انت هنا الان : شبكة جامعة بابل > موقع الكلية > نظام التعليم الالكتروني > مشاهدة المحاضرة
الكلية كلية الطب
القسم الاحياء المجهرية
المرحلة 3
أستاذ المادة هيام خالص عنفوص المسعودي
6/8/2011 11:49:24 AM
Helminthology
The designation (helminth) means (worm). It comprises two large phyla, the platyhelminthes(flat worms) and the nematodes (true round worms).
The two classes of the platyhelminthes to be considered, the trematoda(flukes) and cestoda (tape worms) are parasitic in all or most of their life cycle stage. Many spp. of the phylum nematoda are free living .
Trematoda
The Trematoda is a class within the phylum Platyhelminthes , The parasites are so named because of their conspicuous suckers, the organs of attachment (trematos means "pierced with holes"). All the flukes that cause infections in humans belong to the group of digenetic trematodes. Trematodes are commonly referred to as flukes. This term can be traced back to the Old English name for flounder, and refers to the flattened, rhomboidal shape of the worms.
Features of digenic trematodes
-
Digenic trematodes are unsegmented leaf-shaped worms that are flattened dorsoventrally.
-
They bear 2 suckers, one surrounding the mouth (oral sucker) and another on the ventral surface of the body (ventral sucker). These serve as the organs of attachment.
-
The sexes of the parasites are not separate (monecious). An exception is schistosomes, which are diecious (unisexual).
-
The alimentary canal is incomplete, and no anus is present.
-
The excretory system is bilaterally symmetrical. It consists of flame cells and collecting tubes. These flame cells provide the basis for the identification of the species.
-
The reproductive system consists of male and female reproductive organs and is complete in each fluke.
-
The flukes are oviparous. They lay operculated eggs. An exception is schistosome eggs, which are not operculated.
-
All have complicated life cycles, with alternating asexual and sexual developments in different hosts.
Life cycles
Almost all trematodes infect mollusks as the first host in the life cycle, and most have a complex life cycle involving other hosts. Most trematodes are monoicous and alternately reproduce sexually and asexually. The two main exceptions to this are the Aspidogastrea, which have no asexual reproduction, and the schistosomes, which are dioecious.
In the definitive host, in which sexual reproduction occurs, eggs are commonly shed along with host feces. Eggs shed in water release free-swimming larval forms that are infective to the intermediate host, in which asexual reproduction occurs.
eggs get swallowed by a snail and here they hatch into tiny, transparent larva (miracidium). These larvae grow and take on a sac-like appearance. This stage is known as the sporocyst and it forms a central body in the snail s digestive gland that extends into a brood sac in the snail s head, muscular foot and eye-stalks. It is in the central body of the sporocyst where the parasite replicates itself, producing lots of tiny embryos (redia). These embryos move to the brood sac and mature into cercaria.
Classification of trematodes according to their habitat
-
Blood flukes -Schistosoma haematobium, Schistosoma mansoni, Schistosoma japonicum, Schistosoma mekongi, and Schistosoma intercalatum
-
Liver flukes -F hepatica, Fasciola gigantica, C sinensis, Opisthorchis felineus, O viverrini, Dicrocoelium dendriticum, and Dicrocoelium hospes
-
Pancreatic flukes -Eurytrema pacreaticum, Eurytrema coelomaticum, and Eurytrema ovis
-
Lung flukes -P westermani, Paragonimus mexicana, and Paragonimus skrjabini
-
Intestinal flukes -F buski, M yokogawai, Echinostoma ilocanum, Watsonius watsoni, H heterophyes, and Gastrodiscoides hominis
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
|