By C. Javier. University of Nebraska, Lincoln. 2018.
One of these was a fair quality trial of 300 patients (42 percent of patients reporting this outcome) 100 mg trazodone free shipping. This was a poor quality trial of 345 patients (49 percent of patients reporting this outcome) purchase trazodone 100mg on line. Fifty-eight percent of patients were in poor quality trials cheap trazodone 100mg with amex, and 42 percent were in a fair quality trial. The evidence was therefore insufficient to support the use of one treatment over the other for this outcome. The larger of 131 132 these (92 percent of patients reporting this outcome) was rated good quality, and the smaller (n=40) was rated poor quality due to noncomparable groups at baseline. At 6 weeks, the latter 132 trial showed a statistically nonsignificant treatment effect of 0. The risk of bias was considered low; 92 percent of patients reporting this outcome were in the good quality trial. Eye Symptoms 90 131 Two trials assessed eye symptoms, one at 2 weeks (N=345) and one at 8 weeks (N=454). This trial was rated poor quality due to inappropriate analysis of results (not intention to treat). Evidence for the outcome of eye symptoms at 2 weeks was insufficient to support the use of 90 one treatment over the other. At 8 116 weeks, the evidence also is insufficient to support the use of one treatment over the other. Quality of Life 62, 98 98 Two trials assessed quality of life at 2 weeks using different measures. The larger trial (83 percent of patients reporting this outcome) was rated fair quality and showed a treatment 62 effect of 0. More patients treated with combination therapy reported moderate to significant improvement using a 7-point Likert scale (significantly worse to significantly improved) than patients treated with intranasal corticosteroid monotherapy. Evidence for quality of life outcomes at 2 weeks is insufficient to support one treatment over 62, 98 the other. Adjusted mean differences reported by Carr, 2012, mean differences calculated by authors with available data (Hampel, 2010). Trial size ranged from 102 to 898 patients randomized to treatment groups of interest. In all five trials, the nasal antihistamine was azelastine, and the intranasal corticosteroid was fluticasone propionate. Three 115 trials from the same article used a newly approved combination product comprising both 117, 121 drugs, and two trials used a separate nasal inhaler for each drug in the combination. Of two 117, 121 121 trials that reported the proportions of other races, one included approximately 20 percent Hispanic patients. Individual nasal symptoms (congestion, rhinorrhea, sneezing, and itching) and eye symptoms (itching, tearing, and redness) were rated on a scale from 0 (no symptoms) to 3 (severe symptoms). Morning and evening scores were summed to give a maximum score of 6 for each individual symptom. As shown in these tables and noted above, several trials reported on each outcome. Four trials (85 percent of patients reporting this outcome) were included in meta- analyses for each nasal outcome. Variance estimates necessary for pooling were not reported by 117 Hampel (2010), preventing inclusion of this trial in the meta-analyses. All five trials showed greater improvement in congestion with combination therapy than with 117 intranasal corticosteroid monotherapy. In three trials, including Hampel (2010), treatment effects were statistically significant and ranged from 0. For the outcome of congestion, the risk of bias was rated as low based on the quality of the 115, 121 trials. Statistical heterogeneity of a meta-analysis of four trials was low, and the pooled 117 effect was consistent with the effect reported in the one trial not included in the meta-analysis. The body of evidence supporting a conclusion of equivalence of combination therapy and intranasal corticosteroid for this outcome was therefore considered precise. All five trials showed greater improvement in rhinorrhea with combination therapy than with intranasal corticosteroid monotherapy. For the outcome of rhinorrhea, the risk of bias was rated as low based on the quality of the 115, 121 trials. Statistical heterogeneity of a meta-analysis of four trials was low, and the pooled 117 effect was consistent with the effect reported in the one trial not included in the meta-analysis. The body of evidence supporting a conclusion of equivalence of combination therapy and intranasal corticosteroid for this outcome was therefore considered precise. All five trials showed greater improvement in sneezing with combination therapy than with 117 intranasal corticosteroid monotherapy. In four trials, including Hampel (2010), treatment effects were statistically significant and ranged from 0. For the outcome of sneezing, the risk of bias was rated as low based on the quality of the 115, 121 trials. Statistical heterogeneity of a meta-analysis of four trials was low, and the pooled 117 effect was consistent with the effect reported in the one trial not included in the meta-analysis. The body of evidence supporting a conclusion of equivalence of combination therapy and intranasal corticosteroid for this outcome was therefore considered precise. All five trials showed greater improvement in nasal itch with combination therapy than with 117 intranasal corticosteroid monotherapy. For the outcome of nasal itch, the risk of bias