《医学生理学 Medical Physiology》参考教材资料（PDF电子书籍）Ross and WIlson Anatomy and Physiology in Health and Illness, 9th edition 2004

INTH EDITION Ross and wilson Anatomy and Physiology Health andⅢness Anne Waugh Allison Grant N

diti Ross and wilson Anatomy and Physiology in health and llness Anne Waugh BSc(Hons)MSc CertEd SRN RNT ILTM Senior Lecturer, School of Acute and Continuing Care Nursing. Napier University, Edinburgh, UK Allison grant BSc PhD RGN Lecturer, School of Biological and Biomedical Sciences, Glasgow Caledonian University, Glasgow, UK Illustrations by Graeme Chambers LIVINGSTONE EDINBURGH LONDON NEW YORK OXFORD PHILADELPHIA ST LOUIS SYDNEY AND TORONTO 2001

Ninth Edition Ross and Wilson Anatomy and Physiology in Health and Illness Anne Waugh BSc(Hons)MSc CertEd SRN RNT ILTM Senior Lecturer, School of Acute and Continuing Care Nursing, Napier University, Edinburgh, UK Allison Grant Bsc PHD RGN Lecturer, School of Biological and Biomedical Sciences, Glasgow Caledonian University, Glasgow, UK Illustrations by Graeme Chambers CHURCHILL LIVINGSTONE EDINBURGH LONDON NEW YORK OXFORD PHILADELPHIA ST LOUIS SYDNEY AND TORONTO 2001

CHURCHILL LIVINGSTONE oE&s li O Longman Group Limited 1973, Pearson Professional Limited 1997 Harcourt Brace and Company Limited 1998 Harcourt Publishers Limited 2001 o Elsevier Science Limited 2002. All rights reserved o Elsevier Limited 2004. All rights res he right of Anne Waugh to be identified as author of this work has been asserted by her in accordance with the Copyright, Designs and Patents Act 1988 No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without either he prior permission of the publishers or a licence permitting estricted copying in the United Kingdom issued by the Copyright Licensing Agency, 90 Tottenham Court Road, London WIT4LP MiSsion directly from Elsevier's Health Science Rights Department in Philadelphia, USA: Phone: (+1)215 238 7869, 2239. e-mail: h ssions@elsevier.com ou may also complete your request on-line via the Elsevier Science homepage(http://www.elsevier.com),byselecting'customer Support and then'Obtaining Permission First edition 1963 International Student Edition Second edition 1966 First published 1991 Third edition 1968 Eighth edition 1996 Fourth edition 1973 th edition 2001 Fifth edition 1981 Reprinted 2001, 2002, 2003(twice), 2004 Sixth edition 1987 Seventh edition 1990 ISBN0443064695 inth edition 200] Reprinted2001,2002203,2004 SBN0443064687 British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloging in Publication Data A catalog record for this book is available from the Library of Congress Note Medical knowledge is constantly changing. As new information becomes available, changes in treatment, procedures, equipment and the use of drugs become necessary. The authors and the publishers have taken care to ensure that the information given in this text is accurate and up to date. However, readers are strongly advised to confirm that the information, especially with regard to drug usage, complies with the latest legislation and standards of practice in the health sciences ww.elsevierhealth com from sustainable forests Printed in Spain

CHURCHILL LIVINGSTONE An imprint of Elsevier Limited © E. & S. Livingstone Ltd 1963,1966,1968 © Longman Group Limited 1973,1981,1987,1990 © Pearson Professional Limited 1997 © Harcourt Brace and Company Limited 1998 © Harcourt Publishers Limited 2001 © Elsevier Science Limited 2002. All rights reserved. © Elsevier Limited 2004. All rights reserved. The right of Anne Waugh to be identified as author of this work has been asserted by her in accordance with the Copyright, Designs and Patents Act 1988 No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without either the prior permission of the publishers or a licence permitting restricted copying in the United Kingdom issued by the Copyright Licensing Agency, 90 Tottenham Court Road, London WIT 4LP. Permissions may be sought directly from Elsevier's Health Sciences Rights Department in Philadelphia, USA: phone: (+1) 215 238 7869, fax: (+1) 215 238 2239, e-mail: healthpermissions@elsevier.com. You may also complete your request on-line via the Elsevier Science homepage (http://www.elsevier.com), by selecting 'Customer Support' and then 'Obtaining Permissions'. First edition 1963 International Student Edition Second edition 1966 First published 1991 Third edition 1968 Eighth edition 1996 Fourth edition 1973 Ninth edition 2001 Fifth edition 1981 Reprinted 2001,2002,2003 (twice), 2004 Sixth edition 1987 Seventh edition 1990 ISBN 0443 06469 5 Eighth edition 1996 Ninth edition 2001 Reprinted 2001, 2002,2003, 2004 ISBN 0 443 06468 7 British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloging in Publication Data A catalog record for this book is available from the Library of Congress Note Medical knowledge is constantly changing. As new information becomes available, changes in treatment, procedures, equipment and the use of drugs become necessary. The authors and the publishers have taken care to ensure that the information given in this text is accurate and up to date. However, readers are strongly advised to confirm that the information, especially with regard to drug usage, complies with the latest legislation and standards of practice. ELSEVIER injournals the health science ands multimedia pape policy is to use r manufactured WWW.elsevierhealth.com from sustainable forests Printed in Spain

