Cellular Adaptations and Cell Death 2022 Part 1 PDF

Cellular Adaptations and Cell Death: Part 1 Learning Outcomes Describe physiological and pathological examples of hyperplasia, hypertrophy, atrophy and metaplasia Define the terms dysplasia and neoplasia Explain the patterns of cellular adaptation seen secondary to non-lethal cell dam...

Cellular Adaptations and Cell Death: Part 1 Learning Outcomes Describe physiological and pathological examples of hyperplasia, hypertrophy, atrophy and metaplasia Define the terms dysplasia and neoplasia Explain the patterns of cellular adaptation seen secondary to non-lethal cell damage Outline the causes and patterns of cellular response to noxious stimuli Outline the mechanisms and targets of cell damage  Normal Functioning of Cells For cellular homeostasis the cell must exist in a narrow range of physiological parameters e.g. pH, temperature, oxygenation Change in these leads to cell injury or cell stress The cell will try to reach a new steady state (adapt) to preserve its vitality If this is not possible it will be injured and may die Cellular Responses to Injury and Stress Reversible if stimulus minor, transient and removed Normal Cell Inherentl y STRES injurious S stimulus Stress exceeds Adaptation adaptabilit Cell Injury y Irreversib Severe and le progressive Cell death is Cell Death: the key event Apoptosis or in the Necrosis development of many  Cell Adaptation Adaptations are reversible changes in cells in response to changes in the environment – stimuli may arise under physiological or pathological conditions Adaptation reflects an attempt to preserve cell vitality and meet the change in conditions, it can involve changes in: Depends upon the – Cell number proliferative capacity of – Cell size the tissue – Cell type  What proliferative capacity do Three classes: cells have? Labile cells – Continuously dividing in adult life Stable cells – Infrequent divisions but rapid division if needed (‘conditional renewal cells’) Permanent cells – Never divide in adult life – Some cells do divide but not to a clinically significant level  What proliferative capacity do cells have? Labile cells – Continuously dividing in adult life – Cells exposed to external environment – Continuous ‘wear and tear’  What proliferative capacity do cells have? Stable cells – Infrequent divisions but rapid division if needed (‘conditional renewal cells’) – Mainly quiescent – Divide if need to  What proliferative capacity do cells have? Permanent cells – Never divide in adult life – Terminally differentiated – Some cells do divide but not to a clinically significant level  Definitions Cell adaptation Hypertrophy Hyperplasia Atrophy Metaplasia  Hyperpla sia Increase in the number of cells within a tissue Cells must be labile or stable (not permanent)  Physiological Hyperplasia Hormonal – EXAMPLE: Endometrium  Physiological Hyperplasia Compensatory – EXAMPLE: Partial hepatectomy  Pathological Hyperplasia Causes: Excessive hormone / growth factor stimulation  Pathological Hyperplasia Causes: Chronic irritation  Pathological Hyperplasia Some increased risk of tumour development Increased proliferation -> dysregulation -> tumour May occur alongside hypertrophy  Hypertrophy Increase in cell size Can occur in any cells, but is common when permanent cells experience increased demands ( ) More cellular structural proteins produced (not just cell swelling) to meet new demands  Physiological Hypertrophy Increased functional demand – Skeletal muscle  Physiological Hypertrophy Hormonal / growth factor – Uterine muscle in pregnancy – Combination with hyperplasia  Pathological Hypertrophy Increased functional demand EXAMPLE: Cardiac muscle – Left ventricle primarily in Hypertension Aortic stenosis  Definitions Cell adaptation Abnormal growth Neoplasia Hypertrophy Dysplasia Hyperplasia Atrophy Metaplasia  Atrophy Shrinkage in cell size by loss of cell substance Cellular atrophy involves self digestion of organelles – autophagy Sometimes used more loosely – reduction in organ size through cell loss – more strictly referred to as involution  Atrophy Reduced workload Loss of nerve supply Reduced blood supply Inadequate nutrition Loss of endocrine stimulation Ageing  Atrophy Reduced workload  Atrophy Loss of nerve supply  Atrophy Reduced blood supply  Atrophy Inadequate nutrition  Atrophy Loss of endocrine stimulation  Atrophy Ageing Metaplasia  Physiological Metaplasia Normal growth and development EXAMPLE: Glandular to squamous epithelium in the cervix due to acidity of vagina Ecto  Pathological Metaplasia Abnormal environment causes adaptive response EXAMPLE: Squamous to glandular in reflux oesophagitis i.e. Barrett’s Column Squamou ar s  Definitions Cell adaptation Abnormal growth Neoplasia Hypertrophy Dysplasia Hyperplasia Atrophy Metaplasia  Dysplasia Premalignant condition Increased cell growth Cellular atypia Increased nucleus : cytoplasm Cellular and nuclear pleomorphism Hyperchromatism Altered differentiation Can range from mild to severe  Dysplasia Sites – Oesophagus  Dysplasia Sites – Colon  Neoplasia Abnormal growth of cells which persists after initiating stimulus has been removed Cell growth has escaped from normal regulatory mechanisms Benign Malignant – invasion and metastases Neoplasia: Benign Neoplasia: Malignant Neoplasia: Malignant  Definitions Cell adaptation Abnormal growth Neoplasia Hypertrophy Dysplasia Hyperplasia Atrophy Metaplasia