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Contributors

Carl Clare RN DipN BSc (Hons) MSc (Lond) PGDE (Lond)

Senior Lecturer, Department of Adult Nursing and Primary Care, School of Health and Social Work, University of Hertfordshire, Hatfield, Hertfordshire, UK

Carl began his nursing career as a Nursing Auxiliary in 1990. He later undertook a 3-year student nurse training at Selly Oak Hospital (Birmingham). He moved to the Royal Devon and Exeter Hospitals, then to the Northwick Park Hospital and finally to the Royal Brompton and Harefield NHS Trust as a Resuscitation Officer and Honorary Teaching Fellow of Imperial College (London). He has worked in nurse education since 2001. His key areas of interest are physiology, sociology, cardiac care and resuscitation. Carl has previously published work in the field of cardiac care and resuscitation.

Louise McErlean RGN MA BSc (Hons)

Senior Lecturer, Department of Adult Nursing and Primary Care, School of Health and Social Work, University of Hertfordshire, Hatfield, Hertfordshire, UK

Louise began her nursing career in 1986 in Glasgow, becoming a Registered General Nurse. She later completed the intensive care course for RGNs while working in Belfast as a staff nurse. Louise moved to London in 1997 and worked towards a Junior Sister’s role in Intensive Care. She moved to the University of Hertfordshire in 2005 where she is currently employed as a senior lecturer. Her key areas of interest are learning and teaching pre-registration nursing and intensive care nursing.

Janet G. Migliozzi RGN BSc (Hons) MSc (London) PGD Ed. FHEA

Senior Lecturer, Department of Adult Nursing and Primary Care, School of Health and Social Work, University of Hertfordshire, Hatfield, Hertfordshire, UK

Janet commenced her nursing career in London, becoming a Staff Nurse in 1988. She has worked at a variety of hospitals across London, predominately in vascular, orthopaedic and high-dependency surgery before specialising in infection prevention and control. She has worked in nurse education since 1999. Her key interests include microbiology, particularly in relation to healthcare-associated infection, vascular/surgical nursing, health informatics and nurse education. Janet has previously published work in the field of minimising risk in relation to healthcare-associated infection and is a member of the Infection Prevention Society.

Muralitharan Nair SRN RMN DipN (Lond) RNT Cert Ed. Cert in Counselling BSc (Hons) MSc (Surrey) FHEA

Senior Lecturer, Department of Adult Nursing and Primary Care, School of Health and Social Work, University of Hertfordshire, Hatfield, Hertfordshire, UK

Muralitharan commenced his nursing career in 1971 at Edgware General Hospital, becoming a Staff Nurse. In 1975, he commenced his mental health nurse training at Springfield Hospital and worked as a Staff Nurse for approximately 1 year. He has worked at St Mary’s Hospital, Paddington and Northwick Park Hospital, returning to Edgware General Hospital to take up the post of Senior Staff Nurse and then Charge Nurse. He has worked in nurse education since 1989. His key interests include physiology, diabetes, surgical nursing and nurse education. Muralitharan has published in journals and co-edited and written textbooks, and he is an experienced nurse educator.

Ian Peate EN(G), RGN, DipN (Lond), RNT, BEd (Hons), MA(Lond), LLM

Visiting Professor of Nursing, School of Nursing, Midwifery and Healthcare, Faculty of Health and Human Sciences, University of West London, Brentford, Middlesex, UK; Independent Consultant and Editor-in-Chief British Journal of Nursing

Ian began his nursing career in 1981 at the Central Middlesex Hospital, becoming an Enrolled Nurse working in an intensive care unit. He later undertook a 3-year student nurse training at Central Middlesex and Northwick Park Hospitals, becoming a Staff Nurse and then a Charge Nurse. He has worked in healthcare education since 1989. He is currently Professor of Nursing. His key areas of expertise focus on nursing theory and practice, sexual health, HIV and men’s health. He is widely published and an experienced healthcare educator.