Contents Preface Acknowledgements Common prefixes, suffixes and roots SECTION 1 The body and its constituents 1 Introduction to the human body Introduction to the chemistry of life 3 The cells, tissues and organisation of the body SECTION 2 Communication 4 The blood 5 The cardiovascular system 6 The lymphatic system 7 The nervous system 8 The special senses 9 The endocrine system 213 SECTION 3 Intake of raw materials and the elimination of waste237 10 The respiratory system 11 Introduction to nutrition 12 The digestive system 281 13 The urinary system SECTION 4 Protection and survival 359 14 The skin 36 15 Resistance and immunity 373 16 The skeleton 17 The joints 413 18 The muscular system 19 The reproductive systems 437 Normal values Bibl oara Index

Contents Preface Acknowledgements Common prefixes, suffixes and roots SECTION 1 The body and its constituents 1 Introduction to the human body Introduction to the chemistry of life The cells, tissues and organisation of the body SECTION 2 Communication The blood The cardiovascular system The lymphatic system The nervous system The special senses The endocrine system 5 6 SECTION 3 Intake of raw materials and the elimination of waste 10 The respiratory system 11 Introduction to nutrition 12 The digestive system 13 The urinary system SECTION 4 Protection and survival 14 The skin 15 Resistance and immunity 16 The skeleton The joints The muscular system 19 The reproductive systems Normal values Bibliography Index vii vii viii 1 3 17 29 57 59 77 129 139 191 213 237 239 269 281 339 359 361 373 387 413 429 437 459 461 463

Preface Ross and wilson has been a core text for students of The later chapters are gathered together into three anatomy and physiology for almost 40 years. This latest further sections, reflecting three areas essential fe edition is aimed at health care professionals including normal body function: communication; intake of raw nurses,nursing students, students of the professions materials and elimination of waste; and protection and allied to medicine, Paramedics, ambulance technicians survival. Much of the material for this edition has been and complementary therapists. It retains the straightfor- extensively revised and rewritten. There is a new chapter ward approach to the description of body systems and on immunology, reflecting the growing importance of w they work, and the normal anatomy and physiology this subject in physiology is followed by a section that covers common disorders The artwork has been completely redrawn using full and diseases: the pathology colour, and many new diagrams have been included The human body is described system by system. The a new list of common prefixes, suffixes and roots has reader must, however, remember that physiology is an been prepared for this edition, giving meanings and integrated subject and that, although the systems are con- providing examples of common terminology used in sidered in separate chapters, they must all function the study of anatomy and physiology. Some biological together for the human body to operate as a healthy unit. values have been extracted from the text and presented The first three chapters provide an overview of the body as an Appendix for easy reference. In some cases, slightly and describe its main constituents. a new section different'normals' may be found in other texts and used introductory biochemistry is included, forming the basis by different medical practitioners of a deeper understanding of body function Edinburgh 2001 Anne Waugh Acknowledgements The ninth edition of this textbook would not have been We are grateful to readers of the eighth edition for possible without the efforts of many people In preparing their constructive comments, many of which have influ this edition we have built on the foundations established enced the content of the ninth by Kathleen Wilson and we would like to acknowledge We are also grateful to the staff of Churchill her immense contribution to the success of this title Livingstone, particularly Mairi McCubbin and Kirsty We are grateful to Graeme Chambers for the prepara- Guest, for their support and hospitality tion of the new artwork for the ninth edition Thanks are also due to our families, Andy, Michael, Seona and Struan, for their patience and acceptance of

