SECTION -I
The Cell in Health and Disease
SECTION CONTENTS
- Chapter 1: Introduction to Pathology
- Chapter 2: Techniques for the Study of Pathology
- Chapter 3: Cell Structure, Metabolism and Cellular Ageing
- Chapter 4: Etiology and Pathogenesis of Cell Injury
- Chapter 5: Morphology of Cell Injury
- Chapter 6: Intracellular Accumulations
- Chapter 7: Amyloidosis
- Chapter 8: Genetic and Paediatric Diseases
- Chapter 9: Nutritional Disorders and Common Vitamin Deficiencies
STUDY OF DISEASES
DEFINITION OF PATHOLOGY
The word ‘Pathology’ is derived from two Greek words—pathos meaning suffering, and logos meaning study. Pathology is, thus, scientific study of structure and function of the body in disease; or in other words, pathology consists of the abnormalities that occur in normal anatomy (including histology) and physiology owing to disease. Another commonly used term with reference to study of diseases is ‘pathophysiology’ comprised by two words: patho=suffering;physiology= study of normal function. Pathophysiology, thus, includes study of disordered function or breakdown of homeostasis in diseases. Pathologists are the diagnosticians of disease. Therefore, knowledge and understanding of pathology is essential for all would-be doctors, general medical practitioners and specialists since unless they know the causes, mechanisms, nature and type of disease, and understand the language spoken by the pathologist in the form of laboratory reports, they would not be able to institute appropriate treatment or suggest preventive measures to the patient.
While the medical students learn the entire subject of pathology (that includes General and Systemic Pathology) during their second phase, the undergraduate students of dentistry learn pathology in two phases: General Pathology in second year and Oral Pathology in their third year; thus some overlapping in teaching of these subjects in dentistry is more likely. For a student of any system of medicine, the discipline of pathology forms a vital bridge between initial learning phase of preclinical sciences and the final phase of clinical subjects. Remember the prophetic words of Sir William Osler, an eminent founder of modern medicine in late 19th and early 20th century “Your practice of medicine will be as good as your understanding of pathology.”
HEALTH AND DISEASE
Before there were humans on earth, there was disease, albeit in early animals. Since pathology is the study of disease, then what is disease? In simple language, disease is opposite of health i.e. what is not healthy is disease. Health may be defined as a condition when the individual is in complete accord with the surroundings, while disease is loss of ease (or comfort) to the body (i.e. dis-ease). However, it must be borne in mind that in health there is a wide range of ‘normality’ e.g. in height, weight, blood and tissue chemical composition etc. It also needs to be appreciated that at cellular level, the cells display wide range of activities within the broad area of health similar to what is seen in diseased cells. Thus, health and disease are not absolute but are considered as relative states.
A term commonly confused with disease is illness. While disease suggests an entity with a cause, illness is the reaction of the individual to disease in the form of symptoms (complaints of the patient) and physical signs (elicited by the clinician). Though disease and illness are not separable, the study of diseases is done in pathology while the learning and management of illnesses is done in wards and clinics.2
In addition to disease and illness, there are syndromes (meaning running together) characterised by combination of symptoms caused by altered physiologic processes.
TERMINOLOGY IN PATHOLOGY
It is important for a beginner in pathology to be familiar with the language used in pathology:
- Patient is the person affected by disease.
- Lesions are the characteristic changes in tissues and cells produced by disease in an individual or experimental animal.
- Pathologic changes or morphology consists of examination of diseased tissues.
- Pathologic changes can be recognised with the naked eye (gross or macroscopic changes) or studied by microscopic examination of tissues.
- Causal factors responsible for the lesions are included in etiology of disease (i.e. ‘why’ of disease).
- Mechanism by which the lesions are produced is termed pathogenesis of disease (i.e. ‘how’ of disease).
- Functional implications of the lesion felt by the patient are symptoms and those discovered by the clinician are the physical signs.
- Clinical significance of the morphologic and functional changes together with results of other investigations help to arrive at an answer to what is wrong (diagnosis), what is going to happen (prognosis), what can be done about it (treatment), and finally what should be done to avoid complications and spread (prevention) (i.e. ‘what’ of disease).