Anthony Wheeldon RN Dip HE BSc (Hons) MSc (Lond) PGDE

Senior Lecturer, Department of Adult Nursing and Primary Care, School of Health and Social Work, University of Hertfordshire, Hatfield, Hertfordshire, UK

After qualification in 1995, Anthony worked as a Staff Nurse and a Senior Staff Nurse in the Respiratory Directorate at the Royal Brompton and Harefield NHS Trust. He began teaching on postregistration courses in 2000 before moving into full-time nurse education at Thames Valley University in 2002. Anthony has a wide range of nursing interests, including cardiorespiratory nursing, anatomy and physiology, respiratory assessment and nurse education. He is currently a Senior Lecturer at the University of Hertfordshire.

Acknowledgements

We would like to thank all of our colleagues for their help, support, comments and suggestions.

Muralitharan would like to thank his wife, Evangeline, and his daughters, Samantha and Jennifer, for their continued support and patience.

Ian would like to thank his partner Jussi Lahtinen for all of his continued support and encouragement.

Copyright Information

Several Wiley publications have contributed artwork to this book. We are grateful for permission to use and adapt the artwork.

Artwork reproduced with permission from third-parties is credited at the end of the appropriate caption.

Preface

This second edition of the hugely popular Fundamentals of Applied Pathophysiology provides you with an up to date overview of pathophysiology and related care. This edition supplements a nursing focus by broadening the professional base to include all healthcare students; hence the title change to Fundamentals of Applied Pathophysiology: An Essential Guide for Nursing and Healthcare Students.

An integrated, multidisciplinary approach to the provision of health and social care is high up on the agendas of those who provide health and social care. This edition goes some way to ensuring that healthcare students work as a part of an interdisciplinary team. This text will help you develop critical thinking, innovation and creativity in relation to the health and well-being of the people you have the privilege to care for.

There are a number of new features that have been added in order to enhance learning and to encourage application of the theoretical principles to care provision – wherever this may be. Each chapter now incorporates two case studies related to the chapter content; there are questions at the end of each case study that provoke reflection and further thought. Word searches, fill in the blanks and label the diagram activities are provided at the end of each chapter, with answers given on the accompanying website; and on the website are 10 multiple choice questions for each chapter Each chapter offers a list of further resources that the reader may wish to use to enhance and develop learning. A glossary of terms is included at the end of each chapter.

How to Get the Best Out of Your Textbook

Welcome to the new edition of Fundamentals of Applied Pathophysiology: An Essential Guide for Nursing and Healthcare Students. Over the next few pages you will be shown how to make the most of the learning features included in the textbook.

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Features Contained within Your Textbook

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Your textbook is full of useful illustrations, photographs and tables.

Every chapter ends with a conclusion summing up what you’ve learnt, a glossary, references and a range of activities to test your understanding of what you’ve been studying.

We hope you enjoy your new textbook. Good luck with your studies!

How to Use the Website

Don’t forget to visit the companion website for this book:

www.wiley.com/go/fundamentalsofappliedpathophysiology

There you will find valuable instructor and student material designed to enhance your learning, including:

• instructor image bank
• interactive multiple choice questions
• interactive true/false exercises
• word searches
• label the diagram activities
• searchable glossary
• further reading and resources

Introduction

Ian Peate¹ and Muralitharan Nair²

¹Visiting Professor of Nursing, School of Nursing, Midwifery and Healthcare, Faculty of Health and Human Sciences, University of West London, Brentford, Middlesex; Independent Consultant and Editor in Chief British Journal of Nursing.

²Senior Lecturer, Department of Adult Nursing and Primary Care, School of Health and Social Work, University of Hertfordshire, Hatfield, Hertfordshire, UK.

Pathophysiology

Pathophysiology is concerned with the disturbance of normal mechanical, physical and biochemical functions. The disturbance is either caused by disease, an abnormal syndrome or a condition. Porth (2009) looks at the word ‘pathophysiology’ – it is a combined word, from the Greek pathos, meaning disease, and physiology, meaning related to the various normal functions of the human body. Pathophysiology addresses both the cellular and the organ changes that occur with disease, as well as the effects these changes have on body function. When something impacts upon the normal physiological functioning of the body (i.e. disease), this then becomes a pathophysiological issue. It must, however, be remembered that normal health is not and cannot be exactly the same in any two individuals; therefore, the term ‘normal’ must be treated with caution.

This text has been written with the intention of making the sometimes complex subject of pathophysiology accessible and exciting. The human body has an extraordinary ability to respond to disease in a number of physiological and psychological ways; it is able to compensate for the changes that occur as a result of the disease process. This text considers those changes (the pathophysiological processes) and the effect they can have on a person.

