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It is characterized by defecation difficulty untary control over the muscular mechanisms of conti- or failure cheap zoloft 100mg free shipping. This condition is tested clinically by distending an colon buy cheap zoloft 50mg line, because the proximal colon may become grossly intrarectal balloon order 25 mg zoloft mastercard. The healthy subject will perceive the enlarged with impacted feces order 100 mg zoloft with visa, or congenital agan- distension with an instilled volume of 15 mL or less purchase zoloft 50mg online, glionosis, because the ganglia of the ENS fail to develop whereas the sensory-deprived patient either will not report in the terminal region of the large intestine. Mutations in any sensation at all or will require much larger volumes RET or endothelin genes account for the disease in some before becoming aware of the distension. Incompetence of the internal anal sphincter is usually Enteric neurons may be absent in the rectosigmoid re- related to a surgical or mechanical factor or perianal dis- gion only, in the descending colon, or in the entire colon. Disorders of the The aganglionic region appears constricted as a result of neuromuscular mechanisms of the external sphincter and continuous contractile activity of the circular muscle, pelvic floor muscles may also result from surgical or me- whereas the normally innervated intestine proximal to the chanical trauma, such as during childbirth. Physiological deficiencies of the skeletal motor mech- The constricted terminal segment of the large intestine anisms can be a significant factor in the common occur- in Hirschsprung’s disease presents a functional obstruc- rence of incontinence in older adults. Constriction ing tone of the internal anal sphincter does not seem to and narrowing of the lumen of the segment reflects un- decrease with age, the strength of contraction of the ex- controlled myogenic contractile activity in the absence of ternal anal sphincter does weaken. Moreover, the stri- inhibitory motor neurons ated muscles of the external anal sphincter and pelvic Incontinence is an inappropriate leakage of feces and floor lose contractile strength with age. This condition flatus to a degree that it disables the patient by disrupting occurs in parallel with a deterioration of nervous func- routine daily activities. As discussed earlier, the mecha- tion, reflected by decreased conduction velocity in fibers nisms for maintaining continence involve the coordinated of the pelvic nerves. Clinical examination with intra-anal interactions of several different components. Conse- manometry reveals a decreased ability of the patient quently, sensory malfunction, incompetence of the inter- with disordered voluntary muscle function to increase in- nal anal sphincter, or disorders of neuromuscular mecha- tra-anal pressure when asked to “squeeze” the intra-anal nisms of the external sphincter and pelvic floor muscles catheter. This oc- Control by Inhibitory Motor Neurons of the Length of In- curs coincidently with control of contractile strength. Con- testine Occupied by a Contraction and the Direction of tractions can only occur in segments where ongoing inhi- Propagation of Contractions. The state of activity of in- bition has been inactivated, while it is prevented in hibitory motor neurons determines the length of a con- adjacent segments where the inhibitory innervation is ac- CLINICAL FOCUS BOX 26. As a re- Failure of peristalsis in the esophageal body or failure of the sult, the ingested material does not enter the stomach and lower esophageal sphincter to relax will result in dysphagia accumulates in the body of the esophagus. Some people show abnormally megaesophagus, in which distension and gross enlarge- high pressure waves as peristalsis propagates past the ment of the esophagus are evident. This condition, cases of achalasia, peristalsis does not occur in response called nutcracker esophagus, is sometimes associated to a swallow. Achalasia is a disorder of inhibitory motor neurons in In diffuse spasm, organized propagation of the peri- the lower esophageal sphincter. The number of neurons staltic behavioral complex fails to occur after a swallow. In- in the lower esophageal sphincter is reduced, and the lev- stead, the act of swallowing results in simultaneous con- els of the inhibitory neurotransmitter VIP and the enzyme tractions all along the smooth muscle esophagus. This degenerative disease manometric tracings, this response is observed as a syn- results in a loss of the inhibitory mechanisms for relaxing chronous rise in intraluminal pressure at each of the the sphincter with appropriate timing for a successful recording sensors. Myogenic contraction occurs in segments of intestine where inhibitory motor neurons are inactive. Sequential inactivation in the oral direction permits logical ileus occurs in segments of intestine where the inhibitory oral propagation of contractions. The oral and aboral boundaries of a contracted seg- vomiting, the integrative microcircuits of the ENS inacti- ment reflect the transition zone from inactive to active in- vate inhibitory motor neurons in a reverse sequence, allow- hibitory motor neurons. This is the mechanism by which ing small intestinal propulsion to travel in the oral direction the ENS generates short contractile segments during the and propel the contents toward the stomach (see Clinical digestive (mixing) pattern of small intestinal motility and Focus Box 26. Transiently Activated for Timed Opening As a result of the functional syncytial properties of the and the Passage of Luminal Contents musculature, inhibitory motor neurons are necessary for control of the direction in which contractions travel along The circular muscle of sphincters remains tonically con- the intestine. The directional sequence in which inhibitory tracted to occlude the lumen and prevent the passage of motor neurons are inactivated determines whether contrac- contents between adjacent compartments, such as between tions propagate in the oral or aboral direction (Fig. Inhibitory motor neurons are nor- Normally, the neurons are inactivated sequentially in the mally inactive in the sphincters and are switched on with aboral direction, resulting in contractile activity that prop- timing appropriate to coordinate the opening of the sphinc- agates and moves the intraluminal contents distally. During ter with physiological events in adjacent regions CLINICAL FOCUS BOX 26. At the same time, the longitudinal During emesis (vomiting), powerful propulsive peristalsis muscle of the esophagus and the gastroesophageal junc- starts in the midjejunum and travels to the stomach. The overall result is the formation of a funnel- result, the small intestinal contents are propelled rapidly like cavity that allows the free flow of gastric contents into and continuously toward the stomach.

