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And if an artery or arteriole dilates to twice its initial radius order detrol 1 mg free shipping symptoms during pregnancy, then resistance in the vessel will decrease to 1/16 of its original value and flow will increase 16 times generic detrol 4 mg otc symptoms 7 weeks pregnant. The Roles of Vessel Diameter and Total Area in Blood Flow and Blood Pressure Recall that we classified arterioles as resistance vessels, because given their small lumen, they dramatically slow the flow of blood from arteries. Notice in parts (a) and (b) that the total cross-sectional area of the body’s capillary beds is far greater than any other type of vessel. Although the diameter of an individual capillary is significantly smaller than the diameter of an arteriole, there are vastly more capillaries in the body than there are other types of blood vessels. Part (c) shows that blood pressure drops unevenly as blood travels from arteries to arterioles, capillaries, venules, and veins, and encounters greater resistance. However, the site of the most precipitous drop, and the site of greatest resistance, is the arterioles. This explains why vasodilation and vasoconstriction of arterioles play more significant roles in regulating blood pressure than do the vasodilation and vasoconstriction of other vessels. Part (d) shows that the velocity (speed) of blood flow decreases dramatically as the blood moves from arteries to arterioles to capillaries. This is a leading cause of hypertension and coronary heart disease, as it causes the heart to work harder to generate a pressure great enough to overcome the resistance. Arteriosclerosis begins with injury to the endothelium of an artery, which may be caused by irritation from high blood glucose, infection, tobacco use, excessive blood lipids, and other factors. Artery walls that are constantly stressed by blood flowing at high pressure are also more likely to be injured—which means that hypertension can promote arteriosclerosis, as well as result from it. Moreover, circulating triglycerides and cholesterol can seep between the damaged lining cells and become trapped within the artery wall, where they are frequently joined by leukocytes, calcium, and cellular debris. The term for this condition, atherosclerosis (athero- = “porridge”) describes the mealy deposits (Figure 20. This clot can further obstruct the artery and—if it occurs in a coronary or cerebral artery—cause a sudden heart attack or stroke. Alternatively, plaque can break off and travel through the bloodstream as an embolus until it blocks a more distant, smaller artery. Even without total blockage, vessel narrowing leads to ischemia—reduced blood flow—to the tissue region “downstream” of the narrowed vessel. Hypoxia involving cardiac muscle or brain tissue can lead to cell death and severe impairment of brain or heart function. A major risk factor for both arteriosclerosis and atherosclerosis is advanced age, as the conditions tend to progress over time. Arteriosclerosis is normally defined as the more generalized loss of compliance, “hardening of the arteries,” 908 Chapter 20 | The Cardiovascular System: Blood Vessels and Circulation whereas atherosclerosis is a more specific term for the build-up of plaque in the walls of the vessel and is a specific type of arteriosclerosis. There is also a distinct genetic component, and pre-existing hypertension and/or diabetes also greatly increase the risk. However, obesity, poor nutrition, lack of physical activity, and tobacco use all are major risk factors. Treatment includes lifestyle changes, such as weight loss, smoking cessation, regular exercise, and adoption of a diet low in sodium and saturated fats. In angioplasty, a catheter is inserted into the vessel at the point of narrowing, and a second catheter with a balloon-like tip is inflated to widen the opening. This operation is typically performed on the carotid arteries of the neck, which are a prime source of oxygenated blood for the brain. In a coronary bypass procedure, a non-vital superficial vessel from another part of the body (often the great saphenous vein) or a synthetic vessel is inserted to create a path around the blocked area of a coronary artery. Venous System The pumping action of the heart propels the blood into the arteries, from an area of higher pressure toward an area of lower pressure. If blood is to flow from the veins back into the heart, the pressure in the veins must be greater than the pressure in the atria of the heart. First, the pressure in the atria during diastole is very low, often approaching zero when the atria are relaxed (atrial diastole). Skeletal Muscle Pump In many body regions, the pressure within the veins can be increased by the contraction of the surrounding skeletal muscle.