was rated as low based on the quality of the 115, 121 trials. Statistical heterogeneity of a meta-analysis of four trials was low, and the pooled 117 effect was consistent with the effect reported in the one trial not included in the meta-analysis. The body of evidence supporting a conclusion of equivalence of combination therapy and intranasal corticosteroid for this outcome was therefore considered precise. Statistical heterogeneity of a meta-analysis of four trials was low, and the 117 pooled effect was consistent with the effect reported in the one trial not included in the meta- analysis. The body of evidence supporting a conclusion of equivalence of combination therapy and intranasal corticosteroid for this outcome was therefore considered precise. The pooled effect from a meta-analysis of three trials (85 percent of 117 patients reporting this outcome; Hampel  excluded) was 0. Statistical 115 heterogeneity of a meta-analysis of three trials was low, and the pooled effect was consistent 117 with the effect reported in the one trial not included in the meta-analysis. The body of evidence supporting a conclusion of equivalence of combination therapy and intranasal corticosteroid for this outcome was therefore considered precise. Congestion at 2 weeks meta-analysis: combination intranasal corticosteroid plus nasal antihistamine versus intranasal corticosteroid 128 Figure 22. Rhinorrhea at 2 weeks meta-analysis: combination intranasal corticosteroid plus nasal antihistamine versus intranasal corticosteroid Figure 23. Sneezing at 2 weeks meta-analysis: combination intranasal corticosteroid plus nasal antihistamine versus intranasal corticosteroid 129 Figure 24. Nasal itch at 2 weeks meta-analysis: combination intranasal corticosteroid plus nasal antihistamine versus intranasal corticosteroid Figure 25.
Preparations can include: Investigator must have the appropriate scientific knowledge buy 100mg trazodone amex, supplies buy trazodone 100mg line, and equipment to carry out the investigation discount trazodone 100mg overnight delivery. It might be difficult for the health extension worker to fully investigate the epidemic, hence, he/she should inform and involve other high level health professionals from the outset. Verify (confirm) the existence of an epidemic This initial determination is often made on the basis of available data. Compare the number of cases with the past levels to identify whether the present occurrence is in excess of its usual frequency. For example the already collected blood film slides can be seen by laboratory experts to check whether the initial report was correct. It is important to investigate the index case (the first case that comes to the attention of health authorities) and other early cases. The importance of the index case and other early cases for diseases that are known to occur in epidemic form, such as relapsing fever, is as an indication to health authorities of the possible start of an outbreak. The sooner the index case and other early cases are investigated, the greater the opportunity to arrest the outbreak at earliest stage possible. The health extension worker requests support from the Woreda Health Office or the nearest Health Center for confirming the diagnosis. Case definition is defined as a standard set of criteria to differentiate between cases and non cases. They can also be identified by stimulated passive case detection, for example by alerting the public about the epidemic and requesting them to report to the nearest health institution when they have signs and symptoms of that disease. The health extension worker can identify and count cases based on the sign and symptoms of the disease. If there is effective drug for the treatment of that disease, cases can be treated while identifying them. Additionally other control measures can be taken side by side to arrest the epidemic before many people are affected. Describe the epidemic with respect to person, place and time Each case must be defined according to standard epidemiologic parameters: the date of onset of the illness, the place where the person lives or became ill, and the sociodemographic characteristics (age, sex, education level, occupation). In epidemic curve the distribution of cases is plotted over time, usually in the form of histogram, with the date of onset of cases on the horizontal axis, and the number of cases corresponding to each date of onset on the vertical axis. One limitation of spot map is that it does not take into account underlying geographic differences in population density. Person specific attack rates: The tool that is important for the analysis of disease outbreaks by personal characteristics is person specific attack rates like attack rates by age, sex, occupation, income, religion etc. Identify the causes of the epidemic All factors that can contribute to the occurrence of the epidemic should be assessed. In addition to knowing the etiologic agent, more emphasis should be given to identify the risk factors. Investigate the environmental conditions such as food sanitation, suspected breeding sites, animal reservoirs, according to the type of disease outbreak being investigated. Management of epidemic and follow up Although it is discussed late, intervention must start as soon as possible depending on the specific circumstances. For example, an outbreak might be controlled by destroying