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eFigure 35–25. Life cycle of Schistosoma mansoni (blood fluke). Contact with water exposes skin to cercarial penetration. Worms mature in the liver and migrate to mesenteric vessels, where females lay eggs that work through into the lumen of the large intestine and pass out in human wastes. Eggs captured in intestinal tissues or liver are encapsulated in a granulomatous response (inset). Susceptible intermediate host snails (Biomphalaria) are penetrated by miracidia that hatch from eggs that reach snail-inhabited water. Sporocyst multiplication in the snail results in large numbers of infective cercariae that leave the snail and seek to penetrate human skin. 1–9: The skin is penetrated by a cercaria, which breaks off its forked tail and passes into the dermis through a hair follicle (1). A mature pair of worms in the liver (2) migrates up mesenteric vessels (3) to egg-laying sites near or within villi. The eggs cytolyze or mechanically work their way through villi into the gut lumen (4), enter water with feces (5), and quickly hatch, releasing ciliated miracidia (6) that penetrate a host snail. The penetrating larva passes through two or perhaps several generations of sporocysts (7). Cercariae produced by the final sporocyst generation pass into the water (8) and collect near the surface, suspended by their forked tails (9), awaiting the stimulus of nearby human skin for penetration and onset of a new cycle. (Reproduced, with permission, from Goldsmith R, Heyneman D [editors]. Tropical Medicine and Parasitology. Originally published by Appleton & Lange. Copyright © 1989 by The McGraw-Hill Companies, Inc.)

Current Medical Diagnosis & Treatment 2018 > Protozoal & Helminthic Infections

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eFigure 35–28. Life cycles of Fasciola hepatica and F gigantica (liver flukes). A grazing cow ingests vegetation contaminated with metacercariae. Young flukes excyst, penetrate through the intestine, and pass directly into the liver parenchyma and bile ducts, where maturation of flukes follows. Undeveloped eggs are excreted via bile into stool. If this occurs in marshy or wet areas inhabited by host snails (Lymnaea), the miracidia within the eggs develop, hatch, and infect the snails by penetration. In the snail, miracidia become sporocysts that produce rediae that multiply and finally produce swarms of cercariae. These motile larvae emerge, swim from the snail, and encyst on nearby aquatic vegetation. 1–10: After excystation (1), the fluke passes through the gut wall directly into the liver and bile ducts (3). The mature fluke (2) produces large numbers of undeveloped eggs (4) that pass in feces from the host, mature in water (5), hatch, and release miracidia (6) that invade a suitable snail in which multiplication occurs through sporocyst formation and successive generations of rediae (7, 8), resulting finally in shedding from the snail of great numbers of cercariae (9). These swimming larvae encyst on aquatic or immersed vegetation (10), the source of infection of cattle and other herbivores or of humans. (Reproduced, with permission, from Goldsmith R, Heyneman D [editors]. Tropical Medicine and Parasitology. Originally published by Appleton & Lange. Copyright © 1989 by The McGraw-Hill Companies, Inc.)

Current Medical Diagnosis & Treatment 2018 > Protozoal & Helminthic Infections

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eFigure 9–41. Normal lung ventilation with xenon-133. With the patient's single full breath, inhaled radioxenon is evenly distributed to all lung areas, reaching the terminal airways and alveoli in the normal patient (A, posterior view). There is a less noticeable gradient of activity from the upper to the lower lung fields than is seen in perfusion lung images. Fifteen-second images obtained during closed-system rebreathing of a xenon–oxygen mixture show uniform distribution at 120 seconds (B). Serial 15-second frames after switching the patient to room air breathing (C to G) show a homogeneous pattern of washout from all lung areas. This sequence mainly evaluates the posterior lung regions. To better localize gas trapping in specific lung segments or more anterior regions, the acquisition may be modified after the rebreathing phase by rotating the patient into posterior oblique positions. Selected images from a complete study include single breath (H, posterior view), the late phase of rebreathing (I, posterior view), posterior washout (J), left posterior oblique washout (K), and right posterior oblique washout (L). No gas is retained in this patient, which is normal, but in obstructive airway disease gas retention persists and is better localized in the oblique views than in a posterior view alone. A small amount of alveolar xenon normally crosses the alveolar membrane to reach the blood and be distributed throughout the body. Because it is highly soluble in lipids, xenon accumulates in adipose tissue, including the liver, which is faintly seen with prolonged rebreathing. Liver activity should not be mistaken for delayed washout of xenon from the base of the lung. Occasionally, splenic blood pool radioactivity or swallowed xenon in the stomach may also be seen. (SIN BRE = single breath, L REB =late rebreathe, WO =washout.) (Reproduced, with permission, from Baum S et al. Atlas of Nuclear Medicine Imaging, 2nd ed. Originally published by Appleton & Lange. Copyright © 1993 by The McGraw-Hill Companies, Inc.)

Current Medical Diagnosis & Treatment 2018 > Pulmonary Disorders

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eFigure 9–41. Normal lung ventilation with xenon-133. With the patient's single full breath, inhaled radioxenon is evenly distributed to all lung areas, reaching the terminal airways and alveoli in the normal patient (A, posterior view). There is a less noticeable gradient of activity from the upper to the lower lung fields than is seen in perfusion lung images. Fifteen-second images obtained during closed-system rebreathing of a xenon–oxygen mixture show uniform distribution at 120 seconds (B). Serial 15-second frames after switching the patient to room air breathing (C to G) show a homogeneous pattern of washout from all lung areas. This sequence mainly evaluates the posterior lung regions. To better localize gas trapping in specific lung segments or more anterior regions, the acquisition may be modified after the rebreathing phase by rotating the patient into posterior oblique positions. Selected images from a complete study include single breath (H, posterior view), the late phase of rebreathing (I, posterior view), posterior washout (J), left posterior oblique washout (K), and right posterior oblique washout (L). No gas is retained in this patient, which is normal, but in obstructive airway disease gas retention persists and is better localized in the oblique views than in a posterior view alone. A small amount of alveolar xenon normally crosses the alveolar membrane to reach the blood and be distributed throughout the body. Because it is highly soluble in lipids, xenon accumulates in adipose tissue, including the liver, which is faintly seen with prolonged rebreathing. Liver activity should not be mistaken for delayed washout of xenon from the base of the lung. Occasionally, splenic blood pool radioactivity or swallowed xenon in the stomach may also be seen. (SIN BRE = single breath, L REB =late rebreathe, WO =washout.) (Reproduced, with permission, from Baum S et al. Atlas of Nuclear Medicine Imaging, 2nd ed. Originally published by Appleton & Lange. Copyright © 1993 by The McGraw-Hill Companies, Inc.)

Current Medical Diagnosis & Treatment 2018 > Pulmonary Disorders

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