Cell Adaptation, Injury, and Death - Lab 1 (PDF)

Lab 1: Cell adaptation, cell injury, cell death First part PRACTICAL SURGERY 1 SECOND STAGE Lecturer M.Sc Zainab K. shaheen Definition of cell injury: If the limits of adaptive responses are exceeded, or if cells are exposed to injurious agents or stress, deprived of essen...

Lab 1: Cell adaptation, cell injury, cell death First part PRACTICAL SURGERY 1 SECOND STAGE Lecturer M.Sc Zainab K. shaheen Definition of cell injury: If the limits of adaptive responses are exceeded, or if cells are exposed to injurious agents or stress, deprived of essential nutrients, or become compromised by mutations that affect essential cellular constituents, a sequence of events follows that is termed cell injury Homeostasis is defined as a self- regulating process by which cells can maintain internal stability while adjusting to changing external conditions. Reversible cell Irreversible injury injury: and cell death: Functional and Type of cell With continuing morphologic injury damage, the injury changes are becomes reversible if the irreversible, at damaging which time the cell stimulus is cannot recover and removed. it dies Causes of cell injury: 1. (Hypoxia): Deficiency of oxygen, causes cell injury by reducing aerobic oxidative respiration. Reduced blood flow (Ischemia) Inadequate oxygenation of the blood due to cardiorespiratory failure, and Decreased oxygen-carrying capacity of the blood, as in anemia or carbon monoxide poisoning or After severe blood loss. 2. Physical agents: Mechanical trauma, extremes of temperature (burns and deep cold), sudden changes in atmospheric pressure, radiation 3. Chemical agents and drugs: 4. Infectious agents: Viruses, Bacteria, fungi, Rickettsia, parasites. 5. Immunologic reaction: Anaphylactic reaction and Autoimmune diseases 6. Genetic abnormalities: Congenital malformations, enzyme deficiency (storage diseases). Type of cells Cell cycle Cell adaptation  In order to survive and continue to functions Cells adjust their structure and functions Cellular adaptations Reversible on withdrawal of stimulus 5 types of adaptation 1. Hypertrophy: increase in the size of the cell 2. Hyperplasia: increased number of cells 3. Atrophy: size/number decreasing 4. Metaplasia: the transformation of cell type to another 5. Dysplasia: disorderly growth  Hyperplasia DEFINITION Increase in the number of cells, not size of cell, resulting in enlargement of the organ or tissue. seen in tissues made up of labile cells and stable cells (not in permanent cells) - they can divide. May or may not be seen together with hypertrophy. MECHANISM Increased production of growth factors, growth factor receptors Eg. after partial hepatectomy growth factors are produced in the liver that engage receptors on the surviving cells and activate signaling pathways that stimulate cell proliferation → Hypertrophy. Type of hyperplasia 1. Physiologic hyperplasia Hormonal hyperplasia 1. Hyperplasia of female breast at puberty, pregnancy and lactation. 2. Enlarged size of the uterus in pregnancy is an example of physiologic hypertrophy as well as Non prg. Prg. hyperplasia (as figure). 3. Proliferation of endometrium after a normal and menstrual cycle. 2. Pathologic hyperplasia 2. Formation of skin warts from hyperplasia of epidermis due 1. Endometrial hyperplasia following oestrogen excess. to human papilloma virus (HPV)  Hypertrophy DEFINITION Increase in the size of cells, not number of cells, leading to an increase in the size of the organ Seen tissues made up of labile cells, stable cells, and permanent cells Mechanism Increased size is not due to cellular swelling, its due to more structural components/ cellular proteins Type of hypertrophy 1. Physiologic hypertrophy 2. Pathological hypertrophy The enlarged size of the uterus in Skeletal muscle in response to exercise. pregnancy is an example of physiologic hypertrophy as well as hyperplasia.  Atrophy DEFINITION Decrease in cell size and number of cells (with or without accompanying shrinkage of the organ or tissue) Mechanism Shrinkage in cell size is due to a reduction in cell organelles, chiefly mitochondria, myofilaments, and ER Type of Atrophy 1. Physiologic Atrophy Atrophy of lymphoid tissue with age. Atrophy of thymus in adult life. Atrophy of gonads after menopause. Decrease in the size of the uterus that occurs shortly after parturition Atrophy of brain with aging. 2. Pathological Atrophy Starvation atrophy general weakness, emaciation and anemia known as cachexia seen in cancer and severely ill patients. Ischaemic atrophy atrophic kidney in atherosclerosis of renal artery. Neuropathic atrophy →e.g. Poliomyelitis,  Metaplasia DEFINITION A reversible change in which one mature/adult cell type is replaced by another mature/adult cell type If injury or stress abates, the metaplastic tissue may revert to its original type Mechanism Metaplasia does not result from a change in the phenotype of an already differentiated cell type; Metaplasia is the result of reprogramming of stem cells that are known to exist in normal tissues  Type of metaplasia 1. squamous metaplasia Normal columnar epithelium squamous epithelium EXAMPLES 1. In bronchus (normally lined by pseudostratified columnar ciliated epithelium) in chronic smokers. 2. In uterine endocervix (normally lined by simple columnar epithelium) in prolapse of the uterus 3. In gallbladder (normally lined by simple columnar epithelium) in cholelithiasis. 4. In prostate (normally lined by simple columnar epithelium) in chronic prostatitis 5. Vitamin A deficiency, squamous metaplasia in the nose, bronchi, lacrimal and salivary glands. 2. columnar metaplasia Normal squamous epithelium columnar epithelium EXAMPLES 1. Barrett's esophagus change of normal squamous epithelium to columnar epithelium 2. Cervical erosion → change of normal squamous epithelium to columnar epithelium.  Dysplasia DEFINITION Disordered cellular development Characterised by cellular cytologic change Cytological changes 1. Increased number of layers 2. Disorderly arrangement of cells from basal layer to surface layer 3. Loss of basal polarity i.e. nuclei lying away from the basement membrane 4. Cellular and nuclear pleomorphism 5. Increased nucleocytoplasmic (N/C) ratio 6. Nuclear hyperchromatism 7. Increased mitotic activity Normal endocervical cells dysplasia On removal of stimulus, the changes may disappear. Sometimes dysplasia may progress into carcinoma in situ o invasive cancer.