Ross and Wilson Anatomy and Physiology in Health and Illness Ninth Edition PDF

 Ninth Edition Ross and Wilson Anatomy and Physiology in Health and Illness For Churchill Livingstone: Senior Commissioning Editor: Sarena Wolfaard Designer. Sarah Russell Project Development Editor. Mairi McCubbin Page Layout: Alan Palfreyman ...

 Ninth Edition Ross and Wilson Anatomy and Physiology in Health and Illness For Churchill Livingstone: Senior Commissioning Editor: Sarena Wolfaard Designer. Sarah Russell Project Development Editor. Mairi McCubbin Page Layout: Alan Palfreyman  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 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. 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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 journals and multimedia policy is to use in the health sciences WWW.elsevierhealth.com from paper manufactured sustainable forests Printed in Spain Contents Preface vii Acknowledgements vii Common prefixes, suffixes and roots viii SECTION1Thebodyanditsconstituents 1 1 Introduction to the human body 3 Introduction to the chemistry of life 17 The cells, tissues and organisation of the body 29 SECTION2Communication 57 The blood 59 5 The cardiovascular system 77 6 The lymphatic system 129 The nervous system 139 The special senses 191 The endocrine system 213 SECTION3Intakeofrawmaterialsandtheeliminationofwaste 237 10 The respiratory system 239 11 Introduction to nutrition 269 12 The digestive system 281 13 The urinary system 339 SECTION 4 Protection and survival 359 14 The skin 361 15 Resistance and immunity 373 16 The skeleton 387 The joints 413 The muscular system 429 19 The reproductive systems 437 Normal values 459 Bibliography 461 Index 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 for 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 how 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 on 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 Allison Grant 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 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, agranulocyte, -itis inflammation appendicitis, hepatitis, asystole, anaemia cystitis, gastritis -aemia of the blood anaemia, hypoxaemia, lact- milk lactation, lactic, lacteal uraemia, hypovolaemia lymph- lymph tissue lymphocyte, lymphatic, angio- vessel angiotensin, haemangioma lymphoedema anti- against antidiuretic, anticoagulant, lyso-/-lysis breaking down lysosome, glycolysis, antigen, antimicrobial lysozyme -blast germ, bud reticuloblast, osteoblast -mega- large megaloblast, acromegaly, brady- slow bradycardia splenomegaly, hepatomegaly broncho- bronchus bronchiole, bronchitis, micro- small microbe, microtubules, bronchus microvilli card- heart cardiac, myocardium, myo- muscle myocardium, myoglobin, tachycardia myopathy, myosin chole- bile cholecystokinin, neo- new neoplasm, gluconeogenesis, cholecystitis, cholangitis neonate cyto-/-cyte cell erythrocyte, cytosol, nephro- kidney nephron, nephrotic, cytoplasm, cytotoxic nephroblastoma, nephrosis derm- skin dermatitis, dermatome, neuro- nerve neurone, neuralgia, dermis neuropathy dys- difficult dysuria, dyspnoea, -oid resembling myeloid, sesamoid, sigmoid dysmenorrhoea, dysplasia -oma tumour carcinoma, melanoma, -ema swelling oedema, emphysema, fibroma lymphoedema -ophth- eye xerophthalmia, endo- inner endocrine, endocytosis, ophthalmic, exophthalmos endothelium -ory referring to secretory, sensory, erythro- red erythrocyte, erythropoietin, auditory, gustatory erythropoiesis osteo- bone osteocyte, osteoarthritis, exo- outside exocytosis, exophthalmos osteoporosis extra- outside extracellular, extrapyramidal -path- disease pathogenesis, neuropathy, -fferent carry afferent, efferent nephropathy gast- stomach gastric, gastrin, gastritis, -plasm substance cytoplasm, neoplasm gastrointestinal pneumo- lung/air pneumothorax, pneumonia, -gen- origin/ gene, genome, genetic, pneumotoxic production antigen, pathogen, poly- many polypeptide, polyuria. allergen polycythaemia -globin protein myoglobin, haemoglobin -rrhagia excessive flow menorrhagia haem- blood haemostasis, haemorrhage, -rrhoea discharge dysmenorrhoea, diarrhoea, haemolytic rhinorrhoea -hydr- water dehydration, hydrostatic, sub- under subphrenic, subarachnoid, hydrocephalus sublingual hepat- liver hepatic, hepatitis, tachy- excessively fast tachycardia hepatomegaly, hepatocyte thrombo- clot thrombocyte, thrombosis, hyper- excess/above hypertension, thrombin, thrombus hypertrophy, hypercapnia -tox- poison toxin, cytotoxic, hepatotoxic hypo- below/under hypoglycaemia, hypotension, -uria urine anuria, polyuria, haematuria, hypovolaemia nocturia intra- within intracellular, intracranial, vas, vaso- vessel vasoconstriction, vas intraocular deferens, vascular -ism condition hyperthyroidism, dwarfism, rheumatism This page intentionally left blank The body and its constituents 1 Introduction to the human body 3 Introduction to the chemistry of life 17 The cells, tissues and organisation of the body 29 This page intentionally left blank Introduction to the human body Intake of raw materials and elimination of Levels of structural complexity waste 11 Intake of oxygen 11 Dietary intake 11 The internal environment and Elimination of waste 12 homeostasis 4 Protection and survival 12 Homeostasis 5 Protection against the external Negative feedback mechanisms 6 environment 12 Positive feedback mechanisms 7 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 Internal communication 9 Aetiology 15 Communication with the external Pathogenesis 15 environment 10  The 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 structure and function, and the aim of this book is to explain the fundamental structures and processes THE INTERNAL ENVIRONMENT involved. 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 study of abnormalities and how they affect body After studying this section you should be able to: functions, often causing illness. Building on the normal define the terms internal environment and anatomy and physiology, relevant illnesses are considered homeostasis at the end of the later chapters. compare and contrast negative and positive feedback control mechanisms outline the potential consequences of homeostatic _4 LEVELS OF STRUCTURAL imbalance. COMPLEXITY The external environment surrounds the body and pro- vides the oxygen and nutrients required by all the cells of Learning outcome the 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- vides a barrier between the dry external environment state the levels of structural complexity within the and the watery environment of most body cells. body. 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 (p. 30) confers certain prop- are 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- specialised, 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.  Introduction to the human body 5_ 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 ing', 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 internal 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 listed in Box 1.1. maintains homeostasis.  