Introduction to Pathology

Chapter 1


Introduction to Pathology






Disease


Pathology is the study of diseases that can cause abnormalities in the structure or function of various organ systems. In essence, a disease is the pattern of the body’s response to some form of injury that causes a deviation from or variation of normal conditions. Diseases may be hereditary or may result from a broad spectrum of traumatic, infectious, vascular, or metabolic processes manifesting as a set of characteristics known as signs and symptoms. Signs represent the measurable or objective manifestations of the disease process. The experiences the patient feels and describes are the symptoms, those (subjective) manifestations that are not measurable or observable. They may reflect alterations of cell growth, as in neoplasia (tumors), or they may even be caused by physicians and their treatment (iatrogenic). Incidences of the development of infections at the acute care facility are called nosocomial, whereas infections that develop outside the healthcare facility are known as community acquired. In some cases the underlying cause is unknown, and the disease is termed idiopathic.



Radiographer Notes


Radiography of patients with underlying pathologic conditions can present problems for even the most experienced radiographers. Adjustments in patient position may be necessary to prevent excessive pain caused by the body’s response to trauma or certain disease processes. A change in routine projections may be indicated to visualize subtle alterations in the normal radiographic appearance. Many disease processes also alter the density of the structures being radiographed and therefore require changes in technique. For example, extensive edema may require an increased technique, whereas severe atrophy may require a decreased technique. Unless the radiographer has access to previous images with recorded exposure factors, a standard technique chart should be used to determine the initial exposures. Any necessary adjustments can then be made on subsequent images.


Box 1-1 lists the relative attenuation of x-rays that can be expected in advanced stages of various disease processes. In chest radiography, 110 to 125 kilovolts peak (kVp) is optimal; therefore, milliampere-second (mAs) factors should be adjusted to control density. In skeletal radiography, when bone quality changes are expected, the best exposure factor to change is the kilovolt peak (beam quality change for structural change). When bone quantity changes, the mAs value is the exposure factor to change to control density (beam quantity increases to ensure that enough radiation reaches the image receptor without changing the contrast). For example, in osteoporosis there is a decrease in bone quantity and quality; however, a decrease in kilovolts produces a higher-quality image. The normal kilovolt peak easily penetrates the diseased bone, producing a low-contrast image with loss of visibility of detail. As imaging progresses into the digital imaging arena, the same theories apply; however, the processing algorithm will control brightness (density) and contrast. The exposure index (number) will represent the over- or under-exposure of the image.



Box 1-1   Relative Attenuation of X-Rays in Advanced Stages of Diseases






From Thompson TT: Cahoon’s formulating x-ray techniques, ed 9, Durham, NC, 1979, Duke University Press.


Certain diseases suppress the normal immune response. Immunocompromised patients (such as those with advanced leukemia) may require special care to prevent their acquiring a disease from the radiographer. Personal protective equipment (PPE) aids in preventing the spread of microorganisms to the patient and to the healthcare worker. The patient may have to be placed in protective isolation (or “reverse” isolation), and the radiographer may be required to put on a mask, gown, and gloves before approaching the patient. Diseases such as AIDS and hepatitis require that the radiographer wear rubber or latex gloves to be protected against exposure to blood and body fluids, which could contaminate any area near the patient. When examining a patient with AIDS who has a productive cough, the radiographer must wear a mask and possibly protective eye goggles if there is a need to be very close to the patient’s face. It is important to remember that many patients undergoing radiographic procedures have not been diagnosed and thus all patients should be treated as though they may have a communicable disease. Therefore, whenever exposure to any type of body secretion or blood may occur, the healthcare worker should wear appropriate PPE.


This chapter discusses several basic reactions of the body that characterize the underlying mechanisms for the radiographic manifestations of most pathologic conditions. These processes are inflammation, edema, ischemia and infarction, hemorrhage, and alterations of cell growth leading to the development of neoplasms (tumors). In addition, this chapter deals with hereditary diseases and immune reactions, such as acquired immunodeficiency syndrome (AIDS).




