hp

• Histology is the study of microscopic anatomy, focusing on the various cells and components of human tissue
• Histopathology is the study of disease manifestation through microscopic anatomy
• Histopathology relies on both macroscopic and microscopic observation of organs and tissues
• Histotechnologists help prepare tissues for microscopic examination by fixing, sectioning, and staining them
• Cells are the basic unit of tissue, traditionally divided into epithelial and mesenchymal types
• Cellular adaptation and injury are two types of cellular response
• Cell adaptation can include hypertrophy, hyperplasia, atrophy, and metaplasia
• Hypertrophy refers to an increase in the size of tissues or organs due to the enlargement of individual cells
• Physiological hypertrophy is normal, while pathological hypertrophy is disease-related
• Hyperplasia is an increase in the number of cells in a tissue or organ, often as a compensatory mechanism
• Physiological hyperplasia can be hormonal or compensatory, such as in liver regeneration
• Pathological hyperplasia can be caused by excess hormones or growth factors, and may lead to cancer if dysregulated
• Metaplasia is the conversion of one differentiated cell type to another, such as in smokers' bronchial epithelium
• Mesenchymal metaplasia involves the transformation of one adult type of mesenchymal tissue to another, like osseous metaplasia
• Metaplasia can progress to dysplasia, characterized by disordered cellular development and atypical hyperplasia
• Atrophy is a decrease in the size and function of a cell, tissue, or organ, caused by various conditions like reduced demand or nutrient supply
• Physiological atrophy can occur after inactivity or with aging, while pathological atrophy can result from conditions like ischemia or neuropathy
• Cell injury can result from severe stress, damaging agents, or intrinsic abnormalities, progressing through reversible or irreversible stages
• Causes of cell injury include hypoxia, physical agents, chemical agents, infectious agents, genetic derangements, and aging
• Pathogenesis of cell injury depends on the type, duration, and severity of the injurious agent, as well as the target cell's adaptability and underlying intracellular phenomena
• Reversible cell injury can manifest as degeneration, with morphologic forms like hydropic change, hyaline change, mucoid change, and fatty change
• Hydropic change is the accumulation of water within the cytoplasm of the cell, leading to cellular swelling and vacuolar degeneration
• Hyaline change refers to a glassy, homogenous, eosinophilic appearance of material in histologic sections
• Hyaline change is a histologic term describing a glassy, homogenous, eosinophilic appearance of material in H&E-stained sections
• Hyaline change does not refer to any specific substance and can be associated with heterogeneous pathologic conditions
• Hyaline change may be intracellular or extracellular
• Mucoid change is associated with mucus secreted by mucous glands, which is a combination of proteins complexed with mucopolysaccharides
• Mucin, a glycoprotein, is the chief constituent of mucus and is normally produced by epithelial cells of mucous membranes and mucous glands
• Mucoid change may be epithelial or connective mucin, with connective tissue mucin termed as myxoid
• Fatty change (steatosis) occurs in hypoxic injury and different forms of toxic or metabolic injury
• Fatty change is characterized by the appearance of lipid vacuoles in the cytoplasm and is mainly seen in cells involved in fat metabolism like hepatocytes and myocardial cells
• Nuclear changes in irreversible cell injury include pyknosis, karyolysis, and karyorrhexis
• Necrosis is the sum of degradative and inflammatory reactions occurring after tissue death caused by injury such as hypoxia and exposure to toxic chemicals
• Necrotic cells are unable to maintain membrane integrity and their contents often leak out, eliciting inflammation in the surrounding tissue
• Patterns of tissue necrosis include coagulative necrosis, liquefactive necrosis, caseous necrosis, fat necrosis, and fibrinoid necrosis
• Coagulative necrosis is the most common type of necrosis caused by irreversible focal injury, often from sudden cessation of blood flow (ischemia)
• Liquefactive necrosis results in characteristic digestion, softening, and liquefaction of tissue, commonly seen in ischemic injury to the CNS
• Caseous necrosis occurs when the immune system cannot successfully remove foreign noxious stimuli, combining features of coagulative and liquefactive necrosis
• Fat necrosis occurs in traumatic or enzymatic forms, with acute pancreatitis leading to enzymatic fat necrosis
• Fibrinoid necrosis is associated with vascular damage and exudation of plasma proteins, often due to autoimmunity or immune complex deposition