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The four muscles of the quadriceps femoris muscle are the rectus femoris buy cheap metformin 500 mg line, vastus lateralis buy metformin 500mg cheap, vastus medialis metformin 500 mg discount, and vastus intermedius discount 500 mg metformin visa. Posterior buy discount metformin 500 mg, or Flexor, Muscles The rectus femoris muscle occupies a superficial position There are three posterior thigh muscles, which are antagonistic to and is the only one of the four quadriceps that functions in both the quadriceps femoris muscles in flexing the knee joint. The laterally positioned vastus lateralis muscles are known as the hamstrings (fig. It is a common The name derives from the butchers’ practice of using the tendons intramuscular injection site in infants who have small, underde- of these muscles at the knee of a hog to hang a ham for curing. Muscular System © The McGraw−Hill Anatomy, Sixth Edition Companies, 2001 Chapter 9 Muscular System 281 The biceps femoris muscle occupies the posterior lateral aspect of the thigh. It has a superficial long head and a deep short head, and causes movement at both the hip and knee joints. The superficial semitendinosus muscle is fusiform and is located on the posterior medial aspect of the thigh. The flat semimembranosus muscle lies deep to the semitendinosus on the posterior medial aspect of the thigh. The posterior thigh muscles that move the leg at the knee joint are summarized in table 9. The relative positions of the muscles of the thigh are illustrated in figure 9. The injury usually occurs when sudden lateral or medial stress to the knee joint tears the muscles or tendons. Because of its struc- ture and the stress applied to it in competition, the knee joint is highly susceptible to injury. Altering the rules in contact sports could reduce the incidence of knee injury. At the least, additional support and pro- tection should be provided for this vulnerable joint. Muscles of the Leg That Move the Joints of the Ankle, Foot, and Toes The muscles of the leg, the crural muscles, are responsible for the movements of the foot. There are three groups of crural mus- cles: anterior, lateral, and posterior. The anteromedial aspect of the leg along the body of the tibia lacks muscle attachment. Anterior Crural Muscles The anterior crural muscles include the tibialis anterior, extensor digitorum longus, extensor hallucis longus, and peroneus tertius mus- cles (figs. Adductor longus Pubis—below pubic crest Linea aspera of femur Adducts, flexes, and laterally rotates Obturator n. Muscular System © The McGraw−Hill Anatomy, Sixth Edition Companies, 2001 TABLE 9. Muscular System © The McGraw−Hill Anatomy, Sixth Edition Companies, 2001 Chapter 9 Muscular System 283 Patellar tendon FIGURE 9. These two muscles are synergistic in flexing the ankle joint palpated on the anterior lateral portion of the tibia (fig. The extensor digitorum longus muscle is positioned lateral to the tibialis ante- Posterior Crural Muscles rior on the anterolateral surface of the leg. The superficial group is composed of the gas- small peroneus tertius muscle is continuous with the distal por- trocnemius, soleus, and plantaris muscles (fig. It consists of two distinct heads that arise from the posterior brevis (figs. This The long, flat peroneus longus muscle is a superficial lat- muscle and the deeper soleus muscle insert onto the calcaneus eral muscle that overlies the fibula. The peroneus brevis muscle via the common tendo calcaneus (tendon of Achilles). This is the lies deep to the peroneus longus and is positioned closer to the strongest tendon in the body, but it is frequently ruptured from Van De Graaff: Human IV. Muscular System © The McGraw−Hill Anatomy, Sixth Edition Companies, 2001 284 Unit 4 Support and Movement FIGURE 9. The popliteus muscle two muscles are frequently referred to as a single muscle, the tri- is a medial rotator of the knee joint during locomotion. The soleus and gastrocnemius muscles have a bipennate flexor hallucis longus muscle lies deep to the soleus common insertion, but the soleus acts on only the ankle joint, in muscle on the posterolateral side of the leg. It has a very long, slender ten- soleus, and it parallels the flexor hallucis longus muscle on the don of insertion onto the calcaneus.