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The ureters enter the base of the bladder obliquely buy 25 mg zoloft visa, Micturition is fortunately under voluntary control in forming a valvular flap that passively prevents the reflux of healthy adults zoloft 25mg visa. In the young child order zoloft 100 mg online, however buy discount zoloft 100mg, it is purely re- urine during contractions of the bladder cheap 25 mg zoloft with amex. The ureters are in- nervated by sympathetic and parasympathetic nerve fibers. Sensory fibers mediate the intense pain that is felt when a stone distends or blocks a ureter. Descending aorta L1 Inferior vena cava The Bladder Stores Urine Until It Can Be L2 Sympathetic trunk Conveniently Emptied L3 The urinary bladder is a distensible hollow vessel contain- ing smooth muscle in its wall (Fig. The muscle is called the detrusor (from Latin for “that which pushes down”). The neck of the bladder, the involuntary internal sphincter, also contains smooth muscle. The bladder body and neck are innervated by parasympathetic pelvic nerves S2 and sympathetic hypogastric nerves. The external sphinc- Right ureter S3 ter, the compressor urethrae, is composed of skeletal mus- Hypogastric S4 cle and innervated by somatic nerve fibers that travel in the pudendal nerves. Pelvic, hypogastric, and pudendal nerves nerve Pelvic nerve contain both motor and sensory fibers. Bladder The bladder has two functions: to serve as a distensible Pudendal nerve reservoir for urine and to empty its contents at appropriate intervals. When the bladder fills, it adjusts its tone to its ca- Internal (involuntary) pacity, so that minimal increases in bladder pressure occur. The first sensation of bladder filling is sphincter experienced at a volume of 100 to 150 mL in an adult, and the first desire to void is elicited when the bladder contains FIGURE 24. A person becomes uncom- parasympathetic pelvic nerves arise from spinal fortably aware of a full bladder when the volume is 350 to cord segments S2 to S4 and supply motor fibers to the bladder 400 mL; at this volume, hydrostatic pressure in the bladder musculature and internal (involuntary) sphincter. Sympathetic motor fibers supply the bladder via the hypogastric nerves, which is about 10 cm H2O. With further volume increases, blad- arise from lumbar segments of the spinal cord. The pudendal der pressure rises steeply, partly as a result of reflex con- nerves supply somatic motor innervation to the external (volun- tractions of the detrusor. Sensory afferents (dashed lines) from the bladder creates pain and often loss of control. The sensations of travel mainly in the pelvic nerves but also to some extent in the bladder filling, of conscious desire to void, and painful dis- hypogastric nerves. Grant’s Atlas of tension are mediated by afferents in the pelvic nerves. At about 21/2 years of age, it begins to come under result of enlargement of the surrounding prostate gland. Damage to the nerves that supply the it results in decreased urine stream, overdistension of the bladder and its sphincters can produce abnormalities of bladder as a result of incomplete emptying, and increased micturition and incontinence. A 60-year-old woman is always thirsty items of incomplete statements in this the largest percentage of filtered Mg2 and wakes up several times during the section is followed by answers or is the night to empty her bladder. Select the (A) Proximal convoluted tubule osmolality is 295 mOsm/kg H2O ONE lettered answer or completion that is (B) Thick ascending limb (normal range, 281 to 297 mOsm/kg BEST in each case. Which of the following body fluid (E) Medullary collecting duct are higher than normal. The volume of the extracellular fluid is (A) Cardiac failure artery most closely related to the amount of (B) Decreased plasma levels of (E) Stimulation of renal sympathetic which solute in this compartment? Arginine vasopressin (AVP) is synthesized in the (C) Insulin administration 14. A homeless man was found comatose, (A) Adrenal cortex (D) Intravenous infusion of a NaHCO3 lying in the doorway of a downtown (B) Anterior hypothalamus solution department store at night. His plasma (C) Anterior pituitary (E) Skeletal muscle injury osmolality was 370 mOsm/kg H2O (D) Collecting ducts of the kidneys 9. Parathyroid hormone (PTH) (normal, 281 to 297 mOsm/kg H2O), (A) Decreases tubular reabsorption of plasma [Na ] was 140 mEq/L (normal, (E) Posterior pituitary Ca2 136 to 145 mEq/L), plasma [glucose] 4. A 60-kg woman is given 10 microcuries ( CI) (370 kilobecquerels) (B) Decreases tubular reabsorption of 100 mg/dL (normal fasting level, 70 to of radioiodinated serum albumin phosphate 110 mg/dL), and BUN 15 mg/dL (RISA) intravenously.