Healthcare Provision

The provision of healthcare is in a constant state of flux, not least because it should aim to respond to the global shift in the burden of disease; a larger number of people affected by long-term conditions is now seen. An integrated approach to health and social care is essential if the needs of people accessing services are to be met safely and effectively.

People who are affected by long-term conditions (patients and families) can often experience physical and mental health problems at the same time either as a consequence of their illness or independent of it, and they are entitled to receive care from healthcare professionals who are knowledgeable, kind, caring and compassionate.

There are a number of factors that impinge on the provision of healthcare, the maintenance of health and the prevention of disease, e.g.:

• health inequalities
• technological advances
• public expectation
• the role and function of the healthcare professional
• the role and function of other healthcare providers
• personal, social and cultural factors.

To be able to care for people, safely and effectively, the healthcare professional must have the appropriate knowledge and skills to meet needs:

• in a complex and diverse society where social inequality exists
• inside and outside hospital and across health and social care
• across public, private and voluntary health provider organisations
• of an increasing older population
• of those with long-term conditions
• across the patient care pathway
• in supporting lifestyle changes
• using disease prevention and health promotional interventions
• by treating patients as partners in healthcare and maximising choice
• through the use of technological advances
• in new and emerging roles that cross professional boundaries
• as leaders and members of multidisciplinary and interdisciplinary teams
• as lifelong learners in an ever-evolving healthcare environment.

In order for the healthcare student to aspire to and provide care that takes the above points into account, there must be a sound understanding of pathophysiological principles.

Fundamentals of Applied Pathophysiology

This is a foundation text that will enable the reader to grow personally and professionally in relation to the provision of healthcare. This textbook is primarily intended for healthcare students who will come into contact with patients who may have a variety of physically-related healthcare problems, such as pneumonia, diabetes mellitus and Alzheimer’s disease, in both the hospital and community settings. The focus of the text is on the adult person. Illness and disease are discussed explicitly, emphasising the fact that individuals do become ill and experience disease.

It is the intention of this text to develop knowledge and skills both in theory and practice, and to apply this knowledge in order to provide safe and effective high-quality care. The overriding aim is to relate normal body function to pathological changes that may lead to disease processes, preventing the individual from leading a ‘normal’ life.

The level at which the text has been written will provide readers with a straightforward understanding of applied pathophysiology, providing healthcare students with an essential/fundamental understanding of applied pathophysiology in order to deliver high-quality care in any setting.

Fundamentals of Applied Pathophysiology is not only intended as a valuable textbook for students during their lectures, but also as a reference resource to be used in the practice setting (wherever this may be). It is not our intention that this text be read from cover to cover – the reader is encouraged to delve in and out of it; we aim to entice and encourage the reader to read further and in so doing instil a sense of curiosity. The book is written with healthcare students in mind and provides an approach to pathophysiological issues in a more user-friendly manner. Illustrations are used in abundance to assist the reader in understanding and appreciating the complex disease patterns that are being discussed.

Using a fundamental approach will provide readers with an essential understanding of applied pathophysiology. A result of working in a variety of healthcare settings is that students may find themselves assisting and working with other healthcare professionals in the care and management of the patient, e.g. assisting in radiology departments in the safe preparation of patients for special investigations, such as a barium meal, or re-enforcing the dietary advice given to patients by a dietician. An understanding of ‘normal’ and ‘abnormal’ pathophysiology can help the student and the patient.

A Note about the Terms Used

There are a plethora of terms used to describe people who are the recipients of healthcare and choosing the correct term, one that will be appreciated by all readers, is challenging.

The term ‘patient’ can refer to all groups and individuals who have direct or indirect contact with all health and social care workers. Patient is the expression that is commonly used within the National Health Service (NHS) and it is a term that has been used throughout this text. It is recognised and respected that not everyone supports the use of the passive concept that can be associated with this term, but it is used here in the knowledge that it is widely understood; it may apply to those who are recipients of health and social care in hospitals, in the person’s own home, in the primary care setting and in the independent and voluntary sector. We could have used other expressions, e.g. service user, client or consumer; however, for the sake of brevity the phrase patient has been used.