The body and its constituents Box 1.1 Examples of physiological variables ^PlWiP Temperature Water and electrolyte concentrations pH (acidity or alkalinity of body fluids Blood glucose levels Blood and tissue oxygen and carbon dioxide levels Blood pressure system. The thermostat (temperature detector) is sensitive to changes in room temperature (variable factor). The ther- mostat is connected to the boiler control unit (control cen- tre), which controls the boiler (effector). The thermostat constantly compares the information from the detector with the preset temperature and, when necessary, adjust- ments are made to alter the room temperature. When the thermostat detects the room temperature is low it sends an input to the boiler control unit, switching it on. The result is output of heat by the boiler, warming the room. When the preset temperature is reached, the system is reversed. The thermostat detects the higher room temperature and sends an input to the boiler control unit, turning it off. The output of heat from the boiler stops and the room slowly _6 cools as heat is lost. This series of events is a negative feed- back mechanism and it enables continuous self-regulation or control of a variable factor within a narrow range. Body temperature is a physiological variable con- trolled by negative feedback (Fig. 1.4). When body tem- perature falls below the preset level, this is detected by specialised temperature sensitive nerve endings. They transmit this information as an input to groups of cells in the hypothalamus of the brain which form the control centre. The output from the control centre activates mechanisms that raise body temperature (effectors). These include: stimulation of skeletal muscles causing shivering narrowing of the blood vessels in the skin reducing the blood flow to, and heat loss from, the peripheries Figure 1.3 Example of a negative feedback mechanism: control of behavioural changes, e.g. we put on more clothes or room temperature by a domestic boiler. curl up. When body temperature rises to within the normal range, the temperature sensitive nerve endings no longer Negative feedback mechanisms stimulate the cells of the control centre and therefore the In systems controlled by negative feedback the effector output of this centre to the effectors ceases. response decreases or negates the effect of the original Most of the homeostatic controls in the body use nega- stimulus, restoring homeostasis (thus the term negative tive feedback mechanisms to prevent sudden and serious feedback). Control of body temperature is similar to the changes in the internal environment. Many more of these non-physiological example of a domestic central heating are explained in the following chapters.  Introduction to the human body SURVIVAL NEEDS OF THE BODY Learning outcomes After studying this section you should be able to: describe the role of the body transport systems outline the roles of the nervous and endocrine systems in internal communication outline how raw materials are absorbed by the body state the waste materials eliminated from the body outline activities undertaken by an individual for protection and survival. By convention, the body systems are described sepa- rately in the study of anatomy and physiology, but in reality they are all interdependent. This section provides an introduction to body activities linking them to sur- vival needs (Table 1.1). The later chapters build on this Figure 1.4 Example of a physiological negative feedback framework, exploring human structure and functions in mechanism: control of body temperature. health and illness using a systems approach. 7_ Positive feedback mechanisms There are only a few of these amplifier or cascade systems in the body. In positive feedback mechanisms, the stimulus Table 1.1 Survival needs and related body activities progressively increases the response, so that as long as the stimulus is continued the response is progressively Survival need Body activities being amplified. Examples include blood clotting and uterine contractions during labour. Communication Transport systems: blood, During labour, contractions of the uterus are stimu- circulatory system, lymphatic lated by the hormone oxytocin. These force the baby's system Internal communication: nervous head into the cervix of the uterus stimulating stretch system, endocrine system receptors there. In response to this, more of the hormone External communication: special oxytocin is released, further strengthening the contrac- senses, verbal and non-verbal tions and maintaining labour. After the baby is born the communication stimulus (stretching of the cervix) is no longer present Intake of raw materials Intake of oxygen and the release of oxytocin stops (see Fig. 9.5, p. 219). and elimination of waste Dietary intake Elimination of waste: carbon dioxide, urine, faeces Homeostatic imbalance Protection and survival Protection against the external This arises when the fine control of a factor in the internal environment: skin environment is inadequate and the level of the factor falls Resistance and immunity: outside the normal range. If control cannot achieve non-specific and specific defence mechanisms homeostasis, an abnormal state develops that may Body movement threaten health, or even life. Many of these situations are Reproduction explained in later chapters.  The body and its constituents Communication chemical substances synthesised by body cells, e.g. hormones In this section, transport and communication are consid- waste materials produced by body cells to be ered. Transport systems ensure that all cells have access eliminated from the body by excretion. to the internal and external environments; the blood, the circulatory system and lymphatic system are involved. Blood cells. There are three distinct groups, classified All communication systems involve receiving, collating according to their functions (Fig. 1.5). and responding to appropriate information. Erythrocytes (red blood cells) are concerned with the There are different systems for communicating with transport of oxygen and, to a lesser extent, carbon dioxide the internal and external environments. Internal commu- between the lungs and all body cells. nication involves mainly the nervous and endocrine sys- Leukocytes (white blood cells) are mainly concerned tems; these are important in the maintenance of with protection of the body against microbes and other homeostasis and regulation of vital body functions. potentially damaging substances that gain entry to the Communication with the external environment involves body. There are several types of leukocytes which carry the special senses, and verbal and non-verbal activities, out their protective functions in different ways. These and all of these also depend on the nervous system. cells are larger than erythrocytes and are less numerous. Thrombocytes (platelets) are tiny cell fragments which play an essential part in the very complex process of Transport systems blood clotting. Blood The blood transports substances around the body Circulatory system (Ch. 5) through a large network of blood vessels. In adults the This consists of a network of blood vessels and the heart body contains 5 to 6 1 of blood (Ch. 4). It consists of two (Fig. 1.6). parts —a sticky fluid called plasma and cells which are suspended in the plasma. Blood vessels. There are three types: arteries, which carry blood away from the heart _8 Plasma. This is mainly water with a wide range of sub- veins, which return blood to the heart stances dissolved or suspended in it. These include: capillaries, which link the arteries and veins. nutrients absorbed from the alimentary canal Capillaries are tiny blood vessels with very thin walls oxygen absorbed from the lungs consisting of only one layer of cells. They are the site of Figure 1.5 Blood cells after staining in the laboratory viewed through a microscope. Figure 1.6 The circulatory system.  