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With these facts in mind metformin 500mg overnight delivery, it is appropriate to make 3) it shows bone (and skull fractures) to advantage; and 4) a few general comments on these imaging techniques and what it is less expensive than MRI 500mg metformin fast delivery. For details of the meth- 1) it does not clearly show acute or subacute infarcts or is- ods and techniques of CT and MRI consult sources such as chemia generic metformin 500mg overnight delivery, or brain edema; 2) it does not clearly differentiate Grossman (1996) purchase 500mg metformin amex, Lee et al cheap metformin 500 mg with mastercard. Magnetic Resonance Imaging (MRI): The tissues Tissue density is measured by the effects of x-rays on atoms of the body contain proportionately large amounts of pro- within the tissue as these x-rays pass through the tissue. Protons have a positive nucleus, a shell of Atoms of higher number have a greater ability to attenuate negative electrons, and a north and south pole; they func- (stop) x-rays while those with lower numbers are less able to tion like tiny spinning bar magnets. The various attenuation intensities are are arranged randomly in relation to each other due to the computerized into numbers (Hounsfield units or CT num- constantly changing magnetic field produced by the elec- bers). MRI uses this characteristic of protons to generate air is given a value of 1,000 and is black. When the fre- arachnoid hemorrhage illustrates the various shades seen in a quency of the RP matches the frequency of the spinning pro- CT (Fig. In general, the following table summarizes the ton, the proton will absorb energy from the radio wave (res- white to black intensities seen for selected tissues in CT. First, the magnetic effects of some protons are cancelled out and second, the magnetic effects and energy levels in others are increased. When the RP is turned off, the relaxed protons release energy (an “echo”) that is received by a coil and computed into an im- age of that part of the body. The two major types of MRI images (MRI/T1 and MRI/T2) are related to the effect of RP on protons and the reactions of these protons (relaxation) when the RP is turned off. In general, those cancelled out protons return slowly to their original magnetic strength. On the other hand, those protons that achieved a higher energy level (were not cancelled-out) lose their energy more rapidly as they return to their original state; the image con- structed from this time constant is T2 (Fig. The cre- 1-1 Computed Tomography (CT) in the axial plane of a patient ation of a T1-weighted image versus a T2-weighted image is with subarachnoid hemorrhage. Bone is white, acute blood (white) outlines the subarachnoid space, brain is grey, and cerebrospinal fluid based on a variation in the times used to receive the “echo” in third and lateral ventricles is black. Edema Dark grey Light grey to white Tumor Variable Variable Enhanced tumor White (Rarely done) Acute infarct Dark grey Light grey to white The following table summarizes the white to black inten- Subacute infarct Dark grey Light grey to white sities seen in MRI images that are T1-weighted versus T2- Acute ischemia Dark grey Light grey to white weighted. It should be emphasized that a number of varia- Subacute ischemia Dark grey Light grey to white tions on these two general MRI themes are routinely seen in the clinical environment. The advantages of MRI are 1) it can be manipulated to vi- sualize a wide variety of abnormalities or abnormal states Chapter 2 within the brain; and 2) it can show great detail of the brain This chapter presents 1) the gross anatomy of the spinal cord in normal and abnormal states. The disadvantages of MRI and its principal arteries; 2) the external morphology of the are 1) it does not show acute or subacute subarachnoid hem- brain, accompanied by MRIs and drawings of the vascula- orrhage or hemorrhage into the substance of the brain in any ture patterns from the same perspective; 3) cranial nerves detail; 2) it takes a much longer time to do and, therefore, as seen in specimens and in MRI; and 4) the meninges and is not useful in acute situations or in some types of trauma; ventricular spaces. Emphasis is placed on correlating exter- 3) it is, comparatively, much more expensive than CT, and nal brain and spinal cord anatomy with the respective vas- 4) the scan is extremely loud and may require sedation in cular patterns and on correlating external brain structures children. In some sections, considerable flexi- nization of the meninges includes clinical correlations, ex- bility has been designed into the format; at these points, amples of extradural, so-called “subdural”, and subarach- some suggestions are made as to how the atlas can be used. In addition, new clinical correlations and examples have The section showing the structure and relations of the ven- been included and a new chapter of USMLE-style review tricular system now includes samples of hemorrhage into questions has been added. Chapter 3 The dissections in Chapter 3 offer views of some of those brain structures introduced in Chapter 2. Certain structures and/or structural relationships—for example, the orienta- tion of the larger association bundles—are particularly suited to such a presentation. This chapter uses a represen- tative series of dissected views to provide a broader basis for learning human neuroanatomy. Because it is not feasible to illustrate every anatomic feature, the views and structures selected are those that are usually emphasized in medical neurobiology courses. These views provide basic informa- 1-3 A sagittal T2 weighted Magnetic Resonance Image (MRI). Brain is grey, blood vessels frequently appear black, and cerebrospinal tion necessary to make more detailed dissections, if appro- fluid is white. This scheme continues rostrally into the caudal nuclei of the dorsal thalamus and the poste- The study of general morphology of the hemisphere and rior limb of the internal capsule.

