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.