General Veterinary Pathology deals about the fundamental processes of diseases of animals that are common to more than one tissue or organ. Study of diseases is an essential component of pathology. Subject in bulleted points and schematic diagram are given for easy understanding and remembrance.
This book deals about the introduction and scope, causes, haemodynamic derangements, degeneration, necrosis, gangrene, cell injury, pigmentation, calcification, photosensitization, growth disturbances, inflammation, healing and immunopathology.
This book can serve as a quick ready reckoner. It will be useful to students of both under graduate and post graduate level as well as researchers, scientists and Veterinarians.
Pathology is a bridging subject between basic anatomy, physiology and biochemistry and clinical subjects of medicine, surgery and obstetrics and gynecology. Pathology provides understanding of the disease processes underlying each disease condition that is applied in diagnosis, prognosis and treatment of diseases. Veterinary Pathology is the subject of terminology. One should learn it and have knowledge of it to understand the subject and in future applications and the terms are later phases of learning. The study of Veterinary Pathology begins with general conditions common to disease processes-systemic and/or special/specific diseases. It is the beginning of learning process in Veterinary Pathology. General Veterinary Pathology deals about the fundamental processes of diseases of animals that are common to more than one tissue or organ. Study of diseases is an essential component of pathology. Subject in bulleted points and schematic flow diagram. This book deals about the introduction and scope, causes, haemodynamic derangements, degeneration, necrosis, gangrene, cell injury, pigmentation, calcification, photosensitization, growth disturbances, inflammation, healing and immunopathology.
Introduction and Scope of Veterinary Pathology • The aim of study of veterinary and animal sciences is to produce a competent veterinarians. The veterinarians are involved in the diagnosis of diseases of livestock, poultry, wild animals and captive animal species. The study of diseases is essential component of pathology. • Pathology (Gr. Path(o) - Disease; logos: science, treatise, sum of knowledge in a particular subject) • Pathology is the subject linking basic subjects of anatomy, histology, embryology, physiology and biochemistry to clinical subjects of medicine, surgery and obstetrics and gynaecology. • Pathology is a subject of terminology. • It is important to familiarize with different terminologies used in describing events/ disease conditions. The definition of each terminology is the gateway to understanding the particular disease process.
Definition • Aetiology is defined as study of causation of disease. Classification of Causes • There are several agents or factors that can produce diseases in animals and can originate from within the body (intrinsic) or outside the body. (extrinsic). Causes are classified into two categories 1. Predisposing causes (Intrinsic/Endogenous factors) 2. Definitive causes (Extrinsic/Exogenous factors) Predisposing Causes • Make the animal susceptible to definitive causes.
Hyperaemia and Congestion Definition Hyperaemia is increased volume of blood in affected tissue or part. Hyperaemia (Active Hyperaemia) Occurs in arterioles or arteries Increased blood flow in capillaries Congestion (Passive Hyperaemia) Occurs due to impaired venous drainage Stasis of blood in veins classification of hyperaemia
Amyloid • Amyloid (G. Amylon; Amyl(o) - STARCH) means starch-like. • Amyloid is a pathologic glycoprotein deposited in the extracellular spaces and forms fibrils on polymerization. Histological characteristics • Amyloid is specially stained with Congo Red. • Under polarized light, green birefringence is noticed because of alignment of fibrils. • Amyloid fibrils are 7.5 to 10 nm in diameter, rigid, non-branching hollow-cored tubules of unknown length. • β-pleated sheet configuration is seen in X-ray diffraction. • The P-component which is a glycosa-amino-glycan (GAG) facilitates polymerization of amyloid.
Causes and Mechanism I. External Causes/ Extrinsic Causes 1. Physical Causes 1. Trauma by cutting objects and blunt objects 2. Electrical – Lightning, high frequency current 3. Heat -Sun stroke, burns, fever 4. Cold Local tissue freezing, cold shock 5. Radiation UV / X /cosmic radiations 6. Pressure Increased or decreased pressure
Definition Gangrene is a necrotic area invaded by saprophytic organisms leading to putrefaction. Types of Gangrene There are three types of gangrene 1. Dry gangrene 2. Moist gangrene 3. Gas gangrene 1. Dry Gangrene Dry gangrene represents an area of coagulation necrosis resulting from infarction followed by mummification. The extremities of the body like tail, ears, legs and udder are affected.
