcription of pre-mRNA from the DNA message. There are cleavage enzymes that make mature mRNA from the pre-mRNA molecule.

As mentioned, most proteins do not stay linear in nature and are often three-dimensional. Some proteins require no assistance in order to become the shape they need to be, while others require chaperone molecules to help it obtain the necessary shape. These help the protein form its tertiary structure, which is its final shape. The core of the protein is generally hydrophobic, while the outside is generally hydrophilic. The quaternary structure of a protein is defined as the protein connecting with several other proteins to make a completely functional and active protein in the cell.

Proteins come in three major classifications: fibrous proteins, globular proteins, and membrane proteins. Globular proteins are soluble in water. Most enzymes are globular proteins. Fibrous proteins are structural proteins and are made into substances such as actin, collagen, and elastin. Membrane proteins exist within the membranes of cells and form receptors that are acted upon by chemical messengers in the extracellular space.

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Simple Sugars Simple sugars are the main component of larger molecules called carbohydrates. Most sugars are monosaccharides. Monosaccharides are the basic component of a sugar that cannot be broken down into anything else that is a sugar. Typical monosaccharides in the body are galactose, fructose, and glucose. Typical disaccharides (that can also be referred to as simple sugars) include lactose (milk sugar), sucrose (which is table sugar), and maltose (which is malted grain sugar).

Figure 3 describes the simple sugars seen in nature:

Figure 3 Diets high in sugar are not believed to be healthy. The average American consumes about 50 pounds of sugar per year, mostly as sucrose (table sugar) which is derived from sugar beets and sugar cane. A diet

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high in sugar is believed to be an underlying factor in developing obesity, dementia, diabetes, tooth decay, and heart disease.

Sugars are found in animals but to a much greater degree are part of the plant cell. Substances such as sugarcane and sugar beets have large amounts of sugar and are used to extract their sugars which is refined then into sucrose table sugar. The average person eats about fifty pounds of sugar each year, which may not be good for human health. Many diseases have are thought to be exacerbated by a high sugar diet, including but not limited to heart disease, diabetes, tooth decay, dementia, and obesity.

Sugars can be monosaccharides, disaccharides, oligosaccharides, or polysaccharides. When they become large, they are called carbohydrates. In humans, the most important sugar is glucose as it is utilized to make energy in all basic cellular metabolic functions. All-natural sugars consist only of oxygen, hydrogen, and carbon. Some artificial sugars, such as sucralose, taste sweet but are not used by the body. Sucralose is synthesized by chlorinating sucrose and is used as an artificial sweetener. In order to form a polysaccharide, a glycosidic bond must be made between two adjacent sugars, with a loss of a single water molecule in the process of making the bond.

Sugars can exist in a cyclic form or chain form. By far, most sugars exist in nature as the ring-form of the molecule. Glucose, in fact, is 99.9 percent of the time found as a sugar ring, with only a small portion being linear or an “open-chain” form. Only the ring form has the capability of forming a glycosidic bond in the making of a polysaccharide.

Types of Sugars The simplest types of sugars are monosaccharides, which have the chemical structure of C 6H12O6. Each of them has five different hydroxyl groups (-OH) and one carbonyl (C=O) group. They can exist in levoform (left-handed) and dextro form (right-handed).

While there are many kinds of sugar, the three primary monosaccharides are fructose, glucose, and galactose. Fructose or “fruit sugar” is found in honey, sugarcane, fruits, and certain root vegetables. It is the sweetest among all the sugars and is paired with glucose to make table sugar. High fructose corn syrup is extremely sweet because some of the glucose in the syrup is converted into sweeter fructose.

A primary feature of galactose is that it is part of the antigenic surface of the red blood cells and helps to form a person’s blood type. It is rarely found simply as a monosaccharide and is mostly found as a disaccharide along with glucose to make lactose or “milk sugar”. It isn’t very sweet, which is why milk isn’t very sweet.

Glucose can be called “dextrose” or grape sugar. It is found in plants, mostly because it is the main endproduct of photosynthesis. Most of the sugars ingested by humans gets turned into glucose in the digestive process, when it is then absorbed and enters the bloodstream to go to different cells to be used in the process of cellular energy production. Glucose syrup is rarely used in food-making but can be made by degrading starch (which is the plant form of a long-chain glucose molecule).

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Lactose is referred to as milk sugar because it is the main type of sugar found in milk. It takes lactase in the gut to transform the disaccharide into galactose and glucose. If a person is deficient in the enzyme lactase, they cannot digest lactose and will have indigestion and stomach upset when consuming milk products. About sixty-five percent of adults are lactose intolerant because of a deficiency of lactase. It is estimated that ninety percent of adult East Asians are lactose intolerant.

