Cellular Pathology PDF - @September 25, 2024

🧪 Cellular Pathology Module Cellular and Systematic Pathology Date @September 25, 2024 Lecturer Dr. Debra O'Donnell Week Week 1 Learning Outcomes...

🧪 Cellular Pathology Module Cellular and Systematic Pathology Date @September 25, 2024 Lecturer Dr. Debra O'Donnell Week Week 1 Learning Outcomes Learning objectives Causes of cell injury Cell and Tissue responses Physiological changes Pathological changes Mechanisms of Cell Injury & Death Effects of the lack of ATP Neoplasia and types of tumour Pathology Pathology is the study of disease and disease processes; focusing on the causes of disease and changes in cells, tissues which leads to different symptoms. We study this to prevent damage / to put damage right. There are 2 types of pathology; general and systematic: Cellular Pathology 1  General: Common patterns of cell injury e.g. inflammation. Systematic: specific to organs or systems. Main Disciplines Histopathology / Cytopathology – Investigation of changes in tissue/cells Haematology - blood cells/Coagulation Microbiology - bacteria, viruses, fungi, parasites Immunopathology- HIV, AIDS, body defence Chemical pathology – diagnosis based on chemical changes in fluids and tissues Toxicology – effects of poisons Forensic Pathology – pathology to support legal processes Genetics – Gene and chromosomal abnormalities Experimental Pathology – use of animal models or cell culture to mimic disease Cellular Pathology 2  Causes of Disease There are two types of causes of disease; congenital and acquired. Congenital can be genetic and shows abnormalities in DNA A gain / loss of chromosomes / parts of them There are changes in the base sequences of genes, for example; colour blindness, albinism, haemophilia. They can be recessive / dominant; Recessive - requires 2 faulty copies of a gene (cystic fibrosis is a recessive disease). Dominant - requires only one copy of a faulty gene (Huntington's disease is a dominant condition) Acquired conditions are caused by environmental factors following birth. Cell Injury Cell injury can be caused by: Physical agents Chemicals / drugs Microbiological Immune Nutritional balance genetic ischaemic / hypoxia aging Cellular adaptations to disease Cellular Pathology 3  Cells adapt by homeostasis, by adapting this means the cells have a stable environment, despite the environment to be constantly changing. To a degree this can prevent tissue damage / disease / death. Cells can also adapt in normal physiology; e.g. temperature, nutrition etc. Adaptations normally occur mainly at the biochemical level; This occurs through the fine regulation of metabolic function. Fatty acids are metabolised during fasting for energy and Ca2+ is released from bones during a relative lack thereof. Changes can also be structural. Structural changes can be physiological and metabolic. Physiological structural adaptations increased cell size / numbers (due to and increase in the functional demands / a hormonal stimulation) decreased cellular activity (due to a reduction in the demand of numbers / cells) Severe changes in cell metabolism are termed pathological stimuli: The boundary between normal physiology and pathology is not a clearly defined one. However we do know that an injury to one persons cells does not always cause an injury to another persons cells. For example; we are all affected differently by sunbathing. Cellular response to injury / damage Pathological stimuli does bring about a cell stress response (also called UPR), this can be beneficial; such as changes in metabolism. This promotes the cells survival and decreases the output of normal structural proteins whilst increasing the output of proteins with organising protective functions. The cells stress proteins are vital for survival. Chaperone proteins correct the protein folding patterns. The stress proteins remove old / damages proteins using the ubiquitin-proteasome pathway. However, this only protects against certain levels of damage as severe stimuli leads to cell death. Ubiquitin protease pathway: Cellular Pathology 4  In response to damage cells adapt processes, metabolism and structure. The inability for the cells to adapt leads to sub-lethal damage or cell death. Not all cells are easily damaged; e.g. brain neurones are highly susceptible to damage but fibroblasts are extremely resilient. Cells have growth patterns, these are termed below: Cell size; atrophy (reduction in cell size) hypertrophy (increase in size of cells). Cell number; involution (decrease in cell number), hyperplasia (increase in cell numbers) Change in cell type; metaplasia (a stable change to another cell type) Cellular Pathology 5  You can get multiple different cell changes at once, as demonstrated above. Hypertrophy Hypertrophy is defined as an increase in cell size. PHYSIOLOGICAL EXAMPLES: PATHOLOGICAL EXAMPLES: Cellular Pathology 6  Hyperplasia PHYSIOLOGICAL: Thyroid gland increases in size in pregnancy due to an increased metabolic demand Bone marrow cells increase in high altitudes due to an increased need for erythropoietin Wound healing (scarring) in response to tissue damage. PATHOLOGICAL: Psoriasis Paget’s disease (of the bone) bone