Inflammation


Acute inflammation is the initial response of body tissues to local injury. The various types of injury include those caused by blunt or penetrating trauma, infectious organisms, and irritating chemical substances. Regardless of the underlying cause, the inflammatory response consists of four overlapping events that occur sequentially (Box 1-2).



The earliest bodily response to local injury is dilation of arterioles, capillaries, and venules, leading to a dramatic increase in blood flow in and around the injury site. This hyperemia produces the heat and redness associated with inflammation. As hyperemia develops, the venules and capillaries become abnormally permeable, allowing passage of protein-rich plasma across vessel walls into the interstitium. This inflammatory exudate in the tissues results in the swelling associated with inflammation, which produces pressure on sensitive nerve endings and causes pain. The protein-rich exudate of inflammation must be differentiated from a transudate, a low-protein fluid such as that seen in the pulmonary edema that develops in congestive heart failure.


Very early in the inflammatory response, leukocytes (white blood cells, especially neutrophils and macrophages) of the circulating blood migrate to the area of injury. These white blood cells cross the capillary walls into the injured tissues, where they engulf and enzymatically digest infecting organisms and cellular debris, a process called phagocytosis.


The removal of necrotic debris and any injurious agents, such as bacteria, makes possible the repair of the injury that triggered the inflammatory response. In many tissues, such as the lung after pneumococcal pneumonia, regeneration of parenchymal cells permits reconstitution of normal anatomic structure and function. However, some tissues, such as the heart after myocardial infarction, cannot heal by regeneration. A fibrous scar replaces the area of destroyed tissue with granulation tissue. Granulation tissue refers to a combination of young developing capillaries and actively proliferating fibroblasts, which produce connective tissue fibers (collagen) that replace the dead tissue. Eventually the strong connective tissue contracts to produce a fibrous scar. In the abdomen, such fibrous adhesions can narrow loops of intestine and result in an obstruction. The accumulation of excessive amounts of collagen (more common in African Americans) may produce a protruding, tumor-like scar known as a keloid. Unfortunately, surgery to remove a keloid is usually ineffective because the subsequent incision tends to heal in the same way.


Many injuries heal by a combination of regeneration and scar tissue formation. An example is the response of the liver to repeated and persistent alcoholic injury; the result is cirrhosis, in which irregular lobules of regenerated liver cells are crisscrossed and surrounded by bands of scar tissue. Scar tissue formation consists of fibrous connective tissue, which can be divided into primary union (surgical incision) and secondary union (nonsurgical; gunshot wound).


The five clinical signs of acute inflammation are rubor (redness), calor (heat), tumor (swelling), dolor (pain), and loss of function. The localized heat and redness result from increased blood flow in the microcirculation at the site of injury. The swelling occurs because the exudate increases the amount of interstitial fluid, resulting in pressure on nerve endings and thus pain, which results in a loss of function.


Acute inflammation can also lead to systemic manifestations. Fever is especially common in inflammatory conditions associated with the spread of organisms into the bloodstream. The number of circulating white blood cells also increases (leukocytosis).


Some bacterial organisms (such as staphylococci and streptococci) produce toxins that damage the tissues and incite an inflammatory response. The presence of pyogenic bacteria leads to the production of a thick, yellow fluid called pus, which contains dead white blood cells, inflammatory exudate, and bacteria. A suppurative inflammation is one that is associated with pus formation. When a pyogenic infection occurs beneath the skin or in a solid organ, it produces an abscess, a localized, usually encapsulated, collection of pus. All pyogens, wherever they become implanted, have the ability to invade blood vessels to produce bacteremia, with the potential involvement of other organs and tissues in the body.


A granulomatous inflammation manifests as a distinct pattern seen in relatively few diseases, including tuberculosis, syphilis, and sarcoidosis. A granuloma is a localized area of chronic inflammation, often with central necrosis. It is characterized by the accumulation of macrophages, some of which fuse to form multinucleated giant cells.


Apr 10, 2017 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Introduction to Pathology
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