By T. Fabio. Kentucky State University.
Articulations © The McGraw−Hill Anatomy cheap 800mg viagra vigour mastercard erectile dysfunction doctors in ny, Sixth Edition Companies generic viagra vigour 800 mg with mastercard erectile dysfunction treatments herbal, 2001 Chapter 8 Articulations 205 FIGURE 8. Note the diagrammatic representation showing the direction of with the base of the first metacarpal bone. Suture Edges of articulating bones frequently jagged; None Sutures between bones of the skull separated by thin layer of fibrous tissue 2. Syndesmoses Articulating bones bound by interosseous ligament Slightly movable Joints between tibia-fibula and radius-ulna 3. Gomphoses Teeth bound into dental alveoli of bone by Slightly movable Dentoalveolar joints (teeth secured in periodontal ligament dental alveoli) Cartilaginous Joints Skeletal elements joined by fibrocartilage or hyaline cartilage 1. Symphyses Articulating bones separated by pad of fibrocartilage Slightly movable Intervertebral joints; symphysis pubis 2. Synchondroses Mitotically active hyaline cartilage located None Epiphyseal plates within long bones; between skeletal elements costal cartilages of rib cage Synovial Joints Joint capsule containing synovial membrane and synovial fluid 1. Gliding Flattened or slightly curved articulating surfaces Sliding Intercarpal and intertarsal joints 2. Hinge Concave surface of one bone articulates with Bending motion in one plane Knee; elbow; joints of phalanges convex surface of another 3. Pivot Conical surface of one bone articulates with Rotation about a central axis Atlantoaxial joint; proximal depression of another radioulnar joint 4. Condyloid Oval condyle of one bone articulates with Movement in two planes Radiocarpal joint; elliptical cavity of another metacarpophalangeal joint 5. Saddle Concave and convex surface on each Wide range of movements Carpometacarpal joint of thumb articulating bone 6. Ball-and-socket Rounded convex surface of one bone articulates Movement in all planes and Shoulder and hip joints with cuplike socket of another rotation Van De Graaff: Human IV. Articulations © The McGraw−Hill Anatomy, Sixth Edition Companies, 2001 Developmental Exposition cleft eventually enlarges to become the joint cavity. Thin pads of The Synovial Joints hyaline cartilage develop on the surfaces of the epiphyses that contact the joint cavity. As the joint continues to develop, a EXPLANATION highly vascular synovial membrane forms on the inside of the The sites of developing synovial joints (freely movable joints) are joint capsule and begins secreting a watery synovial fluid into the discernible at 6 weeks as mesenchyme becomes concentrated in joint cavity. At this In certain developing synovial joints, the mesenchymal stage, the future joints appear as intervals of less concentrated cells do not migrate away from the center of the joint cavity. As cartilage cells develop within a forming Rather, they give rise to cartilaginous wedges called menisci, as bone, a thin flattened sheet of cells forms around the cartilagi- in the knee joint, or to complete cartilaginous pads called articu- nous model to become the perichondrium. Most synovial joints have formed completely by the end Surrounding the gap, the flattened mesenchymal cells differenti- of the third month. Shortly thereafter, fetal muscle contrac- ate to become the joint capsule. During the early part of the third month of development, the Joint movement enhances the nutrition of the articular carti- mesenchymal cells still remaining within the joint capsule begin to lage and prevents the fusion of connective tissues within migrate toward the epiphyses of the adjacent developing bones. At 12 weeks, the synovial joints are formed and have either (c) a free joint cavity (e. Articulations © The McGraw−Hill Anatomy, Sixth Edition Companies, 2001 Chapter 8 Articulations 207 Extension MOVEMENTS AT SYNOVIAL JOINTS In extension, which is the reverse of flexion, the joint angle is Movements at synovial joints are produced by the contraction of increased (fig. Extension returns a body part to anatomi- skeletal muscles that span the joints and attach to or near the cal position. In an extended joint, the angle between the articu- bones forming the articulation. An exception is the ankle joint, in which levers, the muscles provide the force, and the joints are the fulcra, there is a 90° angle between the foot and leg in anatomical posi- or pivots. Examples of extension are straightening of the elbow or Objective 10 List and discuss the various kinds of knee joints from flexion positions. Hyperextension occurs when movements that are possible at synovial joints.