The Chapters

The format of this text allows the reader to use it either as a quick reference guide to pathophysiology or in a more in-depth manner; this is an easy-to-use textbook providing the fundamental concepts associated with pathophysiological processes. The processes of specific diseases are introduced; treatments and care are provided in a clear and concise manner.

The text uses a sound evidence base throughout, drawing on contemporary literature to support discussion. The use of standards/frameworks produced by voluntary and statutory organisations is also included, e.g. patient safety and risk assessment. Government policy, in the guise of the National Service Frameworks, is referred to and readers are encouraged to probe deeper to inform their practice with the overriding aim of the provision of safe and effective care. However, the reader should always make reference to local guidance when necessary.

Each chapter begins with a list of key words, introducing the reader at an early stage to terms that will be discussed within the chapter. To assess current knowledge, the reader is invited to test this at the start of each chapter and again at the end. The intended learning outcomes outline what the chapters will cover. Illustrations have been included in order to ease and facilitate learning. There are two case studies in each chapter that bring to life the pathophysiology being discussed and at the end of each case study, a number of questions that encourage you to dig deeper and to give more thought to the issues being discussed.

At the end of each chapter, there are also another set of questions provided for you to test your knowledge; this can help you determine how far you have progressed after reading and assimilating the contents of the chapter. Other features that aim to enhance learning and aid retention of facts are various exercises for you to complete, a word search, fill in the blanks and a diagram that you are asked to label – the intention is to test yourself and to broaden your learning. In each chapter there are further resources related to the topics covered in the chapter to further enhance learning. A glossary of terms is available at the end of each chapter, providing you with the opportunity to develop your vocabulary further in relation to the terminology being used.

This interactive approach is provided in an attempt to prompt thinking and to encourage you to investigate and explore a field further in relation to the pathophysiological issues discussed or even those that have not been discussed.

Our overriding objective is to encourage and motivate you, as well as to instil confidence and competence to become a proficient provider of care. Providing care with a sound knowledge base and the desire to care with compassion and understanding is a hallmark of a healthcare professional. We believe that understanding and applying this understanding is the key to the provision of high-quality, safe and effective care, as well developing critical thinking, innovation and creativity.

The contributors have enjoyed the challenges of writing this second edition, and we hope that you find the chapters stimulating and thought provoking; above all, we hope that those you care for benefit as a result of your learning.

Reference

Porth, C.M. (2009). Pathophysiology Concepts of Altered States, 8th edn. Philadelphia: Lippincott.

1

Cell and Body Tissue Physiology

Anthony Wheeldon

Senior Lecturer, Department of Adult Nursing and Primary Care, School of Health and Social Work, University of Hertfordshire, Hatfield, Hertfordshire, UK

Don’t forget to visit to the companion website for this book ( www.wiley.com/go/fundamentalsofappliedpathophysiology) where you can find self-assessment tests to check your progress, as well as lots of activities to practise your learning.

Introduction

To understand the human body and how it works (and also how it fails to work properly), it is important to understand the anatomy and physiology of the cell. Living organisms show a wide diversity as regards their size, shape, colour, behaviour and habitat. In spite of this, however, there are many similarities between organisms, and this fundamental similarity is known as the ‘cell theory’. This cell theory states that all living organisms are composed of one or more cells and the products of cells. Despite the fact that the cells belong to different organisms, and cells within the same organism may have different functions, there are many similarities between them. For example, there are similarities in their chemical composition, their chemical and biochemical behaviour and in their detailed structure.

All cells have many characteristics, but these characteristics can differ from cell to cell, such as:

• Cells are able to carry out certain specific functions, i.e. they are active.
• Cells need to consume food to live and to carry out their functions. Although they do not have mouths, they are still able to ‘catch’ and digest their food and use it for growth and reproduction. The correct term for this is endocytosis – they surround and engulf organisms such as bacteria and digest them.
• Cells can grow and repair.
• Similarly, cells can reproduce themselves. They do this by a process known as simple fission. This means that they reproduce themselves by dividing into two, and then each new cell grows to full size before it divides by simple fission and so on. In other words, cells replicate themselves.
• Like humans, cells can become irritable if something upsets or stimulates them.
• The nutrition that cells taken in is also used for the storage and release of energy (just like humans), thus enabling them to grow and repair themselves.
• Similarly, just as humans do not utilise all the food they eat – some of it cannot be used and so is excreted, cells excrete what they do not need or cannot use.
• Just as all humans will eventually die, so will cells. Some have a short life, whilst others survive many years – but eventually they will die.