EVOLUTION OF PATHOLOGY
Pathology as the scientific study of disease processes has its deep roots in medical history. Since the beginning of mankind, there has been desire as well as need to know more about the causes, mechanisms and nature of diseases. The answers to these questions have evolved over the centuries—from supernatural beliefs to the present state of our knowledge of modern pathology.
FROM RELIGIOUS BELIEFS AND MAGIC TO RATIONAL APPROACH (PREHISTORIC TIME TOAD 1500)
Present-day knowledge of primitive culture prevalent in the world in prehistoric times reveals that religion, magic and medical treatment were quite linked to each other in those times. The earliest concept of disease understood by the patient and the healer was the religious belief that disease was the outcome of ‘curse from God’ or the belief in magic that the affliction had supernatural origin from ‘evil eye of spirits.’ To ward them off, priests through prayers and sacrifices, and magicians by magic power used to act as faith-healers and invoke supernatural powers and please the gods. Remnants of ancient superstitions still exist in some parts of the world. The link between medicine and religion became so firmly established throughout the world that different societies had their gods and goddesses of healing; for example: mythological Greeks had Asclepios and Apollo as the principal gods of healing, Dhanvantri as the deity of medicine in India, and orthodox Indians’ belief in Mata Sheetala Devi as the pox goddess.
The period of ancient religious and magical beliefs was followed by the philosophical and rational approach to disease by the methods of observations. This happened at the time when great Greek philosophers—Socrates, Plato and Aristotle, introduced philosophical concepts to all natural phenomena.
But the real practice of medicine began with Hippocrates (460–370 BC), the great Greek clinical genius of all times and regarded as ‘the father of medicine’ (Fig. 1.1). Hippocrates followed rational and ethical attitudes in practice and teaching of medicine as expressed in the collection of writings of that era. He firmly believed in study of patient's symptoms and described methods of diagnosis. Hippocrates also introduced ethical concepts in the practice of medicine and is revered by the medical profession by taking ‘Hippocratic oath’ at the time of entry into practice of medicine.
Greek medicine after Hippocrates reached Rome (now Italy), which controlled Greek world after 146 BC and therefore dominated the field of development of medicine in ancient Europe then. In fact, since ancient times, many tongue-twisting terminologies in medicine have their origin from Latin language which was the official language of countries included in ancient Roman empire (Spanish, Portugese, Italian, French and Greek languages have their origin from Latin).
Figure 1.1: Hippocrates (460–370 BC). The great Greek clinical genius regarded as ‘the father of medicine’. He introduced ethical aspects to medicine.
Hippocratic teaching was propagated in Rome by Roman physicians, notably by Cornelius Celsus (53 BC-7 AD) and Cladius Galen (130–200 AD).
The hypothesis of disequilibrium of four elements constituting the body (Dhatus) finds mention in ancient Indian medicine books compiled about 200 AD—Charaka Samhita, the finest document by Charaka on medicine listing 500 remedies, and Sushruta Samhita, similar book of surgical sciences by Sushruta, and includes about 700 plant-derived medicines.
The end of Medieval period was marked by backward steps in medicine. There were widespread and devastating epidemics which reversed the process of rational thinking again to supernatural concepts and divine punishment for ‘sins.’ The dominant belief during this period was that life was due to influence of vital substance under the control of soul (theory of vitalism).
FROM HUMAN ANATOMY TO ERA OF GROSS PATHOLOGY (AD 1500 to 1800)
The backwardness of Medieval period was followed by the Renaissance period i.e. revival of learning. The Renaissance began from Italy in late 15th century and spread to whole of Europe. During this period, there was quest for advances in art and science. Since there was freedom of thought, there was emphasis on philosophical and rational attitudes again.
The beginning of the development of human anatomy took place during this period with the art works and drawings of human muscles and embryos by famous Italian painter Leonardo da Vinci (1452–1519). Dissection of human body was started by Vesalius (1514–1564) on executed criminals. His pupils, Gabriel Fallopius (1523–1562) who described human oviducts (Fallopian tubes) and Fabricius who discovered lymphoid tissue around the intestine of birds (bursa of Fabricius) further popularised the practice of human anatomic dissection for which special postmortem amphitheatres came into existence in various parts of ancient Europe (Fig. 1.2).