Introduction to the human body exchange of substances between the blood and body tis- larger than those of the blood capillaries. Lymph is tissue sues, e.g. nutrients, oxygen and cellular waste products. fluid containing large molecules, e.g. proteins, fragments Blood vessels form a network that transports blood to: of damaged tissue cells and microbes. It is transported along lymph vessels and is returned to the bloodstream. the lungs (pulmonary circulation) where oxygen is There are collections of lymph nodes situated at various absorbed from the air in the lungs and at the same points along the length of the lymph vessels. Lymph is time carbon dioxide is excreted from the blood into filtered as it passes through the lymph nodes, and the air microbes, noxious substances and some waste materials cells in all parts of the body (general or systemic are removed. circulation). The lymphatic system provides the sites for formation and maturation of lymphocytes, the white blood cells Heart. The heart is a muscular sac. It pumps the blood involved in immunity. round the body and maintains the blood pressure in the lungs and general circulation. This is essential for life. The heart muscle is not under conscious (voluntary) Internal communication control. At rest, the heart contracts between 65 and 75 Communication and the nervous system times per minute. The rate may be greatly increased dur- The nervous system is a rapid communication system ing physical exercise, when the oxygen and nutritional (Ch. 7). The main components are shown in Figure 1.8. needs of the muscles moving the limbs are increased, and in some emotional states. The central nervous system consists of: The rate at which the heart beats can be counted by taking the pulse. The pulse can be felt most easily where the brain, situated inside the skull an artery lies close to the surface of the body and can be the spinal cord, which extends from the base of the pressed gently against a bone. The wrist is the site most skull to the lumbar region and is protected from commonly used for this purpose. injury by the bones of the spinal column. Lymphatic system The peripheral nervous system is a network of nerve The lymphatic system (Ch. 6) consists of a series of lymph fibres, which are: 9 vessels, which begin as blind-ended tubes in the spaces sensory or afferent, providing the brain with 'input' between the blood capillaries and tissue cells (Fig. 1.7). from organs and tissues, or Structurally they are similar to veins and blood capillar- motor or efferent, which convey nerve impulses ies but the pores in the walls of the lymph capillaries are carrying 'output' from the brain to effector organs: the muscles and glands. Figure 1.7 The lymphatic system: lymph nodes and vessels. Figure 1.8 The nervous system.  The body and its constituents The somatic (common) senses are pain, touch, heat and cold, levels of particular substances in the blood, including and they arise following stimulation of specialised sen- specific hormones. Changes in blood hormone levels are sory receptors at nerve endings found throughout the controlled by negative feedback mechanisms (Fig. 1.3). skin. There are different receptors in muscles and joints The endocrine system provides slower and more precise that respond to changes in the position and orientation of control of body functions than the nervous system. the body, maintaining posture and balance. Yet other receptors are activated by stimuli in internal organs and Communication with the external maintain control of vital body functions, e.g. heart rate, respiratory rate and blood pressure. Stimulation of any of environment these receptors sets up impulses that are conducted to the Special senses brain in sensory (afferent) nerves. Communication along These senses arise following stimulation of specialised nerve fibres (cells) is by electrical impulses that are gener- sensory receptor cells located in sensory organs or tissues ated when nerve endings are stimulated. in the head. The senses and the special organs involved Communication between nerve cells is also required, are shown in Box 1.2. since more than one nerve is involved in the chain of Although these senses are usually considered separate events occurring between the initial stimulus and the and different from each other, one sense is rarely used physiological reaction to it. Nerves communicate with alone (Fig. 1.9). For example, when the smell of smoke is each other by releasing a chemical (the neurotransmitter) perceived then other senses such as sight and sound are into tiny gaps between them. The neurotransmitter used to try and locate the source of a fire. Similarly, taste quickly travels across the gap and either stimulates or and smell are closely associated in the enjoyment, or oth- inhibits the next nerve cell, thus ensuring the message is erwise, of food. The brain collates incoming information transmitted. with information from the memory and initiates a Sensory nerves and chemical substances circulating in response by setting up electrical impulses in motor (effer- the blood provide information to appropriate parts of the ent) nerves to effector organs, muscles and glands. Such brain, which collates it and then responds via motor responses enable the individual to escape from the fire, or nerves to effector organs, often through a negative feed- to prepare the digestive system for eating. back mechanism (Fig. 1.3). Some of these activities are understood and perceived, e.g. pain, whereas others take Verbal communication place subconsciously, e.g. changes in blood pressure. Sound is a means of communication and is produced in 10 Nerve impulses travel at great speed along nerve fibres the larynx as a result of blowing air through the space leading to rapid responses; adjustments to many body between the vocal cords during expiration. Speech is the functions occur within a few seconds. manipulation of sound by contraction of the muscles of the throat and cheeks, and movements of the tongue and Communication and the endocrine system lower jhaw. The endocrine system consists of a number of endocrine glands situated in different parts of the body. They syn- Non-verbal communication thesise and secrete chemical messengers called hormones Posture and movements are associated with non-verbal that circulate round the body in the blood. Hormones communication, e.g. nodding the head and shrugging the stimulate target glands or tissues, influencing metabolic and other cellular activities and regulating body growth and maturation. Endocrine glands detect and respond to Box 1.2 The senses and related sense organs Sight-eyes Hearing-ears Balance-ears Smell-nose Taste-tonguef Figure 1.9 Combined use of the special senses: vision, hearing, smell and taste.  