1. INTRODUCTION TO GENERAL VETERINARY PATHOLOGY.pdf

08/09/2024 GENERAL VETERINARY PATHOLOGY: An Introduction CF Omar Bernardino D. Domingo, DVM, MSc Assistant Professor II...

08/09/2024 GENERAL VETERINARY PATHOLOGY: An Introduction CF Omar Bernardino D. Domingo, DVM, MSc Assistant Professor II DMMMSU-CVM Health and Disease Health is the condition in which the individual is in complete harmony with its environment! surroundings. Disease is a change in that condition, as a result the individual suffers from discomfort. In other words, disease is a condition in which an individual shows a structural, functional, or chemical deviation from the normal. At times it is difficult to determine if an individual is in health or disease. The animal could be clinically healthy, but pathologically diseased. 1  08/09/2024 For example, one kidney may be absent. The remaining kidney may become twice its normal size, since it assumes the function of the missing kidney. This change is called compensatory hypertrophy, and if it comes about gradually, the individual remains clinically healthy and continues to lead a normal life. But, pathologically, he is in disease, because absence of a kidney is a structural deviation from the normal. Thus, the pathologist’s concept of a disease is not necessarily the same as that of a clinician. Defining Pathology Pathology is the study of disease. (G. pathos = suffering or disease + logos = study). Disease is that condition in which the individual suffers from discomfort (L. dis = not + ease, i.e., not at ease). Just as anatomy is the study of the structure and physiology its functions, pathology is the study of structure and function of the body in disease. 2  08/09/2024 Pathology deals with the structural and functional changes in cells, tissues, and organs that underlie disease. It is a discipline that bridges basic science and clinical practice. To understand the structural and functional changes, pathologists use modern microbiological, immunological, and molecular techniques. Pathology is therefore central to an understanding of disease by explaining how altered structures produce lesions and disordered functions symptoms. Thus, pathology occupies a pivotal position in the study of veterinary medicine. The object of pathology is to acquaint the student with the changes occurring in tissues as the result of disease. By studying pathology the student learns to apply the knowledge of basic subjects, and as one progresses to junior and senior years, one has a better understanding of the changes that take place within an animal as the result of disease. Thus, pathology serves as a bridge between the basic subjects of anatomy, physiology, and biochemistry on the one hand, and medical, surgical, and gynecological treatment on the other. In other words, pathology is that correlating study by which the pre- pathology courses are coordinated so that a better understanding of clinical subjects is possible. 3  08/09/2024 The Scope of Pathology Earlier, pathology was mostly confined to the study of morphological changes, both gross and microscopic. With advances in knowledge, immunological and molecular mechanisms that underlie the morphologica1changes became an integral part of modem pathology. Remarkable progress in molecular pathology has now clearly established that disease is produced first at a molecular level and progresses further into the macroscopic, or gross level. Structural Disease at the changes at an molecular level electron Light (Biochemical / microscopical microscopical Gross lesions molecular level lesions lesions) (Ultrastructural lesions) General Pathology V Systemic Pathology Pathology is divided into "General Pathology" and "Systemic or Special Pathology". General pathology is concerned with the basic reactions of cells and tissues to injurious stimuli. The systemic or special pathology is the application of these basic reactions to the various body systems, or to various specific diseases. 4  08/09/2024 The Five Aspects of a Disease Process Pathology covers five aspects of a disease process: Its cause (etiology), The mechanisms of its development (pathogenesis), The structural changes produced in cells and organs (morphological changes), The functional consequences of the morphological changes (clinical significance), and The result or termination of the disease process 5  08/09/2024 Cause (Etiology) There are two major classes of etiological factors: genetic / intrinsic and acquired / extrinsic (infectious, nutritional, chemical, physical, etc.). However, the concept of "one cause - one disease" is no longer adequate. Genetic factors clearly affect environmentally induced diseases, and the environment may have profound influence on certain genetic diseases. Types of Etiology Causes are of two types: intrinsic or endogenous, and extrinsic or exogenous. The intrinsic (endogenous) causes of disease, also known as the predisposing factors, are those characteristics over which an individual has no control and which determine the type of disease present. The extrinsic (exogenous) causes of disease are those environmental factors (physical, chemical, thermal, infectious, immunological, nutritional) that are capable of producing disease in the individual. 