Figure 1.2: In 16th Century, postmortem amphitheatre in Europe was a place of learning human anatomic dissection conducted and demonstrated by professors to eager learners and spectators.
Antony van Leeuwenhoek (1632–1723), a cloth merchant by profession in Holland, during his spare time invented the first ever microscope by grinding the lenses himself. He also introduced histological staining in 1714 using saffron to examine muscle fibres.
Marcello Malpighi (1624–1694) used microscope extensively and observed the presence of capillaries and described the malpighian layer of the skin, and lymphoid tissue in the spleen (malpighian corpuscles). Malpighi is known as ‘the father of histology.’
The credit for beginning of the study of morbid anatomy (pathologic anatomy), however, goes to Italian anatomist-pathologist, Giovanni B. Morgagni (1682–1771). Morgagni was an excellent teacher in anatomy, a prolific writer and a practicing clinician. By his work, Morgagni demolished the ancient humoral theory of disease and published his life-time experiences based on 700 postmortems and their corresponding clinical findings. He, thus, laid the foundations of clinicopathologic methodology in the study of disease and introduced the concept of clinicopathologic correlation (CPC), establishing a coherent sequence of cause, lesions, symptoms, and outcome of disease.
Sir Percival Pott (1714–1788), famous surgeon in England, identified the first ever occupational cancer in the chimney sweeps in 1775 and discovered chimney soot as the first carcinogenic agent. However, the study of anatomy in England during the latter part of 18th Century was dominated by the two Hunter brothers: John Hunter (1728–1793), a student of Sir Percival Pott, rose to become the greatest surgeon-anatomist of all times and he, together with his elder brother William Hunter (1718–1788) who was a reputed anatomist-obstetrician (or man-midwife), started the first ever museum of pathologic anatomy. John Hunter made a collection of more than 13,000 surgical specimens from his flourishing practice, arranged them into separate organ systems, made comparison of specimens from animals and plants with humans, and included many clinical pathology specimens as well, and thus developed the first museum of comparative anatomy and pathology in the world which became the Hunterian Museum, now housed in Royal College of Surgeons of London. Amongst many pupils of John Hunter was Edward Jenner (1749–1823) whose work on inoculation in smallpox is well known. The era of gross pathology had three more illustrious and brilliant physician-pathologists in England who were colleagues at Guy's Hospital in London:
- Richard Bright (1789–1858) who described non-suppurative nephritis, later termed glomerulonephritis or Bright's disease;
- Thomas Addison (1793–1860) who gave an account of chronic adrenocortical insufficiency termed Addison's disease; and
- Thomas Hodgkin (1798–1866), who observed the complex of chronic enlargement of lymph nodes, often with enlargement of the liver and spleen, later called Hodgkin's disease.
R.T.H. Laennec (1781–1826), a French physician, dominated the early part of 19th century by his numerous discoveries. He described several lung diseases (tubercles, caseous lesions, miliary lesions, pleural effusion, bronchiectasis), chronic sclerotic liver disease (later called Laennec's cirrhosis) and invented stethoscope.
Morbid anatomy attained its zenith with appearance of Carl F. von Rokitansky (1804–1878), self-taught German pathologist who performed nearly 30,000 autopsies himself. He described acute yellow atrophy of the liver, wrote an outstanding monograph on diseases of arteries and congenital heart defects.
ERA OF TECHNOLOGY DEVELOPMENT AND CELLULAR PATHOLOGY (AD 1800 TO 1950s)
Up to middle of the 19th century, correlation of clinical manifestations of disease with gross pathological findings at autopsy became the major method of study of disease. Sophistication in surgery led to advancement in pathology. The anatomist-surgeons of earlier centuries got replaced largely with surgeon-pathologists in the 19th century.
Pathology started developing as a diagnostic discipline in later half of the 19th century with the evolution of cellular pathology which was closely linked to technology advancements in machinery manufacture for cutting thin sections of tissue, improvement in microscope, and development of chemical industry and dyes for staining.
