W4 -YR1 Lecture 1H - Introduction to Pathology PDF 2021

Introduction to Pathology Dr Tristan Rutland B.Pharm MBBS FRCPA Anatomical Pathologist Liverpool Hospital Lecturer in Pathology WSU Medical School 1 Learning objectives · Define cellular adaptations as hyperplasia, hypertrophy, atrophy and metaplasia and give examples of their causes · Describe home...

Introduction to Pathology Dr Tristan Rutland B.Pharm MBBS FRCPA Anatomical Pathologist Liverpool Hospital Lecturer in Pathology WSU Medical School 1 Learning objectives · Define cellular adaptations as hyperplasia, hypertrophy, atrophy and metaplasia and give examples of their causes · Describe homeostatic mechanisms that cells use to create and maintain internal environments that are different to their external environments · Describe the concept of cell injury as the basis of disease · Know the four core aspects of disease as defined by pathology aetiology, pathogenesis, structural changes and functional manifestations 2 Overview 1. Pathology 4 components: aetiology, pathogenesis, structural changes, clinical manifestations 2. Cell responses to stress and injury Adaptation: hyperplasia, hypertrophy, atrophy, metaplasia Others: intracellular accumulations, ageing, autophagy Death: necrosis, apoptosis 3 Pathology Pathos – suffering, Logos - study Study of disease and underlying processes Branch of Teaching/research Clinical medicine Lab examination of body samples - diagnostic or forensic Anatomical (tissue) pathology Microbiology Haematology Immunopathology Genetics 4 Pathology For a given disease, characterizing: 1. Aetiology 2. Pathogenesis 3. Structural changes 4. Clinical features 5 1. Aetiology  Cause of disease  Ancient concept - personal sins, evil spirits, gods  Celsus (23BC – 50AD ‘De Medicina’) - credible alternatives ◼Unbalanced diet ◼Lack of exercise ◼Poor personal hygiene  Often multifactorial 1. Primary – necessary for disease ◼ E.g. Myocardial infarction (MI) - coronary artery atherosclerosis with blocked blood flow 2. Contributory – risk factors ◼ Allows for primary cause to evolve and take effect ◼ E.g. MI - hypertension, smoking, age, male, cholesterol 6 1. Aetiology Intrinsic/genetic or acquired/environmental E.g. cirrhosis (irreversible, diffuse liver scarring): Intrinsic single gene multiple genes (e.g. haemochromatosis) “familial”: genes suspected but not identified Acquired physical chemical (e.g. alcohol) biological (e.g. viral hepatitis B & C) 7 2. Pathogenesis Mechanism of disease: Sequence of events from introduction of aetiological agent/s to structural and clinical changes 8 E.g. Cirrhosis due to Haemochromatosis 1. Born with genetic mutation → uncontrolled dietary iron absorption 2. Body has no well defined excretory pathway for iron → builds up in organs 3. In liver, iron build up → progressive hepatocyte death and inflammation 4. With on-going cell death and inflammation → fibrosis (scarring) eventually replaces liver = cirrhosis 5. Cirrhosis → hepatic failure 9 3. Structural changes Characteristic features of disease seen in tissues and organs both grossly/macroscopically (naked eye) and microscopically In biopsied or surgically resected tissues (pathology) 10 Anatomical Pathology /Histopathology 11 11 E.g. Cirrhosis - Different causes, including viral hepatitis B&C, EtOH abuse: Different causes may produce same structural change - Cases of viral hepatitis B may look completely different: Same causes may produce different appearances, depending on the stage of disease evolution 12 4. Clinical features Functional manifestations of disease  Evident during bedside examination  E.g. cirrhosis - liver failure (jaundice, bleeding, altered mental status) Usually ~ severity of structural changes  E.g. mild hepatitis and early fibrosis ≠ liver failure 13 Two important pathological concepts to understand this semester Cell response to stress and injury (this lecture) -----------------------------------------------------------Inflammation and healing 14 Cell theory ‘Cell’ - cork under compound microscope (Robert Hooke 1635 – 1703) ‘All organisms are made up of one or more cells’ – original cell theory (Matthias Schleiden and Theodor Schwann 1839) ‘All cells come from pre-existing cells and pathological changes are the result of reactions of cells’ - modified cell theory (Rudolf Virchow 1858) 15 Cell responses to stress and injury All forms of organ injury start with molecular &/or structural changes in cells, the fundamental unit of organisms (Cell theory) Understanding cell injury requires knowledge of cell structure PUTM modules (Anatomy) Microtubule organising centre 16 Normal cell Integrity - homeostasis (constant ‘maintenance’) Continuous, complex series of reactions and cell signaling Keeps cell structure and metabolism within acceptable limits Limit to homeostasis If environment particularly harsh, then cells: Adapt Live with some damage Die 17 Adaptation Hyperplasia Hypertrophy Atrophy Metaplasia 18 Hyperplasia ↑ cell numbers (↑organ size) In dividing cells ↑DNA synthesis and mitosis Due to Hormonal/Growth factors Compensatory Hyperplasia can also be Physiological Pathological Robbins, Stanley L., Cotran, Ramzi S., Kumar, Vinay, Editor, Abbas, Abul K., Editor, and Aster, Jon C., Editor. Robbins and Cotran Pathologic Basis of Disease. 10th ed. 2021. Web. Examples Physiological Hormonal Pathological Uterus in pregnancy Compensatory Liver regeneration after partial resection Hormonal pituitary tumour causing Cushing disease Endometrium due to excess estrogen Compensatory Hypertrophy of arterial walls 20 Hypertrophy ↑cell size (↑organ size) No new cells Due to: Compensatory (increased functional demand) or growth factors/hormonal stimulation In non-dividing cells skeletal and cardiac muscles Physiological vs Pathological Examples Physiological Increased functional demand Weightlifter → increased skeletal muscle Pathological Increased functional demand Hypertension or aortic valve disease → increased myocyte size Hormonal Uterus → increased cell size (and number!) 22 Physiological Gravid uterus Normal smooth muscle Hypertrophic smooth muscle 23 Robbins, Stanley L., Cotran, Ramzi S., Kumar, Vinay, Editor, Abbas, Abul K., Editor, and Aster, Jon C., Editor. Robbins and Cotran Pathologic Basis of Disease. 10th ed. 2021. Web. Hypertrophy - Cellular Adaptations Synthesis of structural components e.g. myofilaments Switch of proteins types Eg α-myosin heavy chains → adult to fetal isoforms No mitosis cell cycle arrest, nuclei increased DNA content. 24 Hypertrophy - Limitations If not relieved degenerative changes in cellular proteins Eg myocardial fibers Enlarge cells can disrupt cellular signalling Aberrant electrical conduction in cardiac muscle Can lead to apoptosis or necrosis of cells 25 Hypertrophy Hypertrophy and hyperplasia have similar stimuli A mixture of both can often happen Example is uterus Both increase smooth muscle cell mass and size. 26 Atrophy Reduction in size and number of cells (i.e. decreased organ size) Physiological E.g. thymus involution after birth Pathological Decreased workload Denervation Ischaemia Malnutrition Endocrine hypofunction Aging Compression, e.g. by adjacent tumour Examples Physiological Pathological Branchial clefts during embryological life Decreased workload Decreased Hormones Ischaemia Uterus after pregnancy → decreased cell size (and number) Limb immobilised due to a fracture, → muscle atrophy Lower limbs skin in patients with PVD Loss of endocrine stimulation Adrenal gland atrophy due to anterior pituitary dysfunction 28 Atrophy - Mechanisms Decreased protein synthesis and increased protein degradation in cells Alzheimer's disease reduced metabolic activity. Mechanism involves ubiquitin being attached to proteins Ubiquitin acts as a “tag”. These proteins degraded by lysosomes. Often accompanied by increased autophagy (see latter). (ab7780), A., 2021. Anti-Ubiquitin Antibody (Ab7780) | Abcam. [online] Abcam.com. Available at: [Accessed 7 January 2021]. 29 Metaplasia Mature (differentiated) cell type replaced by another type better suited to stress Reversible Undesirable Considered premalignant, esp in epithelial tissues Susceptible to mutations Due to reprograming of stems cells Examples Squamous metaplasia Lung (columnar to squamous) Smoking Cervix (columnar to squamous) Intestinal Oesophagus (squamous to columnar) GORD Stomach (gastric to intestinal) Likely H.Pylori 31 Autophagy Relatively new concept in medicine. Process where cell eats own contents. Result of cell starvation and recycling organelles. 