Introduction to pathology. Methods of study of the pathological anatomy. Experimental methods in pathological physiology.
Reading File
Finding Sources
Finding Sources
Searching PubMed
pathology education AND experimental pathology
Searching the Web
pathological anatomy methods autopsy biopsy cytology experimental pathology physiology
Reading File
Finding Sources
Finding Sources
Finding Sources
Searching the Web
site:ncbi.nlm.nih.gov/books pathology autopsy biopsy cytology pathology methods experimental models
1. Introduction to Pathology
Pathology is the scientific study of disease. It explains:
- Etiology: cause of disease
- Pathogenesis: sequence of events by which the cause produces disease
- Morphologic changes: structural abnormalities in cells, tissues, and organs
- Functional consequences: disturbances of organ function and their clinical manifestations
Pathology forms the bridge between the basic sciences and clinical medicine. A disease may be understood as:
Cause → mechanism of injury → structural change → functional disturbance → symptoms and signs.
Main divisions
| Division | Main focus |
|---|---|
| General pathology | Basic reactions of cells and tissues to injury, such as degeneration, cell death, inflammation, repair, circulatory disturbances, and tumors |
| Systemic or special pathology | Diseases as they occur in individual organs or organ systems |
| Pathological anatomy | Structural changes caused by disease |
| Pathological physiology | Functional disturbances and mechanisms of disease |
| Clinical pathology | Laboratory examination of blood, urine, body fluids, and other specimens for diagnosis and management |
| Forensic pathology | Application of pathology to legal investigation, especially determination of cause and manner of death |
2. Pathological Anatomy
Pathological anatomy studies the macroscopic, microscopic, ultrastructural, molecular, and chemical changes in organs and tissues produced by disease.
It answers questions such as:
- What organ or tissue is affected?
- What visible and microscopic changes are present?
- How extensive is the lesion?
- Is the process inflammatory, degenerative, neoplastic, infectious, or vascular?
- Can the lesion explain the patient’s illness or death?
Structural pathology is interpreted together with clinical data, imaging, laboratory results, and functional studies. Morphological findings alone should not be treated as the complete diagnosis.
3. Methods of Study in Pathological Anatomy
A. Autopsy or postmortem examination
An autopsy is the systematic examination of a body after death.
Types
- Clinical or hospital autopsy
- Performed to determine disease processes, assess the cause of death, and correlate clinical and pathological diagnoses.
- Medicolegal or forensic autopsy
- Performed when death is sudden, suspicious, violent, unexplained, or legally significant.
- Academic or teaching autopsy
- Used for medical education and research, subject to legal and ethical requirements.
Main steps
- Review of clinical history and available investigations
- External examination
- Internal examination of body cavities and organs
- Measurement and weighing of organs
- Gross examination of lesions
- Tissue sampling for microscopy, microbiology, toxicology, and molecular tests
- Histopathological examination
- Preparation of final pathological diagnosis and cause-of-death statement
Value
- Establishes or confirms the cause of death
- Detects unsuspected disease
- Assesses complications of treatment or surgery
- Helps audit clinical diagnosis and improve medical practice
- Provides material for teaching and research
Limitations
- Postmortem decomposition can alter tissues.
- Findings must be interpreted in clinical context.
- Consent, legal authorization, dignity, infection-control procedures, and confidentiality are essential.
B. Surgical pathology
Surgical pathology examines tissue removed during surgery or obtained by biopsy.
It is used to diagnose and classify disease, especially tumors, inflammatory conditions, infections, and organ injury.
Specimens include
- Excised organ or tumor
- Resected bowel, stomach, lung, uterus, lymph node, etc.
- Curettings
- Endoscopic biopsies
- Skin biopsies
- Needle-core biopsies
Important components
- Gross examination
- Size, shape, color, consistency, margins, necrosis, hemorrhage, relation to adjacent structures.
- Tissue processing
- Fixation, usually in formalin.
- Embedding in paraffin.
- Thin sectioning with a microtome.
- Staining.
- Microscopic examination
- Assessment of cells, tissue architecture, inflammatory response, invasion, necrosis, and other features.
- Reporting
- Diagnostic category, tumor type and grade, margin status, stage-related features, and ancillary-test results.
