Essentials of Medical Physiology 6th Edition PDF

Click here to visit www.thedentalhub.org.in eBook Brought to you By “ The Dental Hub ” Visit our Website for More Dental stuffs www.thedentalhub.org.in Click here to visit www.thedentalhub.org.in Medical Physiology Essentials of Click here to visit www.thedentalhub.org.in Essentials of Medical Physiology Sixth Edition K Sembulingam PhD and Prema Sembulingam PhD Madha Medical College & Research Institute Kundrathur Main Road, Kovur, Thandalam (Near Porur) Chennai, Tamil Nadu, India Formerly Click here to visit www.thedentalhub.org.in MR Medical College Gulbarga, Karnataka, India Sri Ramachandra Medical College and Research Institute Chennai, Tamil Nadu, India School of Health Sciences, Universiti Sains Malaysia Kelantan, Malaysia Sri Lakshmi Narayana Institute of Medical Sciences Puducherry, India Sri Manakula Vinayagar Medical College and Hospital Puducherry, India and Shri Sathya Sai Medical College and Research Institute Kanchipuram, Tamil Nadu, India ® JAYPEE BROTHERS MEDICAL PUBLISHERS (P) LTD New Delhi Panama City London Dhaka Kathmandu ® Jaypee Brothers Medical Publishers (P) Ltd Headquarters Jaypee Brothers Medical Publishers (P) Ltd 4838/24, Ansari Road, Daryaganj New Delhi 110 002, India Phone: +91-11-43574357 Fax: +91-11-43574314 Email: [email protected] Overseas Offices J.P. Medical Ltd Jaypee-Highlights Medical Publishers Inc. 83 Victoria Street, London City of Knowledge, Bld. 237, Clayton SW1H 0HW (UK) Panama City, Panama Phone: +44-2031708910 Phone: + 507-301-0496 Fax: +02-03-0086180 Fax: + 507-301-0499 Email: [email protected] Email: [email protected] Jaypee Brothers Medical Publishers (P) Ltd Jaypee Brothers Medical Publishers (P) Ltd Click here to visit www.thedentalhub.org.in 17/1-B Babar Road, Block-B, Shaymali Shorakhute, Kathmandu Mohammadpur, Dhaka-1207 Nepal Bangladesh Phone: +00977-9841528578 Mobile: +08801912003485 Email: [email protected] Email: [email protected] Website: www.jaypeebrothers.com Website: www.jaypeedigital.com © 2012, Jaypee Brothers Medical Publishers All rights reserved. No part of this book may be reproduced in any form or by any means without the prior permission of the publisher. Inquiries for bulk sales may be solicited at: [email protected] This book has been published in good faith that the contents provided by the authors contained herein are original, and is intended for educational purposes only. While every effort is made to ensure accuracy of information, the publisher and the authors specifically disclaim any damage, liability, or loss incurred, directly or indirectly, from the use or application of any of the contents of this work. If not specifically stated, all figures and tables are courtesy of the authors. Where appropriate, the readers should consult with a specialist or contact the manufacturer of the drug or device. Essentials of Medical Physiology First Edition: 1999 Second Edition: 2000 Third Edition: 2004 Fourth Edition: 2006 Fifth Edition: 2010 Sixth Edition: 2012 ISBN 978-93-5025-936-8 Printed at Click here to visit www.thedentalhub.org.in Our beloved students Dedicated to Click here to visit www.thedentalhub.org.in Foreword to the Sixth Edition Madha Medical college & ReseaRch institute Approved by Medical Council of India, New Delhi, Affiliated to Tamil Nadu Dr. M.G.R. Medical University, Chennai, Proc. No. AffIn. III (3)/4206/2010 Thandalam, Kovur (Near Porur), Chennai-600 122. Phone : 044 - 2478 0333, 2478 0055 E-mail: [email protected] Dr S MaDaN KuMar MD, Dip. A & E Director It is my privilege and pleasure to give this foreword to sixth edition of the textbook Essentials of Medical Physiology Click here to visit www.thedentalhub.org.in written by two of our dedicated and renowned teachers Dr K Sembulingam and Dr Prema Sembulingam. Since the publication of first edition in the year 1999, this book has been accepted by the faculty of many universities in and out of country. It has become popular among medical, dental and paramedical students because of its elegant presentation, simple language and clear illustrations with diagrams, flow charts and tables. The authors have taken concerted efforts to improve the contents and update the information in every subsequent edition of this book. This sixth edition with newly formatted and updated tables, flow charts and self-explanatory diagrams will help the students in better understanding and performance in various types of examinations. Clinical physiology with updated information in this edition will help the students for their clinical knowledge to a great extent. I congratulate Dr K Sembulingam and Dr Prema Sembulingam on their great effort in bringing sixth edition of this book. Dr S Madan Kumar MD, Dip. A & E Director Madha Medical College & Research Institute Thandalam, Kovur (Near Porur) Chennai, Tamil Nadu, India Click here to visit www.thedentalhub.org.in Foreword to the First Edition sRi RaMachandRa Medical college and ReseaRch institute (deeMed univeRsity) 1, RAMAChANDRA NAGAR, PoRUR, ChENNAI-600 116 Dr TK ParTha SaraThy FRCs (C) FACs  off : 4828027-29, 31-33 Diplomate of the American Board of surgery Fax : 091-44-48277008 vICE-ChANCElloR Telex : 41-25050 PCo IN It is indeed with a great sense of pleasure and privilege that I give this foreword to the book Essentials of Medical Physiology written by two of our dedicated teachers Dr K Sembulingam and Dr Prema Sembulingam. The students Click here to visit www.thedentalhub.org.in have always appreciated the efforts of these two teachers and their ability to make physiology easily comprehended and interesting. Why one more book in physiology, is what I asked myself first before I reviewed the book. The book has been largely directed to the broad and specific needs of the undergraduate students, and simplicity and clarity have been emphasized. The students can easily assimilate the logical sequence in which the subjects have been presented not only for them to understand the same but also perform well in the various types of objective and routine examinations. Several readily understandable diagrams and tables have been included to make subject comprehension and revision easy. Applied physiology, clinical importance and altered situations in pediatrics, geriatrics and pregnancy have been well brought out. The approach utilized in dealing with the subject of physiology would be appreciated by other teachers as well. I have no doubts that this will be a valuable addition to the armamentarium of a student of physiology who is preparing for examination and is seeking a strong foundation to build further on. Here at Sri Ramachandra Medical College and Research Institute (Deemed University), Chennai, Tamil Nadu, India, the faculty involved in writing and editing books of this nature are greatly appreciated, and I as its Vice-Chancellor wish to congratulate the Sembulingams on their great effort. TK Partha Sarathy FRCS (C) FACS Diplomate of the American Board of Surgery Vice-Chancellor Sri Ramachandra Medical College and Research Institute (Deemed University) Porur, Chennai, Tamil Nadu, India Click here to visit www.thedentalhub.org.in Preface to the Sixth Edition With this Sixth edition, Sembulingam’s Essentials of Medical Physiology enters into its second decade and the core subject matter with updated physiological information remain as green as ever. We live in an era where the thirst for knowledge and urge for learning is so much increased that even a layman knows the fundamentals of common disorders like diabetes mellitus, hypertension, jaundice, etc. So, it becomes doubly important to fulfill the expectations of the educated mass, especially in medical field. We are humbly thankful and heavenly happy for the popularity of this book among the undergraduate and postgraduate students of medical, dental and paramedical courses, doctors and other health professionals in and out of our country. Like many other successful textbooks, this book also has sailed through the years smoothly, fruitfully and successfully. May be because, it meets the needs of every group of the readers. Students are happy because it is student-friendly while reading, and exam-friendly while revising. Knowledge seekers are happy because they get the updated and recent developments in the field of physiology. Doctors are happy because applied aspects are covered adequately. Our thirst for improving this textbook is growing every year by seeing outright acceptance of this book by the students, and the appreciation and overwhelming support given by our fellow teachers. The most comments and the suggestions, we receive from our readers, are responsible for better shaping of this book in every edition. Click here to visit www.thedentalhub.org.in This edition is enriched with addition of many more flow charts, tables and descriptive diagrams to make the subject matter easier and approachable for all class of students. Many chapters are upgraded as per the suggestions from our colleagues and fellow teachers from various institutes and universities in and out of India. Our thirst for improving this book is still alive. The improvement is possible only by the comments and suggestions expressed by the readers. So, we welcome the opinions, comments and valuable suggestions from one and all who happen to come across this book. K Sembulingam [email protected] Prema Sembulingam [email protected] Click here