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Pathology is the study and diagnosis of disease through examination of organs, tissues, bodily fluids, and whole bodies (autopsies). Or The scientific study of diseases. Purpose Includes knowledge and understanding of structural, functional, genetic and biochemical changes in disease. Ultimate goal is to identify causes of disease to enable prevention of disease. Gross or macroscopic pathology The study of the alterations and organisation of cells, tissues and organs which are associated with disease. Histopathology The investigation and diagnosis of disease from the examination of tissues at the microscopic level. Cytopathology The study of cells which may be abnormal, Investigates and diagnoses disease from the examination of isolated cells. Chemical Pathology / Clinical Pathology Studying disease at the molecular level. The study of biochemical alterations associated with disease. Often evident in body fluids eg. blood, plasma, urine. Cross-sectional analysis of the cause and mechanisms of the disease, and the effect of the disease upon organs and systems of the body. Forensic pathology Branch of pathology concerned with the application of medical knowledge to legal problems eg cause of death, crime. interaction between law and medicine General Pathology Current understanding of the causation, mechanisms and characteristics of the major categories of disease. Systematic Pathology Current knowledge of specific diseases as they affect individual organs or systems Autopsy Necropsy, Postmortem examination Disease is a condition in which some structural, functional, biochemical or genetic abnormailty of the body causes a loss of normal health (dis-ease) Pathology also encompasses the related scientific study of disease processes, called general pathology. Medical pathology is divided into two main branches, anatomical pathology and clinical pathology. General pathology, also called investigative pathology, experimental pathology, or theoretical pathology, is a broad and complex scientific field which seeks to understand the mechanisms of injury to cells and tissues, as well as the body's means of responding to and repairing injury.

Areas of study include cellular adaptation to injury, necrosis, inflammation, wound healing, and neoplasia. It forms the foundation of pathology, the application of this knowledge to diagnose diseases in humans and animals. The term ''general pathology'' is also used to describe the practice of both anatomical and clinical pathology.

ISCHEMIA Definition: Ischemia occurs when living tissue is deprived of oxygen. While any decrease in the oxygen supply to tissue can be called ischemia, in reality there is a threshold that must be crossed before true ischemia occurs. This is a result of biological processes that give living tissue a certain amount of reserve capacity. This reserve capacity differs among tissue types. For example, the arm muscles have a higher reserve capacity than the heart. Tissue experiencing ischemia is said to be ischemic. In the human body, oxygen supply to tissue is accomplished primarily by supplying the tissue with a continuous flow of oxygenated blood. Anything which interrupts or decreases the flow of blood thus causes ischemia. In this sense, depriving tissue of adequate blood flow is the same as depriving tissue of oxygen. Thus, ischemia in living systems is often used to describe situations of impaired blood flow. Ischemia causes rapid damage to tissue of all types, though some tissues are more sensitive than others. Ischemia in the brain causes stroke, while ischemia in the heart leads to a heart attack (also known as a myocardial infarction). High blood pressure makes the tissues of the circulatory system more vulnerable to ischemia (by reducing their reserve capacity) while at the same time increasing the risk that ischemia may occur (by increasing their need for oxygen).

OR Ischemia is any reduction in blood flow resulting in decreased oxygen and nutrient supplies to a tissue. Ischemia may be reversible, in which case the affected tissue will recover if blood flow is restored, or it may be irreversible, resulting in tissue death. Ischemia can also be acute, due to a sudden reduction in blood flow, or chronic, due to slowly decreasing blood flow. Ischemia can occur anywhere in the body. Heart attacks and strokes can both result from ischemia. Although less well known, ischemia can also affect the intestines, resulting in abdominal pain, bloody stool, and even intestinal rupture or gangrene. Peripheral ischemia can lead to loss of fingers or toes. Pain is a common symptom associated with ischemia, but does not always occur. Brain ischemia can cause cognitive, sensory or motor problems. Heart attacks and intestinal ischemia can cause nausea and vomiting. Peripheral ischemia can cause pallor, bluish discoloration, or darkening of the skin of the nose, ears, fingers, toes, or other surface areas. Risk factors for ischemia include vascular diseases, such as arteriosclerosis (hardening of the arteries), trauma, high blood pressure, heart problems, diabetes (chronic disease that affects your body’s ability to use sugar for energy), tobacco use, high cholesterol, physical inactivity, stress, family history of ischemic diseases, and increasing age. Treatment of ischemia depends on the cause, but generally is aimed at restoring blood flow and reducing further tissue injury and death. Because ischemia can lead to permanent injury, acute ischemia is always a medical emergency for chest pain or pressure; difficulty breathing; severe headache; abdominal pain; sudden difficulty with memory, thinking, talking, comprehension, writing or reading; confusion or loss of consciousness for even a brief moment; numbness; paralysis or inability to move a body part; loss of vision or changes in vision; impaired balance and coordination; vomiting blood, rectal bleeding or bloody stool; profuse sweating; unusual anxiety; or a cold, blue or darkened extremity or patch of skin.