The discovery of existence of disease-causing micro-organisms was made by French chemist Louis Pasteur (1822–1895), thus demolishing the prevailing theory of spontaneous generation of disease and firmly established germ theory of disease. Subsequently, G.H.A. Hansen (1841–1912) in Germany identified Hansen's bacillus as causative agent for leprosy (Hansen's disease) in 1873. While the study of infectious diseases was being made, the concept of immune tolerance and allergy emerged which formed the basis of immunisation initiated by Edward Jenner.
Developments in chemical industry helped in switch over from earlier dyes of plant and animal origin to synthetic dyes; aniline violet being the first such synthetic dye prepared by Perkin in 1856. This led to emergence of a viable dye industry for histological and bacteriological purposes. The impetus for the flourishing and successful dye industry came from the works of numerous pioneers as under:
- Paul Ehrlich (1854–1915), German physician, conferred Nobel prize in 1908 for his work in immunology, described Ehrlich's test for urobilinogen using Ehrlich's aldehyde reagent, staining techniques of cells and bacteria, and laid the foundations of clinical pathology.
- Christian Gram (1853–1938), Danish physician, who developed bacteriologic staining by crystal violet.
- D.L. Romanowsky (1861–1921), Russian physician, who developed stain for peripheral blood film using eosin and methylene blue derivatives.
- Robert Koch (1843–1910), German bacteriologist who, besides Koch's postulate and Koch's phenomena, developed techniques of fixation and staining for identification of bacteria, discovered tubercle bacilli in 1882 and cholera vibrio organism in 1883.
- May-Grunwald in 1902 and Giemsa in 1914 developed blood stains and applied them for classification of blood cells and bone marrow cells.
- Sir William Leishman (1865–1926) who described Leishman's stain for blood films in 1914 and observed Leishman-Donovan bodies (LD bodies) in leishmaniasis.
- Robert Feulgen (1884–1955) who described Feulgen reaction for DNA staining and laid the foundations of cytochemistry and histochemistry.
Simultaneous technological advances in machinery manufacture led to development and upgradation of microtomes for obtaining thin sections of organs and tissues for staining by dyes for enhancing detailed study of sections.
Until the end of the 19th century, the study of morbid anatomy had remained largely autopsy-based and thus had remained a retrospective science. Rudolf Virchow (1821–1905) in Germany is credited with the beginning of microscopic examination of diseased tissue at cellular level and thus began histopathology as a method of investigation. Virchow gave two major hypotheses:
- All cells come from other cells.
- Disease is an alteration of normal structure and function of these cells.
Virchow came to be referred as Pope in pathology in Europe and is aptly known as the ‘father of cellular pathology’ (Fig. 1.3). Thus, sound foundation of diagnostic pathology had been laid which was followed and promoted by numerous brilliant successive workers. Knowledge and skill gained by giving accurate diagnosis on postmortem findings started being applied to surgical biopsy and thus emerged the discipline of surgical pathology.
Virchow also described etiology of embolism (Virchow's triad—slowing of blood-stream, changes in the vessel wall, changes in the blood itself), metastatic spread of tumours (Virchow's lymph node), and components and diseases of blood (fibrinogen, leukocytosis, leukaemia).
The concept of frozen section examination when the patient was still on the operation table was introduced by Virchow's student, Julius Cohnheim (1839–1884). In fact, during the initial period of development of surgical pathology around the turn of the 19th century, frozen section was considered more acceptable by the surgeons. Then there was the period when morphologic examination of cells by touch imprint smears was favoured for diagnostic purposes than actual tissue sections. Subsequently, further advances in surgical pathology were made possible by improved machinery and development of dyes and stains.
A few other landmarks in further evolution of modern pathology in this era are as follows:
- Karl Landsteiner (1863–1943) described the existence of major human blood groups in 1900 and was awarded Nobel prize in 1930 and is considered father of blood transfusion.
- Ruska and Lorries in 1933 developed electron microscope which aided the pathologist to view ultrastructure of cell and its organelles.
