醫(yī)學寄生蟲學：線蟲概論

1、HelminthsWorms with well developed organs systems. Two major groupsPhylum Platyhelminths （扁形動物門）or flatworms扁形蟲 Turbellarians 渦蟲Trematodes or flukes 吸蟲Cestodes or tapeworms 絳蟲Phylum Nemathelminthes（線形動物門）Nematodes or roundworms 線蟲Nematodes impact human life in many ways There are many, many nematode

2、s - both species and individuals:20,000 nematode species have been described, only a small fraction is parasitic The majority of nematodes are small predators and saprophytesNematode are important pests of many cropsNematodes are abundant pathogens in life-stock and pets Nematodes cause numerous hum

3、an diseasesNematodes provide powerful genetic models to study the basis of development, aging and many diseasesGeneral morphologyElongated, cylindricalTapered at both endsBilaterally symmetricalComplete digestive tract in most species Dioecious 雌雄異體and show considerable sexual dimorphism: females ar

4、e usually larger and the tail of males is more curled. Reproductive organs are tubular and lie coiled in the body cavity. Most females usually have two ovaries, oviducts and uterus.Partners are attracted to each other by pheromones 信息素Morphological characteristics Cross section through the midgut re

5、gion The body wall of nematodes is covered: Cuticle (角皮層): noncellular, cortical zone/median/ basal zoneHypodermis (皮下層): cellular or syncytial; formation of the cuticle protrudes into the pseudocoelom to form dorsal and ventral cords, lateral cords. Musculature (肌層): tightly attached to the hypoder

6、mis and cuticlePseudocoelom/pseudocoel （假體腔/原體腔）False body cavity: A tube within a tube，between the tubes is the fluid-filled pseudocoelom, in which the reproductive system and other structures are found No peritoneal liningContaining: transport of solution, electrolytes, proteins, fats Function: hy

7、drostatic skeleton流體靜力骨骼for protecting the internal organs, helping the movement and excretion of the wormeggVitelline layer (卵黃膜)Chitinous layer (殼質(zhì)層)Ovum or embryoLipid layer (蛔甙層)proteinaceous layer (蛋白質(zhì)外膜)Eggs consist of different morphologic eggshells and contents respectively.Eggshell may cons

8、ist of proteinaceous layerThe contents of eggs include cells, embryo or larva respectively. Oviparous 卵生 Ovoviviparous卵胎生Chitinous layer by light microscopyLife cycleThe development proceeds through 4 larval stages before reaching adulthood Ecdysis (molting of cuticle 蛻皮） is required at each stepMan

9、y nematodes can develop a specialized resting or Dauer version of the L3 larval stageIn parasitic nematodes this L3 larvae is often the infectious stage for the final hostKinds of life cycle in nematodesDirect life cycle: There are no intermediate host needed in the life cycle (The nematodes are cal

10、led geonematodes 土源性線蟲). Ascaris lumbricoides Trichuris trichiura Enterobius vermicularis HookwormsIndirect life cycle: There are one or more intermediate hosts required in the life cycle .(The nematodes are called bionematodes 生物源性線蟲 ). Trichinella spiralis FilariaPathology 1)Larvae： ( 1) dermatiti

11、s caused by cutaneous invasion and subcutaneous migration of larva ( 2) injury to organs or tissues by migration of larvae in the body2) Adults： (1) injury to intestinal mucosa caused by the parasites living in gastro- intestinal system (2) injury to lymphatic system, muscles or nervous system cause

12、d by the parasites living in tissuesDevelopmentCaenorhabdites elegans (秀麗隱桿線蟲)Freely live Model genome of Human Genome Project Simple anatomyTransparent: individual cells can be visualized and manipulatedSmall number of cells: 558 in first larval stageCells have stereotyped pattern of development: invariant lineageGenome sequenced: has 19,000 genes Introduction to Nematode Medical Parasitology Protozoa Helmi