32 Autophagy Important as plays a role in disease, especially neoplasia (development of tumours) and degenerative diseases of the nervous system. New field of research. Numerous different pathway discovered, e.g. Macroautophagy Microautophagy Chaperone-mediated autophagy 33 Autophagy Complex mechanism which degrades damaged, excess or modified cellular components via lysosomes. Also can cause autophagic cell death Involves process summaries below (simplified). Autophagy and disease Autophagy removed potential damaging substances from cell (“organic pollutants”) Misfolded proteins, substances causing oxidative stress, viral particles. Dysregulation can lead to neurodegenerative diseases, cancer, etc Can also induce autophagic cell death via p53 pathway “Turned on” during starvation, “turn off” during feeding (i.e. abundant amount of energy. Again complex and involves various pathways such as mTORC1 ?? Way intermediate fasting works?? Macroautophagy Living with cell injury 1. Intracellular accumulation 2. Ageing 37 Intracellular accumulations are either Normal constituent Abnormal Endogenous Exogenous VS Intranuclear Intracytoplasmic Produced by cell Produced elsewhere Transient Permanent 38 Mechanisms Example Substrate Enzyme Fat Too much Not enough A1-antitrypsin deficiency Mutated Mutated Carbon dust Foreign Absent 39 E.g. Steatosis = lipid (fat) in hepatocytes 40 Mechanisms Substrate Too much e.g. fatty liver Mutated e.g. alpha 1 antitrypsin deficiency Foreign e.g. anthracosis Enzymes Not enough e.g. again, fatty liver Mutated e.g. lysosomal storage diseases Absent/Ingestible e.g. again, anthracosis 41 Cross, Simon S. Underwood's Pathology : A Clinical Approach. Seventh ed. 2019. Normal liver Steatosis Lobular architecture distorted by marked macrovesicular steatosis that expands and distorts hepatocyte cytoplasm. 42 Steatosis 43 Fatty change Accumulation of triglycerides, mainly in liver (major organ of fat metabolism) Disruption of fat metabolic pathway due to EtOH NASH (Insulin resistance syndrome) Anorexia and malnutrition Complications of steatosis 44 With progressive steatosis, inflammatory hepatocyte destruction - steatohepatitis Subsequent scarring ->-> cirrhosis Cirrhosis -> ↑ risk of hepatocellular carcinoma E.g. Early atherosclerosis = lipid in arterial wall macrophages Subintimal accumulation of foamy cells (lipid laden macrophages) that form fatty streaks, which can evolve to atheroma complicated by thrombus 45 Pathogenesis of atherosclerosis 46 Cell ageing Accumulation of genetic and metabolic damage Increased susceptibility for carcinogenesis Loss of replicative capacity Telomeric shortening of chromosomes 47 Senescence  Terminal non-dividing cell state  Only a finite number of divisions for each somatic cell  Hayflick limit (1960’s)  Direct contradiction of Alexis Carrel - widely held brief that under optimal conditions, cells in culture will divide indefinitely 48 Mechanism of senescence Telomeres repetitive DNA sequence at the end of chromosomes ‘protective cap’ Due to inherent ‘rules’ of DNA replication, telomeres progressively shorten with each cell division Eventual shortening to a critical length blocks further cell division = senescence i.e. inherent counting mechanism 49 Telomerase & telomeres 50 Expressed in stem cells and cancerous cells Enzyme with own RNA template that extends shortened telomeres Overcoming normal restrictions on cell replicative capacity Cell death Two types, may co-exist in affected tissue: 1. Necrosis 2. Apoptosis* *NB “Autophagic cell death” is sort of misnomer but similar to apoptosis (in context of this lecture) Cell Injury and Cell Death Reversible Reversible & irreversible cell injury Depends on numerous factors Duration, type and severity of injury Also the adaptability of the injured cell Irreversible 52 Reversible Cell Injury Reversible if limits of adaptive response are not exceeded and/or the cell is exposed to harmful agents or stress only to a sub-lethal degree, recovery is possible Can manifest in a numerous of ways (on morphology): Hydropic change/vacuolar degeneration (H+E) (swollen) Due to lack of ATP (failure of ion pumps) Appear more eosinophilic (red) Due to loss of RNA Fatty change Due to metabolic pathways →accumulation of triglyceridefilled lipid vacuoles Normal Reversible Hydropic change 53 