to visit www.thedentalhub.org.in Preface to the First Edition The need for having a simple book with basic principles of Medical Physiology has been felt since long. A sincere and maiden attempt has been made with the idea of fulfilling the requirements of present-day curriculum. The script of the book is formatted in such a way that it will be suitable not only for medical students, but also for dental students and the students of allied health subjects like Physiotherapy, Occupational Therapy, Pharmacy, Nursing, Speech, Hearing and Language, etc. Written in a textbook form, this book encompasses the knowledge of basic principles of physiology in each system. An attempt is also made to describe the applied physiology in each system. To give an idea of the matters to be studied, the topics are listed at the beginning of each chapter. Most of the figures are given in schematic form to enable students to understand and reproduce the facts. The probable questions given for each section will help the students preparing for examinations. However, it will be ideal for the students to read each section thoroughly before referring to the questions. We will be very happy to receive opinions, comments and valuable suggestions from all our senior colleagues, fellow teachers and students so that, every aspect of the book can be reviewed in succeeding editions. K Sembulingam Click here to visit www.thedentalhub.org.in Prema Sembulingam Click here to visit www.thedentalhub.org.in Acknowledgments We express our profound gratitude to Late Mr NPV Ramasamy Udayar, Founder Chancellor, Sri Ramachandra Medical College and Research Institute (Deemed University), Chennai, Tamil Nadu, India for his keen interest in all the academic activities of the faculty members. We would like to express our sincere gratitude to Sri VR Venkatachalam, the Chancellor of Sri Ramachandra Medical College and Research Institute (Deemed University) for accepting to grace the occasion of ‘Book Releasing Ceremony’ of Essentials of Medical Physiology—first edition and for releasing the book. We are very much thankful to the former Vice-Chancellor of this University Dr TK Partha Sarathy, who honored us by attending the function and received the first copy of the book. We are also overwhelmed by his magnanimity for his encouragement and for going through the entire script before giving the foreword. We sincerely thank Mrs Radha Venkatachalam, Registrar and Administrative Director, Sri Ramachandra Medical College and Research Institute (Deemed University), who always encouraged the faculty of the university for publications. We thank Dr Sylvia Walter, Professor Emeritus, Department of Physiology, Sri Ramachandra Medical College and Research Institute (Deemed University), who is the inspiration for us to bring out this book. We are also indebted to her for giving many valuable clues to modify the script in many chapters. Our special thanks to Dr V Srinivasan, Former Professor and Head, Department of Physiology, Sri Ramachandra Medical College and Research Institute Click here to visit www.thedentalhub.org.in (Deemed University) for his strong belief in this project, constant encouragement and valuable suggestions. We are very much grateful to Dr V Srinivasan for his keen interest and valuable suggestions for upgrading the script in each edition. We thank all our fellow teachers and senior professors from various institutes and universities in and out of India for their comments and suggestions, which enabled us to bring out each edition of the book successfully. We are deeply indebted to our students of Sri Ramachandra Medical College and Research Institute (Deemed University), Chennai, Tamil Nadu, India and MR Medical College, Gulbarga, Karnataka, India who were the spirit behind the idea of bringing out this book. Our special thanks to Dr M Chandrasekar, Vice-Principal and Head, Department of Physiology, Meenakshi Medical College, Kanchipuram, Tamil Nadu, India for writing a review article on this book in the Journal ‘Biomedicine’ (Vol 20, No. 1). Many valuable suggestions from him enabled us to upgrade the book in each edition. We are grateful to Professor Mafauzy Mohamad, Director, Health Campus, Universiti Sains Malaysia, Kelantan, Malaysia for providing the photos of endocrine disorder patients. We are thankful to Dr Nivaldo Medeiros, Former Director of Hematology and Cytology Services, Central Laboratory, University of Säo Paulo, School of Medicine, USA for giving us the hematology pictures. Our profound thanks are due to Dr S Peter, Founder and Chairman, Madha Group of Academic Institutions for the recognition, appreciation and encouragement given to us in bringing out this edition. We are thankful to Dr S Madan Kumar, Director, Madha Medical College & Research Institute for his keen interest in publishing this edition. We also thank him for accepting and rendering foreword for this edition. We thank Dr K Gajendran, Principal, Madha Medical College & Research Institute for his constant encouragement in bringing out this edition. We are thankful to Shri Jitendar P Vij (CEO), Mr Tarun Duneja (Director-Publishing) and Mr KK Raman (Production Manager) of M/s Jaypee Brothers Medical Publishers (P) Ltd, New Delhi, India for publishing the book in the same format as we wanted. We thank Ms Chetna Malhotra Vohra (Senior Business Executive Manager) for coordinating the processing of this edition. We thank Ms Sajini SV (Project Leader), Ms Hemalata Malini B and Mr Samiulla (DTP Operators); Ms Nandini N, Ms Ramya VR, Ms Bhavya M, and Ms Nikita G (Proofreaders) of Bengaluru Production Unit, M/s Jaypee Brothers Medical Publishers (P) Ltd, Bengaluru Branch, for their wholehearted contribution while formatting the book. We also thank Ms Shilpa K Bhat (Graphic Designer), of Bengaluru Production Unit for making the figures attractive. Special Acknowledgments We sincerely acknowledge the following fellow teachers for their valuable suggestions. All the points suggested by them were acknowledged and incorporated in this edition. 1. Dr M Chandrasekar 6. Dr S Manikandan Vice Principal and Head Associate Professor Department of Physiology Department of Physiology Meenakshi Medical College Tagore Medical College Kanchipuram, Tamil Nadu, India Chennai, Tamil Nadu, India 2. Dr P Sai Kumar 7. Dr NV Mishra Vice Principal and Professor Associate Professor Department of Physiology Department of Physiology Sri Balaji Medical College and Hospital Medical College Chennai, Tamil Nadu, India Nagpur (MS), Maharashtra, India 3. Dr B Vishwanatha Rao 8. Dr KS Udayashankar Professor Professor and Head Click here to visit www.thedentalhub.org.in Department of Physiology Department of Physiology Madras Medical College Sri Rajarajeshwari Medical College and Hospital Chennai, Tamil Nadu, India Bengaluru, Karnataka, India 4. Dr K Sarayu 9. Dr MG Hymavthi Professor and Head Professor Department of Physiology Department of Physiology KAT Viswanathan Government Medical College Sri Rajarajeshwari Medical College and Hospital Trichy, Tamil Nadu, India Bengaluru, Karnataka, India 5. Dr D Venkatesh Professor Department of Physiology MS Ramaiah Medical College Bengaluru, Karnataka, India Contents SECTIoN 1 GENERAL PHySIoLoGy 1. Cell.....................................................................................................................................3 2. Cell Junctions.................................................................................................................22 3. Transport through Cell Membrane................................................................................27 4. Homeostasis...................................................................................................................38 5. Acid-Base Balance.........................................................................................................42 SECTIoN 2 BLooD AND BoDy FLUIDS 6. Body Fluids.....................................................................................................................51 Click here to visit www.thedentalhub.org.in 7. Blood...............................................................................................................................58 8. Plasma Proteins..............................................................................................................61 9. Red Blood Cells..............................................................................................................66 10. Erythropoiesis................................................................................................................71 11. Hemoglobin and Iron Metabolism.................................................................................77 12. Erythrocyte Sedimentation Rate...................................................................................83 13. Packed Cell Volume and Blood Indices........................................................................86 14. Anemia.............................................................................................................................89 15. Hemolysis and Fragility of Red Blood Cells................................................................95 16. White Blood Cells...........................................................................................................97 