contaminated foods, disinfecting contaminated water, or destroying mosquito breeding sites or an infectious food handler could be suspended from the job and treated. General principles in the management of epidemics Management of epidemics requires an urgent and intelligent use of appropriate measures against the spread of the disease. However, the actions can be generally categorized as presented below to facilitate easy understanding of the strategies. Measures Directed Against the Reservoir 62 Understanding the nature of the reservoir is necessary in the selection of an appropriate control methods and their likelihood of success. The following are examples of control measures against diseases with various reservoirs: Domestic animals as reservoir: Immunization. This is not suitable in the control of diseases in which a large proportion are inapparent infection (without signs and symptoms) or in which maximal infectivity precedes overt illness. Quarantine- is the limitation of freedom of movement of apparently healthy persons or animals who have been exposed to a case of infectious disease. Cholera, Plague, and yellow fever are the three internationally quarantinable diseases by international agreement. Now quarantine is replaced in some countries by active surveillance of the individuals; maintaining close supervision over possible contacts of ill persons to detect infection or illness promptly; their freedom of movement is not restricted. Measures that interrupt the transmission of organisms Action to prevent transmission of disease by ingestion: i. Example vaccination for meningitis Chemoprophylaxis: for example, use of chloroquine to persons traveling to malaria endemic areas. After the epidemic is controlled, strict follow up mechanisms should be designed so as to prevent similar epidemics in the future. Report of the investigation At the end prepare a comprehensive report and submit to the appropriate/concerned bodies like the Woreda Health Office. The report should follow the usual scientific format: introduction, methods, results, discussion, and recommendations. Passive surveillance Passive surveillance may be defined as a mechanism for routine surveillance based on passive case detection and on the routine recording and reporting system. The information provider comes to the health institutions for help, be it medical or other preventive and promotive health services. Advantages of passive surveillance covers a wide range of problems does not require special arrangement it is relatively cheap 69 covers a wider area The disadvantages of passive surveillance The information generated is to a large extent unreliable, incomplete and inaccurate Most of the time, data from passive surveillance is not available on time Most of the time, you may not get the kind of information you desire It lacks representativeness of the whole population since passive surveillance is mainly based on health institution reports Active surveillance Active surveillance is defined as a method of data collection usually on a specific disease, for relatively limited period of time. It involves collection of data from communities such as in house-to-house surveys or mobilizing communities to some central point where data can be collected. This can be arranged by assigning health personnel to collect information on presence or absence of new cases of a particular disease at regular intervals. Example: investigation of out-breaks 70 The advantages of active surveillance the collected data is complete and accurate information collected is timely. The disadvantages of active surveillance it requires good organization, it is expensive it requires skilled human power it is for short period of time(not a continuous process) it is directed towards specific disease conditions Conditions in which active surveillance is appropriate Active surveillance has limited scope. These conditions are: For periodic evaluation of an ongoing program For programs with limited time of operation such as eradication program 71 In unusual situations such as: New disease discovery New mode of transmission When a disease is found to affect a new subgroup of the population. In this strategy several activities from the different vertical programs are coordinated and streamlined in order to make best use of scarce resources. The activities are combined taking advantage of similar surveillance functions, skills, resources, and target population. Integrated disease surveillance strategy recommends coordination and integration of surveillance activities for diseases of public health importance. Diseases included in the integrated disease surveillance system Among the most prevalent health problems 21 (twenty one) communicable diseases and conditions are selected for integrated disease surveillance to be implemented in Ethiopia. Epidemic-Prone Diseases 74 Cholera Diarrhea with blood (Shigella) Yellow fever Measles Meningitis Plague Viral hemorrhagic fevers*** Typhoid fever Relapsing fever Epidemic typhus Malaria B. Principles and Practice of Public Health Surveillance, second edition, Oxford University Press, Oxford, 2000. They are intended to provide the clinician, especially trainees, easy access to basic information needed in day-to-day decision-making and care. Grade A One (or more) mucosal breaks no longer than 5 mm that do not extend between the tops of two mucosal folds.
