Ameba Biology PDF

Ameba: Greek word "amibe“ meaning change it my be free-living or intestinal Reproduction : occurs by fission and budding. Trophozoite Trophozoite is the vegetative or growing stage of the parasite. lt is the only form present in tissues. -1t is irregular in shape and varies in -It is large and activ...

Ameba: Greek word "amibe“ meaning change it my be free-living or intestinal Reproduction : occurs by fission and budding. Trophozoite Trophozoite is the vegetative or growing stage of the parasite. lt is the only form present in tissues. -1t is irregular in shape and varies in -It is large and actively motile in freshly-passed dysenteric stool -The endoplasm contains nucleus, food vacuoles, erythrocytes, occasionally leukocytes and tissue debris. the phagocytosed red cells are not found in any other commensal intestinal amebae and it is a diagnostic features. -Pseudopodia are finger-like projections formed by sudden jerky movements of ectoplasm in one direction, followed by the streaming in of the whole endoplasm. -the newly developed one after the rupture of the cyst is called Metacystic trophozoites which is do not colonize in the small intestine, but are carried to the cecum. Precystic Stage Trophozoites undergo encystment in the intestinal lumen. Encystment does not occur in the tissues nor in feces outside the body. Before encystment, the trophozoite extrudes its food vacuoles and becomes round or oval, This is the precystic stage of the parasite. It contains a large glycogen vacuole and two chromatid bars. It then secretes a highly retractile cyst wall around it and becomes cyst. Cystic Stage -The cyst is spherical in shape The early cyst contains a s ingle nucleus and two other structures: (1) a mass of glycogen (2) 1-4 chromatoid bodies or chromidial bars, which are cigar shaped refractile rods with rounded ends. As the cyst matures, the glycogen mass and chromidial bars disappear and the nucleus undergoes two successive mitotic divisions to form two and then four nuclei. The mature cyst is, thus quadrinucleate nd it is the Infective Form which can remain viable under moist conditions for about 10 days The cyst wall is a highly refractile membrane, which makes it highly resistant to gastric juice and unfavorable environmental conditions. Excystation: When the cyst reaches cecum or lower part of the ileum, due to the alkaline medium, the cyst wall is damaged by trypsin, leading to excystation. called Metacyst which is quadrinucleate ameba Amebic ulcer The ulcers are multiple and are confined to the colon, being most numerous in the cecum. Ulcers appear initially on the mucosa as raised nodules with pouting edges measuring pinhead to l inch. They later break down discharging brownish necrotic material containing large numbers of trophozoites.the typical amebic ulcer is flask-shaped in cross section, with mouth and neck being narrow and base large and rounded. Extraintestinal Amebiasis - Hepatic amebiasi: Although trophozoites reach the liver in most case of amebic dysentery, only in a small proportion do they manage to lodge and multiply there. - Pulmonary amebiasis: most often follow extension of hepatic abscess through the diaphragm and therefore, the lower part of the right lung is the usual area affected. - Metastatic amebiasis: in kidney, brain, spleen and adrenals have been noticed. - Genitourinary amebiasis: which is acquired through anal intercourse.