In fact no consistent correlation has been found between the appearance purchase viagra vigour 800 mg erectile dysfunction desensitization, distribution and number of amyloid plaques and either neuronal loss or the degree of dementia purchase viagra vigour 800mg otc erectile dysfunction getting pregnant, although the latter correlates with the number of neurofibrillary tangles, which tend to precede plaques in appearance by some years. Also cortical amyloid deposits can be found in non-demented elderly patients. Thus the basic question appears to be: does the disease process, whatever that is, cause the development of AzD as well as the pro- duction of b-amyloid or is there production of b-amyloid, which then causes AzD? AETIOLOGY If b-amyloid deposition is responsible for AzD, it is important to know what causes its production. Since AzD is most common in the elderly and as b-amyloid is found in the normal aged brain, it is likely that AzD depends on some predisposing factor that increases amyloid production and which may strike early in life but is more likely to become apparent during ageing. Mutations of the APP gene on chromosome 21, the apolipoprotein E (ApoE) gene on chromosome 19, the presenilin 1 (Ps1) gene on chromosome 14 and presenilin 2 (Ps2) gene on chromosome 1 have all been implicated in AzD. GENETIC MUTATION A number of family mutations of the APP gene on chromosome 21 have been found, generally in early-onset AzD patients in different countries, all of which lead to increased b-amyloid production. Also chromosome 21 is abnormally trisomic in Down Syndrome and most Down sufferers develop AzD if they reach 40 years. In transgenic mice, expressing familial AzD mutations of APP, the overexpression of APP is accompanied by increased amyloid deposition but whether this is due to the mutation or overexpression of APP is uncertain. Also not all the animals show memory loss and that tends to precede the amyloid disposition. Three distinct forms of ApoE, E2, E3 and E4 are encoded on chromosome 19 but it is the ApoE, E4 allele that occurs at a much higher frequency in late-onset AzD patients (50%) compared with controls (16%) and binds to and possibly increases the formation of b-amyloid. The precise physiological role of these 463 and 448 amino-acid transmembrane proteins is unclear but plasma and brain tissue from patients with PS mutations contain above-normal levels of the b-amyloid protein as do transgenic mice expressing PS mutations and cells transfected with mutant PS. Thus all the above genetic mutations can lead to increased amyloid deposition and possibly AzD (see Smith 1998). Unfortunately familial AzD represents only the minority of cases and so other causes need to be considered. HEAD INJURIES It has been estimated that up to 15% of head injuries may lead to AzD with dementia being common among boxers (dementia pugilistica). Certainly such trauma is associated with diffuse amyloid deposits (not plaques) and a number of neurofibrillary tangles apparently identical to those in AzD. ALUMINIUM Reported positive associations between AzD and a high aluminium level in drinking water promoted that element as a risk factor for, or cause of, AzD. Since then aluminium in silicate form has been found in plaques and tangles and shown to impair the axonal transport of neurofilament. However, the occurrence of high brain levels of aluminium, either through environmental exposure or dialysis encephalopathy, is not associated with a greater incidence of AzD and the neurofibrillary changes it produces appear different from those of AzD. Currently while aluminium is accepted to be neurotoxic, it is thought to be a more likely cause of neurological impairments than AzD. INFLAMMATION The finding that patients treated with non-steroidal anti-inflammatory drugs (NSAIDs) like asprin were less likely to develop AzD stimulated the suggestion that AzD may have an inflammatory component and indeed NSAIDs have been shown to have a protective effect against AzD. It remains to be seen whether this is a true anti- inflammatory effect or whether the NSAIDs are protecting by reducing free radical production. SUMMARY Even if there is a link between the presence of tangles and plaques and the emergence of AzD, it is by no means certain how those markers could be responsible for all the symptoms. They do not seem to be sufficiently numerous or widely spread to disrupt brain function to the extent that eventually occurs in AzD, although their preferential location in the hippocampus and the known association of that area with memory processing could explain the loss of that faculty. Since therapy for AzD, like that for the other major neurodegenerative disorder Parkinsonism, could depend on establishing to what extent its pathology is associated 380 NEUROTRANSMITTERS, DRUGS AND BRAIN FUNCTION with the loss of neurotransmitter function, it is important to consider NT changes in AzD. NEUROTRANSMITTER CHANGES IN AzD The NT most consistently implicated in AzD is ACh. ACETYLCHOLINE It is 20 years since a 50% reduction was noted in the level of choline acetyltransferase (ChAT), the enzyme responsible for ACh synthesis, in the frontal cortex and hippocampus of AzD patients (Bowen et al. ACh itself was not easily measured at that time but a reduced synthesis of ACh from 14C glucose was observed in brain tissue from AzD patients. There is in fact a significant correlation between the reduction in ChAT and both the increased number of plaques and tangles at death and the severity of mental impairment six months before death (Perry et al. ACh loss is not global, no change being found in the striatum or some parts of the cortex. Recently reduced ACh levels have been reported in CSF obtained by lumbar puncture, though it is surprising that it survived degradation (Tohgi et al.