Cell death - causes Oxygen deprivation (ischaemia) Physical (e.g. trauma, radiation, temperature extremes) Chemical agents (drugs) Infection Immunological reactions Genetic derangements Malnutrition 54 Cell death - pathogenesis Mitochondrial damage Depletion of ATP Accumulation of oxygenderived free radicals (oxidative stress) Defects in membrane permeability 55 Oxidative stress Produced by oxygen-derived free radicals Free radical: chemical species with single unpaired electron in its outer orbit Unstable: energy released to adjacent molecules, converting them to further free radicals Small amounts usually from mitochondria removed by homeostasis ↑ amounts from mitochondrial dysfunction Harmful effects on cell membranes, proteins and DNA 56 Defects in membrane permeability Affect all cell membranes Cytoplasmic membrane damage Loss of osmotic balance with extracellular fluid Influx of water and ions Loss of proteins, enzymes, coenzymes, RNA and metabolites needed for ATP Lysosomal membrane damage Leakage of enzymes into cytoplasm (e.g. DNases, proteases) – autodigestion 57 Necrosis Unscheduled Always pathological Cell membranes disrupted Cell contents leak, with 2’ inflammation 58 Patterns of Tissue Necrosis 1. Coagulative necrosis 2. Liquefactive necrosis 3. Gangrenous necrosis 4. Caseous necrosis 5. Fat necrosis 6. Fibrinoid necrosis 59 Coagulative necrosis Architecture of dead tissues is preserved. Necrotic tissue removed by phagocytosis by immune cells Usually caused by infarctions (also see in tumours → ‘tumour necrosis’) 60 Liquefactive necrosis In contrast to coagulative necrosis, tissue turns into a liquid mass Infarctions in CNS result in liquefactive necrosis Occasional due to focal bacterial/fungi infections 61 Gangrenous necrosis Not a specific pattern of cell death, but commonly used in clinically practice Usually applied to a limb that has lost blood supply and undergone (coagulative) necrosis → “dry gangrene” If bacterial infection superimposed, more liquefactive necrosis→ referred to as “wet gangrene” 62 Caseous necrosis Necrosis with “cheese-like” material Commonly associated with tuberculosis infection 63 Fat necrosis Not really a pattern, more a clinical term Due to breakdown of fat Can be due to acute pancreatitis → enzyme leak into fat → breakdowns fat into triglyceride esters → Reacts with calcium (fat saponification) 64 Fibrinoid necrosis Refers to immune reactions involving blood vessels Walls of blood vessels contain bright pink fibrinoid material (fibrinlike) 65 Apoptosis Programmed cell death, Greek ‘falling off’ Physiological or pathological Scheduled: enzymes degrade own DNA and proteins Cytoplasmic membrane remains intact: cell breaks up into small membrane-bound bodies containing cytoplasm, organelles, nuclear fragments Bodies phagocytosed by macrophages before their contents leak → no inflammation (removed ‘without a trace’, c.f. necrosis) Adjacent healthy cells replace deleted cells by migration &/or cell division. 66 Apoptosis – physiological (removing unwanted cells) Programmed destruction of cells during embryogenesis Hormone-dependent involution in adult e.g. endometrial cell breakdown in menstrual cycle Cell deletion in proliferating populations e.g. intestinal epithelium to maintain constant number Elimination of cells that are past their purpose e.g. neutrophils after acute inflammation Apoptosis – pathological (removing damaged cells) Cell death after DNA injury e.g. radiation and cytotoxic drugs, mild to moderate thermal injury (if more severe → necrosis) Cell injury by viruses e.g. virus hepatitis B/C Cell elimination after duct obstruction - organ atrophy e.g. pancreas, salivary gland, kidney blocked by stone Conclusions 1. Pathology 4 essential parts to characterizing disease: aetiology, pathogenesis, structural changes, clinical manifestations 2. Cells respond to stress by Adaptation: hyperplasia, hypertrophy, atrophy, metaplasia Live with injury: intracellular accumulation, ageing Death: necrosis, apoptosis References 1. Robbins Pathological Basis of Disease, Chapter 1 Cellular Responses to Stress and Toxic Insults (8th ed. Kumar et al.) 2. PUTM modules – Introduction to Cells/Tissues (Anatomy practicals) 3. Next lecture on inflammation and healing 4. Introductory microscopy session 70