C. Biopsy
A biopsy is removal of tissue from a living person for pathological examination. It is a central method of antemortem diagnosis.
| Type | Description |
|---|---|
| Excisional biopsy | Entire lesion is removed |
| Incisional biopsy | Representative part of a large lesion is removed |
| Needle-core biopsy | A core of tissue is obtained by a hollow needle |
| Fine-needle aspiration | Cells and small tissue fragments are aspirated for cytology |
| Endoscopic biopsy | Sample obtained through an endoscope |
| Punch biopsy | Cylindrical skin sample, commonly used in dermatology |
| Trephine biopsy | Core sample, commonly from bone marrow |
Advantages
- Provides a diagnosis during life
- Guides treatment planning
- May establish tumor type, grade, receptor status, or molecular alteration
- Can help assess response to therapy
Limitations
- Sampling error: a small sample may not represent the whole lesion.
- Crush artifact, necrosis, poor fixation, and inadequate tissue may limit diagnosis.
- Some conditions require clinicoradiological correlation or repeat sampling.
D. Cytopathology
Cytopathology studies isolated cells or small groups of cells rather than intact tissue architecture.
Sources
- Cervical smear
- Fine-needle aspiration of thyroid, lymph node, breast, or other masses
- Sputum
- Urine
- Pleural, peritoneal, or pericardial fluid
- Bronchial washings or brushings
- Cerebrospinal fluid
Examples
- Pap smear: screening for cervical precancer and cancer
- Fine-needle aspiration cytology: rapid assessment of a lump or mass
- Fluid cytology: detection of malignant cells or inflammation in body fluids
Strengths
- Minimally invasive
- Rapid and relatively inexpensive
- Useful in screening and initial assessment
Limitation
Because cellular architecture is often limited, a tissue biopsy may be needed for final classification.
E. Histopathology and routine staining
Histopathology examines stained tissue sections under a microscope.
- The routine stain is hematoxylin and eosin (H&E).
- Hematoxylin stains nuclei blue-purple.
- Eosin stains cytoplasm and extracellular proteins pink.
Special stains may demonstrate particular substances or organisms:
| Stain / technique | Main use |
|---|---|
| Periodic acid-Schiff (PAS) | Glycogen, basement membranes, fungi |
| Ziehl-Neelsen | Acid-fast bacilli |
| Gram stain | Bacteria |
| Congo red | Amyloid |
| Masson trichrome | Collagen and fibrosis |
| Reticulin stain | Reticulin framework |
| Prussian blue | Iron / hemosiderin |
F. Frozen-section examination
A frozen section is a rapid intraoperative pathological examination.
Procedure: fresh tissue is frozen, cut in a cryostat, stained quickly, and examined microscopically.
Uses
- Determine whether a lesion is benign or malignant
- Assess surgical resection margins
- Confirm presence of tissue, such as parathyroid tissue
- Decide whether further surgery is necessary
Limitation
It is faster but generally less detailed than permanent paraffin sections. The final diagnosis should rely on permanent sections and ancillary tests when required.
G. Immunohistochemistry, molecular pathology, and electron microscopy
Immunohistochemistry (IHC)
IHC uses antibodies to detect specific antigens in cells and tissues.
Applications:
- Identify cell lineage and tumor origin
- Distinguish similar-looking tumors
- Detect hormone receptors and predictive biomarkers
- Detect certain infectious agents
Molecular pathology
Uses DNA, RNA, and protein-based methods, including:
- Polymerase chain reaction (PCR)
- Fluorescence in situ hybridization (FISH)
- Sequencing
- Next-generation sequencing
- Gene-expression testing
Applications include diagnosing inherited disorders, detecting infections, identifying mutations in tumors, and selecting targeted treatment.
Electron microscopy
Examines ultrastructure at very high magnification. It has selected roles in renal pathology, muscle pathology, ciliary disorders, storage diseases, and research.
4. Experimental Methods in Pathological Physiology
Pathological physiology studies how disease alters the functions of cells, organs, and whole-body systems. Its experimental approach aims to reproduce, observe, and explain disease mechanisms.
Objectives
Experimental pathological physiology is used to:
- Identify causes and mechanisms of disease.
- Reproduce individual components of disease under controlled conditions.
- Study the sequence of functional changes.
- Test preventive and therapeutic interventions.
- Relate structural lesions to physiological dysfunction.
A model should be viewed as a representation of part of a disease mechanism, not necessarily an exact copy of the human disease. Modern disease models, including genetically modified animals, can identify causal roles of particular cells, pathways, and molecules, but animal models do not fully reproduce human disease.
A. In vivo animal experiments
These are studies performed in living animals.