Introduction to the human body shoulders. The skeletal system provides the bony frame- end in alveoli, millions of tiny air sacs in each lung. They work of the body (Ch. 16), and movement takes place at are surrounded by a network of tiny capillaries and are joints between bones. Skeletal muscles which move the the sites where the vital process of gas exchange between bones lie between them and the skin. They are stimulated the lungs and the blood takes place (Fig. 1.11). by the part of the nervous system under conscious Nitrogen, which makes up about 80% of atmospheric (voluntary) control. Some non-verbal communication, air, is breathed in and out but, in this gaseous form, it e.g. changes in facial expression, may not involve the cannot be used by the body. The nitrogen needed by the movement of bones. body is present in protein-containing foods, mainly meat and fish. Intake of raw materials and Dietary intake elimination of waste Nutrition is considered in Chapter 11. A balanced diet is This section considers the substances that must be taken important for health and provides nutrients, substances into and excreted from the body. Oxygen, water and food that are absorbed, often following digestion, and pro- are the substances the body needs to take in, and carbon mote body function. Nutrients include water, carbohy- dioxide, urine and faeces are those excreted. drates, proteins, fats, vitamins and mineral salts. They are required for: Intake of oxygen maintaining water balance within the body Oxygen is a gas that makes up about 21 % of atmospheric energy production, mainly carbohydrates and fats air. A continuous supply is essential for human life synthesis of large and complex molecules, using because most chemical activities that take place in the mineral salts, proteins, fats, carbohydrates and body cells can occur only in its presence. Oxygen is vitamins needed in the series of chemical reactions that result in cell building, growth and repair, especially proteins. the release of energy from nutrients. The respiratory system carries air between the nose Digestion and the lungs during breathing (Ch. 10). Air passes The digestive system has developed because the food 11 through a system of passages consisting of the pharynx eaten is chemically complex and seldom in a form the (also part of the alimentary canal), the larynx (voice box), body cells can use. Its function is to break down or digest the trachea, two bronchi (one bronchus to each lung) and food so that it can be absorbed into the circulation and a large number of bronchial passages (Fig. 1.10). These then used by body cells. The digestive system consists of the alimentary tract and accessory glands (Fig. 1.12). Alimentary canal. This is a tube that begins at the mouth and continues through the pharynx, oesophagus, stomach, small and large intestines, rectum and anus. Glands. The accessory organs situated outside the ali- mentary canal with ducts leading into it are the salivary Figure 1.10 The respiratory system. Figure 1.11 Alveoli: the site of gas exchange.  The body and its constituents Figure 1.12 The digestive system. Figure 1.13 The urinary system. glands, the pancreas and the liver. There are also many waste products mainly of protein breakdown, e.g. urea. small glands situated in the walls of the alimentary canal. Under the influence of hormones from the endocrine sys- Most of these glands synthesise digestive enzymes that are tem the kidneys regulate water balance within the body. involved in the chemical breakdown of food. They also play a role in maintaining blood pH within the normal range. The bladder stores urine until it is excreted Metabolism during micturition. The process of micturition (passing 12 This is the sum total of the chemical activity in the body. urine) also involves the nervous system. It consists of two groups of processes: Faeces anabolism, building or synthesising large and complex The waste materials from the digestive system are substances excreted as faeces containing: catabolism, breaking down substances to provide energy and raw materials for anabolism, and indigestible food residue that remains in the substances for excretion as waste. alimentary canal because it cannot be absorbed bile from the liver, which contains the waste products The sources of energy are mainly the carbohydrates and from the breakdown of red blood cells fats provided by the diet. If these are in short supply, large numbers of microbes. proteins are used. Elimination of faeces (defecation) also involves the nervous system. Elimination of waste Carbon dioxide This is continually excreted by the respiratory system, as Protection and survival described above. Carbon dioxide is a waste product In this section relevant activities will be outlined under of cellular metabolism. It dissolves in water to form an the following headings: protection against the external acid that must be excreted in appropriate amounts to environment, resistance and immunity, movement and maintain the pH (acidity or alkalinity) of the blood in its reproduction. normal range. Urine Protection against the external environment This is formed by the kidneys, which are part of the uri- On the body surface, the skin (Ch. 14) mainly provides nary system (Ch. 13). The organs of the urinary system this. It consists of two layers: the epidermis and the are shown in Figure 1.13. Urine consists of water and derrnis.  Introduction to the human body The epidermis lies superficially and is composed of sev- Following exposure to an antigen, lifelong immunity eral layers of cells that grow towards the surface from its against further invasion by the same antigen usually deepest layer. The surface layer consists of dead cells that develops. Over a lifetime, an individual gradually builds are constantly being rubbed off and replaced from below. up immunity to millions of antigens. Allergic reactions The epidermis constitutes the barrier between the moist are abnormally powerful immune responses to an anti- environment of the living cells of the body and the dry gen that usually poses no threat to the body. atmosphere of the external environment. The dermis contains tiny sweat glands that have little canals or ducts, leading to the surface. Hairs grow from Movement follicles in the dermis. The layers of the skin form a barrier Movement of the whole body or parts of it are essential against: for: invasion by microbes obtaining food chemicals avoiding injury dehydration. reproduction. Sensory nerve endings present in the dermis are Most body movement is under conscious (voluntary) stimulated by pain, temperature and touch. If the control. The exceptions include protective movements finger touches a very hot plate, it is removed immedi- which are carried out before the individual is aware of ately. This cycle of events is called a reflex action and is a them, e.g. the reflex action of removing the finger from a very rapid motor response (contraction of muscles) to a very hot surface. sensory stimulus (stimulation of sensory nerve endings The skeleton provides the bony framework of the in the skin). This type of reflex action is an important body and movement takes place at joints between two or protective mechanism that is mediated by the nervous more bones. Skeletal muscles (Fig. 1.14) move the joints system. and they are stimulated to contract by the nervous sys- The skin also plays an important role in the regulation tem. A brief description of the skeleton is given in of body temperature. Chapter 3, and a more detailed account of bones, muscles and joints is presented in Chapters 16,17 and 18. 