Preface Ross and Wilson has been a core text for students of anatomy and physiology for almost 40 years. This latest edition is aimed at health care professionals including nurses, nursing students, students of the professions allied to medicine, paramedics, ambulance technicians and complementary therapists. It retains the straightfor￾ward approach to the description of body systems and how they work, and the normal anatomy and physiology is followed by a section that covers common disorders and diseases: the pathology. The human body is described system by system. The reader must, however, remember that physiology is an integrated subject and that, although the systems are con￾sidered in separate chapters, they must all function together for the human body to operate as a healthy unit. The first three chapters provide an overview of the body and describe its main constituents. A new section on introductory biochemistry is included, forming the basis of a deeper understanding of body function. The later chapters are gathered together into three further sections, reflecting three areas essential for normal body function: communication; intake of raw materials and elimination of waste; and protection and survival. Much of the material for this edition has been extensively revised and rewritten. There is a new chapter on immunology, reflecting the growing importance of this subject in physiology. The artwork has been completely redrawn using full colour, and many new diagrams have been included. A new list of common prefixes, suffixes and roots has been prepared for this edition, giving meanings and providing examples of common terminology used in the study of anatomy and physiology. Some biological values have been extracted from the text and presented as an Appendix for easy reference. In some cases, slightly different 'normals' may be found in other texts and used by different medical practitioners. Edinburgh 2001 Anne Waugh Allison Grant Acknowledgements The ninth edition of this textbook would not have been possible without the efforts of many people. In preparing this edition, we have built on the foundations established by Kathleen Wilson and we would like to acknowledge her immense contribution to the success of this title. We are grateful to Graeme Chambers for the prepara￾tion of the new artwork for the ninth edition. We are grateful to readers of the eighth edition for their constructive comments, many of which have influ￾enced the content of the ninth. We are also grateful to the staff of Churchill Livingstone, particularly Mairi McCubbin and Kirsty Guest, for their support and hospitality. Thanks are also due to our families, Andy, Michael, Seona and Struan, for their patience and acceptance of lost evenings and weekends

Common prefixes, suffixes and roots The terminology used in the book is easier to learn and use when it is understood. To facilitate this, the common parts of such terms: prefixes(beginnings), roots(middle parts)and suffixes(endings), are listed here, in alphabetical order. Meanings are also given, along with some examples of their uses Prefix/suffix/root To do with Examples in the text Prefix/suffix/root To do with Examples in the text a-an- lack of anuria, granulocyte, inflammation appendicitis, hepatitis, asystole. ystitis, gastritis nia of the blood anaemia, hypoxaemia, lactation lactic, lacteal ang angiotensin, haemangioma against coagulant, breaking down lysosome, glycolysis, antigen, antimicrobial blast ge! reticuloblast, osteoblast megaloblast, acromegaly, renomegaly, hepatomegaly bronchiole, bronchitis, micro sma∥ microbe, microtubules bronchus microvilli card- cardiac, myocardium, musc/ myocardium, myoglobin, myopathy, myosin chole holecystoki neoplasm, gluconeogenesis, neonate yto/-cyte nephro nephron, nephrotic cytoplasm, cytotoxic nephroblastoma, nephrosis de kin dermatitis, dermatome neuro- dys esembling myeloid, sesamoid, sigmoid menorrhoea, dysplasia carcinoma melanoma -ema edema, emphysem -ophth- xerophthalmia Inner endocrine, endocytosis ophthalmic, exophthalmos endothelium rring ecretory, sensory erythro auditory, gustatory one osteocyte, osteoarthri exocytosis, exophthalmos extra. utside extracellular, extrapyramidal path- ase pathogenesis, neuropathy fferent carry afferent efferent st stomach plasm substance pneumo- pneumonia gen- origin/ gene, genome, genetic, production antigen, pathogen, many polypeptide, polyuria, -globin protein myoglobin, haemoglobin -phagia excessive flow menorrhagia a hinorrhoea water hydration, hydrostatic sub- phrenic, subarachnoid, oce pat- hepatic, hepatitis excessively fast tachycardia hepatomegaly, hepatocyte thrombo. thrombocyte, thrombosis, hyper- excess/above thrombin thrombus hypertrophy, hypercapnia -tox- cytotoxic, hepatotoxic ypo- below/under hypoglycaemia, hypotension, urine anuria, polyuria, haematuria tracellular, intracranial vas, vaso ve Iction intraocular deferens vascular ondition hyperthyroidism, dwarfism