It is to be distinguished from the swelling of the red cell membrane that accounts for target cell in some patients with obstructive jaundice buy cheap detrol 4mg line medicine disposal. Some authors 255 Hematology believe that it is the result of the reticulocytosis that accompanies the hemolytic component of the anemia associated with liver dysfunction buy generic detrol 1 mg on line medications similar to abilify. Similarly, macrocytosis, often in the absence of anemia, is seen in patients who consume large amounts of alcohol, and this is sometimes used as a criterion for the diagnosis of chronic alcoholism. Anemia associated with hypothyroidism can have various morphologic characteristics, but is sometimes macrocytic in nature, for reasons that are not entirely clear. The postsplenectomy state is often associated with mild macrocytosis, in addition to the formation of some target cells and acanthocytes; these changes are due to the fact that young red cells normally undergo a process of surface remodeling, with loss of some of their redundant red cell membrane, with the spleen, and thus splenectomy may be associated with cells containing excessive plasma membrane material. Erythrocytes during the neonatal period are normally macrocytic and are then replace by cells of normal size. In the presence of high serum levels of erythropoietin 256 Hematology stimulated by anemia and the attendant hypoxemia, there is early release of immature red blood cells from the bone marrow, that is, a “shift” of immature bone marrow reticulocytes into the peripheral blood. Macrocytosis of mild degree is often seen as well in conditions in which the anemia is due to a decease in erythropoietic tissue in the bone marrow, for example, aplastic anemia, pure red cell aplasia, or the bone marrow suppression caused by chemotherapy. In these situations there is also a high titer of erythropoietin in the plasma, and this causes a rapid rate of ingress of young red blood cells into the peripheral blood. Major causes of macrocytic anemia that are megaloblastic in nature are vitamin B12 or folic acid deficiency, both of which have multiple causes. This result in ineffective erythropoiesis, that is, death of immature erythyroid cells before release from the bone marrow, associated with some early destruction of circulating erythrocytes as well. It is known that a state of unbalanced growth exists in the marrow 259 Hematology cells of patients with megaloblastic anemia. Although most anemias characterized by megaloblastic erythropoiesis are due to either vitamin B12 or folic acid deficiency, there are several other causes of megaloblastic hematopoiesis. Laboratory findings • Pancytopenia : As a result of ineffective erythropoiesis, 260 Hematology granulopoiesis, and thrombopoiesis, and premature destruction of defective cells in the peripheral blood, it is unusual to find a patient with megaloblastic anemia who does not have depression of all three cell lines in the peripheral blood. Occasionally it is 2 to 3 percent, but the reticulocyte production index is low, a reflection of a functionally defective marrow. It has been suggested that these abnormalities result from 261 Hematology fragmentation of the abnormal large red cells as they pass through small arterioles. As the megaloblastic anemia becomes more sever, bizarre shapes such as triangles and helmets increases proportionately. Normally no more than 1 percent of polys have six nuclear lobes, but in megaloblastic anemia many have six or more, even ten, lobes. Despite hemolysis the reticulocyte production index is reduced because of the ineffective erythropoiesis in the bone marrow. Morphologically, the megaloblastic erythropoiesis is characterized by the presence of large cells, with asynchronism between nuclear and cytoplasmic development. Vitamin B12 Since vitamin B12 is common in human diets, almost all deficiencies of vitamin B12 are a result of malabsorption. This structure is analogous to the porphyrin structure of heme, with position of the heme iron being occupied by a cobalt atom. The vitamin B12 synthesized by microbes is deposited in animal tissues, such as liver, eggs, and 263 Hematology milk, and is therefore plentiful in fish and meat products. The average diet contains 5 to 30µg of vitamin B12 daily, 1 to 2µg of which usually is absorbed and retained. In the adult a storage pool of 3000 to 5000µg is present, of which 1000 to 3000µg is stored in the liver. If malabsorption of vitamin B12 occurs, it will take 2 to 5 years before body stores are exhausted and megaloblastic erythropoiesis supervenes. Normal subjects will excrete in their urine 7 percent or more of the radioactivity taken orally, whereas patients with pernicious anemia or other causes of vitamin B12 malabsorption will excrete well less than 7 percent. In part three of the Schilling test a 2-week course of antibiotic therapy with tetracycline, 250mg four times per day, is prescribed. If bacterial overgrowth was responsible for the abnormal second part of the Schilling test, then tetracycline treatment should normalize vitamin B12 absorption. Much less commonly the deficiency may be caused by veganism in which the diet lacks B12 (usually in Hindu Indians), gastrectomy or small intestinal lesions.