13 Resistance and immunity The body has many means of self-protection from invaders (Ch. 15). They are divided into two categories: specific and nonspecific defence mechanisms. Nonspecific defence mechanisms These are effective against any invaders. The protection provided by the skin is outlined above. In addition there are other protective features at body surfaces, e.g. mucus secreted by mucous membranes traps microbes and other foreign materials on its sticky surface. Some body fluids contain antimicrobial substances, e.g. gastric juice contains hydrochloric acid, which kills most ingested microbes. Following successful invasion other non- specific processes may occur including the inflammatory response, which is also involved in tissue healing. Specific defence mechanisms The body generates a specific (immune) response against any substance it identifies as foreign. Such substances are called antigens and include: bacteria and other microbes cancer cells or transplanted tissue cells pollen from flowers and plants. Figure 1.14 The skeletal muscles.  The body and its constituents Reproduction (Ch. 19) When the ovum is not fertilised it passes out of the uterus accompanied by bleeding, called menstruation. The cycle Successful reproduction is essential in order to ensure the in the female, called the menstrual cycle, has phases asso- continuation of a species from one generation to the next. ciated with changes in the concentration of hormones Bisexual reproduction results from the fertilisation of a involving the endocrine system. There is no similar cycle female egg cell or ovum by a male sperm cell or spermato- in the male but hormones similar to those of the female zoon. Ova are produced by two ovaries situated in the are involved in the production and maturation of the female pelvis (Fig. 1.15). Usually only one ovum is spermatozoa. released at a time and it travels towards the uterus in the uterine tube. The spermatozoa are produced in large num- bers by the two testes, situated in the scrotum. From each testis spermatozoa pass through a duct called the deferent duct (vas deferens) to the urethra. During sexual inter- INTRODUCTION TO THE STUDY course (coitus) the spermatozoa are deposited in the OF ILLNESS female vagina. They then pass upwards through the uterus and fer- tilise the ovum in the uterine tube. The fertilised ovum Learning outcomes (zygote] then passes into the uterus, embeds itself in the uterine wall and grows to maturity during pregnancy or After studying this section you should be able to: gestation, in about 40 weeks. The newborn baby is entirely dependent on others for food and protection that list factors that commonly cause disease was provided by the mother's body before birth. define the following terms: aetiology, pathogenesis One ovum is produced about every 28 days during the and prognosis child-bearing years between puberty and the menopause. name some common disease processes that can affect many of the body systems. 14 In order to understand the specific diseases described in later chapters, a knowledge of the relevant anatomy and physiology is necessary, as well as familiarity with the pathological processes outlined below. Many different illnesses, disorders and diseases are known, and these vary from minor, but often very trouble- some conditions, to the very serious. The study of abnor- malities can be made much easier when a systematic approach is adopted. In order to achieve this in later chap- ters where specific diseases are explained, the headings shown in Box 1.3 will be used as a guide. Causes (aetiology) are outlined first when there are clear links between them and the effects of the abnormality (pathogenesis}. Figure 1.15 The reproductive systems: male and female. Box1.3Sugestdframwokunderstaig es Atiolgy:causeofthdiasePthognesi: atureofhdisaeprocsnditefconrmalbdyfunctiogCmplicatons:herc quneswhicmgtarseifhdaseprog Progensi:thlkeyoucmBx  Introduction to the human body Aetiology Abnormal immune mechanisms (p. 383) —these are a response of the normally protective immune system Disease is usually caused by one or more of a limited that causes undesirable effects. number of factors including: Thrombosis, embolism and infarction (p. 117) —these are genetic abnormalities, either inherited or acquired the effects and consequences of abnormal changes in infection by microbes or parasites, e.g. viruses, the blood and/or blood vessel walls. bacteria or worms Degeneration — this is often associated with normal chemicals ageing but also arises prematurely when structures ionising radiation deteriorate causing impaired function. physical trauma Metabolic abnormalities —cause undesirable effects (e.g. degeneration, e.g. excessive use or ageing. phenylketonuria (p. 185)). Genetic abnormalities — may be either inherited or In some diseases more than one of the aetiological factors caused by environmental factors such as exposure to listed above is involved, while in others, no specific cause ionising radiation. has been identified and these may be described as essen- tial, idiopathic or spontaneous. For some diseases of which Box 1.4 is a glossary of disease-associated terminology. the precise cause is unknown, links may have been estab- lished with predisposing factors, or risk factors. latrogenic Box 1.4 Glossary of terminology associated with conditions are those that result from harm caused by disease members of the caring professions. Acute: a disease with sudden onset often requiring urgent treatment (compare with chronic). Pathogenesis Acquired: a disorder which develops any time after The main processes causing illness or disease are as birth (compare with congenital). follows. Chronic: a long-standing disorder which cannot Inflammation (p. 375) — this is a tissuhe response to usually be cured (compare with acute). damage by, e.g. trauma, invasion of microbes*. Congenital: a disorder which one is born with 15 Inflammatory conditions are recognised by the suffix (compare with acquired). -itis, e.g. appendicitis. Sign: an abnormality seen or measured by people Tumours (p. 53) — these arise when the rate of cell other than the patient production exceeds that of normal cell destruction causing a mass to develop. Tumours are recognised Symptom: an abnormality described by the patient. by the suffix -oma, e.g. carcinoma. Syndrome: a collection of signs and symptoms which tend to occur together. *The term microbe, used throughout the text, includes all types of organisms that can only be seen by using a microscope. Specific microbes are named where appropriate. This page intentionally left blank 2 Introduction to the chemistry of life Atoms, molecules and compounds 18 Amino acids and proteins 23 Lipids 24 Atomic structure 18 Nucleotides 24 Atomic number and atomic weight 18 Nucleic acids 24 Molecules and compounds 19 Deoxyribonucleic acid (DNA) 24 Electrolytes 20 Ribonucleic acid (RNA) 25 Molecular weight 21 Adenosine triphosphate (ATP) 25 Molar concentration 21 Enzymes 26 Acids, alkalis and pH 21 The pH scale 21 Movement of substances within pH values of the body fluids 22 the body 26 Buffers 22 Diffusion 26 Acidosis and alkalosis 22 Osmosis 27 Important biological molecules Body fluids 27 23 Extracellular fluid 27 Carbohydrates 23 Intracellular fluid 28  The body and its constituents In all the following chapters, the cells, tissues and organs of the body will be studied in more depth. However, on a smaller scale even than the cell, all living matter is made up of chemical building blocks. The basis of anatomy and Particle Mass Electric charge physiology