HYPOXIA Hypoxia is a pathological condition in which the body as a whole (generalized hypoxia) or a region of the body (tissue hypoxia) is deprived of adequate oxygen supply. Variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise. A mismatch between oxygen supply and its demand at the cellular level may result in a hypoxic condition. Hypoxia in which there is complete deprivation of oxygen supply is referred to as anoxia. Hypoxia differs from hypoxemia. In the latter, the oxygen concentration within the arterial blood is abnormally low. . It is possible to experience hypoxia and have a low oxygen content (e.g., due to anemia) but maintain high oxygen partial pressure (pO2). Incorrect use of these terms can lead to confusion, especially as hypoxemia is among the causes of hypoxia (in hypoxemic hypoxia). Generalized hypoxia occurs in healthy people when they ascend to high altitude, where it causes altitude sickness leading to potentially fatal complications: high altitude pulmonary edema (HAPE) and high altitude cerebral edema (HACE). Hypoxia also occurs in healthy individuals when breathing mixtures of gases with a low oxygen content, e.g. while diving underwater especially when using closedcircuit rebreather systems that control the amount of oxygen in the supplied air. A mild and non-damaging intermittent hypoxia is used intentionally during altitude trainings to develop an athletic performance adaptation at both the systemic and cellular level. NECROSIS Necrosis is the morphologic changes that follow cell death in living tissue. A necrotic cell cannot reverse back to normal cell. Changes of necrosis occur due to: (1) Denaturation of proteins and (2)Enzymatic digestion of cell by-Autolysis (Which is the self-digestion of cells after their death. It occurs due to the action of it’s own enzymes like prosteases, lipases, esterases, ribonuclease, deoxyribonuclease mainly derived from lysosomes of the injured cell. These act at low pH.)

-Heterolysis (It is the digestion of cells by enzymes from lysosomes of immigrant leucosytes, during inflammatory reactions. These changes take hours, e.g. 4 to 12 hours in myocardial necrosis.) Types of necrosis Coagulative necrosis develops when denaturation is the primary pattern, and liquifactive necrosis develops when enzyme digestion is dominant. Types 1 and 2 are basic types and others are distinctive types of necrosis. 1. Cogulative necrosis: This results primarily from denaturation of structural and enzymic proteins due to increasing intracellular acidosis of cell. The cellular shape, cell outlines and tissue architecture is maintained. This is structured necrosis. The cell takes acidophilic stain. Examples: Hypotoxic death of cells in all tissues except brain, e.g. infract of heart, kidney, spleen,. 2. Liquefactive necrosis or Colliquative necrosis: Enzyme digestion is dominant. This results from autolysis or heterolysis by action of powerful catalytic enzymes. Liquefactive necrosis occurs in : (a) Suppurative inflammation (b) Hypoxic death of cells within brain-infraction of brain. There occurs softening of the necrosed area. It then break up and turns into fl;uid. There may be a cyst formation (c)Caseous material as secondary change. 3. Caseous necrosis: This is a distinctive type of coagulative necrosis. It occurs most commonly in the tubercle which is a granuloma. The architecture in the necrosed area is lost and the cell outlines are not preserved. There is formation of soft, friable, amorphous granular debris resembling cheesy material. Lysis of macrophages results in the formation of caseating granulomas. 4. Fat necrosis: It occurs in adipose tissue due to action of lipase.They are of two types(A). Acute pancreatic fat necrosis: Enzymatic fat necrosis of pancreas and omental tissue occurs in acute pancreatic necrosis. There is patchy necrosis of pancreas and of fatty tissue throughout the abdopmen by pancreatic enzymes.

(B). Traumatic fat necrosis: It occurs usually in the breast. The necrosed area may be surrounded by inflammatory changes with accumulation of neutrophils, lipid laden macrophages, giant cells and fibroblasts. Finally the area is replaced by scar tissue which may produce skin reaction and clinically may resemble scirrhous carcinoma. 5. Fibrinoid necrosis: It is a morphologic descriptive term of a variety of changes. There is necrosis of collagen. Fibrocytes undergo necrosis of collagen. Fibrocytes undergo necrosis and it’s fibres appear to degenerate. In this there is swelling and fragmentation of the collagen fibres. 6. Gangrenous necrosis: Gangrene is necrosis of tissue with superadded putrefaction by bacteria.

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