In Epidemiologic study it is common to specify three characteristics of a person – age generic detrol 4 mg online treatment quad strain, sex and ethnic group or race order detrol 2 mg line medications hyponatremia. Ethnic group and Race: Many diseases differ markedly in frequency, severity, or both in different racial or ethnic groups. Other personal variables: There are also other personal variables that should be considered during epidemiologic studies. An area defined by natural boundaries may have a high or low frequency of certain diseases because it is characterized by some particular environmental or climatic conditions, such as temperature, humidity, rainfall, altitude, mineral content of soil, or water supply. The most common types of periodicity are in relation to seasonal changes, or in relation to changes in the number of susceptible persons in a population. Malaria is one of the example of diseases with seasonal periodicity, where high peaks occur in relation to the rainy season. Epidemic of malaria are common in October and November, when stagnant water bodies are convenient for the breeding of mosquitoes. In cross sectional studies, information about the status of an individual with respect to the presence or absence of exposure and disease is assessed at a point in time. Data can be collected by using questionnaire, interview, self- administered questionnaire, observation, applying laboratory tests etc. Health status of a community is assessed by the collection, compilation, analysis and interpretation of data on illness (morbidity), death (mortality), disability and utilization of health services. Such information is useful for public health planners and administrators for proper allocation of health care resources in a particular community. However, to investigate distributions and determinants of disease, it is also necessary to know the size of the source population from which affected individuals were counted. One of the central concerns of epidemiology is to find and enumerate appropriate denominators in order to describe and compare groups in a meaningful and useful way. It expresses the relationship between two numbers in the form of x: y or x/y X k Example: -The ratio of males to females (M:F) in Ethiopia. It is a specific type of ratio in which the numerator is included in the denominator and the result is expressed as a percentage. Example: The proportion of all births that was male Male births x 100 Male + Female births Rate Rate is the most important epidemiological tool used for measuring diseases. It is 33 the measure that most clearly expresses probability or risk of disease in a defined population over a specified period of time, hence, it is considered to be a basic measure of disease occurrence. Accurate count of all events of interest that occur in a defined population during a specified period is essential for the calculation of rate. Rate = Number of events in a specific period x k Population at risk of these events in a specified Period Example: The number of newly diagnosed pneumonia cases in 1999 per 1000 under five children. Incidence rate The incidence of a disease is defined as the number of new cases of a disease that occur during a specified period of time in a population at risk for developing the disease. Incidence rate = Number of new cases of a disease over a period of time X K 34 Total Population during the given period of time The critical element in the definition of incidence is new cases of disease. The appropriate denominator for incidence rate is population at risk but knowing the population at risk is difficult at this level. For incidence to be a measure of risk we must specify a period of time and we must know that all of the individuals in the group represented by the denominator have been followed up for that entire period. The choice of time period is arbitrary: We could calculate incidence rate in one week, one month, one year, 5 years, and so on. If the incidence rate of a certain disease is high in one area, then the risk of acquiring that disease by other healthy individuals will be high. Answer- Incidence rate = 50 X 1000 = 10 new cases per 1000 population 5000 35 That means out of every 1000 people living in “Kebele X”, 10 of them acquired relapsing fever in Ginbot 1995. Attack rate = 90 X 100 = 90 cases of diarrhea per 100 people 100 That means out of 100 people who ate the food served by Ato Alemitegnaw, 90 of them developed diarrhea on Tir 8, 1995. Uses incidence rate Incidence rate is important as a fundamental tool for etiologic studies of diseases since it is a direct measure of risk. If the incidence rate is 36 significantly higher in one area, then the cause of that disease can be systematically searched. Prevalence rate Prevalence rate measures the number of people in a population who have a disease at a given time. Point Prevalence rate: measures the proportion of a population with a certain condition at a given point in time. Point Prevalence rate = All persons with a specific Condition at one point in time X K Total population Example: One health extension worker conducted a survey in one of the nearby elementary schools on Hidar 10, 1996 to know the prevalence of trachoma in that school.
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