Chapter 4: Cellular Biology

Chapter 4: Cellular Biology This chapter explores altered cellular and tissue biology, focusing on cellular adaptation, injury, manifestations of cellular injury, cellular death, aging, and the various types of cell death such as necrosis and apoptosis. Cellular adaptation allows cells to respond to physiological and pathological conditions, but severe or prolonged stressors can lead to cellular injury or death. Common sources of cell injury include lack of oxygen, free radicals, infections, inflammation, and metabolic derangements. Cellular aging also contributes to changes in structure and function. Bullet points CHAPTER OUTLINE: Altered Cellular and Tissue Biology ● Cellular Adaptation ○ Atrophy ○ Hypertrophy ○ Hyperplasia ○ Dysplasia: Not a True Adaptive Change ○ Metaplasia ● Cellular Injury ○ General Mechanisms of Cell Injury ○ Ischemic and Hypoxic Injury ○ Ischemia-Reperfusion Injury ○ Free Radicals and Reactive Oxygen Species-Oxidative Stress ○ Chemical or Toxic Injury ○ Unintentional and Intentional Injuries ○ Infectious Injury ○ Immunologic and Inflammatory Injury ● Manifestations of Cellular Injury ○ Cellular Manifestations: Accumulations ○ Water ○ Lipids and Carbohydrates ○ Glycogen ○ Proteins ○ Pigments ○ Calcium ○ Urate ● Systemic Manifestations of Cellular Injury ● Cellular Death ○ Necrosis ○ Apoptosis ○ Autophagy ● Aging and Altered Cellular and Tissue Biology ○ Normal Life Span and Life Expectancy ○ Frailty ○ Somatic Death Notes: ● The majority of diseases are caused by multiple factors acting together or a single factor interacting with a genetically susceptible person ● Injury to cells or their surrounding environment leads to tissue and organ damage ● Cells can adapt to increased demands and stress to maintain homeostasis ● Cellular adaptations can be reversible or occur in pathologic conditions ● Cellular injury can result from various factors, including lack of oxygen, free radicals, infection, and inflammation ● Types of cellular death include necrosis, apoptosis, and autophagy ● Cellular aging can lead to decreased recovery capacity and cell death Cell Adaptation ● Adaptations are reversible changes affecting cell size, number, phenotype, metabolic activity, or function ● Adaptive responses have limits; additional stress can compromise essential cell functions leading to cell injury or death ● Cell adaptation may be central to many disease states Types of Cell Adaptation ● Atrophy: decrease in cell size ● Hypertrophy: increase in cell size ● Hyperplasia: increase in cell number ● Metaplasia: reversible replacement of one mature cell type by another, less mature cell type or change in cell phenotype ● Dysplasia: deranged cellular growth, not considered a true cellular adaptation but rather atypical hyperplasia Atrophy ● Atrophy refers to a decrease in cell size; if it affects enough cells, the organ itself shrinks ● Physiologic atrophy occurs with early development or age-related changes ● Pathologic atrophy occurs in organs due to decreases in workload, pressure, use, blood supply, nutrition, hormonal stimulation, or neural stimulation ● Atrophic muscle cells contain less endoplasmic reticulum, fewer mitochondria, and fewer myofilaments compared to normal cells ● Mechanisms of atrophy include decreased protein synthesis, increased protein degradation, or both ● Atrophy can be associated with autophagy, where self-destructive autophagic vacuoles containing cellular debris and hydrolytic enzymes are created within the cell Role of vacuoles ● Vacuoles prevent uncontrolled cell destruction in neighboring cells and tissue ● Some substances within autophagic vacuoles may persist as membranebound residual bodies within tissues ● Lipofuscin refers to yellow-brown pigmented granules that persist after lysosomal destruction and tend to accumulate in various tissues as individuals age Hypertrophy ● Hypertrophy is an increase in cell size in response to mechanical load or stress ● Common triggers include repetitive stretching, chronic pressure, and volume overload ● Hypertrophy occurs in the heart and kidneys, often presenting as muscle enlargement ● It can be either physiologic (normal and preserved structure) or pathologic (associated with fibrosis, cell death, and abnormal function) Hyperplasia ● Hyperplasia is an increase in the number of cells due to increased cellular division ● It occurs in response to severe or prolonged damage or cell death ● Growth factors and tissue stem cells play a role in stimulating cell division and regeneration ● Hyperplasia can occur alongside hypertrophy in the same tissue Physiologic hyperplasia includes compensatory and hormonal hyperplasia