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Similarly generic metformin 500mg free shipping, values in children differ from those in adults discount 500mg metformin, and values in young adults sometimes differ from those in the elderly generic metformin 500 mg overnight delivery. Commonly effective 500 mg metformin, the “non-diseased” group consists of several different conditions order 500 mg metformin visa, for each of which the test specificity may vary. The overall specificity will depend on the “mix” of alternative diagnoses: the proportion of people in each of the categories that constitute the non-diseased; for example, prostate specific antigen may have a lower specificity in older people or those with prostatic symptoms, as it is elevated in men with benign prostatic hypertrophy. However, the decision to use a test is usually made because of the presenting problem of the patient and the route by which they reached the examining clinician. Hence, the actual range of variability in patients without the target condition will depend on the mechanism by which patients have ended up in that particular situation. As an example, consider a group of ambulant outpatients presenting with symptoms of venous thromboembolism without having this disease compared to a group of inpatients suspected of venous thromboembolism but actually having a malignancy. The specificity of a D-dimer test in outpatients will be lower than that in inpatients. The discriminatory power of tests often varies across settings because patients presenting with a clinical problem in one setting – for example primary care – are very different from those presenting to a secondary care facility with that clinical problem. These patients have been through a referral filter to get to the tertiary care centre. This concept can best be considered using the hypothetical results of a diagnostic test evaluation in primary care (Table 6. Imagine that patients are referred from this population to a source of secondary care, and that all the test positive patients are referred, but only a random half of the test negative patients. However, there appears to be a shift in threshold, with an increased sensitivity and a decreased specificity. If the practitioner is correct in identifying patients about whom there is an increased risk of disease, the table could well turn out like Table 6. In this case, because of the clinician’s skill and the use of other information, not only does the test threshold appear to be shifted, but the overall test performance of the test in secondary care has been eroded, as shown by the reduced odds ratio. The more successfully the primary care practitioner detects cases that are test negative but which nevertheless need Table 6. Disease Test Present Absent Total Positive 60 40 100 Negative 40 60 100 Total 100 100 200 Sensitivity 0. Disease Test Present Absent Total Positive 60 40 100 Negative 20 30 50 Total 80 70 150 Sensitivity 0. Disease Test Present Absent Total Positive 60 40 100 Negative 25 25 50 Total 85 65 150 Sensitivity 0. In many situations several tests are being used and the value of a particular test may depend on what tests have been done before,27 or simple prior clinical information. However, if the tests are conditionally dependent or associated with each other within diseased and non-diseased groups, for example because they both measure a similar metabolite, then the overall test performance of B is eroded, as judged by the OR changing from 2. In addition, there appears to be a threshold shift: the test is more sensitive but less specific in patients for whom A is positive than in those for whom A is negative. In other words, not only is the discrimination of the new test (B) less if done after the existing test (A), as judged by the odds ratio, but the calibration appears to differ depending on the result of the prior test. Have disease No disease A A Total A A Total B 36 24 60 16 24 40 B 24 16 40 24 36 60 Total 60 40 100 40 60 100 “Crude” sensitivity and specificity of both A and B 0. Have disease No disease A A Total A A Total B 40 20 60 20 20 40 B 20 20 40 20 40 60 Total 60 40 100 40 60 100 “Crude” sensitivity and specificity of both A and B 0. An example is provided by Mol and colleagues,30 who evaluated the performance of serum hCG (human chorionic gonadotrophin) measurement in the diagnosis of women with suspected ectopic pregnancy. As a consequence, an uncritical generalisation of the “unconditional” sensitivity will overestimate the diagnostic performance of this test if it is applied after an initial examination with ultrasound, as is the case in clinical practice. For example, whole-body positron emission tomography (PET) contributed most additional diagnostic information in the subgroup of patients in whom prior conventional diagnostic methods had been equivocal. For assessment of replacement value, the cross- classification of the tests is not necessary to obtain unbiased estimates of how the diagnostic performance of the new test differs from that of the existing 106 DESIGNING STUDIES FOR TRANSFERABILITY one. However, information about how they are associated from a cross- classification will provide extra useful information and improve precision. The clinician may be using test A to alter the mix of A and A s that get through to secondary care, and the test performance of B reflects the way in which this mix has occurred.

