HISTOPATH Lab Mod 1

• Cells are the basic units of tissue in the human body, divided into epithelial and mesenchymal cells
• Virchow published the cellular theory of disease in 1859, stating that diseases occur due to abnormalities at the cellular level
• Abnormalities in structure and function of cells in disease have remained the focus of understanding diseases
• Most diseases begin with cell injury followed by loss of cellular function
• To understand the disease process at the cellular level, knowledge of causes and mechanisms of cell injury and cellular adaptations is essential
• Cell injury is a variety of stresses a cell encounters due to changes in its internal and external environment
• Cells have built-in mechanisms to deal with changes in the environment to an extent
• The cellular response to stress varies depending on the type of cell and tissue involved, extent and type of cell injury
• Various forms of cellular responses to cell injury include adaptation, recovery, and cell death
• Factors disrupting homeostasis in the body can lead to cell injury and eventual death
• Adaptations are reversible responses to physiologic stresses and some pathologic stimuli, allowing cells to survive and function
• Hypertrophy is an increase in cell size without a change in cell number, leading to organ or tissue enlargement
• Hyperplasia is an increase in the number of cells resulting in organ or tissue enlargement
• Hyperplasia and hypertrophy frequently occur together and may be triggered by the same external stimulus
• Hypertrophy with hyperplasia occurs under various conditions, such as smooth muscle cells in the urinary bladder thickening due to obstruction by a hyperplastic prostate
• Physiologic hypertrophy of uterine smooth muscle cells during pregnancy is accompanied by hyperplasia
• Metaplasia is a reversible change where one differentiated cell type is replaced by another cell type
• Epithelial metaplasia is more common and includes squamous metaplasia and columnar metaplasia
• Mesenchymal metaplasia involves the transformation of one adult type of mesenchymal tissue to another
• Dysplasia, or disordered cellular development, often accompanies metaplasia and hyperplasia
• Epithelial dysplasia is characterized by cellular proliferation and cytologic changes
• The two most common examples of dysplastic changes are found in the uterine cervix and the respiratory tract
• Atrophy is the decrease in the size of a cell, tissue, organ, or the entire body
• Physiologic atrophy is a normal process of aging in some tissues, while pathologic atrophy can be due to various factors
• Cell injury can result from severe stress, damaging agents, or intrinsic abnormalities
• Causes of cell injury include hypoxia, physical agents, chemical agents, infectious agents, genetic derangements, nutritional imbalances, aging, and more
• Morphologic features of atrophy include small, shrunken organs with smaller cells due to reduction in cell organelles
• Pathogenesis of cell injury involves the type, duration, and severity of the injurious agent, adaptability of the target cell, underlying intracellular phenomena, and morphologic consequences
• Morphology of cell injury includes hydropic change, which is the accumulation of water within the cytoplasm of the cell
• In single-celled organisms, substances can easily enter the cell due to a short distance, while in multicellular organisms, the distance is larger due to a higher surface area to volume ratio
• Multicellular organisms require specialised exchange surfaces for efficient gas exchange of carbon dioxide and oxygen due to their higher surface area to volume ratio
• Necrosis is characterized by nuclear shrinkage and increased basophilia, as well as karyorhexis where the pyknotic nucleus undergoes fragmentation
• Subcellular alterations in cell injury include:

  • Cytoskeletal changes such as defective microtubules, defective microfilaments, and accumulation of intermediate filaments
  • Lysosomal changes like heterophagy, autophagy, indigestible materials, and storage diseases
  • SER changes
  • Mitochondrial changes including megamitochondria, alterations in the number of mitochondria, oncocytoma, and myopathies
• The Greek word "necros," meaning "dead," is used in medical terminology to construct various words
• • Gross appearance includes yellowish-white firm deposits, while microscopic appearance shows basophilic calcium deposits and inflammation
• Fibrinoid necrosis:

  • Associated with vascular damage and exudation of plasma proteins
  • Occurs due to immune complex deposition and type 3 hypersensitivity
  • Microscopic appearance includes bright pink amorphous appearance with fibrinoid deposits surrounding blood vessels
• Apoptosis is an "active" form of cell death that is energy-dependent and requires the activation of a specific set of genes and enzymes
• Apoptosis is also known as programmed cell death, with genes activated in apoptosis being referred to as suicide genes
• Characteristics of apoptosis include nuclear changes like pyknosis, karyorrhexis, and karyolysis
• Cell shrinkage, chromatin condensation, and formation of cytoplasmic blebs and apoptotic bodies are also features of apoptosis