So, cells are not all that different from humans in many respects. They do what humans do – albeit in different ways.

Anatomy of the Cell

Each cell has a structure that is almost as complex as the human body (Figure 1.1). For example, each cell contains as many molecules as the body has cells. There is no such thing as a typical cell. However, each cell is surrounded by a membrane and contains protoplasm. This protoplasm consists of a nucleus, which is kept separate from the rest of the cell by a nuclear membrane (although the nuclear membrane disappears during the process of cell division), and an opaque substance called cytoplasm (Watson, 2005). The cells themselves consist of water, proteins, lipids, carbohydrates and various ions such as potassium (K⁺) and magnesium (Mg²⁺). Within the cytoplasm there are also many complex protein structures called organelles.

Figure 1.1 Simplified structure of a cell.

Cells vary in size from 2 to 20 µm. For example, a lymphocyte (a type of blood cell) is about 8–10 µm in diameter.

All the cells in the body, apart from those on the surface of the body, are surrounded by a fluid that is known as extracellular fluid (i.e. fluid outside of the cell).

The Cell Membrane

The cell membrane can vary from 7.5 to 10 nm in thickness. It acts just like a ‘skin’ that protects the cell from the outside environment. In addition, it regulates the movement of water, nutrients and waste products into and out of the cell.

The cell membrane is made up of a double layer (bilayer) of phospholipid (fatty) molecules with protein molecules interspersed between them (Figure 1.2). A phospholipid molecule consists of a polar ‘head’ which is hydrophilic (water loving) and ‘tails’ which are hydrophobic (water hating). The hydrophilic ‘heads’ are attracted to water and are found on the inner and outer surfaces of the cell (water is the main component of both extracellular and intracellular environments), whilst the hydrophobic ‘tails’ are found in the middle of the cell membrane where they can avoid water. These phospholipid molecules are arranged as a bilayer with the heads facing outwards. This means that the bilayer is self-sealing. It is the central part of the plasma membrane, consisting of the hydrophobic ‘tails’, that makes the cell membrane impermeable to water-soluble molecules, and so prevents the passage of these molecules into and out of the cell (Marieb, 2010). However, if the membrane just consisted of these phospholipid molecules, then cells would not be able to function – within the cell membrane there are also plasma membrane proteins (PMPs), which can be either integral or peripheral.

Figure 1.2 The cell membrane.

Some of the integral PMPs are embedded amongst the tails of the phospholipid molecules, whilst others penetrate the membrane completely (Figure 1.2). Subunits of some of these integral proteins can form channels which allow for the transportation of materials into and out of the cell. Other subunits are able to bind to carbohydrates to form receptor sites. These receptor sites are important, as will be discussed in Chapter 3 – inflammation, immune response and healing.

Peripheral PMPs bind loosely to the surface of the cell membrane and so can easily be separated from it. Some of them function as enzymes to catalyse cellular reactions, whilst others are receptors for hormones and other chemicals, or function as binding sites for attachment to other structures (Marieb, 2010).

Functions

• Endocytosis and exocytosis – the transport of fluids and other matter into and out of the cell.
• Endocytosis is the intake of extracellular fluid and particulate material (small particles) ranging in size from macromolecules to whole cells (e.g. the bacteria engulfed and destroyed by macrophage cells).
• Exocytosis is the bulk transport of material out of the cells.

There are three types of endocytosis:

• Phagocytosis – involves the ingestion of large particles, even whole microbial cells.
• Pinocytosis – involves the ingestion of small particles and fluids.
• Receptor-mediated endocytosis – involves large particles, notably proteins, but also has the important feature of being highly selective.

Endocytosis involves part of the cell membrane being drawn into the cell along with the particles or fluid to be ingested (Figure 1.3). This membrane is then pinched off to form a membrane-bound vesicle within the cell, while at the same time the cell membrane as a whole reseals itself. Inside the cell, the fate of this vesicle depends upon the type of endocytosis involved as well as the material it contains. In some cases, the endocytic vesicle ultimately fuses with an organelle called a lysosome, after which processing of the ingested material can occur. Endocytosis is also the means by which many simple organisms obtain their nutrients.