Excess H is excreted as titratable acid and H2CO3 HbO2 HHb O2 HCO3 (27) NH4 ; these processes add new HCO3 to the blood metformin 500mg lowest price, This reaction raises the plasma [HCO3 ] buy discount metformin 500mg. This compensation takes tory acidosis discount metformin 500mg otc, such chemical buffering processes in the body several days to fully develop generic metformin 500 mg on line. Bicar- creases metformin 500 mg for sale, on average, by 4 mEq/L for each 10 mm Hg rise in bonate is not a buffer for H2CO3 because the reaction PCO2 (see Table 25. This rise exceeds that seen with acute respiratory acidosis because of the renal addition of H2CO3 HCO3 HCO3 H2CO3 (28) HCO3 to the blood. One would expect a person with is simply an exchange reaction and does not affect the pH. Basic Concepts and duces a rise in PCO2 and a fall in pH and is often associated Clinical Management. These changes stimulate breathing (see a Empirically determined average changes measured in people with Chapter 22) and diminish the severity of the acidosis. CHAPTER 25 Acid-Base Balance 441 With chronic respiratory acidosis, time for renal com- chronic hyperventilation and a PCO2 of 20 mm Hg, the pensation is allowed, so blood pH (in this example, 7. The difference between the two situ- Respiratory alkalosis is most easily understood as the ations is largely a result of renal compensation. Metabolic Acidosis Results From a Gain of Alveolar hyperventilation causes respiratory alkalosis. Noncarbonic Acid or a Loss of Bicarbonate Metabolically produced CO2 is flushed out of the alveo- lar spaces more rapidly than it is added by the pul- Metabolic acidosis is an abnormal process characterized monary capillary blood. This situation causes alveolar by a gain of acid (other than H2CO3) or a loss of HCO3. Hyperventilation and respira- Either causes plasma [HCO3 ] and pH to fall. If a strong 2 tory alkalosis can be caused by voluntary effort, anxiety, acid is added to the body, the reactions direct stimulation of the medullary respiratory center by H HCO H CO H O CO (35) some abnormality (e. This increase occurs only tran- ing respiratory alkalosis more than 95% of chemical siently, however, because the body is an open system, buffering occurs within cells. PCO2 actually falls below normal because an acidic blood pH stimulates phosphates liberate H ions, which are added to the ventilation (see Fig. Many conditions can produce metabolic acidosis, in- cluding renal failure, uncontrolled diabetes mellitus, lac- With acute respiratory alkalosis, plasma [HCO3 ] falls by about 2 mEq/L for each 10 mm Hg drop in PCO2 (see tic acidosis, the ingestion of acidifying agents such as Table 25. For example, if PCO drops from 40 to 20 mm 2 NH4Cl, abnormal renal excretion of HCO3 , and diar- Hg ([CO2(d)] 0. In renal failure, the kidneys cannot excrete H fast mEq/L, and the pH will be 7. Ingested NH4Cl is converted into urea and a strong acid, HCl, in the liver. Diarrhea causes a If plasma [HCO3 ] had not changed, the pH would loss of alkaline intestinal fluids. Excess acid is chemically buffered in extracellular and intracellular fluids and bone. Although hyperventilation acidosis, roughly half the buffering occurs in cells and causes respiratory alkalosis, hyperventilation also causes bone. This action lowers blood [H2CO3] and tends to alkalinize the blood, Renal Compensation. Metabolic acidosis is ac- ratory alkalosis by excreting HCO3 in the urine, thereby, companied on average by a l. A reduced PCO2 reduces H secretion l mEq/L drop in plasma [HCO3 ] (see Table 25. As a result, some of the fil- for example, the infusion of a strong acid causes the plasma tered HCO3 is not reabsorbed. If there was no res- more alkaline, titratable acid excretion vanishes and little piratory compensation and the PCO2 did not change from its ammonia is excreted. The enhanced output of HCO3 normal value of 40 mm Hg, the pH would be 7. Chronic respiratory alkalosis is accompanied by a 4 mEq/L fall in plasma [HCO3 ] for each l0 mm Hg drop in pH 6. The consequent reduction in 2 Diabetes mellitus is a common disorder characterized by blood [H2CO3] acts to move the blood pH back toward nor- an insufficient secretion of insulin or insulin-resistance by mal. The labored, deep breathing that accompanies severe the major target tissues (skeletal muscle, liver, and uncontrolled diabetes is called Kussmaul’s respiration. A severe metabolic acidosis may develop in The kidneys compensate for metabolic acidosis by re- uncontrolled diabetes mellitus.

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