remodelling osteoblasts and osteoclasts bone deformities Hypertrophy and Hyperplasia Both of these can occur independently and when a stimulus is removed, the tissues revert to normal. Hyperplasia is not always uniform; it can form nodules. E.g. Chronic hepatitis - Liver fibrosis sees a loss of hepatocytes (hyperplasia). Cellular Pathology 7  Breasts in pregnancy is an example of hypertrophy and hyperplasia. Atrophy / Involution This is a normal response when there is a reduced need for cell or organ. This is a reduction in organ or tissue (decreased cell size / decreased cell numbers. can also cause apoptosis). This process can be pathological as well as physiological. The reduction in cells is achieved by increased catabolism of structural proteins by autophagy. This occurs due to a lack of nutrients and degradation of cytoplasmic components within lysosomes. Physiological - A decrease in the thyroid gland after pregnancy and skeletal muscle in old age. Thymus gland in adolescence, testis size in old age, gums, and bones in elderly females. Pathological reduction in cell mass: Disuse atrophy, immobilised limb leads to a decrease in muscle size. Denervation atrophy - this is damage to axons supplying muscles causing atrophy. Ischaemic atrophy - a gradual reduction in blood supply to cells which results in a loss of function and circulatory problems. Metaplasia Tissues may adapt to stimuli by changing to new stable type better equipped to deal with stress. Metaplasia → Dysplasia → Tumour Cellular Pathology 8  Barret's disease (research this - step before oesophageal cancer) Cell Injury and Death Cells die due to irreversible cell injury. The primary targets for damaging stimuli are; cellular membranes, mitochondria, protein synthesis (the packing machinery), cellular DNA. Cytoplasmic organelle damage leads to a variety of injury patterns. Acute injuries tend to damage an entire cell, therefore specific organelle damage is irrelevant. There are many causes of cell death, and many biochemical pathways which can trigger cell injury and furthermore lead to cell death. Damaging stimuli can trigger one or more biochemical pathways which can all be activated simultaneously. Cellular response to injury depends on the cause, severity and duration of the stimulus. Cell death occurs when the damage threshold is passed, such as a decrease in O2 and nutrients or by toxins e.g. cyanide - leading to a decrease in ATP production. The primary cell membrane injury can be due to; oxygen free radicals, immune mediated damage and direct actions of bacterial toxins. Mitochondria are susceptible to virtually all types of injurious stimuli. Cellular Pathology 9  Effects of lack of ATP A deficiency of oxygen leads to the failure of many metabolic processes that require energy. These failures can be due to a failure of ATP generation and a lack of ATP. A failure of Ca2+ pumps can cause severe damage. The cytosolic free Ca2+ is an intracellular 2nd messenger, and therefore is closely regulated. Ca2+ levels are low in cytosol in comparison to extracellular levels, causing cytosolic concentrations to increase An abnormal cytosolic Ca2+ can result in uncontrolled enzyme activation which can have further damaging effects. E.g. proteases causing a membrane / cytoskeletal protein breakdown. Uncontrolled entry of Ca2+ into the cell is an important final pathway within cell death, it leads to the activation of caspases and an increase in mitochondrial permeability. Reactive oxygen metabolites Oxygen free radicals are metabolic intermediates of toxins and drugs (e.g. paracetamol). Chemical species with a single unpaired electron within their outer orbit are unstable and react with inorganic / organic materials. Reactive oxygen metabolites can damage cells through: Damaging effects (peroxidation) of membrane lipids causing an increased permeability. Critical protein damage; e.g. Na/K ATPase pumps. Influx of sodium and efflux of potassium Accumulation of water inside the cell and swelling Morphological change associated with reversible cell injury DNA fragmentation has a possible role in malignancy Oxygen free radicals are scavenged by protective antioxidant systems such as superoxide dismutase and Vitamin E. Cellular Pathology 10  Necrosis Necrosis occurs due to disintegration of cellular structure by activation of lysosomal enzymes. Apoptosis / necrosis Apoptosis is usually a normal process, it: removes unnecessary cells but can also remove damaged cells. Leaves the plasma membrane intact Causes no leakage of cell contents No activation of the inflammatory response. Necrosis is pathological: The plasma membrane is damaged cellular contents leak from cells it leads to an inflammatory response Cellular Pathology 11  Necroptosis shares features of both necrosis and apoptosis If during an adaptive response, the stimulus is removed, alterations in the cell growth revert to normal. In contrast; certain stimuli change genetic material that result in a permanent alteration of the normal cellular growth patter, this is called neoplasia. Such altered cells are termed neoplastic or cancerous. Neoplasm Causes of most neoplasms are not yet identified. However we do know