is therefore a chemical one, and before launch- Proton 1 unit 1 positive ing into the study of the subject it is necessary to consider briefly some aspects of chemistry and biochemistry. Neutron 1 unit neutral Electron negligible 1 negative ATOMS, MOLECULES AND carries one unit of negative electrical charge and its mass COMPOUNDS is so small that it can be disregarded when compared with the mass of the other particles. Table 2.1 summarises the characteristics of these subatomic particles. In all atoms the number of positively charged protons After studying this section, you should be able to: in the nucleus is equal to the number of negatively charged electrons in orbit around the nucleus and definethefollowingterms: atomic number, atomic therefore an atom is electrically neutral. weight, isotope, motecular weight, on, electrolyte, pH,acid and alkali Atomic number and atomic weight describe thestructureof an atom What makes one element different from another is the discuss the types of bonds that hold molecules number of protons in the nuclei of its atoms. For instance, together hydrogen has only one proton per nucleus, oxygen has eight and sodium has 11. The number of protons in the outline the concept of molr concentration nucleus of an atom is called the atomic number; the 18 atomic numbers of hydrogen, oxygen and sodium are discuss the importance of buffers in the maintenance oftherefore body pH 1, 8 and 11 respectively. It therefore follows that each element has its own atomic number (Fig. 2.2). The atomic weight of an element is the sum of the protons The atom is the smallest particle of an element which can and neutrons in the atomic nucleus (Fig. 2.2). exist as a stable entity. An element is a chemical substance The electrons are shown in Figure 2.1 to be in concen- whose atoms are all of the same type; e.g. iron contains tric rings round the nucleus. These shells diagrammati- only iron atoms. Compounds contain more than one type cally represent the different energy levels of the electrons of atom; for instance, water is a compound containing both hydrogen and oxygen atoms. There are 92 naturally occurring elements. The body structures are made up of a great variety of combinations of four elements: carbon, hydrogen, oxygen and nitro- gen. In addition small amounts of others are present, collectively described as mineral salts (p. 276). Atomic structure Atoms are made up of three main types of particles. Protons are particles present in the nucleus or central part of the atom. Each proton has one unit of positive electrical charge and one atomic mass unit. Neutrons are also found in the nucleus of the atom. They have no electrical charge and one atomic mass unit. Electrons are particles which revolve in orbit around the nucleus of the atom at a distance from it (Fig. 2.1), as the planets revolve round the sun. Each electron Figure 2.1 The atom showing the nucleus and four electron shells.  Introduction to the chemistry of life Figure 2.3 The isotopes of hydrogen. 35 (with 18 neutrons in the nucleus) and the other 37 (with 20 neutrons in the nucleus). Because the proportion of these two forms is not equal, the average atomic weight Figure 2.2 The atomic structures of the elements hydrogen, oxygen and sodium. is 35.5. Molecules and compounds in relation to the nucleus, not their physical positions. It was mentioned earlier that the atoms of each element The first energy level can hold only two electrons and is have a specific number of electrons around the nucleus. filled first. The second energy level can hold only eight When the number of electrons in the outer shell of an ele- electrons and is filled next. The third and subsequent ment is the optimum number (Fig. 2.1), the element is energy levels hold increased numbers of electrons, each described as inert or chemically unreactive, i.e. it will not containing more than the preceding level. easily combine with other elements to form compounds. The electron configuration denotes the distribution of the These elements are the inert or noble gases —helium, electrons in each element, e.g. sodium is 2 8 1 (Fig. 2.2). neon, argon, krypton, xenon and radon. An atom is most stable when its outermost electron Molecules consist of two or more atoms which are chem- shell is full. Once electrons have filled the first two shells, ically combined. The atoms may be of the same element, the atom can reach a level of stability by having either the e.g. a molecule of atmospheric oxygen (O2) consists of two 19 full complement of 18, or exactly eight, electrons in its oxygen atoms. Most molecules, however, contain two or third shell. When the outermost shell does not have a more different elements; e.g. a water molecule (H,O) con- stable number of electrons, the atom is reactive and will tains two hydrogen atoms and an oxygen atom. As men- combine with other reactive atoms, forming the wide tioned earlier, when two or more elements combine, the range of the complex molecules of life. This will be resulting molecule can also be referred to as a compound. described more fully in the section discussing molecules Compounds which contain the element carbon are and compounds. classified as organic, and all others as inorganic. The body contains both. Isotopes. These are atoms of an element in which there is a different number of neutrons in the nucleus. This does Covalent and ionic bonds. The vast array of chemical not affect the electrical activity of these atoms because processes on which body functioning is based is com- neutrons carry no electrical charge, but it does affect their pletely dependent upon the way atoms come together, atomic weight. For example, there are three forms of the bind and break apart. For example, the simple water mol- hydrogen atom. The most common form has one proton ecule is a crucial foundation of all life on Earth. If water in the nucleus and one orbiting electron. Another form was a less stable compound, and the atoms came apart has one proton and one neutron in the nucleus. A third easily, human biology could never have evolved. On the form has one proton and two neutrons in the nucleus and other hand, the body is dependent upon the breaking one orbiting electron. These three forms of hydrogen are down of various molecules (e.g. sugars, fats) to release called isotopes (Fig. 2.3). energy for cellular activities. When atoms are joined Taking into account the isotopes of hydrogen and the together, they form a chemical bond which is generally proportions in which they occur, the atomic weight of one of two types: covalent or ionic. hydrogen is 1.008, although for many practical purposes Covalent bonds are formed when atoms share their it can be taken as 1. electrons with each other. Most atoms use this type of Chlorine has an atomic weight of 35.5, because it exists bond when they come together; it forms a strong and in two forms; one isotope has an atomic weight of stable link between them, because atoms are most stable  The body and its constituents Figure 2.4 A water molecule, showing the covalent bonds between hydrogen (yellow) and oxygen (green). when their outer electron shells are filled. A water mole- cule is built using covalent bonds. Hydrogen has one elec- tron in its outer shell, but the optimum number for this shell is two. Oxygen has six electrons in its outer shell, but the optimum number for this shell is eight. Therefore, if