Moreover order 100 mg trazodone with amex, the angiography can increase the risks of fatal Message: In the present paper the authors describe their experience in complications purchase 100 mg trazodone fast delivery. Produced in collaboration with the Ethiopia Public Health Training Initiative buy trazodone 100mg line, The Carter Center, the Ethiopia Ministry of Health, and the Ethiopia Ministry of Education. Important Guidelines for Printing and Photocopying Limited permission is granted free of charge to print or photocopy all pages of this publication for educational, not-for-profit use by health care workers, students or faculty. Under no circumstances is it permissible to sell or distribute on a commercial basis, or to claim authorship of, copies of material reproduced from this publication. Except as expressly provided above, no part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage and retrieval system, without written permission of the author or authors. This material is intended for educational use only by practicing health care workers or students and faculty in a health care field. I believe that transfer of scientific knowledge in oral health could be beneficiary to the needy population where oral health is found in a low standard. In our country there is no enough qualified human resource in dental profession, however the need for dental service is increasing. Teaching oral health care to health officer students even to other health science students will definitely will help the people get better service in the area. Majority of the Ethiopian population has no proper dental service; they are getting help by the local practitioners. Even though not to be appreciated, it is undeniable that the local practitioners, had contributed and are contributing a lot to the people, in areas where there is no dental service. Mal practice, lack of knowledge and un sterile instruments had resulted in bad outcomes like fracture of the mandible, dislocation of the temperomandibular joint, Fracture of tooth and roots etc. Even though it is not within the scope of this material to cover all dental related problems, I have tried to include the common dental problem, their management and prevention precisely. I would like to acknowledge Dr Mesfin Addise for the information, supports and useful suggestions which were useful for the preparation. I would like to acknowledge W/t Seblewongel Nigussie, the secretary of the general manager of the Association. My special acknowledgement goes to the Authors of Texts, Journals, and Articles which I referred and used their work. Finally my incredible acknowledgement goes to all my friends, family members, and especially to my daughters, Eden Bekele, Mariam Bekele, Ruth Bekele, Tigist Alemayehu, and Fikiraddis Abate. In the past all Africans were assumed to have good teeth, therefore the need for oral health was not given priority. At present there are about 55 dentists including specialists in some of the special fields of dentistry. At present the center is upgraded to a dental school and training students in bachelor of dental 1 science, Jimma University has recently started training Doctor of Dental Medicine. Preliminary studies done in the past showed that the Ethiopians have good teeth with low rate of caries prevalence; however caries is on the increase because of the replacement of none carious foods of developing countries by sugar rich western foods. Even though in recent years in Ethiopia research works are not done, however, the need for dental service is growing, the resource are scarce and maldistributed, skilled human resource in the country is very few. I hope this type of training in oral health care will contribute in prevention of infections which may be transmitted through mal practices by untrained practitioners. This had influenced peoples’ mind and caused differences in many conditions not 2 excluding medical field. In the field of dentistry, differences in medical terminologies like Dentistry or stomatology, Oral surgery or surgical stomatology were the results of those times. In Boucher’s Dictionary of Clinical Dental Terminology, the defination of terminologies is given as follows: Stomatology is the study of the morphology, structure, function and diseases of the contents and lining of the oral cavity. Dentistry is the science and art of preventing, diagnosing, and treating, diseases, injuries and malformations of the teeth, jaws and mouth and of replacing lost or absent teeth and associated structures. Pediatric Dentistry/pedodontics - conservative Pediatric Dentistry - Surgical Pediatric Dentistry - Othodontics Pediatric Dentistry b. Dental and maxillofacial radiology Course Objective After