17. Immunity........................................................................................................................107 18. Platelets.........................................................................................................................122 19. Hemostasis...................................................................................................................127 20. Coagulation of Blood...................................................................................................129 21. Blood Groups................................................................................................................139 22. Blood Transfusion........................................................................................................146 23. Blood Volume................................................................................................................148 24. Reticuloendothelial System and Tissue Macrophage...............................................151 25. Spleen............................................................................................................................153 26. Lymphatic System and Lymph....................................................................................155 27. Tissue Fluid and Edema..............................................................................................159 xviii Essentials of Medical Physiology SECTIoN 3 MUSCLE PHySIoLoGy 28. Classification of Muscles.............................................................................................167 29. Structure of Skeletal Muscle.......................................................................................169 30. Properties of Skeletal Muscle......................................................................................176 31. Changes during Muscular Contraction......................................................................188 32. Neuromuscular Junction.............................................................................................200 33. Smooth Muscle.............................................................................................................204 34. Electromyogram and Disorders of Skeletal Muscle..................................................210 35. Endurance of Muscle...................................................................................................214 SECTIoN 4 DIGESTIVE SySTEM 36. Introduction to Digestive System...............................................................................219 37. Mouth and Salivary Glands.........................................................................................223 38. Stomach........................................................................................................................230 39. Pancreas........................................................................................................................241 Click here to visit www.thedentalhub.org.in 40. Liver and Gallbladder...................................................................................................249 41. Small Intestine..............................................................................................................261 42. Large Intestine..............................................................................................................266 43. Movements of Gastrointestinal Tract.........................................................................270 44. Gastrointestinal Hormones.........................................................................................281 45. Digestion, Absorption and Metabolism of Carbohydrates.......................................287 46. Digestion, Absorption and Metabolism of Proteins..................................................290 47. Digestion, Absorption and Metabolism of Lipids......................................................292 SECTIoN 5 RENAL PHySIoLoGy AND SKIN 48. Kidney............................................................................................................................301 49. Nephron.........................................................................................................................304 50. Juxtaglomerular Apparatus.........................................................................................309 51. Renal Circulation..........................................................................................................312 52. Urine Formation............................................................................................................315 53. Concentration of Urine.................................................................................................325 54. Acidification of Urine and Role of Kidney in Acid-Base Balance............................330 55. Renal Function Tests...................................................................................................333 56. Renal Failure.................................................................................................................337 Contents xix 57. Micturition.....................................................................................................................339 58. Dialysis and Artificial Kidney......................................................................................346 59. Diuretics........................................................................................................................348 60. Structure of Skin...........................................................................................................351 61. Functions of Skin.........................................................................................................354 62. Glands of Skin..............................................................................................................356 63. Body Temperature........................................................................................................359 SECTIoN 6 ENDoCRINoLoGy 64. Introduction to Endocrinology....................................................................................367 65. Hormones......................................................................................................................371 66. Pituitary Gland..............................................................................................................375 67. Thyroid Gland...............................................................................................................388 68. Parathyroid Glands and Physiology of Bone............................................................399 69. Endocrine Functions of Pancreas..............................................................................415 70. Adrenal Cortex..............................................................................................................425 71. Adrenal Medulla............................................................................................................439 Click here to visit www.thedentalhub.org.in 72. Endocrine Functions of other organs.......................................................................444 73. Local Hormones...........................................................................................................447 SECTIoN 7 REPRoDUCTIVE SySTEM 74. Male Reproductive System..........................................................................................455 75. Seminal Vesicles...........................................................................................................467 76. Prostate Gland..............................................................................................................468 77. Semen............................................................................................................................470 78. Female Reproductive System.....................................................................................473 79. ovary.............................................................................................................................476 80. Menstrual Cycle............................................................................................................482 81. ovulation.......................................................................................................................492 82. Menopause....................................................................................................................494 83. Infertility.......................................................................................................................496 84. Pregnancy and Parturition...........................................................................................498 85. Placenta.........................................................................................................................505 86. Pregnancy Tests...........................................................................................................508 87. Mammary Glands and Lactation.................................................................................510 88. Fertility Control.............................................................................................................513 xx Essentials of Medical Physiology SECTIoN 8 CARDIoVASCULAR SySTEM 89. Introduction to Cardiovascular