Platyhelminthes PDF

Subkingdom Metazoa Phylum Platyhelminthes 1-Class: Turbellaria 2-Class: Trematoda 3-Class: Cestoda ex: planaria ex :Fasciola ex:Taenia  Class: Cestoda Characteristics of class: All of...

Subkingdom Metazoa Phylum Platyhelminthes 1-Class: Turbellaria 2-Class: Trematoda 3-Class: Cestoda ex: planaria ex :Fasciola ex:Taenia  Class: Cestoda Characteristics of class: All of Cestoda are endoparasites and entirely lack an alimentary canal and absorb digested food through their body surface. They usually have long flat worms, composed of a linear series of reproductive units or proglottids. Most hermaphrodite, cestodes require at least two hosts, For examples: Taenia saginata it lives as an adult in the human intestine. A mature adult may reach a length of 10-12 meters, which may have 1000 - 2000 proglottids. Body consists of 3 regions: Scolex: bears hooks, suckers or other attachment organs Neck: It is narrow unsegmented region followed by a linear series of reproductive units or proglottids. The segments followed neck immature segments, then mature segments. Finally gravid segments are formed. A tapeworm, a parasitic flatworm ‫ دودة مفلطحة طفيلية‬، ‫دودة شريطية‬ Units with reproductive structures ‫وحدات ذات تراكيب تكاثرية‬ Scolex Hooks ‫خطاطيف‬ (anterior end) )‫رأس (طرف أمامي‬ Sucker ‫ممصات‬ Taenia saginata Have no digestive organs: absorb nutrients directly from the host’s digestive tract through their tegument highly folded to increase the surface area for absorption Nervous system: Usually comprises a pair of ganglia in scolex and two lateral longitudinal nerve cords which extend longitudinally through each segment. -Excretory system: It composed of flame cells which attached to small canals which lead to the excretory canals. Excretory canals in the scolex are continued along the length of the body by a pair of dorsolateral, and a pair of ventrolateral, excretory canals. These paired canals are connected by a transverse excretory canal near the posterior end of each proglottid. Reproductive system: They are hermaphrodite, every proglottid contain two sets of genitallia, male genital system and female genital system. Male reproductive system: It consists of numerous small scattered spherical testes connected to vasa efferentia that join to become a single vas deferens. The vas deferens commonly leads into seminal vesicle and hence to a papilla-like penis and opens by the male opening Female reproductive system: It consists of one large bilobed ovary, which is posterior in poobed ovary, which is posterior in position connected to oviduct. This passes backwards and unites with the vitelline duct wand, which lies posterior to the ovary. At the place of union of the vitelline duct and oviduct there is a small enlargement, the ootype. The uterus is at first in more mature (gravid) proglottides, and on becoming full of eggs, becomes much branched. The gravid proglottid is longer than the mature proglottides, with a my branched uterus (15-20 main branches on each side) packed with eggs. Life cycle: complicated, involving: one intermediate host harboring the larval stages in which they develop an essential host harboring the mature stages in which they reproduce sexually -Life cycle: - The sperms travel down the vagina to fertilize the ova in the lower part of the of the oviduct. - In the uterus, development of the egg begins straight away, to form a six hooked larva (hexacanth embryo) which is surrounded by hard radially striated embryophore. - When the terminal gravid proglottides with their eggs break off and pass out with the faeces, the proglottides disintegrate and the eggs with the embryos may be scattered on the soil, grass dust, etc., where they may be picked up by grazing cattle. - When the cattle swallows the eggs or proglottides, the egg shells are dissolved off in the intestine and the hexacanth embryos burrow through the intestinal wall into the blood or lymph vessels. - the heart to the muscles, they encyst to become bladderworm (cysticerci). Here in a no ten to twenty weeks the larvae develop svetu weeks the larvae develop an invaginated scolex with suckers. Infection to man takes place by eating insufficiently cooked beef meet cysticerci. - When the cyst wall is dissolved off by the digestive inice bladder is digested, the scolex evaginates and becomes attached to the and new proglottides begin to develop. It takes 2-3 weeks for a matu When man is infected with one of these tapeworms many sin expelled daily from his intestine.It takes 2-3 weeks for a mature worm to form. ne of these tapeworms many single proglottlides are