Maltose is a disaccharide that comes from the germination of barley grains and other grains. It is made from two molecules of glucose and isn’t as sweet as sucrose, fructose, or glucose (as a monosaccharide). Starch is broken down into maltose by amylase in the GI tract. This disaccharide requires “maltase” to break down into glucose molecules. Sucrose, on the other hand, requires “sucrase” to break it down into glucose and fructose.

Carbohydrates The definition of a carbohydrate can be as simple as a monosaccharide or as complex as a “complex saccharide”, which is a long-chain sugar. The hydrogen to oxygen ratio of a carbohydrate is two to one and carbohydrates, by definition only contain carbon, hydrogen, and oxygen. There are a few sugars that do not conform to the typical “sugar” configuration. One of these is deoxyribose, which is a fivecarbon sugar with a different ratio of hydrogen to oxygen. Deoxyribose is the sugar in DNA Deoxyribose nucleic acid. Ribose (the precursor to RNA) is a five-carbon sugar.

Carbohydrates are the main energy source in the body as glucose is used in the Krebs cycle to make ATP for energy. Glycogen is stored in the muscle cells and liver cells. When glucose is needed, enzymes cleave off glucose molecules from the glycogen to make simple glucose molecules that travel to the cells and are utilized in energy production.

The chemical formula of carbohydrates is C n(H2O)n. A carbohydrate can have any number of monomers strung together. The typical carbohydrates found in nature consist solely of glucose, galactose, and fructose; however, N-acetyl groups are added to monosaccharides and make up chitin and sulfate groups are added to polysaccharides called glycosaminoglycans. Sialic acid is a polysaccharide that contains carboxylic acid groups. It also has some deoxy modifications that change the chemical makeup of the molecule.

Fatty Acids A fatty acid is defined as a carboxylic acid that is connected to a long aliphatic side chain, which can be completely covered with hydrogen atoms (being saturated or a “saturated fat”) or partially unsaturated with hydrogen atoms (being monounsaturated or polyunsaturated). Almost all fatty acids in nature have an even number of carbon atoms (from four to twenty-eight) per side chain. Fatty acids can be derived from triglycerides or phospholipids (both of which are types of fats) but are not derived from sterol fats (like cholesterol).

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Figure 4 shows the structure of a triglyceride and cholesterol:

Figure 4 The biggest importance of fatty acids in humans is that they can be used as a great energy source to make ATP for the cell’s energy needs. Fatty acids can be used in place of glucose for cellular energy in all cells of the body except for the brain because long-chain fatty acids cannot cross the blood brain barrier. Only ketone bodies, glucose, short-chain fatty acids, and medium-chain fatty acids can cross the blood-brain barrier. Sterols as well cannot cross the blood brain barrier.

A saturated fatty acid has the maximum possible number of hydrogen atoms on it and has no carboncarbon double bond. Such fatty acids are found in meats and dairy products. Unsaturated fats can be monounsaturated (with one carbon-carbon double bond) or polyunsaturated (with more than one carbon-carbon double bond). These tend to be found as healthier fats in vegetables, seeds, grains, and

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c. Optic d. Vagus e. Abducens Answer: c. It is the optic nerve that sends a signal to the hypothalamus to indicate how much light is reaching the retina.

151. What region of the limbic system generates stress responses by sending signals to the hypothalamus? a. Medulla b. Hippocampus c. Mammillary bodies d. Amygdala e. Prefrontal cortex Answer: d. The amygdala is the part of the limbic system that sends signals to the hypothalamus in order to influence the autonomic nervous system and endocrine systems.

152. What is the name for the sympathetic fibers that project to the heart, leading to increased contractility and heart rate? a. Solitary tract b. Vasomotor nerve c. Vagus nerve d. Hypoglossal nerve e. Cardiac accelerator nerve Answer: e. The cardiac accelerator nerve sends signals from the brain to the heart to increase heart rate using sympathetic nervous system tone.

153. What is not included in the total lung capacity? a. Vital capacity b. Reserve volume c. Inspiratory reserve volume d. Expiratory reserve volume e. Tidal volume Answer: a. The total lung capacity (TLC) is the RV + IRV + ERV + TV. The vital capacity (VC) is not included in this calculation.

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154. What center controls the rate of breathing? a. Aortic center b. Apneustic center c. Pneumotaxic center d. Dorsal respiratory group e. Ventral respiratory group Answer: c. The pneumotaxic center in the pons controls the rate of breathing.

155. Gas exchange that occurs at the level of the tissues is called what? a. external respiration b. Interpulmonary respiration c. Pulmonary ventilation d. Alveolar ventilation e. Internal respiration Answer: e. Gas exchange at the level of the tissues is called internal respiration.

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