System.....................................................................519 90. Properties of Cardiac Muscle......................................................................................525 91. Cardiac Cycle................................................................................................................533 92. Heart Sounds................................................................................................................544 93. Cardiac Murmur............................................................................................................549 94. Electrocardiogram (ECG).............................................................................................551 95. Vector.............................................................................................................................558 96. Arrhythmia....................................................................................................................562 97. Effect of Changes in Electrolyte Concentration on Heart........................................570 98. Cardiac output..............................................................................................................572 99. Heart-Lung Preparation...............................................................................................582 100. Cardiac Function Curves.............................................................................................584 101. Heart Rate......................................................................................................................587 102. Hemodynamics.............................................................................................................595 103. Arterial Blood Pressure...............................................................................................602 Click here to visit www.thedentalhub.org.in 104. Venous Pressure..........................................................................................................617 105. Capillary Pressure........................................................................................................620 106. Arterial Pulse................................................................................................................622 107. Venous Pulse................................................................................................................627 108. Coronary Circulation....................................................................................................629 109. Cerebral Circulation.....................................................................................................634 110. Splanchnic Circulation.................................................................................................638 111. Capillary Circulation.....................................................................................................640 112. Circulation through Skeletal Muscle..........................................................................644 113. Cutaneous Circulation.................................................................................................646 114. Fetal Circulation and Respiration...............................................................................648 115. Hemorrhage..................................................................................................................651 116. Circulatory Shock and Heart Failure..........................................................................654 117. Cardiovascular Adjustments during Exercise...........................................................664 SECTIoN 9 RESPIRAToRy SySTEM AND ENVIRoNMENTAL PHySIoLoGy 118. Physiological Anatomy of Respiratory Tract.............................................................673 119. Pulmonary Circulation.................................................................................................678 120. Mechanics of Respiration............................................................................................682 121. Pulmonary Function Tests...........................................................................................690 Contents xxi 122. Ventilation.....................................................................................................................700 123. Inspired Air, Alveolar Air and Expired Air..................................................................703 124. Exchange of Respiratory Gases.................................................................................705 125. Transport of Respiratory Gases.................................................................................711 126. Regulation of Respiration............................................................................................716 127. Disturbances of Respiration........................................................................................723 128. High Altitude and Space Physiology..........................................................................737 129. Deep Sea Physiology...................................................................................................743 130. Effects of Exposure to Cold and Heat........................................................................746 131. Artificial Respiration....................................................................................................749 132. Effects of Exercise on Respiration.............................................................................751 SECTIoN 10 NERVoUS SySTEM 133. Introduction to Nervous System.................................................................................757 134. Neuron...........................................................................................................................759 135. Classification of Nerve Fibers.....................................................................................764 136. Properties of Nerve Fibers...........................................................................................766 Click here to visit www.thedentalhub.org.in 137. Degeneration and Regeneration of Nerve Fibers......................................................770 138. Neuroglia.......................................................................................................................773 139. Receptors......................................................................................................................775 140. Synapse.........................................................................................................................780 141. Neurotransmitters........................................................................................................787 142. Reflex Activity...............................................................................................................795 143. Spinal Cord...................................................................................................................803 144. Somatosensory System and Somatomotor System.................................................828 145. Physiology of Pain.......................................................................................................838 146. Brainstem......................................................................................................................844 147. Thalamus.......................................................................................................................847 148. Internal Capsule............................................................................................................853 149. Hypothalamus...............................................................................................................855 150. Cerebellum....................................................................................................................863 151. Basal Ganglia................................................................................................................878 152. Cerebral Cortex.............................................................................................................884 153. Limbic System..............................................................................................................898 154. Reticular Formation......................................................................................................901 155. Preparations of Animals for Experimental Studies...................................................906 156. Proprioceptors..............................................................................................................908 157. Posture and Equilibrium..............................................................................................913 158. Vestibular Apparatus....................................................................................................919 159. Electroencephalogram (EEG)......................................................................................929 160. Physiology of Sleep.....................................................................................................931 161. Epilepsy.........................................................................................................................935 162. Higher Intellectual Functions......................................................................................937 