Common prefixes, suffixes and roots The terminology used in the book is easier to learn and use when it is understood. To facilitate this, the common parts of such terms: prefixes (beginnings), roots (middle parts) and suffixes (endings), are listed here, in alphabetical order. Meanings are also given, along with some examples of their uses. Prefix/suffix/root a-/an- -aemia angio￾anti- -blast brady￾broncho￾card￾chole￾cyto-/-cyte derm￾dys- -ema endo￾erythro￾exo￾extra- -fferent gast- -gen- -globin haem- -hydr￾hepat￾hyper￾hypo￾intra- -ism To do with lack of of the blood vessel against germ, bud slow bronchus heart bile cell skin difficult swelling inner red outside outside carry stomach origin/ production protein blood water liver excess/above below/under within condition Examples in the text anuria, agranulocyte, asystole, anaemia anaemia, hypoxaemia, uraemia, hypovolaemia angiotensin, haemangioma antidiuretic, anticoagulant, antigen, antimicrobial reticuloblast, osteoblast bradycardia bronchiole, bronchitis, bronchus cardiac, myocardium, tachycardia cholecystokinin, cholecystitis, cholangitis erythrocyte, cytosol, cytoplasm, cytotoxic dermatitis, dermatome, dermis dysuria, dyspnoea, dysmenorrhoea, dysplasia oedema, emphysema, lymphoedema endocrine, endocytosis, endothelium erythrocyte, erythropoietin, erythropoiesis exocytosis, exophthalmos extracellular, extrapyramidal afferent, efferent gastric, gastrin, gastritis, gastrointestinal gene, genome, genetic, antigen, pathogen, allergen myoglobin, haemoglobin haemostasis, haemorrhage, haemolytic dehydration, hydrostatic, hydrocephalus hepatic, hepatitis, hepatomegaly, hepatocyte hypertension, hypertrophy, hypercapnia hypoglycaemia, hypotension, hypovolaemia intracellular, intracranial, intraocular hyperthyroidism, dwarfism, rheumatism Prefix/suffix/root -itis lact￾lymph￾lyso-/-lysis -mega￾micro￾myo￾neo￾nephro￾neuro- -oid -oma -ophth- -ory osteo- -path- -plasm pneumo￾poly- -rrhagia -rrhoea sub￾tachy￾thrombo- -tox- -uria vas, vaso￾To do with inflammation milk lymph tissue breaking down large small muscle new kidney nerve resembling tumour eye referring to bone disease substance lung/air many excessive flow discharge under excessively fast clot poison urine vessel Examples in the text appendicitis, hepatitis, cystitis, gastritis lactation, lactic, lacteal lymphocyte, lymphatic, lymphoedema lysosome, glycolysis, lysozyme megaloblast, acromegaly, splenomegaly, hepatomegaly microbe, microtubules, microvilli myocardium, myoglobin, myopathy, myosin neoplasm, gluconeogenesis, neonate nephron, nephrotic, nephroblastoma, nephrosis neurone, neuralgia, neuropathy myeloid, sesamoid, sigmoid carcinoma, melanoma, fibroma xerophthalmia, ophthalmic, exophthalmos secretory, sensory, auditory, gustatory osteocyte, osteoarthritis, osteoporosis pathogenesis, neuropathy, nephropathy cytoplasm, neoplasm pneumothorax, pneumonia, pneumotoxic polypeptide, polyuria. polycythaemia menorrhagia dysmenorrhoea, diarrhoea, rhinorrhoea subphrenic, subarachnoid, sublingual tachycardia thrombocyte, thrombosis, thrombin, thrombus toxin, cytotoxic, hepatotoxic anuria, polyuria, haematuria, nocturia vasoconstriction, vas deferens, vascular

The body and its constituents Introduction to the human body 3 Introduction to the chemistry of life 17 The cells, tissues and organisation o 29

Th its constituent e body and s 1 Introduction to the human body 3 Introduction to the chemistry of life 17 The cells, tissues and organisation of the body 29

Introduction to the human bod Levels of structural complexit ntake of raw materials and elimination of The internal environment and Dietary intake 11 Elimination of waste 12 homeostasis 4 Protection and survival 12 Homeostasis 5 Protection against the external Negative feedback mechanisms 6 environment 12 Positive feedback mecha Resistance and immunity 13 Homeostatic imbalance 7 Movement 13 Reproduction 14 Survival needs of the body 7 Communication 8 Introduction to the study of Transport systems 8 illness 14 nternal communication 9 Petiole 15 Communication with the external Pathe environment 10