one oxygen atom and two hydrogen atoms combine, each hydrogen atom will share its electron with the oxygen atom, giving the oxygen atom a total of eight outer elec- trons and thereby conferring stability. The oxygen atom Figure 2.5 Formation of the ionic compound, sodium chloride. shares one of its electrons with each of the two hydrogen atoms, so that each hydrogen atom has two electrons in its outer shell and they too are stable (Fig. 2.4). Electrolytes Ionic bonds are weaker than covalent bonds and are An ionic compound, e.g. sodium chloride, in solution in 20 formed when electrons are transferred from one atom to water is called an electrolyte because it can conduct electric- another. For example, when sodium (Na) combines with ity. Electrolytes are important body constituents because: chlorine (Cl) to form sodium chloride (NaCl) there is some conduct electricity, essential for muscle and a transfer of the only electron in the outer shell of nerve function the sodium atom to the outer shell of the chlorine atom. some exert osmotic pressure, keeping body fluids in (Fig. 2.5). their own compartments This leaves the sodium atom of the compound with some function in acid-base balance, as buffers to resist eight electrons in its outer (second) shell, and therefore pH changes in body fluids. stable. The chlorine atom also has eight electrons in its outer shell, which, although not filling the shell, is a stable In this discussion, sodium chloride has been used as an number. example of the formation of an ionic compound and to The number of electrons is the only change which illustrate electrolyte activity. There are, however, many occurs in the atoms in this type of reaction. There is no other electrolytes within the human body which, though change in the number of protons or neutrons in the nuclei in relatively small quantities, are equally important. of the atoms. The chloride atom now has 18 electrons, Although these substances may enter the body in the each with one negative electrical charge, and 17 protons, form of compounds, such as sodium bicarbonate, they each with one positive charge. The sodium atom has lost are usually discussed in the ionic form, that is, as sodium one electron, leaving 10 electrons orbiting round the ions (Na+) and bicarbonate ions (HCO3-). nucleus with 11 protons. When sodium chloride is dis- The bicarbonate part of sodium bicarbonate is derived solved in water the two atoms separate, i.e. they ionise, from carbonic acid (H2CO3). All inorganic acids contain and the imbalance of protons and electrons leads to the hydrogen combined with another element, or with a formation of two charged particles called ions. Sodium, group of elements called a radical which acts like a single with the positive charge, is a cation, written Na+, and element. Hydrogen combines with chlorine to form chloride is an anion, written Cl~. By convention the num- hydrochloric acid (HC1) and with the phosphate radical to ber of electrical charges carried by an ion is indicated by form phosphoric acid (H3PO4). When these two acids the superscript plus or minus signs. ionise they do so thus:  Introduction to the chemistry of life HC1 -> H+ Cl- H3PO4 3H+ PO43- Table 2.2 Examples of normal plasma levels ?fiB In the second example, three atoms of hydrogen have Substance Amount in Si units Amount in other units each lost one electron, all of which have been taken up by one unit, the phosphate radical, making a phosphate ion Chloride 97-106 mmol/l 97-106mEq/l with three negative charges. Sodium 135-143 mmol/l 135-143 mEq/l A large number of compounds present in the body are not ionic and therefore have no electrical properties Glucose 3.5-5.5 mmol/l 60-100mg/100ml when dissolved in water, e.g. carbohydrates. Iron 14-35 nmoi/I 90-196ng/100 ml Molecular weight The molecular weight of a molecule is the sum of the In physiology this system has the advantage of being a atomic weights of the elements which form its molecules, measure of the number of particles (molecules, atoms, ions) of substances present because molar solutions of different substances contain the same number of parti- Water (H.OH) cles. It has the advantage over the measure milliequiva- 2 hydrogen atoms (atomic weight 1) 2 lents per litre* because it can be used for non-electrolytes, 1 oxygen atom (atomic weight 16) 16 in fact for any substance of known molecular weight. Molecular weight = 18 Many of the chemical substances present in the body are in very low concentrations so it is more convenient to Sodium bicarbonate (NaHCO3) use smaller metric measures, e.g. millimoles per litre 1 sodium atom (atomic weight 23) 23 (mmol/l) or micromoles per litre (umol/1) as a biological 1 hydrogen atom (atomic weight 1) 1 measure (Table 2.2). 1 carbon atom (atomic weight 12) 12 For substances of unknown molecular weight, e.g. 3 oxygen atoms (atomic weight 16) 48 insulin, concentration may be expressed in International Molecular weight = 84 Units per millilitre (IU/ml). Molecular weight, like atomic weight, is expressed sim- 21 ply as a figure until a scale of measurement of weight is applied. Acids, alkalis and pH The number of hydrogen ions present in a solution is a Molar concentration measure of the acidity of the solution. The maintenance This is the term recommended in the Systeme Internationale of the normal hydrogen ion concentration ([H+]) within for expressing the concentration of substances present in the body is an important factor in maintaining a stable the body fluids (SI units). environment, i.e. homeostasis. The mole (mol) is the molecular weight in grams of a substance (formerly called 1 gram molecule). One mole The pH scale of any substance contains 6.023 x 1023 molecules or A standard scale for the measurement of the hydrogen ion atoms. For example, 1 mole of sodium bicarbonate (the concentration in solution has been developed: the pH example above) is 84 grams. scale. Not all acids ionise completely when dissolved in A molar solution is a solution in which 1 mole of a sub- water. The hydrogen ion concentration is a measure, there- stance is dissolved in 1 litre of solvent. In the human fore, of the amount of dissociated add (ionised acid) rather body the solvent is water or fat. A molar solution of than of the total amount of acid present. Strong acids dis- sodium bicarbonate is therefore prepared using 84 g of sociate more freely than weak acids, e.g. hydrochloric acid sodium bicarbonate'dissolved in 1 litre of solvent. Molar concentration may be used to measure quanti- ties of electrolytes, non-electrolytes, ions and atoms, e.g. *Milliequivalents per litre (mEq/1) molar solutions of the following substances mean: _ atomic weight 1 mole of sodium chloride molecules = 58.5 g per litre Equivalent weight = number of electrical charges (NaCl) Concentration is expressed: 1 mole of sodium ions (Na+) = 23 g per litre 1 mole of carbon atoms (C) = 12 g per litre mEq/1 n/ = --------- x number of electrical charges 1 mole of atmospheric oxygen (O2) = 32 g per litre atomic weight  The body and its constituents Table 2.3 pH values of body fluids Body fluid pH Blood 7.35 to 7.45 Saliva 5.4 to 7.5 Figure 2.6 The pH scale. Gastric juice 1.5 to 3.5 dissociates freely into H+ and Cl~, while carbonic acid dis- Bile 6 to 8.5 sociates much less freely into H+ and HCO3-. The number Urine 4.5 to 8.0 of free hydrogen ions in a solution is a measure of its acidity rather