the completion of the course the student will be able to: • Identify and treat common oral and dental diseases • Plan, promote and organize preventive oral health Course content 1. Figure 1: Anatomy of the oral cavity 7 Anatomy of the teeth Tooth is made up of enamel, dentine, pulp and cement. Dentin This sensitive ivory like substance that forms the body of the whole teeth Pulp This is an extremely sensitive mass of thin nerve and blood vessels which enter through apical canal at the apex of each root. Figure 2: Dental anatomy Root Premolar Neck Crown 9 Table 1: Chemical composition of tooth Enamel Dentine Pulp Inorganic subst. According to their development- Deciduous and permanent According to their function -- Incisors, Canines, premolars and molars. Premolars and Molars: Grinding the food in to small pieces before swallowing Arterial Supply to the Teeth and oral cavity The arteries and nerve branches to the teeth are mere terminals of the central systems. This manual will only confine to dental anatomy and the parts immediately associated structures, therefore reference be made only to those branches that supply the teeth and the supporting structures. Internal Maxillary Artery The arterial supply to the jaw bones and the teeth comes from the maxillary artery, which is a branch of the external carotid artery. The branches of the maxillary 12 artery which feed the teeth directly are the inferior alveolar artery and the superior alveolar arteries. Inferior Alveolar Artery The inferior alveolar artery branches from the maxillary artery medial to the ramus of the mandible. It gives off the mylohyoid branch, it supplies: ¾ the premolar and molar teeth ¾ the chin ¾ the anterior teeth ¾ the mandible and teeth. Supperior Alveolar Arteries The posterior superior alveolar artery branches from the maxillary artery superior to the maxillary tuberosity to enter the alveolar canals along with the posterior superior alveolar nerves and supplies: ¾ the maxillary teeth, ¾ Alveolar bone and membrane of the sinus. A middle superior alveolar branch is usually given off by the infraorbital continuation of the maxillary artery. It supplies ¾ the maxillary anterior teeth and their supporting tissues Branches to the teeth, periodontal ligament, and bone are derived from the superior alveolar 14 Figure 3: Branches of maxillary artery 15 Nerve Supply The sensory nerve supply to the jaws and teeth is derived from the maxillary and mandibular branches of the fifth cranial, or trigeminal, nerve, whose ganglion, the trigeminal, is located at the apex of the petrous portion of the temporal bone. Maxillary Nerve The maxillary nerve crosses forward through the wall of the cavernous sinus and leaves the skull through the foramen rotundum. The branches of clinical significance include: ¾ a greater palatine branch that enters the hard palate through the greater palatine foramen and 16 is distributed to the hard palate and palatal gingivae as far forward as the canine tooth; ¾ a lesser palatine branch from the ganglion that enters the soft palate through the lesser palatine foramina; and ¾ a nasopaaltine branch of the posterior or superior lateral nasal branch of the ganglion that runs downward and forward on the nasal septum. Entering the palate through the incisive canal, it is distributed to the incisive papilla and to the palate anterior to the anterior palatine nerve. Posterior superior alveolaris nerve Mandibular Nerve The mandibular nerve leaves the skull though the foramen ovale and almost immediately breaks up into its several branches. The chief branches; ¾ the inferior alveolar nerve, it gives off branches to the molar and premolar teeth and their supporting bone and soft tissues. Lingual nerve Muscles The masticatory muscles concerned with mandibular movements include • the lateral pterygoid, • digastric, • masseter, • medial pterygoid, • temporalis muscles. Masseter Muscle The masseter muscle has a function of : • clenching • sometimes active in facial expression • active during forceful jaw closing • may assist in protrusion of the mandible 23 Medial Pterygoid Muscle The medial pterygoid muscle arises from the medial surface of the lateral pterygoid plate and from the palatine bone. The principal functions of the medial pterygoid muscle are: • Elevation and lateral positioning of the mandible. Historically the term eruption has been used to denote emergence of the tooth through the gingiva although it denotes more completely continuous tooth movement from the dental bud to occlusal contact. Calcification or mineralization (most often visualized radio graphically) of the organic matrix of a tooth, root formation, and tooth eruption are important indicators of dental age.