Types of animal models
| Model type | Example |
|---|---|
| Spontaneous models | Naturally occurring hypertension, diabetes, cancer, or autoimmune disease in certain animal strains |
| Induced models | Chemical, physical, surgical, dietary, infectious, or immunologic induction of disease |
| Genetic models | Transgenic, knockout, knock-in, or gene-edited animals |
| Xenograft models | Implantation of human cells or tumors into immunodeficient animals |
| Humanized models | Animals modified to contain components of the human immune system or human genes |
Examples of induction
- Ischemia by vascular ligation or occlusion
- Hypertension by renal artery constriction, salt loading, or hormonal interventions
- Diabetes by beta-cell toxins or genetic manipulation
- Inflammation by irritants, immune stimulation, or microbial products
- Cancer by carcinogens, radiation, oncogenic viruses, or transplanted tumor cells
- Organ fibrosis by chronic toxic, inflammatory, or obstructive injury
Measurements in vivo
- Blood pressure and electrocardiography
- Respiratory function
- Temperature, body weight, food intake, survival
- Blood chemistry and hormone levels
- Organ function tests
- Imaging
- Behavioral and neurological testing
- Histology and molecular analysis after tissue collection
B. Ex vivo isolated-organ and tissue studies
An organ or tissue is removed from the body and studied under controlled laboratory conditions.
Examples:
- Isolated perfused heart
- Isolated blood vessel ring to study vascular reactivity
- Isolated intestine to study motility and secretion
- Isolated kidney perfusion
- Skeletal muscle or nerve-muscle preparations
Advantages
- Precise control over oxygenation, pressure, temperature, nutrients, and drugs
- Direct measurement of organ-specific effects
- Fewer confounding influences from other systems
Limitations
- Neural, hormonal, immune, and whole-body compensatory responses may be absent.
C. In vitro cell and tissue culture
In vitro methods study cells, tissues, or microorganisms outside the organism.
Examples:
- Primary cell cultures
- Immortalized cell lines
- Co-culture systems
- Three-dimensional cultures
- Organoids
- Organ-on-chip systems
Applications:
- Cell injury and death
- Inflammation and cytokine signaling
- Infection
- Drug toxicity and drug screening
- Tumor growth and invasion
- Fibrosis
- Genetic and molecular mechanisms
Advantages
- High experimental control
- Reduced animal use
- Ability to alter a single variable
- Suitable for genetic manipulation and molecular analysis
Limitations
Cultured cells may not reproduce the normal tissue environment, blood supply, immune system, or systemic compensation.
D. Functional and analytical techniques
Experimental pathophysiology combines disease models with measurements such as:
- Hematology and clinical biochemistry
- Blood-gas analysis and acid-base assessment
- Enzyme assays
- Hormone and cytokine assays
- Flow cytometry
- Microscopy and histomorphometry
- IHC and immunofluorescence
- PCR, sequencing, proteomics, and metabolomics
- Imaging, including ultrasound, CT, MRI, PET, and optical imaging
- Electrophysiology, such as ECG, EEG, EMG, and patch-clamp recording
5. Ethical Principles in Experimental Pathology
Animal studies must follow ethical approval and animal-welfare legislation. The key principle is the 3Rs:
- Replacement: use non-animal alternatives whenever possible.
- Reduction: use the minimum number of animals needed for valid results.
- Refinement: minimize pain, distress, and invasive procedures.
Good experimental design also requires:
- A clear hypothesis
- Appropriate controls
- Randomization and blinding where possible
- Defined inclusion and exclusion criteria
- Transparent reporting
- Recognition that findings from cell culture or animals may not directly translate to humans
Key distinction
| Pathological anatomy | Pathological physiology |
|---|---|
| Studies structural changes in disease | Studies functional changes in disease |
| Asks, “What has changed in the tissue or organ?” | Asks, “How has function changed and why?” |
| Uses autopsy, biopsy, cytology, histology, IHC, molecular tests | Uses experimental models, functional testing, organ studies, and cellular experiments |
| Example: myocardial infarction causes coagulative necrosis of cardiac muscle | Example: infarction decreases contractility and cardiac output, causing shock or heart failure |
Summary: Pathological anatomy establishes the structural basis of disease, whereas pathological physiology explains the disturbed function and mechanisms. Together they connect cause, tissue injury, organ dysfunction, and clinical disease.
This is a shared conversation. Sign in to Orris to start your own chat.