163. Cerebrospinal Fluid (CSF)...........................................................................................949 164. Autonomic Nervous System (ANS).............................................................................954 SECTIoN 11 SPECIAL SENSES 165. Structure of the Eye.....................................................................................................965 166. Visual Process..............................................................................................................978 167. Field of Vision...............................................................................................................987 168. Visual Pathway.............................................................................................................989 169. Pupillary Reflexes.........................................................................................................994 170. Color Vision..................................................................................................................999 171. Errors of Refraction....................................................................................................1004 172. Structure of Ear..........................................................................................................1007 Click here to visit www.thedentalhub.org.in 173. Auditory Pathway.......................................................................................................1013 174. Mechanism of Hearing...............................................................................................1016 175. Auditory Defects.........................................................................................................1022 176. Sensation of Taste......................................................................................................1024 177. Sensation of Smell.....................................................................................................1028 Index..................................................................................................................................1033 Introduction Physiology is the most fascinating and ancient branch of science. It is fascinating because, it unfolds the mystery of complicated functional aspects of individual organs in the body. It is ancient because, it exists ever since the origin of life. Even before knowing the language, culture and society, man knew about the hunger, thirst, pain and fear which are the basics of physiology. Physiology is defined as the study of functions of various systems and different organs of the body. Physiology is of different types namely, Human Physiology, Animal Physiology and Plant Physiology. Human Physiology and Animal Physiology are very much inter-related. Knowledge of Human Physiology is essential to understand the other allied subjects like Biochemistry, Pharmacology, Pathology, Medicine, etc. However, it is worthwhile to have a brief knowledge of anatomy of different systems and various organs to understand the principles of Human Physiology. The basic physiological functions include, provision of oxygen and nutrients, removal of metabolites and other waste products, maintenance of blood pressure and body temperature, hunger and thirst, locomotor functions, special sensory functions, reproduction and the higher intellectual functions like learning and memory. In the unicellular organisms, all the physiological functions are carried out by simple diffusion through the cell membrane. Because of the evolutionary and ecological changes over the years, individual system is developed for each function such as digestive system, cardiovascular system, respiratory system, excretory system, etc. Every Click here to visit www.thedentalhub.org.in system in the body is independent structurally and functionally yet, all the systems are interdependent. Human Physiology is usually studied under the following headings: 1. General Physiology 2. Blood and Body Fluids 3. Muscle Physiology 4. Digestive System 5. Renal Physiology and Excretion 6. Endocrinology 7. Reproductive System 8. Cardiovascular System 9. Respiratory System and Environmental Physiology 10. Nervous System 11. Special Senses Section 1 General Physiology 1. Cell.............................................................................................................. 3 2. Cell Junctions............................................................................................ 22 3. Transport through Cell Membrane............................................................ 27 4. Homeostasis............................................................................................. 38 5. Acid-base Balance.................................................................................... 42 Click here to visit www.thedentalhub.org.in Click here to visit www.thedentalhub.org.in Chapter Cell 1 INTRODUCTION STRUCTURE OF THE CELL CELL MEMBRANE CYTOPLASM ORGANELLES IN CYTOPLASM ORGANELLES WITH LIMITING MEMBRANE ORGANELLES WITHOUT LIMITING MEMBRANE NUCLEUS DEOXYRIBONUCLEIC ACID GENE RIBONUCLEIC ACID Click here to visit www.thedentalhub.org.in GENE EXPRESSION GROWTH FACTORS CELL DEATH CELL ADAPTATION CELL DEGENERATION CELL AGING STEM CELLS INTRODUCTION 5. Shows immediate response to the entry of invaders like bacteria or toxic substances into the body CELL 6. Reproduces by division. There are some exceptions like neuron, which do not reproduce. All the living things are composed of cells. A single cell is the smallest unit that has all the characteristics of life. TISSUE Cell is defined as the structural and functional unit of the living body. Tissue is defined as the group of cells having similar function. There are many types of tissues in the body. All General Characteristics of Cell the tissues are classified into four major types which are called the primary tissues. The primary tissues include: Each cell in the body: 1. Muscle tissue (skeletal muscle, smooth muscle and 1. Needs nutrition and oxygen cardiac muscle) 2. Produces its own energy necessary for its growth, 2. Nervous tissue (neurons and supporting cells) repair and other activities 3. Epithelial tissue (squamous, columnar and cuboidal 3. Eliminates carbon dioxide and other metabolic wastes epithelial cells) 4. Maintains the medium, i.e. the environment for its 4. Connective tissue (connective tissue proper, cartil- survival age, bone and blood). 4 Section 1 t General Physiology ORGAN CELL MEMBRANE An organ is defined as the structure that is formed by Cell membrane is a protective sheath, enveloping the two or more primary types of tissues, which execute the cell body. It is also known as plasma membrane or functions of the organ. Some organs are composed of all plasmalemma. This membrane separates the fluid out the four types of primary tissues. The organs are of two side the cell called extracellular fluid (ECF) and the fluid types, namely tubular or hollow organs and compact or inside the cell called intracellular fluid (ICF). The cell parenchymal organs. Some of the organs in the body are membrane is a semipermeable membrane. So, there is brain, heart, lungs, stomach, intestine, liver, gallbladder, free exchange of certain substances between ECF and pancreas, kidneys, endocrine glands, etc. ICF. Thickness of the cell membrane varies from 75 to 111Å (Fig. 1.2). SYSTEM COMPOSITION OF CELL MEMBRANE The organ system is defined as group of organs that work together to carry out specific functions of the body. Cell membrane is composed of three types of substances: Each system performs a specific function. Digestive 1. Proteins (55%) system is concerned with digestion of food particles. 2. Lipids (40%) Excretory system eliminates unwanted substances. 3. Carbohydrates (5%). Cardiovascular system is responsible for transport of substances between the organs. Respiratory system STRUCTURE OF CELL MEMBRANE is concerned with the supply of oxygen and removal of carbon dioxide. Reproductive system is involved in the On the basis of structure, cell membrane is called a unit reproduction of species. Endocrine system is concerned membrane or a three-layered membrane. The electron with growth of the body and regulation and maintenance microscopic study reveals three layers of cell membrane, of normal life. Musculoskeletal system is responsible for namely, one central electron-lucent layer and two elec- Click here to visit www.thedentalhub.org.in stability and movements of the body. Nervous system tron-dense layers. The two electron-dense layers are controls the locomotion and other activities including the placed one on either side of the central layer. The central intellectual functions. layer is a lipid layer formed by lipid substances. The other two layers are protein layers formed by proteins. STRUCTURE OF THE CELL Cell membrane contains some carbohydrate molecules Each cell is formed by a cell body and a membrane also. covering the cell body called the cell membrane. Cell body has two parts, namely nucleus and cytoplasm Structural Model of the Cell Membrane surrounding the nucleus (Fig. 1.1). Thus, the structure 1. Danielli-Davson model of the cell is studied under three headings: 1. Cell membrane ‘DanielliDavson model’ was the first proposed basic 2. Cytoplasm model of membrane structure. It was proposed by 3. Nucleus. James F Danielli and Hugh Davson in 1935. And it was accepted by scientists for many years. This model was basically a ‘sandwich of lipids’ covered by proteins on both sides. FIGURE 1.1: Structure of the cell FIGURE 1.2: Diagram of the cell membrane Chapter 1 t Cell 5 2. Unit membrane model oily structures and cholesterol helps to ‘pack’ the phospholipids in the membrane. So, cholesterol is In 1957, JD Robertson replaced ‘DanielliDavson model’ responsible for the structural integrity of lipid layer of the by ‘Unit membrane model’ on the basis of electron cell membrane. microscopic studies. 