The patient’s symptom perception may have been influenced by information from family purchase viagra vigour 800 mg visa erectile dysfunction drugs new, friends purchase 800 mg viagra vigour mastercard erectile dysfunction treatment in rawalpindi, or the media, or by consulting the internet. Also, the patient may claim to have benefited from a diagnostic intervention because he does not wish to disappoint the doctor. The key challenge for the investigator is now to evaluate the extent to which applying the diagnostic test has independently changed the doctor’s diagnostic or prognostic assessment of the presented clinical problem, the preferred management option, or the patient’s health status. The latter will generally be influenced indirectly, via clinical management, but can sometimes also be directly affected, for example because the patient feels himself being taken more seriously by the testing per se. Moreover, patient self testing, which is nowadays becoming more common, can influence patient self management. At this point, two important limitations of the before–after design must be emphasised. First, the design is more appropriate to evaluate the impact of “add on” technologies2 (that is, the effect of additional testing) than to compare the impact of different diagnostic technologies or strategies. For the latter purpose one could, in principle, apply both studied technologies, for example colonoscopy and double contrast barium enema, in randomised order, to all included patients, and then compare the impact of disclosing the test results, again in random order, on the clinicians’ assessment. Another example would be to subject patients to both CT and 85 THE EVIDENCE BASE OF CLINICAL DIAGNOSIS NMR head scanning to study their influence on clinicians’ management plans in those with suspected intracranial pathology. However, such comparisons are unrealistic, as the two tests would never be applied simultaneously in practice. Moreover, such studies are very burdensome for patients, not to say ethically unacceptable, and would make it virtually impossible to study the complication rate of each procedure separately. In such situations, a randomised controlled trial is by far the preferred option. Only when the compared tests can be easily carried out together without any problem for the patient, can they be applied simultaneously. This can be done, for instance, when comparing the impact of different blood tests using the same blood sample. However, when the disclosure of the results of the compared tests to the clinicians is then randomised, which would be a good idea, we are in fact in the RCT option. Second, demonstrating an effect of diagnostic testing on the patient’s health outcome is much more difficult than showing a change in the doctor’s assessment and management plan. In fact, this is often impossible, as it usually takes quite some time to observe a health effect that might be ascribed to performance of the test. Controlling for the influence of the many possible confounders over time generally requires a concurrent control group of similar patients not receiving the test. However, a diagnostic before–after study could be convincing in case of: (1) studying a clinical problem with a highly predictable outcome in the absence of testing (such as unavoidable death in the case of imminent rupture of an aneurysm of the aorta), (2) while adding specific diagnostic information (an appropriate imaging technique) leading to a specific therapeutic decision (whether and how to operate) (3), which is aimed at a clearly defined short term effect (prevention of a rupture and survival), possibly followed by less specific long term effects (rehabilitation). Besides, although on the one hand some clinicians would consider such clinical situations to be self evident and not needing evaluation by research, others may still see room for dispute as to what extent clinical events are predictable or unavoidable. Working out the study Pretest baseline The study protocol follows the elements of the research question. The clinical problem could be aspecific symptoms as presented in primary care, with the question being whether the ESR would contribute to the doctor’s 86 THE DIAGNOSTIC BEFORE–AFTER STUDY diagnostic assessment,3,4 or sciatica, in order to study whether radiography would affect therapeutic decision making. The health status of each patient to be included is systematically documented, using standardised measurement instruments for the presented symptoms, patient history, physical examination, and further relevant clinical data. Overseeing all available patient data, the doctor makes a first clinical assessment of the probability of certain diagnoses or diagnostic categories. In primary care, for example, the probability of a severe organic malignant or inflammatory, disorder can be assessed. This can be done for one specified diagnostic category, for a list of specified diagnoses, or in an open approach, just asking the differential diagnosis the doctor has in mind, with the estimated probability of each specific diagnostic hypothesis being considered. Furthermore, the doctor is asked to describe the preferred diagnostic or therapeutic management plan, which can be done, again, according to a prepared list of items or as an open question. At baseline, possibly relevant effect modifying variables should be considered.
