8/22/2023 0 Comments Download worm body![]() Tapeworms are unique in lacking an alimentary canal. Internally, the alimentary, excretory, and reproductive systems can be identified by an experienced observer. Male nematodes of several species possess accessory sex organs that are external modifications of the cuticle. ![]() Prominent external structures of flukes and cestodes are acetabula (suckers) or bothria (false suckers). The outer covering of helminths is the cuticle or tegument. Platyhelminths and nematodes that infect humans have similar anatomic features that reflect common physiologic requirements and functions. Stages of Helminths Commonly Responsible for Pathologic Changes in Humans. The contributions of various stages to disease are listed in Table 86-2. Knowledge of the different stages in relation to their growth and development is the basis for understanding the epidemiology and pathogenesis of helminth diseases, as well as for the diagnosis and treatment of patients harboring these parasites. Table 86-1 gives the names applied to various larval helminths. Helminths develop through egg, larval (juvenile), and adult stages. This chapter deals with the structure and development of the three major groups of helminths. These groups are subdivided for convenience according to the host organ in which they reside, e.g., lung flukes, extraintestinal tapeworms, and intestinal roundworms. Roundworms are nematodes (nemato from the Greek root meaning “thread”). In medically oriented schemes the flatworms or platyhelminths (platy from the Greek root meaning “flat”) include flukes and tapeworms. The helminths are invertebrates characterized by elongated, flat or round bodies.
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