3. Fluid mosaic model Functions of Lipid Layer in Cell Membrane Later in 1972, SJ Singer and GL Nicholson proposed ‘The Lipid layer of the cell membrane is a semipermeable fluid mosaic model’. According to them, the membrane membrane and allows only the fat-soluble substances is a fluid with mosaic of proteins (mosaic means pattern to pass through it. Thus, the fat-soluble substances like formed by arrangement of different colored pieces of oxygen, carbon dioxide and alcohol can pass through stone, tile, glass or other such materials). This model this lipid layer. The water-soluble substances such as is accepted by the scientists till now. In this model, the glucose, urea and electrolytes cannot pass through this proteins are found to float in the lipid layer instead of layer. forming the layers of the sandwich-type model. Protein Layers of the Cell Membrane Lipid Layers of the Cell Membrane Protein layers of the cell membrane are electron-dense The central lipid layer is a bilayered structure. This is layers. These layers cover the two surfaces of the formed by a thin film of lipids. The characteristic feature central lipid layer. Protein layers give protection to the of lipid layer is that, it is fluid in nature and not a solid central lipid layer. The protein substances present in structure. So, the portions of the membrane move from these layers are mostly glycoproteins. one point to another point along the surface of the cell. Protein molecules are classified into two categories: The materials dissolved in lipid layer also move to all 1. Integral proteins or transmembrane proteins. areas of the cell membrane. 2. Peripheral proteins or peripheral membrane Major lipids are: Click here to visit www.thedentalhub.org.in proteins. 1. Phospholipids 2. Cholesterol. 1. Integral proteins 1. Phospholipids Integral or transmembrane proteins are the proteins that pass through entire thickness of cell membrane from one Phospholipids are the lipid substances containing phos- side to the other side. These proteins are tightly bound phorus and fatty acids. Aminophospholipids, sphingo- with the cell membrane. myelins, phosphatidylcholine, phosphatidyletholamine, Examples of integral protein: phosphatidylglycerol, phosphatidylserine and phos- i. Cell adhesion proteins phatidylinositol are the phospholipids present in lipid ii. Cell junction proteins layer of cell membrane. iii. Some carrier (transport) proteins Phospholipid molecules are arranged in two layers (Fig. 1.3). Each phospholipid molecule resembles the iv. Channel proteins headed pin in shape. The outer part of the phospholipid v. Some hormone receptors molecule is called the head portion and the inner portion vi. Antigens is called the tail portion. vii. Some enzymes. Head portion is the polar end and it is soluble in water and has strong affinity for water (hydrophilic). Tail portion is the non-polar end. It is insoluble in water and repelled by water (hydrophobic). Two layers of phospholipids are arranged in such a way that the hydrophobic tail portions meet in the center of the membrane. Hydrophilic head portions of outer layer face the ECF and those of the inner layer face ICF (cytoplasm). 2. Cholesterol Cholesterol molecules are arranged in between the phospholipid molecules. Phospholipids are soft and FIGURE 1.3: Lipids of the cell membrane 6 Section 1 t General Physiology 2. Peripheral proteins 3. Some carbohydrate molecules function as the receptors for some hormones. Peripheral proteins or peripheral membrane proteins are the proteins which are partially embedded in the FUNCTIONS OF CELL MEMBRANE outer and inner surfaces of the cell membrane and do not penetrate the cell membrane. Peripheral proteins 1. Protective function: Cell membrane protects the are loosely bound with integral proteins or lipid layer of cytoplasm and the organelles present in the cyto- cell membrane. So, these protein molecules dissociate plasm readily from the cell membrane. 2. Selective permeability: Cell membrane acts as a Examples of peripheral proteins: semipermeable membrane, which allows only some i. Proteins of cytoskeleton substances to pass through it and acts as a barrier ii. Some carrier (transport) proteins for other substances iii. Some enzymes. 3. Absorptive function: Nutrients are absorbed into the cell through the cell membrane Functions of Proteins in Cell Membrane 4. Excretory function: Metabolites and other waste products from the cell are excreted out through the 1. Integral proteins provide the structural integrity of cell membrane the cell membrane 5. Exchange of gases: Oxygen enters the cell from the 2. Channel proteins help in the diffusion of water- blood and carbon dioxide leaves the cell and enters soluble substances like glucose and electrolytes the blood through the cell membrane 3. Carrier or transport proteins help in the transport of 6. Maintenance of shape and size of the cell: Cell mem- substances across the cell membrane by means of brane is responsible for the maintenance of shape active or passive transport and size of the cell. 4. Pump: Some carrier proteins act as pumps, by which ions are transported actively across the cell CYTOPLASM Click here to visit www.thedentalhub.org.in membrane Cytoplasm of the cell is the jellylike material formed by 5. Receptor proteins serve as the receptor sites for 80% of water. It contains a clear liquid portion called hormones and neurotransmitters cytosol and various particles of different shape and 6. Enzymes: Some of the protein molecules form the size. These particles are proteins, carbohydrates, lipids enzymes and control chemical (metabolic) reactions or electrolytes in nature. Cytoplasm also contains many within the cell membrane organelles with distinct structure and function. 7. Antigens: Some proteins act as antigens and induce Cytoplasm is made up of two zones: the process of antibody formation 1. Ectoplasm: Peripheral part of cytoplasm, situated 8. Cell adhesion molecules or the integral proteins are just beneath the cell membrane responsible for attachment of cells to their neighbors 2. Endoplasm: Inner part of cytoplasm, interposed or to basal lamina. between the ectoplasm and the nucleus. Carbohydrates of the Cell Membrane ORGANELLES IN CYTOPLASM Some of the carbohydrate molecules present in Cytoplasmic organelles are the cellular structures cell membrane are attached to proteins and form embedded in the cytoplasm. Organelles are considered glycoproteins (proteoglycans). Some carbohydrate as small organs of the cell. Some organelles are bound molecules are attached to lipids and form glycolipids. by limiting membrane and others do not have limiting Carbohydrate molecules form a thin and loose membrane (Box 1.1). Each organelle is having a definite covering over the entire surface of the cell membrane structure and specific functions (Table 1.1). called glycocalyx. ORGANELLES WITH LIMITING MEMBRANE Functions of Carbohydrates in Cell Membrance ENDOPLASMIC RETICULUM 1. Carbohydrate molecules are negatively charged and do not permit the negatively charged substances to Endoplasmic reticulum is a network of tubular and move in and out of the cell microsomal vesicular structures which are interconnect- 2. Glycocalyx from the neighboring cells helps in the ed with one another. It is covered by a limiting membrane tight fixation of cells with one another which is formed by proteins and bilayered lipids. The lumen Chapter 1 t Cell 7 BOX 1.1: Cytoplasmic organelles between nucleus and cell membrane by connecting the cell membrane with the nuclear membrane. Organelles with limiting membrane 1. Endoplasmic reticulum Types of Endoplasmic Reticulum 2. Golgi apparatus 3. Lysosome Endoplasmic reticulum is of two types, namely rough 4. Peroxisome endoplasmic reticulum and smooth endoplasmic reti- 5. Centrosome and centrioles culum. Both the types are interconnected and continuous 6. Secretory vesicles with one another. Depending upon the activities of the 7. Mitochondria cells, the rough endoplasmic reticulum changes to 8. Nucleus smooth endoplasmic reticulum and vice versa. Organelles without limiting membrane 1. Ribosomes Rough Endoplasmic Reticulum 2. Cytoskeleton It is the endoplasmic reticulum with rough, bumpy or of endoplasmic reticulum contains a fluid medium called bead-like appearance. Rough appearance is due to the endoplasmic matrix. The diameter of the lumen is about attachment of granular ribosomes to its outer surface. 