Figure 1.3 Endocytosis.

Transport Across the Cell Membrane

One of the key properties of the cell membrane with regards to transport is its selective permeability. This refers to its ability to let certain materials pass through, whilst preventing others from doing so. This selective permeability is based on the hydrophobicity (water hatred) of its component molecules. Because the phospholipid tails in the centre of the bilayer are composed entirely of hydrophobic fatty acid chains (lipids are fats), it is very difficult for water-soluble (hydrophilic) molecules to penetrate to the membrane interior. The result is a very effective permeability barrier.

However, this barrier can be penetrated, but only by way of specific transport systems. These control what goes into and out of the cell, or what crosses from one subcellular compartment to another. Cell membranes control metabolism by restricting the flow of glucose and other water-soluble metabolites in and out of cells and between subcellular compartments. This is known as compartmentation. The cells store energy in the form of transmembrane ion gradients by allowing high concentrations of particular ions to accumulate on one side of the membrane.

Ions pass from inside to outside of the cell (or the other way round) so that there are more supplies of these ions just outside the cell or inside it and the membrane controls the speed/rate at which these ions pass through the membrane. The controlled release of such ion gradients can be used to:

• extract nutrients from surrounding fluids
• pass electrical messages (known as nerve excitability)
• control cell volume and stop cells bursting from excess fluid.

To return to the cell membrane itself, there are four factors that decide the degree of permeability of a membrane:

• Size of molecules – large molecules cannot pass through the integral membrane proteins, but small ones such as water and amino acids can.
• Solubility in lipids (fats) – substances that easily dissolve in lipids can pass through the membrane more easily than non–lipid-soluble substances. Lipid-soluble substances include oxygen, carbon dioxide and steroid hormones.
• If an ion has an electrical charge opposite to that of the membrane, then it is attracted to the membrane and can more easily pass through it.
• Carrier integral proteins can carry substances across the membrane, regardless of their size, ability to dissolve in lipids or membrane electrical charge.

There are two ways in which substances can move across the membrane: passive or active. Passive processes are:

• diffusion
• facilitated diffusion
• osmosis
• filtration.

Active processes are:

• active transport pumps
• endocytosis
• exocytosis.

A passive process is one in which the substances move on their own down a concentration gradient from an area of higher to one of lower concentration. The cell does not expend any energy on the process. Think of it as rolling down a hill from an area of high altitude to one of lower altitude. Little energy is expended just rolling down a hill.

Diffusion is the most common form of passive transport in which a substance of higher concentration moves to an area where there is a lower concentration of that substance (Colbert et al., 2011). This difference between the areas of high concentration and of low concentration is known as a concentration gradient. This process of diffusion is essential for respiration. It is through diffusion that oxygen is transported from the lungs to the blood and carbon dioxide makes the opposite journey from the blood to the lungs (Colbert et al., 2011).

Facilitated diffusion is similar to diffusion, but with one exception. For this process to take place, there needs to be a substance that helps – a facilitator. Glucose is moved using this process. Although glucose can move part of the way through the membrane on its own, it needs something else (a carrier/transport protein) to give it that extra push to get it completely through the membrane (Colbert et al., 2011; McCance et al., 2010).

Osmosis is the process in which water travels through a selectively permeable membrane so that concentrations of a substance that is soluble in water (known as a solute) are the same on both sides of that membrane. This is known as osmotic pressure (Figures 1.4 and 1.5). The higher the concentration of the solute on one side of the membrane, the higher the osmotic pressure available for the movement of the water (Colbert et al., 2011).

Figure 1.4 Osmosis.

Figure 1.5 Osmosis and movement of solute.

Filtration is similar to osmosis, except that pressure is applied in order to ‘push’ water and solutes across that membrane. The heart is a major supplier of the force that can lead to one type of filtration (renal filtration) as it pushes blood into the kidneys where filtration of the blood can take place (Colbert et al., 2011).