Introduction to the human body Levels of structural complexity The internal environment and homeostasis 4 Homeostasis 5 Negative feedback mechanisms 6 Positive feedback mechanisms 7 Homeostatic imbalance 7 Survival needs of the body 7 Communication 8 Transport systems 8 Internal communication 9 Communication with the external environment 10 Intake of raw materials and elimination of waste 11 Intake of oxygen 11 Dietary intake 11 Elimination of waste 12 Protection and survival 12 Protection against the external environment 12 Resistance and immunity 13 Movement 13 Reproduction 14 Introduction to the study of illness 14 Aetiology 15 Pathogenesis 15

he body and its constituents The human body is complex, like a highly technical and human body, cells with similar structures and functions sophisticated machine. It operates as a single entity, but is are found together, forming tissues. The structure and made up of a number of operational parts that work functions of cells and tissues are explored in Chapter 3 interdependently. Each part is associated with a specific, Organs are made up of a number of different types of and sometimes related, function that is essential for the tissue and carry out a specific function. Systems consist of well-being of the individual. The component parts do not a number of organs and tissues that together contribute to operate independently, but rather in conjunction with all one or more survival needs of the body. The human body the others. Should one part fail, the consequences are has several systems, which work interdependently carry likely to extend to other parts, and may reduce the ability ing out specific functions. All are required for health. The of the body to function normally. Integrated working of body systems are considered in later chapters the body parts ensures the ability of the individual to survive. The human body is therefore complex in both its explain the fundamental structures and processes THE INTERNAL ENVIRONMENT Anatomy is the study of the structure of the body and AND HOMEOSTASIS the physical relationships involved between body parts. Physiology is the study of how the parts of the body work, and the ways in which they cooperate together to main- Learning outcomes tain life and health of the individual. Pathology is the After studying this section you should be able to functions, often causing illness. Building on the normal anatomy and physiology, relevant illng a define the terms internal environment and esses are co at the end of the later chapter a compare and contrast negative and positive LEVELS OF STRUCTURAL a outline the potential consequences of homeostatic COMPLEXITY The external environment surrounds the body and pro Learning outcome vides the oxygen and nutrients required by all the cells of body. Waste products of cellular activity are eventu After studying this section you should be able to ally excreted into the external environment. The skin pro m state the levels of structural complexity within the vides a barrier between the dry external environment and the watery environment of most body cells The internal environment is the water-based medium in which body cells exist. Cells are bathed in fluid called interstitial or tissue fluid. Oxygen and other substances Within the body there are different levels of structural they require must pass from the internal transport sys- organisation and complexity(Fig 1.1). The lowest level is tems through the interstitial fluid to reach them chemical Atoms combine to form molecules, of which there Similarly, cell waste products must move through the is a vast range in the body. The structures, properties and interstitial fluid to the transport systems to be excreted functions of important biological molecules are consid- Cells are surrounded by the cell membrane, which pro- ered in Chapter 2. Cells are the smallest independent units vides a potential barrier to substances entering or leaving of living matter and there are millions in the body. They The structure of membranes(. 30)confers certain prop- re too small to be seen with the naked eye, but when erties, in particular selective permeability or semipermeabil- magnified using a microscope different types can be dis- ity. This prevents large molecules moving between the tinguished by their size, shape and the dyes they absorb cell and the interstitial fluid(Fig. 1. 2 ). Smaller particles when stained in the laboratory. Each cell type has become can usually pass through the membrane, some more read- pecialised, and carries out a particular function that con- ily than others, and therefore the chemical composition of tributes to body needs. In complex organisms such as the the fluid inside is different from that outside the cell