than an indication of the type of molecule from which the hydrogen ions originated. amylase, the enzyme present in saliva which initiates the The alkalinity of a solution depends on the number of digestion of carbohydrates. The action of salivary amy- hydroxyl ions (OH-). Water is a neutral solution because lase is inhibited when food containing it reaches the every molecule contains one hydrogen ion and one stomach and is mixed with acid gastric juice. hydroxyl radical. For every molecule of water (H.OH) Blood has a pH value between 7.35 and 7.45. The pH which dissociates, one hydrogen ion (H+) and one range of blood compatible with life is 7.0 to 7.8. The meta- hydroxyl ion (OH-) are formed, neutralising each other. bolic activity of the body cells produces certain acids and The scale for measurement of pH was developed alkalis which alter the pH of the tissue fluid and blood. taking water as the standard. To maintain the pH within the normal range, there are In a neutral solution such as water, where the number substances present in blood that act as buffers. of hydrogen ions is balanced by the same number of hydroxyl ions, the pH = 7. The range of this scale is from Buffers 0 to 14. The optimum pH level is maintained by the balance A pH reading below 7 indicates an acid solution, while between acids and bases produced by cells. Bases are 22 readings above 7 indicate alkalinity (Fig. 2.6). A change of substances that accept (or bind) hydrogen ions and when one whole number on the pH scale indicates a tenfold dissolved in water they produce an alkaline solution. change in [H+]. Therefore, a solution of pH 5 contains ten Buffers are substances such as phosphates, bicarbonates times as many hydrogen ions as a solution of pH 6. and some proteins that maintain the [H+] within normal, Ordinary litmus paper indicates whether a solution is but narrow, limits. Some buffers 'bind' hydrogen ions acid or alkaline by colouring blue for alkaline and red for and others 'bind' hydroxyl ions, reducing their circulat- acid. Other specially treated absorbent papers give an ing levels and preventing damaging changes. For exam- approximate measure of pH by a colour change. When ple, if there is sodium hydroxide (NaOH) and carbonic accurate measurements of pH are required, sensitive pH acid (H2CO3) present, both will ionise to some extent, but meters are used. they will also react together to form sodium bicarbonate (NaHCO3) and water (H.OH). One of the hydrogen ions pH values of the body fluids from the acid has been 'bound' in the formation of the Body fluids have pH values that must be maintained bicarbonate radical and the other by combining with the within relatively narrow limits for normal cell activity. hydroxyl radical to form water. The pH values are not the same in all parts of the body; NaOH H2CO3 NaHCO3 + H.OH e.g. the normal range of pH values of certain body fluids sodium carbonic sodium water are shown in Table 2.3. hydroxide acid bicarbonate The pH value in an organ is produced by its secretion of acids or alkalis which establishes the optimum level. Acidosis and alkalosis The highly acid pH of the gastric juice is maintained by The substances in the complex buffer system that 'bind' hydrochloric acid secreted by the parietal cells in the hydrogen ions are called the alkali reserve of the blood. walls of the gastric glands. The low pH value in the stom- When the pH is below 7.35, and all the reserves of alka- ach provides the environment best suited to the function- line buffer are used up, the condition of acidosis exists. ing of the enzyme pepsin that begins the digestion of When the reverse situation pertains and the pH is above dietary protein. Saliva has a pH of between 5.4 and 7.5 7.45, and the increased alkali uses up all the acid reserve, which is the optimum value for the action of salivary the state of alkalosis exists.  Introduction to the chemistry of life The buffer systems maintain homeostasis by preventing Carbohydrates dramatic changes in the pH values in the blood, but can only function effectively if there is some means by which The carbohydrates are the sugars. Carbohydrates are excess acid or alkali can be excreted from the body. The composed of carbon, oxygen and hydrogen and the organs most active in this way are the lungs and the carbon atoms are normally arranged in a ring, with the kidneys. The lungs are important regulators of blood pH oxygen and hydrogen atoms linked to them. The struc- because they excrete carbon dioxide (CO2). CO2 increases tures of glucose, fructose and sucrose are shown in [H+] in body fluids because it combines with water Figure 2.7. When two sugars link up, the reaction occur- to form carbonic acid, which then dissociates into a ring expels a molecule of water and the resulting bond bicarbonate ion and a hydrogen ion. is called a glycosidic linkage. Simple sugars, like glucose, can exist as single units, CO2 +H 2 O ->H2CO3 ->H + + HCO3- and are referred to as monosaccharides. Glucose is the carbon water carbonic hydrogen bicarbonate main form in which sugar is used by cells, and blood dioxide acid ion ion levels are tightly controlled. Frequently, the monosac- In acidosis, the brain detects the rising [H+] in the blood charides are linked together, the resultant molecule and stimulates breathing, causing increased CO2 loss and ranging from two sugars or disaccharides, e.g. sucrose a fall in [H+]. Conversely, in alkalosis, the brain can (table sugar), to long chains containing many thousands reduce the respiration rate to increase CO2 levels and of sugars. Such complex carbohydrates are called increase [H+], restoring pH towards normal. polysaccharides, e.g. starch. The kidneys have the ability to form ammonia, an Glucose can be broken down (metabolised) in either alkali, which combines with the acid products of protein the presence (aerobically) or the absence (anaerobically) of metabolism which are then excreted in the urine. oxygen, but the process is much more efficient when O2 The buffer and excretory systems of the body together is used. During this process, energy, water and carbon maintain the acid-base balance so that the pH range of the dioxide are released (p. 315) This family of molecules: blood remains within normal, but narrow, limits. serves as a ready source of energy to fuel cellular activities (p. 272) provides a form of energy storage, e.g. glycogen 23 IMPORTANT BIOLOGICAL (p. 315) forms an integral part of the structure of DNA and MOLECULES RNA (p. 25) can act as receptors on the cell surface, allowing the cell to recognise other molecules and cells. Learning outcomes After studying this section, you should be able to: describe in simple terms the chemical nature of Amino acids and proteins sugars, protein, lipids, nucieotides and enzymes Amino acids always contain carbon, hydrogen, oxygen discuss the biological importance of each of these and nitrogen, and many in addition carry sulphur. important groups of molecules. In human biochemistry, 20 amino acids are used as the principal building blocks of protein, although there are Figure 2.7 The combination of glucose and fructose to make sucrose.  The body and its constituents Figure 2.9 Core structure of the fats. (water hating) and therefore lipids do not mix with water. This is important in their function in the cell membrane (p. 30). Other types of lipids include certain vitamins (e.g. E Figure 2