Introduction to Pathology

Course Goals

• The course aims to provide students with essential medical knowledge and a broad understanding of human diseases.
• It will emphasizes "the language of disease" as a necessary foundation for self-education and lifelong learning.

Course Objectives

• To define the keywords and phrases used in the lectures.
• To understand the pathogenesis and epidemiology of diseases.
• To describe and recognize the major cell and tissue alterations associated with diseases.
• To describe how pathological analysis contributes to disease surveillance and the evaluation of therapeutics.

What is Pathology?

• Pathology is the study of the structural, biochemical, and functional changes in cells, tissues, and organs that underlie disease.
• Pathology answers the "whys and wherefores" of diseases through molecular, microbiologic, immunologic, and morphologic techniques.
• Pathology serves as the base and scientific foundation for all of medicine.
• Pathos means suffering and logos means study.

Etiology and Pathogenesis

• Etiology (cause) is grouped into two categories:
• Genetic: inherited mutations and disease-associated gene variants.
• Acquired: infectious, nutritional, chemical, and physical factors.
• Pathogenesis is the sequence of cellular, biochemical, and molecular events that follow the exposure of cells or tissues to an injurious agent.
• Morphologic changes are structural alterations in cells or tissues that are either characteristic of a disease or diagnostic of an etiologic process.

History of Pathology

• Rudolf Virchow (1821-1902), a German physician, is considered the father of modern pathology.
• Virchow is known for the cell theory, cellular pathology, biogenesis, and Virchow's triad.

Branches of Pathology

• Histopathology involves the microscopic examination of a tissue or surgical specimen to diagnose a disease.
• Cytopathology involves the microscopic examination of a single cell to diagnose a disease.
• Haematopathology studies diseases and disorders found in blood cells and organs or tissues involved in hematopoiesis.
• Forensic pathology applies pathology to legal purposes.
• Molecular pathology focuses on studying and diagnosing diseases through the examination of molecules within organs, tissues, or bodily fluids; it also encompasses genetic approaches to disease diagnosis and classification.
• Chemical pathology (clinical biochemistry) involves biochemical investigations of bodily fluids (such as blood, urine, and cerebrospinal fluid) for diagnosing diseases.
• General pathology focuses on the causes, mechanisms, and characteristics of major disease categories and is the basic reaction of cells and tissues in response to abnormal stimuli governing all diseases.
• Systemic pathology focuses on specific diseases occurring within particular organ systems.

Specimens for Diagnosis

• Biopsy involves taking a sample of tissue from the body to examine it more closely and determine the presence or extent of a disease.
• Resection specimen is a therapeutic surgical removal of an entire diseased area or organ (and occasionally multiple organs) in which the diagnosis is already known or strongly suspected.
• Exfoliative cytology: cells are scraped or brushed off from an epithelial surface for diagnosis.
• Fluid cytology: cells withdrawn with the fluid in which they are suspended for examination (e.g. CSF, pleural fluid, ascitic fluid).
• Washings involve flushing cells out of an organ using an irrigating fluid for examination and diagnosis, such as a bronchial wash.
• Fine-needle aspiration cytology is a diagnostic procedure used to investigate lumps or masses, involving the insertion of a thin, hollow needle into the mass to sample cells.
• PAP Smear: A Papanicolaou test procedure to gently remove cells from the cervix with a small brush or spatula so they can be checked under a microscope for precancerous or cancerous processes.

Autopsy

• An autopsy (post-mortem examination, necropsy, or autopsia cadaverum) is a surgical procedure consisting of a thorough examination of a corpse by dissection to determine the cause, mode, and manner of death.
• It is used to evaluate any disease or injury that may be present for research or educational purposes.
• The term "necropsy"is generally reserved for animals.

Tools Used in Diagnostic Pathology

• Light microscope: uses visible light and a system of lenses to generate magnified images of objects.
• Electron microscope: uses a beam of accelerated electrons as a source of illumination and is used in the study of disorders atorganelle level; also used to demonstrate viruses in tissue samples.
• Immunohistochemistry: is used to identify antigens (proteins) in cells of a tissue section by exploiting the binding of antibodies to antigens in biological tissues.
• Flow cytometry: Measures physical and chemical characteristics of a population of cells/particles flowing single-file through laser beam, is commonly used to diagnose blood cancers

Tissue Processing Techniques: Histopathology

• Specimen receipt: Surgical biopsy specimens must be placed in 10% Formalin as soon as possible.
• Gross examination of the specimen.
• Tissue fixation: Blocks will be put in fixative (10% Formalin)

Continued Tissue Processing

• Dehydration: Removes water from the tissue using a dehydrant, like ethyl alcohol.
• Clearing: Following dehydration, the remaining alcohol in the tissue is cleared using Xylene, and completely cleared tissue looks almost transparent.
• Infiltration: Removes the clearing agent.
• Paraffin wax is the most widely used an infiltrant and make the tissue harder.
• Embedding: Formation of a "block" making it ready for microtomy.

Preparation for Viewing Tissues

• Tissue sectioning involves cutting tissue into thin slices using a microtome.
• Slide staining use of Hematoxylin and eosin (H & E) is most common.
• Cover slipping (mounting) protects tissue from scratches and provides better optical quality under microscope.

Frozen Section Procedure

• This pathological laboratory procedure to perform rapid microscopic analysis of specimen, It is used most often in oncological surgery
• Used to assess surgical margin positivity/negativity in malignant tumors during surgery.
• A surgical specimen is placed on metal tissue disc, secured in chuck, and rapidly frozen to about -20 to -30 °C.
• Specimens are embedded in a gel-like medium called OCT (polyethylene glycol and polyvinyl alcohol)
• Which is then cut while frozen using microtome portion of cryosta
• A cut section will picked up on glass slide and stained for examination