Pathology: General and Systemic

• Pathology is the study of disease, bridging science and medicine
• It investigates disease causes, mechanisms, and extent
• Pathology divides into general and systemic branches

General Pathology

• Focuses on fundamental cell and tissue reactions to abnormal stimuli
• Covers common injury/stress responses, regardless of organ system
• Inflammation, the body's response to injury/infection, is key
• Cell injury/death are central concepts, including necrosis, apoptosis, and cellular adaptations
• Studies tissue repair and regeneration as the body attempts to restore normal structure/function
• Examines genetic and environmental disease factors
• Neoplasia (tumor formation) is a major area, covering benign and malignant growths
• Immunopathology studies the immune system's role in disease

Systemic Pathology

• Examines diseases affecting specific organ systems
• Integrates general pathology principles with each organ's unique characteristics
• Cardiovascular pathology addresses heart/blood vessel diseases like atherosclerosis and hypertension
• Respiratory pathology covers lung diseases like pneumonia, asthma, and COPD
• Gastrointestinal pathology includes diseases of the esophagus, stomach, intestines, liver, and pancreas
• Endocrine pathology focuses on hormone-producing gland disorders like the thyroid and adrenal glands
• Genitourinary pathology covers kidney, bladder, and reproductive organ diseases
• Nervous system pathology includes diseases of the brain, spinal cord, and peripheral nerves
• Musculoskeletal pathology focuses on bone, joint, and muscle diseases
• Hematopathology deals with blood/bone marrow diseases, including leukemia and lymphoma

Disease

• It's any deviation from or interruption of normal body structure/function
• It arises from interplay of genetic predispositions, environmental influences, infectious agents, and lifestyle choices
• It manifests as subtle biochemical changes to overt structural/functional abnormalities
• Disease pathogenesis refers to the sequence of events from the initial cause to the disease's manifestations
• Understanding pathogenesis is essential for effective prevention, diagnosis, and treatment

Homeostasis

• The body's ability to maintain a stable internal environment despite external changes
• Achieved through regulatory mechanisms, including feedback loops and hormonal/nervous system control
• Cellular adaptation is the primary mechanism defending against injury
• Maintaining homeostasis is essential for normal cellular function and survival

Cellular Adaptations

• Reversible changes in cell structure/function in response to environmental changes
• Adaptations: hypertrophy, atrophy, hyperplasia, metaplasia, and dysplasia
• Hypertrophy: increased cell size, leading to increased organ size
• Atrophy: decreased cell size, leading to decreased organ size
• Hyperplasia: increased cell number
• Metaplasia: change in cell type
• Dysplasia: disordered cell growth and maturation, a premalignant condition

Cell Injury and Cell Death

• Cell injury occurs when cells are exposed to stress, damaging stimuli, or intrinsic abnormalities exceeding their adaptation capacity
• Cell injury can be reversible or irreversible
• Necrosis is cell death due to irreversible cell injury
• Apoptosis is programmed cell death under normal conditions or in response to stimuli
• Cell injury causes: hypoxia, ischemia, toxins, infections, immunological reactions, genetic defects, and nutritional imbalances

Inflammation

• Protective response to injury, infection, or foreign substances
• Involves vasodilation, increased vascular permeability, and immune cell recruitment
• Acute inflammation: rapid onset, short duration
• Chronic inflammation: prolonged duration, fibrosis, and tissue destruction
• Mediators: cytokines, chemokines, histamine, and prostaglandins

Tissue Repair

• Damaged tissues are restored to normal structure/function after injury/inflammation
• Processes: regeneration and fibrosis
• Regeneration: replacement of damaged cells with same cell type
• Fibrosis: scar tissue formation
• Influencing factors: injury extent, affected tissue type, and individual's health/nutrition

Genetic Disorders

• Caused by abnormalities in genetic material, including gene mutations or chromosome alterations
• Can be inherited or arise spontaneously
• Can affect any organ system, causing a range of signs/symptoms
• Examples: cystic fibrosis, sickle cell anemia, and Down syndrome

Neoplasia

• Abnormal, uncontrolled cell growth, leading to tumor formation
• Tumors can be benign or malignant
• Benign tumors are localized, do not invade or metastasize
• Malignant tumors are aggressive, invade, and can metastasize
• Cancer is a general term for malignant tumors
• Causes: genetic mutations, carcinogen exposure, and viral infections

Immunopathology

• Study of diseases caused by immune system abnormalities
• Immunodeficiency disorders: weakened/absent immune system, making individuals susceptible to infections
• Autoimmune disorders: the immune system attacks the body's own tissues
• Hypersensitivity reactions: the immune system responds inappropriately to harmless substances (allergens)
• Examples: HIV/AIDS, rheumatoid arthritis, and asthma

Infections

• Caused by pathogenic microorganisms like bacteria, viruses, fungi, and parasites
• Can be localized or systemic
• The body defends against infection with physical barriers, the innate immune system, and the adaptive immune system
• Influencing factors: pathogen virulence, host immune status, and treatment availability

Environmental Pathology

• Study of diseases caused by exposure to harmful environmental agents
• Agents include air pollutants, water contaminants, toxins, and radiation
• Exposure can cause respiratory diseases, cancer, and developmental abnormalities
• Examples: mesothelioma (asbestos exposure) and lead poisoning

Nutritional Pathology

• Study of diseases caused by inadequate or excessive nutrient intake
• Malnutrition leads to growth retardation, immune dysfunction, and organ damage
• Obesity increases the risk of diabetes, heart disease, and cancer
• Examples: scurvy (vitamin C deficiency) and rickets (vitamin D deficiency)

Diagnostic Pathology

• Relies on techniques that include:
• Microscopy: Examining tissue samples under a microscope to identify abnormalities
• Molecular diagnostics: Analyzing DNA, RNA, or proteins to diagnose diseases
• Immunohistochemistry: Using antibodies to detect specific proteins in tissue samples
• Flow cytometry: Analyzing cells in suspension to identify and quantify different cell types