400 to 700Å. The endoplasmic reticulum forms the link Hence, it is also called the granular endoplasmic TABLE 1.1: Functions of cytoplasmic organelles Organelles Functions Rough endoplasmic reticulum 1. Synthesis of proteins 2. Degradation of wornout organelles Smooth endoplasmic reticulum 1. Synthesis of lipids and steroids Click here to visit www.thedentalhub.org.in 2. Role in cellular metabolism 3. Storage and metabolism of calcium 4. Catabolism and detoxification of toxic substances Golgi apparatus 1. Processing, packaging, labeling and delivery of proteins and lipids Lysosomes 1. Degradation of macromolecules 2. Degradation of wornout organelles 3. Removal of excess of secretory products 4. Secretion of perforin, granzymes, melanin and serotonin Peroxisomes 1. Breakdown of excess fatty acids 2. Detoxification of hydrogen peroxide and other metabolic products 3. Oxygen utilization 4. Acceleration of gluconeogenesis 5. Degradation of purine to uric acid 6. Role in the formation of myelin 7. Role in the formation of bile acids Centrosome 1. Movement of chromosomes during cell division Mitochondria 1. Production of energy 2. Synthesis of ATP 3. Initiation of apoptosis Ribosomes 1. Synthesis of proteins Cytoskeleton 1. Determination of shape of the cell 2. Stability of cell shape 3. Cellular movements Nucleus 1. Control of all activities of the cell 2. Synthesis of RNA 3. Sending genetic instruction to cytoplasm for protein synthesis 4. Formation of subunits of ribosomes 5. Control of cell division 6. Storage of hereditary information in genes (DNA) 8 Section 1 t General Physiology reticulum (Fig. 1.4). Rough endoplasmic reticulum is vesicular or tubular in structure. Functions of Rough Endoplasmic Reticulum 1. Synthesis of proteins Rough endoplasmic reticulum is concerned with the synthesis of proteins in the cell. It is involved with the synthesis of mainly those proteins which are secreted from the cells such as insulin from βcells of islets of Langerhans in pancreas and antibodies from B lymphocytes. Ribosomes arrange the amino acids into small units of proteins and transport them into the rough endoplasmic reticulum. Here, the carbohydrates are added to the protein units forming the glycosylated proteins or glycoproteins, which are arranged in the FIGURE 1.4: Endoplasmic reticulum form of reticular vesicles. These vesicles are transported mainly to Golgi apparatus for further modification and 3. Storage and metabolism of calcium processing. Few vesicles are transported to other cyto- Smooth endoplasmic reticulum is the major site of plasmic organelles. storage and metabolism of calcium. In skeletal muscle 2. Degradation of worn-out organelles fibers, it releases calcium which is necessary to trigger the muscle contraction. Rough endoplasmic reticulum also plays an important Click here to visit www.thedentalhub.org.in role in the degradation of worn-out cytoplasmic orga- 4. Catabolism and detoxification nelles like mitochondria. It wraps itself around the worn- Smooth endoplasmic reticulum is also concerned out organelles and forms a vacuole which is often called with catabolism and detoxification of toxic substances the autophagosome. Autophagosome is digested by like some drugs and carcinogens (cancer-producing lysosomal enzymes (see below for details). substances) in the liver. Smooth Endoplasmic Reticulum GOLGI APPARATUS It is the endoplasmic reticulum with smooth appearance. Golgi apparatus or Golgi body or Golgi complex is a It is also called agranular reticulum. It is formed by many membrane-bound organelle, involved in the processing interconnected tubules. So, it is also called tubular of proteins. It is present in all the cells except red blood endoplasmic reticulum. cells. It is named after the discoverer Camillo Golgi. Usually, each cell has one Golgi apparatus. Some of the Functions of Smooth Endoplasmic Reticulum cells may have more than one Golgi apparatus. Each Golgi apparatus consists of 5 to 8 flattened membranous 1. Synthesis of non-protein substance sacs called the cisternae. Smooth endoplasmic reticulum is responsible for syn- Golgi apparatus is situated near the nucleus. It has thesis of non-protein substances such as cholesterol two ends or faces, namely cis face and trans face. The and steroid. This type of endoplasmic reticulum is cis face is positioned near the endoplasmic reticulum. abundant in cells that are involved in the synthesis of Reticular vesicles from endoplasmic reticulum enter lipids, phospholipids, lipoprotein substances, steroid the Golgi apparatus through cis face. The trans face hormones, sebum, etc. In most of the other cells, smooth is situated near the cell membrane. The processed endoplasmic reticulum is less extensive than the rough substances make their exit from Golgi apparatus through trans face (Fig. 1.5). endoplasmic reticulum. 2. Role in cellular metabolism Functions of Golgi Apparatus Outer surface of smooth endoplasmic reticulum contains Major functions of Golgi apparatus are processing, many enzymes which are involved in various metabolic packing, labeling and delivery of proteins and other processes of the cell. molecules like lipids to different parts of the cell. Chapter 1 t Cell 9 Types of Lysosomes Lysosomes are of two types: 1. Primary lysosome, which is pinched off from Golgi apparatus. It is inactive in spite of having hydrolytic enzymes 2. Secondary lysosome, which is the active lysosome. It is formed by the fusion of a primary lysosome with phagosome or endosome (see below). Functions of Lysosomes Lysosomes are often called ‘garbage system’ of the cell because of their degradation activity. About 50 different hydrolytic enzymes, known as acid hydroxylases are present in the lysosomes, through which lysosomes execute their functions. FIGURE 1.5: Golgi apparatus Important lysosomal enzymes 1. Proteases, which hydrolyze the proteins into amino 1. Processing of materials acids Vesicles containing glycoproteins and lipids are 2. Lipases, which hydrolyze the lipids into fatty acids transported into Golgi apparatus. Here, the glycoproteins and glycerides and lipids are modified and processed. 3. Amylases, which hydrolyze the polysaccharides Click here to visit www.thedentalhub.org.in into glucose 2. Packaging of materials 4. Nucleases, which hydrolyze the nucleic acids into All the processed materials are packed in the form of mononucleotides. secretory granules, secretory vesicles and lysosomes, which are transported either out of the cell or to another Mechanism of lysosomal function part of the cell. Because of this, Golgi apparatus is called Lysosomal functions involve two mechanisms: the ‘post office of the cell’. 1. Heterophagy: Digestion of extracellular materials 3. Labeling and delivery of materials engulfed by the cell via endocytosis 2. Autophagy: Digestion of intracellular materials such Finally, the Golgi apparatus sorts out the processed and as worn-out cytoplasmic organelles. packed materials and labels them (such as phosphate group), depending upon the chemical content for delivery Specific functions of lysosomes (distribution) to their proper destinations. Hence, the Golgi apparatus is called ‘shipping department of the 1. Degradation of macromolecules cell’. Macromolecules are engulfed by the cell by means of endocytosis (phagocytosis, pinocytosis or receptor- LYSOSOMES mediated endocytosis: Chapter 3). The macromolecules Lysosomes are the membrane-bound vesicular such as bacteria, engulfed by the cell via phagocytosis organelles found throughout the cytoplasm. The lyso- are called phagosomes or vacuoles. The other somes are formed by Golgi apparatus. The enzymes macromolecules taken inside via pinocytosis or synthesized in rough endoplasmic reticulum are receptor-mediated endocytosis are called endosomes. processed and packed in the form of small vesicles in The primary lysosome fuses with the phagosome or the Golgi apparatus. Then, these vesicles are pinched endosome to form the secondary lysosome. The pH in the off from Golgi apparatus and become the lysosomes. secondary lysosome becomes acidic and the lysosomal Among the organelles of the cytoplasm, the enzymes are activated. The bacteria and the other lysosomes have the thickest covering membrane. The macromolecules are digested and degraded by these membrane is formed by a bilayered lipid material. It has enzymes. The secondary lysosome containing these many small granules which contain hydrolytic enzymes. degraded waste products moves through cytoplasm and 10 Section 1 t General Physiology fuses with cell membrane. Now the waste products are ii. Degrade the toxic substances such as hydrogen eliminated by exocytosis. peroxide and other metabolic products by means of detoxification. A large number of peroxisomes 2. Degradation of worn-out organelles are present in the cells of liver, which is the major The rough endoplasmic reticulum wraps itself around organ for detoxification. Hydrogen peroxide is the worn-out organelles like mitochondria and form formed from poisons or alcohol, which enter the the vacuoles called autophagosomes. One primary cell. Whenever hydrogen peroxide is produced lysosome fuses with one autophagosome to form the in the cell, the peroxisomes are ruptured and secondary lysosome. The enzymes in the secondary the oxidative enzymes are released. These lysosome are activated. Now, these enzymes digest the oxidases destroy hydrogen peroxide and the contents of autophagosome. enzymes which are necessary for the production 3. Removal of excess secretory products in the cells of hydrogen peroxide iii. Form the major site of oxygen utilization in the Lysosomes in the cells of the secretory glands remove cells the excess secretory products by degrading the secretory granules. iv. Accelerate