- The development of exfoliative cytology for early detection of cervical cancer began with George N. Papanicolaou (1883–1962), a Greek-born American pathologist, in 1930s who is known as ‘father of exfoliative cytology’ (Fig. 1.4).
Another pioneering contribution in pathology in the 20th century was by an eminent teacher-author, William Boyd (1885–1979), psychiatrist-turned pathologist, whose textbooks—‘Pathology for Surgeons’ (first edition 1925) and ‘Textbook of Pathology’ (first edition 1932), dominated and inspired the students of pathology all over the world due to his flowery language and lucid style for about 50 years till 1970s. M.M. Wintrobe (1901–1986), a pupil of Boyd who discovered haematocrit technique, regarded him as a very stimulating teacher with keen interest in the development of museum.
Figure 1.4: George N. Papanicolaou (1883–1962). American pathologist, who developed Pap test for diagnosis of cancer of uterine cervix.
MODERN PATHOLOGY (1950s TO PRESENT TIMES)
The strides made in the latter half of 20th century until the beginning of 21st century have made it possible to study diseases at molecular level, and provide an evidence-based and objective diagnosis and enable the physician to institute appropriate therapy. The major impact of advances in molecular biology are in the field of diagnosis and treatment of genetic disorders, immunology and in cancer. Some of the revolutionary discoveries during this time are as under (Fig. 1.5):
- Description of the structure of DNA of the cell by Watson and Crick in 1953.
- Identification of chromosomes and their correct number in humans (46) by Tijo and Levan in 1956.
- In Situ Hybridization introduced in 1969 in which a labelled probe is employed to detect and localize specific RNA or DNA sequences ‘in situ’ (i.e. in the original place).
- Recombinant DNA technique developed in 1972 using restriction enzymes to cut and paste bits of DNA.
- In 1983, Kary Mullis introduced polymerase chain reaction (PCR) i.e. “xeroxing” DNA fragments which revolutionised the diagnostic molecular genetics.
- Flexibility and dynamism of DNA invented by Barbara McClintock for which she was awarded Nobel prize in 1983.
- In 1997, Ian Wilmut and his colleagues at Roslin Institute in Edinburgh, successfully used a technique of somatic cell nuclear transfer to create the clone of a sheep; the cloned sheep was named Dolly. This has set in the era of mammalian cloning. Reproductive cloning for human beings, however, is very risky besides being absolutely unethical.
In 1998, researchers in US found a way of harvesting stem cells, a type of primitive cells, from embryos and maintaining their growth in the laboratory, and thus started the era of stem cell research. Stem cells are seen by many researchers as having virtually unlimited application in the treatment of many human diseases such as Alzheimer's disease, diabetes, cancer, strokes, etc. There are 2 types of sources of stem cells: embryonic stem cells and adult stem cells. Since embryonic stem cells are more numerous, therapeutic cloning of human embryos as a source of stem cells for treating some incurable diseases has been allowed in some parts of the world. A time may come when by using embryonic stem cells, insulin-producing cells may be introduced into the pancreas in a patient of insulin-dependent diabetes mellitus, or stem cells may be cultured in the laboratory in lieu of a whole organ transplant. Thus, time is not far when organs for transplant may be ‘harvested’ from the embryo in lieu of a whole organ transplant.
In April 2003, Human Genome Project (HGP) consisting of a consortium of countries, was completed which coincided with 50 years of description of DNA double helix by Watson and Crick in April 1953. The sequencing of human genome reveals that human genome contains approximately 3 billion of the base pairs, which reside in the 23 pairs of chromosomes within the nucleus of all human cells. Each chromosome contains an estimated 30,000 genes in the human genome, contrary to the earlier estimate of about 100,000 genes, which carry the instructions for making proteins. The HGP gave us the ability to read nature's complete genetic blueprint for building each human being. All this has opened new ways in treating and researching an endless list of diseases that are currently incurable. In time to come, medical scientists will be able to develop highly effective diagnostic tools, to better understand the health needs of people based on their individual genetic make-ups, and to design new and highly effective treatments for disease as well as suggest prevention against disease.