Exploring the etiology of content specificity: factors influencing analogic transfer and problem solving purchase viagra vigour 800 mg on line erectile dysfunction at age 35. Diagnostic reasoning of high- and low- domain knowledge clinicians: a re-analysis purchase 800 mg viagra vigour with visa depression and erectile dysfunction causes. Propositional versus structural semantic analyses of medical diagnostic thinking. What goes around comes around: the return of the hypothetico-deductive strategy. Recall of previously unrecallable information following a shift in perspective. Clinical versus statistical prediction:A theoretical analysis and review of the evidence. Family physicians’ attitudes about and use of clinical practice guidelines. VIII: how to use clinical practice guidelines, A: are the recommendations valid? VIII: how to use clinical practice guidelines, B: what are the recommendations and will they help me in caring for my patient? Patient-specific decisions about hormone replacement therapy in postmenopausal women. Probabilistic reasoning in clinical medicine: problems and opportunities. Support theory: a nonextensional representation of subjective probability. Probability judgment in medicine: discounting unspecified probabilities. Differential diagnosis and the competing hypotheses heuristic: A practical approach to judgment under uncertainty and Bayesian probability. Information gathering and integration as sources of error in diagnostic decision making. The accuracy of experienced physicians’ probability estimates for patients with sore throats. Influence of a single example on subsequent electrocardiogram interpretation. Clinical reasoning about new symptoms in the face of pre-existing disease: sources of error and order effects. Time to heal: American medical education from the turn of the century to the era of managed care. Such interventions are audit, individual feedback, peer review, and computer reminders. Resting Membrane Potential 000 CHAPTER 16: The Microcirculation and the Stephen A. Lymphatic System 000 CHAPTER 3: The Action Potential, Synaptic Transmission, and H. Maintenance of Nerve Function 000 CHAPTER 17: Special Circulations 000 Cynthia J. CHAPTER 18: Control Mechanisms in Circulatory Function 000 PART II Thom W. PART V CHAPTER 5: The Motor System 000 RESPIRATORY PHYSIOLOGY • 000 John C. CHAPTER 19: Ventilation and the Mechanics of Breathing 000 CHAPTER 6: The Autonomic Nervous System 000 Rodney A. CHAPTER 20: Pulmonary Circulation and CHAPTER 7: Integrative Functions of the Nervous System 000 Ventilation-Perfusion Ratio 000 Cynthia J. MUSCLE PHYSIOLOGY • 000 CHAPTER 22: The Control of Ventilation 000 CHAPTER 8: Contractile Properties of Muscle Cells 000 Rodney A. PART VI CHAPTER 10: Cardiac Muscle 000 RENAL PHYSIOLOGY AND BODY FLUIDS • 000 Richard A. PART IV CHAPTER 24: The Regulation of Fluid and BLOOD AND CARDIOVASCULAR PHYSIOLOGY • 000 Electrolyte Balance 000 CHAPTER 11: Blood Components, Immunity, and Hemostasis 000 George A. CHAPTER 25: Acid-Base Balance 000 CHAPTER 12: An Overview of the Circulation and George A. GASTROINTESTINAL PHYSIOLOGY • 000 CHAPTER 13: The Electrical Activity of the Heart 000 CHAPTER 26: Neurogastroenterology and Gastrointestinal Thom W.
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