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Parenchymal hemorrhage is best seen on inversion re- covery or T2-weighted sequences generic 50 mg zoloft visa, and is often normal ap- Muscle Strain pearing on T1-weighted images purchase 25 mg zoloft overnight delivery. The appearance of a sub- acute parenchymal bleed is very nonspecific as the blood Muscle strains typically involve the myotendinous junc- does not undergo a phase of methemoglobin formation purchase zoloft 100 mg online, tion of the muscle discount zoloft 50mg free shipping. A sagittal T1-weighted MR of the hip shows a Soft-tissue hemorrhage can collect as a discrete hematoma order zoloft 50mg with amex. The MR joint caused by a large appearance of hematomas is highly variable depending up- hematoma. The MR appearance of muscle hematomas high signal intensity at the anterior periphery follows the same progression as in the brain but the time of the lesion produced course may be longer and less predictable. Acute blood has by methemoglobin low signal intensity on both T1- and T2-weighted images due to the presence of intracellular deoxyhemoglobin. Subacute hematomas have a distinctive appearance due to the formation of methemoglobin, particularly at the pe- riphery of the hematoma (Fig. Methemoglobin pro- duces T1 shortening, resulting in high signal intensity within the hematoma on T1-weighted images. Fluid-fluid levels within the hematoma are common, particularly in large hematomas. In chronic hematoma, some of the iron in the methemoglobin is converted to hemosiderin and fer- ritin, which deposit in the hemorrhage and adjacent tissues. These substances result in signal loss on both T1- and T2- weighted images, producing a low-signal halo around the hematoma. Myositis Ossificans Myositis ossificans is a circumscribed mass of calcified and ossified granulation tissue that forms as a response to trauma. The early MR appearance is very nonspecific and can easily be mistaken for a neoplasm. An axial T2-weighted MR of the periostitis is typically present with this lesion. On excision, the mass was found tis ossificans may show a fat signal centrally due to mar- to beimmature myositis ossificans row formation or there may be persistent granulation- type tissue within its central regions. Compartment Syndrome Acute compartment syndrome is a surgical emergency re- quiring compartment decompression, and MR is not in- dicated in most cases. Compartment syndrome is seen most commonly in the lower extremity, typically be- low the knee, in patients who have undergone injury. However, any location can be involved, including the thigh, forearm and paraspinal musculature. The MR find- ings are nonspecific, though changes limited to all the muscles in a signal compartment should suggest the di- agnosis. Mild unilateral swelling and a slight increase of muscle intensity on T2-weighted images is present (Fig. In chronic compartment syndrome, the pain 4 days after total knee replacement and MR was ordered to evaluate for infection. The MR shows hyperintensity of the deep muscles are very atrophic and often densely fibrotic. Compartment calcification may be present, particularly Compartment pressures were subsequently obtained and confirmed in the peroneal compartment. MR can show the anatom- the diagnosis of compartment syndrome Magnetic Resonance Imaging of Muscle 53 ic extent of the muscle injury and the degree of muscle Gordon BA, Martinez S, Collins AJ (1995) Pyomyositis: charac- loss present. Calcific myonecrosis is an unusual condi- teristics at CT and MR imaging. Radiology 197:279-286) Holobinko JN, Damron TA, Scerpella PR, Hojnowski L. Calcific tion in which either compartment syndrome progresses to myonecrosis: keys to early recognition. The cavity presents as a 32(1):35-40, (2003) fusiform mass filled with liquefied necrotic muscle that Liu GC, Jong YJ, Chiang CH, Jaw TS (1993) Duchenne muscular is surrounded by a thin shell of calcification. Radiology 186:475-480 Lovitt S, Marden FA, Gundogdu B, Ostrowski ML (2004) MRI in myopathy. Neurol Clin 22(3):509-38 Rhabdomyolysis Mellado JM, Pérez del Palomar L, Díaz L, Ramos A, Saurí A (2004) Long-standing Morel-Lavallée lesions of the Infarction of muscle may be due to massive trauma or trochanteric region and proximal thigh: MRI features in five patients. Many other etiologies, includ- Palmer WE, Kuong SJ, Elmadbouh HM (1999) MR imaging of ing vascular abnormalities and unstable diabetes, have myotendinous strain. AJR 173:703-709) been reported to produce the syndrome of rhabdomyoly- Petersilge CA, Pathria MN, Gentili A, Recht MP, Resnick D (1995) sis. JCAT The involved muscles show mild infiltration of the intra- 19:596-600 Restrepo CS, Lemos DF, Gordillo H, Odero R, Varghese T, muscular fat planes but there is a paucity of mass effect.

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