The greater the compliance of an artery buy trazodone 100 mg online, the more effectively it is able to expand to accommodate surges in blood flow without increased resistance or blood pressure trazodone 100 mg mastercard. When vascular disease causes stiffening of arteries purchase 100mg trazodone otc, compliance is reduced and resistance to blood flow is increased. A Mathematical Approach to Factors Affecting Blood Flow Jean Louis Marie Poiseuille was a French physician and physiologist who devised a mathematical equation describing blood flow and its relationship to known parameters. Although understanding the math behind the relationships among the factors affecting blood flow is not necessary to understand blood flow, it can help solidify an understanding of their relationships. Please note that even if the equation looks intimidating, breaking it down into its components and following the relationships will make these relationships clearer, even if you are weak in math. Poiseuille’s equation: 4 Blood fl w = π ΔP r 8ηλ • π is the Greek letter pi, used to represent the mathematical constant that is the ratio of a circle’s circumference to its diameter. One of several things this equation allows us to do is calculate the resistance in the vascular system. Normally this value is extremely difficult to measure, but it can be calculated from this known relationship: Blood fl w = ΔP Resistance If we rearrange this slightly, Resistance = ΔP Blood fl w Then by substituting Pouseille’s equation for blood flow: 8ηλ Resistance = 4 πr By examining this equation, you can see that there are only three variables: viscosity, vessel length, and radius, since 8 and π are both constants. The important thing to remember is this: Two of these variables, viscosity and vessel length, will change slowly in the body. Only one of these factors, the radius, can be changed rapidly by vasoconstriction and vasodilation, thus dramatically impacting resistance and flow. Further, small changes in the radius will greatly affect flow, since it is raised to the fourth power in the equation. We have briefly considered how cardiac output and blood volume impact blood flow and pressure; the next step is to see how the other variables (contraction, vessel length, and viscosity) articulate with Pouseille’s equation and what they can teach us about the impact on blood flow. Water may merely trickle along a creek bed in a dry season, but rush quickly and under great pressure after a heavy rain. Low blood volume, called hypovolemia, may be caused by bleeding, dehydration, vomiting, severe burns, or some medications used to treat hypertension. It is important to recognize that other regulatory mechanisms in the body are so effective at maintaining blood pressure that an individual may be asymptomatic until 10–20 percent of the blood volume has been lost. Hypervolemia, excessive fluid volume, may be caused by retention of water and sodium, as seen in patients with heart failure, liver cirrhosis, some forms of kidney disease, hyperaldosteronism, and some glucocorticoid steroid treatments. Restoring homeostasis in these patients depends upon reversing the condition that triggered the hypervolemia. The viscosity of blood is directly proportional to resistance and inversely proportional to flow; therefore, any condition that causes viscosity to increase will also increase resistance and decrease flow. Conversely, any condition that causes viscosity to decrease (such as when the milkshake melts) will decrease resistance and increase flow. Since the vast majority of formed elements are erythrocytes, any condition affecting erythropoiesis, such as polycythemia or anemia, can alter viscosity. Since most plasma proteins are produced by the liver, any condition affecting liver function can also change the viscosity slightly and therefore alter blood flow. Liver abnormalities such as hepatitis, cirrhosis, alcohol damage, and drug toxicities result in decreased levels of plasma proteins, which decrease blood viscosity. While leukocytes and platelets are normally a small component of the formed elements, there are some rare conditions in which severe overproduction can impact viscosity as well. Vessel Length and Diameter The length of a vessel is directly proportional to its resistance: the longer the vessel, the greater the resistance and the lower the flow. As with blood volume, this makes intuitive sense, since the increased surface area of the vessel will impede the flow of blood. The length of our blood vessels increases throughout childhood as we grow, of course, but is unchanging in adults under normal physiological circumstances. One pound of adipose tissue contains approximately 200 miles of vessels, whereas skeletal muscle contains more than twice that. Gaining about 10 pounds adds from 2000 to 4000 miles of vessels, depending upon the nature of the gained tissue. One of the great benefits of weight reduction is the reduced stress to the heart, which does not have to overcome the resistance of as many miles of vessels. In contrast to length, the diameter of blood vessels changes throughout the body, according to the type of vessel, as we discussed earlier. The diameter of any given vessel may also change frequently throughout the day in response to neural and chemical signals that trigger vasodilation and vasoconstriction. The vascular tone of the vessel is the contractile state of the smooth muscle and the primary determinant of diameter, and thus of resistance and flow. The effect of vessel diameter on resistance is inverse: Given the same volume of blood, an increased diameter means there is less blood contacting the vessel wall, thus lower friction and lower resistance, subsequently increasing flow. A decreased diameter means more of the blood contacts the vessel wall, and resistance increases, subsequently decreasing flow. The influence of lumen diameter on resistance is dramatic: A slight increase or decrease in diameter causes a huge decrease or increase in resistance. This is because resistance is inversely proportional to the radius of the blood vessel (one-half of 4 the vessel’s diameter) raised to the fourth power (R = 1/r ). This means, for example, that if an artery or arteriole constricts to one-half of its original radius, the resistance to flow will increase 16 times. And if an artery or arteriole dilates to twice its initial radius, then resistance in the vessel will decrease to 1/16 of its original value and flow will increase 16 times. 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.
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