6  08/09/2024 Intrinsic Causes Genus Breed Strain Age Sex Color Genus: Examples: Swine fever is a disease of the pig and no other animals are infected with it. Canine distemper is primarily a disease of the dog. It does not affect the horse, cow, sheep, or pig. Breed: Dairy cattle are much more susceptible to diseases than beef cattle. Within the dairy cattle, certain breeds are less resistant to some diseases than others. The same is applicable with certain breeds of dogs. For example, brain tumours are common in the bulldog breeds. The boxer dog has a very high incidence of brain tumours than other breeds. Strain: Certain strains of animals possess unusual resistance to certain diseases. For example, strains of chickens that have unusual resistance to leukosis can be produced, in contrast to other strains which have a very high mortality rate from this disease. Other examples include hernias in pigs, and calves with hydrocephalus (accumulation of fluid in the ventricles of brain). These problems are observed with greater frequency in certain family of animals than others. 7  08/09/2024 Age: Certain diseases are found in a definite age group. Tumours are commonly observed in older animals. Likewise, strangles is a disease of young horses. Caecal coccidiosis in the chicken is a disease of young birds. Sex: Reproductive diseases are more common in the female than in the male. Certain diseases (metritis, mastitis, milk fever) are confined to the female. Nephritis in the dog is 2 to 3 times more common in the male than in the female. In cattle, nephritis is more common in the female. Colour: Cancer melanosarcomas are very common in grey and white horses, but very rare in brown or black horses. Animals with non- pigmented skin are much more susceptible to photodynamic diseases. If pigment is present in the skin, it protects the animal by preventing the sunlight from penetrating the skin, thus inhibiting the chemical reaction Pathogenesis Pathogenesis is the progressive development of a disease process from the time it is initiated to its conclusion, in recovery or death. In other words, pathogenesis refers to the sequence of events in the response of the cells or tissues to the causal agent, from the initial stimulus to the ultimate expression of the disease. 8  08/09/2024 Structural and functional changes These are the morphological and associated functional alterations in cells or tissues. Lesion is the macroscopic or microscopic alteration occurring in the tissue as the result of injury. Example, fracture in a bone is a lesion. Pathognomonic lesion is an alteration that indicates without doubt the cause of a particular disease. For example, Negri body in the cells of the hippocampus and cerebellum in rabies. Disturbance in function may show itself as symptom of disease. Thus, symptom is a clinical sign (fever, swelling, diarrhea, vomiting, lameness, etc.) manifested by the individual as the result of tissue changes. 9  08/09/2024 Clinical significance The structural and functional changes influence normal functions and determine the clinical features (symptoms and signs), course, and prognosis of disease. Clinical pathology involves use of laboratory methods by clinicians to help them in arriving at a diagnosis. It includes the examination of blood, urine, faeces, exudates, skin scrapings, and biopsy material. Clinical pathology is so named because some of the work, especially the collection of material, is done at the bedside of patient (G. clinics, klinike = bed). Diagnosis is the art or act of identifying a disease from its signs and symptoms, and also through various laboratory tests. In other words, diagnosis is to know or recognize disease states through clinical signs (G. dia = through + gnos = to know). 10  08/09/2024 Prognosis is the prospect of recovery as expected from the usual cause of disease, or peculiarities of the case. That is, forecast about the likely course and outcome of a disease. In other words, prognosis is a knowing beforehand (L. & G. pro = before + gnos = to know), or foreknowledge of the chances of recovery. Result or termination It occurs in three ways: recovery, death, and invalidism. If the damage produced by the disease is not much and is repaired, the individual recovers. If body defences are overcome and the tissue damage is great, then life cannot be maintained and individual dies. If, on the other hand, the body is not able to completely repair and the extent of injury is not so great as to kill the animal, invalidism occurs. 11  08/09/2024 Some Definitions to Remember Macroscopic or gross pathology is examination of tissue without the help of a microscope. Microscopic pathology or histopathology is examination of tissue with the help of a microscope, and involves the use of stained tissue sections. Chemical pathology is the study of chemical alterations of the body fluids and tissue that result from disease. Postmortem examination is examination of an animal after death to establish a disease, that is, cause of its death. Postmortem examination of animals and birds is called necropsy. The term autopsy is used for the postmortem examination of humans. Morbid changes are alterations found in tissues at necropsy as a result of disease. Biopsy is examination of tissue removed from the living (G. bios=life) animal to determine the cause of disease. Biopsy is normally performed in a suspected cancer. Syndrome: Syndrome (G. syn = together + drome = to run) literally means' a running together'. Thus, syndrome refers to a group of symptoms that occur together and characterize a particular abnormality, that is, they are characteristic of a certain disease. 12