gluconeogenesis from fats v. Degrade purine to uric acid 4. Secretory function – secretory lysosomes vi. Participate in the formation of myelin Recently, lysosomes having secretory function viii. Play a role in the formation of bile acids. called secretory lysosomes are found in some of the cells, particularly in the cells of immune system. The CENTROSOME AND CENTRIOLES conventional lysosomes are modified into secretory lysosomes by combining with secretory granules (which Centrosome is the membrane-bound cellular organelle contain the particular secretory product of the cell). situated almost in the center of cell, close to nucleus. It consists of two cylindrical structures called centrioles Click here to visit www.thedentalhub.org.in Examples of secretory lysosomes: i. Lysosomes in the cytotoxic T lymphocytes and which are made up of proteins. Centrioles are responsible natural killer (NK) cells secrete perforin and for the movement of chromosomes during cell division. granzymes, which destroy both viral-infected cells and tumor cells. Perforin is a pore-forming SECRETORY VESICLES protein that initiates cell death. Granzymes belong Secretory vesicles are the organelles with limiting to the family of serine proteases (enzymes that membrane and contain the secretory substances. These dislodge the peptide bonds of the proteins) and vesicles are formed in the endoplasmic reticulum and cause the cell death by apoptosis are processed and packed in Golgi apparatus. Secretory ii. Secretory lysosomes of melanocytes secrete vesicles are present throughout the cytoplasm. When melanin necessary, these vesicles are ruptured and secretory iii. Secretory lysosomes of mast cells secrete substances are released into the cytoplasm. serotonin, which is a vasoconstrictor substance and inflammatory mediator. MITOCHONDRION PEROXISOMES Mitochondrion (plural = mitochondria) is a membrane- bound cytoplasmic organelle concerned with production Peroxisomes or microbodies are the membrane of energy. It is a rod-shaped or oval-shaped structure limited vesicles like the lysosomes. Unlike lysosomes, with a diameter of 0.5 to 1 μ. It is covered by a bilayered peroxisomes are pinched off from endoplasmic reticulum membrane (Fig. 1.6). The outer membrane is smooth and and not from the Golgi apparatus. Peroxisomes contain encloses the contents of mitochondrion. This membrane some oxidative enzymes such as catalase, urate oxidase contains various enzymes such as acetyl-CoA synthetase and Damino acid oxidase. and glycerolphosphate acetyltransferase. The inner membrane is folded in the form of shelf-like Functions of Peroxisomes inward projections called cristae and it covers the inner Peroxisomes: matrix space. Cristae contain many enzymes and other i. Breakdown the fatty acids by means of a process protein molecules which are involved in respiration and called betaoxidation: This is the major function synthesis of adenosine triphosphate (ATP). Because of of peroxisomes these functions, the enzymes and other protein molecules Chapter 1 t Cell 11 4. Other functions Other functions of mitochondria include storage of calcium and detoxification of ammonia in liver. ORGANELLES WITHOUT LIMITING MEMBRANE FIGURE 1.6: Structure of mitochondrion RIBOSOMES Ribosomes are the organelles without limiting mem- in cristae are collectively known as respiratory chain or brane. These organelles are granular and small dot-like electron transport system. structures with a diameter of 15 nm. Ribosomes are Enzymes and other proteins of respiratory chain made up of 35% of proteins and 65% of ribonucleic acid i. Succinic dehydrogenase (RNA). RNA present in ribosomes is called ribosomal ii. Dihydronicotinamide adenine dinucleotide (NADH) RNA (rRNA). Ribosomes are concerned with protein dehydrogenase synthesis in the cell. iii. Cytochrome oxidase Types of Ribosomes iv. Cytochrome C v. ATP synthase. Ribosomes are of two types: Inner cavity of mitochondrion is filled with matrix which i. Ribosomes that are attached to rough endo- contains many enzymes. Mitochondrion moves freely in plasmic reticulum the cytoplasm of the cell. It is capable of reproducing ii. Free ribosomes that are distributed in the cyto- Click here to visit www.thedentalhub.org.in itself. Mitochondrion contains its own deoxyribonucleic plasm. acid (DNA), which is responsible for many enzymatic actions. In fact, mitochondrion is the only organelle other Functions of Ribosomes than nucleus, which has its own DNA. Ribosomes are called ‘protein factories’ because of Functions of Mitochondrion their role in the synthesis of proteins. Messenger RNA 1. Production of energy (mRNA) carries the genetic code for protein synthesis from nucleus to the ribosomes. The ribosomes, in turn Mitochondrion is called the ‘power house’ or ‘power arrange the amino acids into small units of proteins. plant’ of the cell because it produces the energy required Ribosomes attached to rough endoplasmic reticulum for cellular functions. The energy is produced during the are involved in the synthesis of proteins such as the oxidation of digested food particles like proteins, carbo- enzymatic proteins, hormonal proteins, lysosomal pro- hydrates and lipids by the oxidative enzymes in cristae. teins and the proteins of the cell membrane. During the oxidative process, water and carbon dioxide Free ribosomes are responsible for the synthesis of are produced with release of energy. The released ener- gy is stored in mitochondria and used later for synthesis proteins in hemoglobin, peroxisome and mitochondria. of ATP. CYTOSKELETON 2. Synthesis of ATP Cytoskeleton is the cellular organelle present throughout The components of respiratory chain in mitochondrion the cytoplasm. It determines the shape of the cell and gives are responsible for the synthesis of ATP by utilizing the support to the cell. It is a complex network of structures energy by oxidative phosphorylation. ATP molecules with varying sizes. In addition to determining the shape of diffuse throughout the cell from mitochondrion. Whenever the cell, it is also essential for the cellular movements and energy is needed for cellular activity, the ATP molecules are broken down. the response of the cell to external stimuli. Cytoskeleton consists of three major protein 3. Apoptosis components: Cytochrome C and second mitochondria-derived activator 1. Microtubule of caspases (SMAC)/diablo secreted in mitochondria are 2. Intermediate filaments involved in apoptosis (see below). 3. Microfilaments. 12 Section 1 t General Physiology 1. Microtubules Microfilaments are present throughout the cytoplasm. The microfilaments present in ectoplasm contain Microtubules are the straight, hollow and tubular only actin molecules (Fig. 1.9) and those present in structures of the cytoskeleton. These organelles without the limiting membrane are arranged in different bundles. endoplasm contain both actin and myosin molecules. Each tubule has a diameter of 20 to 30 nm. Length of Functions of microfilaments microtubule varies and it may be 1000 times more than the thickness. Microfilaments: Structurally, the microtubules are formed by bundles i. Give structural strength to the cell of globular protein called tubulin (Fig. 1.7). Tubulin has ii. Provide resistance to the cell against the pulling two subunits, namely αsubunit and βsubunit. forces iii. Are responsible for cellular movements like Functions of microtubules contraction, gliding and cytokinesis (partition of Microtubules may function alone or join with other cytoplasm during cell division). proteins to form more complex structures like cilia, flagella or centrioles and perform various functions. NUCLEUS Microtubules: i. Determine the shape of the cell Nucleus is the most prominent and the largest cellular ii. Give structural strength to the cell organelle. It has a diameter of 10 µ to 22 µ and occupies iii. Act like conveyer belts which allow the movement about 10% of total volume of the cell. of granules, vesicles, protein molecules and some organelles like mitochondria to different parts of the cell iv. Form the spindle fibers which separate the chromosomes during mitosis Click here to visit www.thedentalhub.org.in v. Are responsible for the movement of centrioles and the complex cellular structures like cilia. 2. Intermediate Filaments Intermediate filaments are the structures that form a FIGURE 1.7: Microtubule network around the nucleus and extend to the periphery of the cell. Diameter of each filament is about 10 nm. The intermediate filaments are formed by ropelike polymers, which are made up of fibrous proteins (Fig. 1.8). Subclasses of intermediate filaments Intermediate filaments are divided into five subclasses: i. Keratins (in epithelial cells) ii. Glial filaments (in astrocytes) iii. Neurofilaments (in nerve cells) iv. Vimentin (in many types of cells) v. Desmin (in muscle fibers). FIGURE 1.8: Intermediate filament Functions of intermediate filaments Intermediate filaments help to maintain the shape of the cell. These filaments also connect the adjacent cells through desmosomes. 3. Microfilaments Microfilaments are long and fine threadlike structures with a diameter of about 3 to 6 nm. These filaments are made up of non-tubular contractile proteins called actin and myosin. Actin is more abundant than myosin. FIGURE 1.9: Microfilament of ectoplasm Chapter 1 t Cell

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