These inventions have set in an era of human molecular biology which is no longer confined to research laboratories but is ready for application as a modern diagnostic and therapeutic tool. Modern day human molecular biology is closely linked to information technology; the best recent example is the availability of molecular profiling by cDNA microarrays in which by a small silicon chip, expression of thousands of genes can be simultaneously measured.
SUBDIVISIONS OF PATHOLOGY
After a retrospective into the historical aspects of pathology, and before plunging into the study of diseases in the chapters that follow, we first introduce ourselves with the branches of human pathology.
Human pathology is the largest branch of pathology. It is conventionally divided into General Pathology dealing with general principles of disease, and Systemic Pathology that includes study of diseases pertaining to the specific organs and body systems. With the advancement of diagnostic tools, the broad principles of which are outlined in the next chapter, the speciality of pathology has come to include the following subspecialities:
A. HISTOPATHOLOGY. Histopathology, used synonymously with anatomic pathology, pathologic anatomy, or morbid anatomy, is the classic method of study and still the most useful one which has stood the test of time. The study includes structural changes observed by naked eye examination referred to as gross or macroscopic changes, and the changes detected by light and electron microscopy supported by numerous special staining methods including histochemical and immunological techniques to arrive at the most accurate diagnosis. Modern time anatomic pathology includes super-specialities such as cardiac pathology, pulmonary pathology, neuropathology, renal pathology, gynaecologic pathology, breast pathology, dermatopathology, gastrointestinal pathology, oral pathology, and so on. Anatomic pathology includes the following 3 main subdivisions:
1. Surgical pathology. It deals with the study of tissues removed from the living body. It forms the bulk of tissue material for the pathologist and includes study of tissue by paraffin embedding techniques and by frozen section for rapid diagnosis.
2. Forensic pathology and autopsy work. This includes the study of organs and tissues removed at postmortem for medicolegal work and for determining the underlying sequence and cause of death. By this, the pathologist attempts to reconstruct the course of events how they may have happened in the patient during life which culminated in his death. Postmortem anatomical diagnosis is helpful to the clinician to enhance his knowledge about the disease and his judgement while forensic autopsy is helpful for medicolegal purposes. The significance of a careful postmortem examination can be summed up in the old saying ‘the dead teach the living’.
3. Cytopathology. Though a branch of anatomic pathology, cytopathology has developed as a distinct subspeciality in recent times. It includes study of cells shed 7off from the lesions (exfoliative cytology) and fine-needle aspiration cytology (FNAC) of superficial and deep-seated lesions for diagnosis.
B. HAEMATOLOGY. Haematology deals with the diseases of blood. It includes laboratory haematology and clinical haematology; the latter covers the management of patient as well.
C. CHEMICAL PATHOLOGY. Analysis of biochemical constituents of blood, urine, semen, CSF and other body fluids is included in this branch of pathology.
D. IMMUNOLOGY. Detection of abnormalities in the immune system of the body comprises immunology and immunopathology.
E. EXPERIMENTAL PATHOLOGY. This is defined as production of disease in the experimental animal and its study. However, all the findings of experimental work in animals may not be applicable to human beings due to species differences.
F. GEOGRAPHIC PATHOLOGY. The study of differences in distribution of frequency and type of diseases in populations in different parts of the world forms geographic pathology.
G. MEDICAL GENETICS. This is the branch of human genetics that deals with the relationship between heredity and disease. There have been important developments in the field of medical genetics e.g. in blood groups, inborn errors of metabolism, chromosomal aberrations in congenital malformations and neo-plasms etc.
H. MOLECULAR PATHOLOGY. The detection and diagnosis of abnormalities at the level of DNA of the cell is included in molecular pathology. Recent advancements in molecular biologic techniques have resulted in availability of these methods not only for research purposes but also as a tool in diagnostic pathology.
The above divisions of pathology into several specialisations are quite artificial since pathology embraces all disciplines of medicine and thus overlapping of specialities is likely. While in the chapters that follow, efforts have been made to present the entire subject covering diseases of the whole human body in an integrated and coordinated manner, knowledge is ever-expanding on a daily basis and the quest for learning more is an ongoing process. Thus, all of us remain lifelong students of the art of pathology of diseases!