that incidence increases with age. Neoplastic cells do not respond to normal cell growth controls as they are transformed cells. An excessive proliferation causes a lump called a neoplasm or a tumour. People equate cancer with malignant neoplasm. Cellular Pathology 12  Neoplastic cytology neoplastic cells show atypical cytology: This can be characterised as: an increased variation in the shape and size of cells an increased variation in the shape and size of nuclei an increased density of nuclear staining. Types of tumour: Benign and Malignant; Genetic changes are transmitted to each new cell The cells fail to differentiate with specific functions. Benign tumours Benign tumours grow slowly but do not penetrate adjacent tissue borders or move to distant sites. the cells are well differentiated, similar to the original cell. They can be deadly depending on the location e.g. the gut or airway. A benign endocrine tumour may cause disease due to uncontrolled release of hormones. Cellular Pathology 13  Malignant tumours Malignant tumours can be: Well differentiated (similar to the original cell) but are less aggressive. Poorly differentiated (dissimilar), this is very aggressive and not confined to the site primary tumour. Cells can invade and destroy the surrounding tissues or migrate to other parts - a secondary tumour. Tumour growth rates Cellular Pathology 14  Neoplastic cells obtain nutrition by developing a new blood supply. Tumours secrete angiogenesis factors that cause new blood vessels to grow providing nutrients. Inadequate nutrients leads to tumour death. Rate of growth depends on many factors: Number of cells in growth cycle as opposed to Non- growth phase The death rate of the cells in the tumour. Tumour cells are prone to Apoptosis. Invasion and metastasis Tumour enlarges and infiltrates normal structures Growth can be extensive, no normal tissue left Results in functional insufficiency Key steps: 1. Initial detachment of tumour cells from neighboring cells 2. Invasion of surrounding connective tissue a. To access Blood/lymphatic vessels b. Degradation of connective tissue through proteases 3. Intravasation a. Degradation of connective tissue through proteases 4. Adherence to endothelium at distant site 5. Extravasation of the cells from the vessel lumen to the tissue Tumour spread Cellular Pathology 15  Cancerous agents - carcinogens Chemical carcinogens: Cellular Pathology 16  Tars in cigarettes, Aromatic amines, Nitrosamines, Alkylating agents (drugs that bind to DNA) Viruses - only a few implicated in neoplasia Irradiation - potent cause Physical agents e.g. Asbestos Biological Hormones play a role in Tumour growth Oestrogens - normally stimulate breast and endometrium also in tumours of these tissues Pre-neoplastic conditions Can be associated with tumour development - Chronic Gastritis, Chronic Colitis Abnormalities in genes regulating cell proliferation underlie neoplasm 3 main genetic mechanisms Oncogenes - stimulate inappropriate growth Loss of activity of Tumour Suppressor Genes Over expression of products that prevent normal cell death Normal cell Proliferation & Differentiation closely regulated Proto-oncogene Genes expressed in normal cells Growth promoting Negative regulation by tumour suppressor genes e.g p53 Encode proteins which stop or reduce tumour formation Cellular Pathology 17  Molecular basis of cancer Abnormal or inappropriately expressed gene responsible for tumour growth Result from mutations which can cause over activation e.g. Ras Normal oncoprotein but excessive production e.g. gene amplification Mutations of TSGs lead to proteins which are non-functional or altered which promotes tumour formation Analysis of tumours Needle, Endoscopic, Incision or Excision Biopsy material for - Routine Histopathology Cytopathology Cells shed naturally into body - Sputum, Urine CSF Pleural fluid Cells obtained by exfoliation Cervical Smear Brush cytology of GIT Cells aspirated by needle. Bone and Bone Marrow Breast Thyroid & pancreas Frozen section Immunohistochemistry Cellular Pathology 18  Electron Microscopy Cell Culture Tumours, and indeed most pathology in tissues, can be analysed using some of the above techniques. Needle aspiration is used to remove fluids from the body, endoscopic analysis involves the insertion of a tube into a hollow cavity to investigate for cellular and structural changes. A biopsy can be incision or excision; an incision biopsy is where a small section of the affected tissue is removed for analysis whereas excision is where the entire mass is removed. Fluids, tissues and cells can be analysed in several different ways and these are just some common examples. Histopathology involves the use of specific stains to enhance particular features of the tissues, the most common of these is haematoxylin and eosin staining (many of the tissues you see in these lectures have been stained with this). An H&E stain shows the pathologist if the tissue initially appears normal, is there any evidence of outgrowths (tumours, polyps), atrophy, hyperplasia, metaplasia etc? Cytopathology is looking particularly at cells and changes therein associated with pathological conditions. Cellular Pathology 19