An active process is one in which substances move against a concentration gradient from an area of lower to one of higher concentration. To do this, the cell must expend energy; this is released by splitting adenosine triphosphate (ATP) into adenosine diphosphate (ADP) and phosphate. ATP is a compound of a base, a sugar and three phosphate groups (triphosphate). These phosphate groups are held together by high-energy bonds, which when broken release a high level of energy. Once one of these phosphate bonds has been broken and a phosphate group has been released, that compound now has only two phosphate groups (diphosphate). The released phosphate group in turn joins up with another ADP group, so forming another molecule of ATP (with energy stored in the phosphate bonds), and the whole process continues to recur.

The energy is required because the cell is attempting to move a substance to an area that already has a high concentration of that substance. Think again of a hill. When walking up a hill, a lot of energy is expended. Obviously, the higher the concentration already present, the more energy required to move further molecules of the particular substance into that area – the steeper the hill, the more energy is used. For example, cells contain a lot of potassium (K⁺); therefore, energy is required to transport more potassium through the membrane and into the cell.

Now, to turn to what is inside the cell membrane, starting with the cytoplasm.

Cytoplasm

Cytoplasm is a ground substance (also known as a matrix) in which various cellular components are found. ‘Cyto’ means cell, so any word that has ‘cyto’ in it is to do with cells.

Cytoplasm, itself, is a thick, semitransparent, elastic fluid containing suspended particles and the cytoskeleton. The cytoskeleton provides support and shape to the cell. In addition, it is involved in the movement of structures in the cytoplasm because some cells can change shape, e.g. phagocytic cells (see Figure 1.3).

Role of Cytoplasm

• Chemically, cytoplasm is 75–90% water plus solid compounds – mainly carbohydrates, lipids and inorganic substances, and it is the substance in which chemical reactions occur.
• The cytoplasm receives raw materials from the external environment (such as from digested food) and converts them into usable energy by decomposition reactions.
• As well as the breakdown of raw materials to make energy, the cytoplasm is also the site where new substances are synthesised (produced) for the use of the cell.
• It is the place where various chemicals are packaged for transport to other parts of the cell, or to other cells in the body.
• It is in the cytoplasm that various chemicals facilitate the excretion of waste materials.

Nucleus

When considering the nucleus, a simple analogy is to think of it as the brain of the cell.

Prokaryotic cells do not have a nucleus, but eukaryotic cells do. Eukaryotic cells are found in animals and plants, whilst prokaryotic cells are very typical of bacteria. In many ways, prokaryotic cells are less complex and often smaller than eukaryotes.

However, not all human cells possess a nucleus. An example of a cell without a nucleus is the red blood cell. Chapter 7 describes the concave shape of the mature red blood cells. This is because the lack of a nucleus means the red blood cell ‘collapses in’ on itself. Also, just to make it more confusing, some cells can have more than one nucleus, e.g. some muscle fibre cells (see Figure 1.12).

Some facts about the nucleus are:

• The nucleus is the largest structure in the cell.
• It is surrounded by a nuclear membrane. This nuclear membrane has two layers and, like the cell membrane, is selectively permeable.
• The protoplasm within the nucleus is not called cytoplasm – it is called nucleoplasm.
• The nucleus assumes a great responsibility for both mitosis and meiosis (see later).
• Inside the nucleus is found the genetic material, consisting principally of deoxyribonucleic acid (DNA). When a cell is not reproducing, the genetic material is a threadlike mass called chromatin.
• Before cell division, the chromatin shortens, and coils into rod-shaped bodies called chromosomes.
• The basic structural unit of a chromosome is a nucleosome – composed of DNA and protein.
• DNA has two main functions:
  • It provides the genetic blueprint which ensures that the next generation of cells is identical to existing ones.
  • It provides the plans for the synthesis of protein by the cell.
• All this information is stored in genes.
• Inside the nucleus are little spherical bodies called nucleoli and these are responsible for the production of ribosomes from ribosomal ribonucleic acid (rRNA).
• In humans, there are 23 pairs of chromosomes in each cell with a nucleus, with the exception of the spermatozoa and ova (sperm and eggs).
• Sperm and ova only have 23 single chromosomes (i.e. one of each).
• The chromosomes are the same for males and females except for one pair – the X and Y chromosomes. It is these chromosomes that determine whether a baby is going to be male or female.

Mitosis and Meiosis