The body and its constituents _4 The human body is complex, like a highly technical and sophisticated machine. It operates as a single entity, but is made up of a number of operational parts that work interdependently. Each part is associated with a specific, and sometimes related, function that is essential for the well-being of the individual. The component parts do not operate independently, but rather in conjunction with all the others. Should one part fail, the consequences are likely to extend to other parts, and may reduce the ability of the body to function normally. Integrated working of the body parts ensures the ability of the individual to survive. The human body is therefore complex in both its structure and function, and the aim of this book is to explain the fundamental structures and processes involved. Anatomy is the study of the structure of the body and the physical relationships involved between body parts. Physiology is the study of how the parts of the body work, and the ways in which they cooperate together to main￾tain life and health of the individual. Pathology is the study of abnormalities and how they affect body functions, often causing illness. Building on the normal anatomy and physiology, relevant illnesses are considered at the end of the later chapters. LEVELS OF STRUCTURAL COMPLEXITY Learning outcome After studying this section you should be able to: • state the levels of structural complexity within the body. Within the body there are different levels of structural organisation and complexity (Fig. 1.1). The lowest level is chemical. Atoms combine to form molecules, of which there is a vast range in the body. The structures, properties and functions of important biological molecules are consid￾ered in Chapter 2. Cells are the smallest independent units of living matter and there are millions in the body. They are too small to be seen with the naked eye, but when magnified using a microscope different types can be dis￾tinguished by their size, shape and the dyes they absorb when stained in the laboratory. Each cell type has become specialised, and carries out a particular function that con￾tributes to body needs. In complex organisms such as the human body, cells with similar structures and functions are found together, forming tissues. The structure and functions of cells and tissues are explored in Chapter 3. Organs are made up of a number of different types of tissue and carry out a specific function. Systems consist of a number of organs and tissues that together contribute to one or more survival needs of the body. The human body has several systems, which work interdependently carry￾ing out specific functions. All are required for health. The body systems are considered in later chapters. THE INTERNAL ENVIRONMENT AND HOMEOSTASIS Learning outcomes After studying this section you should be able to: • define the terms internal environment and homeostasis • compare and contrast negative and positive feedback control mechanisms • outline the potential consequences of homeostatic imbalance. The external environment surrounds the body and pro￾vides the oxygen and nutrients required by all the cells of the body. Waste products of cellular activity are eventu￾ally excreted into the external environment. The skin pro￾vides a barrier between the dry external environment and the watery environment of most body cells. The internal environment is the water-based medium in which body cells exist. Cells are bathed in fluid called interstitial or tissue fluid. Oxygen and other substances they require must pass from the internal transport sys￾tems through the interstitial fluid to reach them. Similarly, cell waste products must move through the interstitial fluid to the transport systems to be excreted. Cells are surrounded by the cell membrane, which pro￾vides a potential barrier to substances entering or leaving. The structure of membranes (p. 30) confers certain prop￾erties, in particular selective permeability or semipermeabil￾ity. This prevents large molecules moving between the cell and the interstitial fluid (Fig. 1.2). Smaller particles can usually pass through the membrane, some more read￾ily than others, and therefore the chemical composition of the fluid inside is different from that outside the cell

Introduction to the human body Salivary gl. (smooth muscle tissue) Serosa Liver Small intestine Large intestine The human being Anus ers or sn level muscle tissue Organ level Figure 1.1 The levels of structural complexity. Homeostasis Homeostasis is maintained by control systems which detect and respond to changes in the internal environ- The composition of the internal environment is main- ment. A control system(Fig. 1. 3)has three basic compo tained within narrow limits, and this fairly constant state nents: detector, control centre and effector. The control is called homeostasis. Literally, this term means'unchang- centre determines the limits within which the variable g, but in practice it describes a dynamic, ever-changing factor should be maintained. It receives an input from the situation kept within narrow limits. When this balance is detector or sensor and integrates the incoming informa- threatened or lost, there is a serious risk to the well-being tion. When the incoming signal indicates that an adjust- of the individual. There are many factors in the intern ment is needed the control centre responds and its output environment which must be maintained within narrow to the effector is changed. This is a dynamic process that limits and some of these are maintains homeostas

Introduction to the human body 5_ Figure 1.1 The levels of structural complexity. Homeostasis The composition of the internal environment is main￾tained within narrow limits, and this fairly constant state is called homeostasis. Literally, this term means 'unchang￾ing', but in practice it describes a dynamic, ever-changing situation kept within narrow limits. When this balance is threatened or lost, there is a serious risk to the well-being of the individual. There are many factors in the internal environment which must be maintained within narrow limits and some of these are listed in Box 1.1. Homeostasis is maintained by control systems which detect and respond to changes in the internal environ￾ment. A control system (Fig. 1.3) has three basic compo￾nents: detector, control centre and effector. The control centre determines the limits within which the variable factor should be maintained. It receives an input from the detector or sensor, and integrates the incoming informa￾tion. When the incoming signal indicates that an adjust￾ment is needed the control centre responds and its output to the effector is changed. This is a dynamic process that maintains homeostasis