introdu. protozoa 2nd year module
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MEDICAL PROTOZOOLOGY
Protozoa are unicellular
microorganisms.They may be free living
or parasitic.
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GENERAL CHARACTERISTIC FEATURES
OF PROTOZOA
The vital functions of the protozoa areperformed by the protoplasm which
is differentiated into cytoplasm andnucleoplasm. The cytoplasm consistsof the ectoplasm and the endoplasmNucleus consists of a nuclearmembrane which surrounds thenucleoplasm. The nucleus may becompact or vesicular.
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Ectoplasm :This is the outer layer of thecytoplasm. It is viscid and finely granular. It isconcerned mainly with movement, ingestion offood, excretion, secretion, respiration, andprotection
Endoplasm is less viscid than the ectoplasm andmore granular. It is concerned with the digestionand reproduction of the protozoon. It contains the
nucleus, food vacuoles, and stored food material inthe form of glycogen. It may also containcontractile vacuoles for regulation of osmotic
pressure as in ciliates and free living amoeba.
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CYTOPLASM
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MOVEMENT IN PROTOZOA
Pseudopodia Flagella Cilia
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Ingestion of Food: According to
the type of protozoa.
Through pseudopodia or
a slit like mouth peristome as inciliates.
Others, feed by diffusion of
already prepared food throughthe cell membrane.
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Excretion:
Metabolic waste products are expelled by theaid of contractile vacuoles (ciliates),
diffusion through the ectoplasm (flagellates),
or
as in malaria the metabolic by-products are
deposited in the form of pigment granules inthe endoplasm.
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Secretion: Various substances are secretedby the protozoa. Entamoeba histolytica can
secrete histiolytic enzymes to aid in itspenetration of tissues, antigenic materialsand some protozoa secrete a cyst wall, as ameans of protection and a means of transmission to a new host.
Respiration: This is either anaerobic as inamoeba or aerobically as the malaria
parasites.Reproduction: This may be sexual or
asexual.
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CLASSIFICATION OF PROTOZOA
They are divided into four phyla:
Sarcomastigophora,
Apicomplexa,
Microspora
and Ciliophora.
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SARCOMASTIGOPHORA
These are the protozoa which move with
the aid of pseudopodia, flagella or bothand include two subphyla Sarcodina andMastigophora
A) SARCODINA
Members of this subphylum arecharacterized by have two stages:
Trophozoites move with the aid of
pseudopodia.Cystic stage
Asexual reproduction is by binary fission
e.g Entamoeba histolytica
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B) MASTIGOPHORA
Members of this subphylum characterizedby have the following characters:
Trophozoites move with the aid of one or
more flagella.Asexual reproduction is mainly bylongitudinal binary fission e.g. blood and
tissue flagellates e.g. Leishmania andTrypanosomes, genito-urinary flagellatese.g. Trichomonas vaginalis and digestive
tract flagellates e.g. Giardia lamblia .
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FLAGELLATES
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APICOMPLEXA
Members of this phylum have the followingcharacters:
They possess an apical complex which can beseen by the electron-microscope.
There is both sexual (sporogony) and asexualreproduction (schizogony).
There are no definite organs of locomotion
The secretion of microemes and rhoptriesfacilitate the entry of the parasite into the host.
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APICOMPLEXA
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The phylum Apicomplexa possess acomplicated life cycle involving sexual andasexual multiplication. These cycles can
occur in the same host or in two differenthosts. Members of Apicomplexa are;
Plasmodia spp. Toxoplasma gondii
Isospora belli Cryptosporidia
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CILIOPHORA
Members of this phylum possess the
following characters
Trophozoites move with the aid of cilia.
They divide asexually by binary fission
and sometimes sexually byconjugation.
They possess contractile vacuoles e.g.
Balantidium coli.