Colouring Agents Colouring agents are called as pigments. Tissues may be discoloured (e.g. Jaundice, tattoo) or excessively coloured (e.g. Melanosis) in diseases. Origin • External or exogenous pigments • Internal or endogenous pigments Exogenous Pigmentations In exogenous pigmentations colouring substances can enter the body by three different routes. • Respiratory route by inhalation • Alimentary route by ingestion • Cutaneous route by injection
Calcification • Calcification is abnormal deposition of calcium salts in tissue other than bone. • Calcium is normally present in blood and deposited in bones. • Calcium if deposited in an abnormal tissue with normal or abnormal blood calcium level is considered as pathological condition. Pathological calcifications are 1. Metatstatic calcification 2. Dystrophic calcification
Photosensitization is activation of photodynamic chemicals on the skin by long wave length UV or occasionally by visible light • Necrosis and edema are produced in the exposed areas of skin of animals. • The cellular damage by photosensitization is due to release of reactive oxygen species leading to mast cell degranulation and production of chemical mediators of inflammation. Factors Necessary for Photosensitization in Animals • Oxygen • Sunlight • Photodynamic chemicals • Skin devoid of hair or wool and lacking pigments
The Disturbances of Growth • The disturbances in growth cover a broader spectrum of changes from no growth (Aplasia) to uncontrolled growth (Neoplasia). • While uncontrolled growth (neoplasm) is not dealt here, the other forms of growth disturbances are considered in this chapter. Cellular Adaptation to Injury • The cells respond to altered physiological or pathological stimuli by adapting themselves. • These changes are reflected as atrophy, hyperplasia, hypertrophy, metaplasia and dysplasia besides aplasia and hypoplasia.
Definitions Reaction of vascularised living tissue to local injury caused by various agents like microbes or necrotic tissue Inflammation − Reaction of blood vessels − Accumulation of fluid and leucocytes in extra vascular tissues Inflammation and repair always go hand in hand Beneficial effects of Inflammation To destroy / dilute the injurious agent (microbes; toxins ) and to protect cell from injury (necrosis) Harmful Effects of Inflammation
Tissue – Proliferating Potential of Cell Types 1. Labile Cells • Continuously dividing cells • e.g. epidermis, epithelial cells, bone marrow cells 2. Stable Cells - Quiescent cells • Undergoes division occasionally • Liver, kidney pancreas, fibroblasts, • Endothelial cells 3. Permanent Cells - Non–dividing cells: Neurons, muscle cells (cardiac, skeletal)
Definition IDD (immunodeficiency diseases) occur when there is a failure of the immune system to protect the host from infectious organisms or the development of cancer. IDD are disorders of immune system that result in immunological deficiency. Immunodeficiency could be from defects in i. B and T- lymphocytes ii. Granulocytes iii. Complement
Definition Hypersensitivity is an altered reaction to a specific antigen that results in pathologic reactions upon the exposure of a sensitized host to that of specific antigen. Explanation Hypersensitivity reactions are inappropriate or misdirected responses to a specific antigen that result in harmful reactions upon exposure of a sensitized host to that specific antigen. Affected animals require a sensitization phase in which the animal must have had either a previous exposure or a prolonged exposure to the antigen so that it can develop an immune response to the inciting antigen. The harmful effects resulting from hypersensitivity reactions occur in the effector phase and are most commonly manifested through inflammation or cell lysis.
Definition The animal reacts to its own tissue (endogenous antigen) to incite production of antibodies or sensitized lymphocytes. There is breakage of tolerance to the self-proteins. • Autoimmune diseases are prevented by elimination of sensitized T and B lymphocytes by the process of apoptosis in the thymus and bone marrow during development (Central tolerance; clonal deletion), in the peripheral tissues (Peripheral tolerance) and clonal anergy (Clonal avoidance) by defective presentation of cells. • The tolerance of CD4+ TH cells is critical in preventing autoimmunity. • Two major autoimmune diseases are thyroiditis and haemolytic anemia. Other conditions are rare in animals
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