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في تصنيف التعليم بواسطة (17.8ألف نقاط)

تلخيص المرحلة الثانية - تحليلات مرضية الفصل الاول


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Introduction

Parasites: are traditionally considered to be protists, worms and arthropods, adapting themselves to live in or on another organisms termed host . Host….. organism harbouring a parasite.

The relationship between two dissimilar organisms that are adapted to living together is called Symbiosis and the associates are symbionts.

General kinds of symbiosis : Commensalism ,Mutualism, and Parasitism.

Commensalism: Occurs when one member of the associating pair, usually the smaller, receives all the benefit and the other member is neither benefited nor harmed, the commensal organism referred as Non-pathogenic, exp. Entamoeba coli

Mutualism: Occurs when each member of the association benefits the other, exp. termites and their flagellates.

Parasitism: The original meaning of the word parasite was one who eats at another's table, or one who lives at another's expense. Parasite benefits, gain shelter and nutrition on the expanse of the other (host).The host may suffer from wide range of functional and organic disturbances due to such association. The parasitic organism referred as pathogenic, exp. Entamoeba histolytica (Pathogenic).

Types of parasites:

1. Ectoparasite : lives on the outside of the body( on the surface)and the relationship called infestation most parasitic arthropods belong to this category.

2. Endoparasite: lives within the body of the host (infection).

3. Temporary or intermittent parasite: visit the host from time to time for food.

4. Facultative parasite: organism that can exist in a free living state or as a parasite.

5. Obligatory parasite: cannot survive without a host

Types of hosts:

1. Definitive or final host: host with adult stage or sexually reproducing forms of the parasite.

2. Intermediate host: host with the larval stage or asexually reproducing forms of parasite.

3. Reservoir host: is an animal (non-human) that harbors the same species of parasite as man, act as source of human infection.

4. Carrier host: human who carries parasites and can pass them on to others.

5. Vector host: is an invertebrate organism (Arthropoda commonly insects) that carries the parasite from one host to another.

The vector may either be a:

1. Mechanical vector, in which no development or multiplication takes place.

2. Biological vector, in which either multiplication or development occurs.

Mode of parasitic infections :

1. Congenital….from mother to fetus.( e.g. ; Toxoplasma).

2. Direct contact….through the skin (e.g.;Mites) or sexually (e.g.; Trichomonas vaginalis ).

3. Ingestion of contaminated food and water …. (e.g.;Entamoeba ) or undercooked meat in which the infective stage has developed (e.g.; Taenia ).

4. Penetration of the skin ….due to contact with water stream (e,g,; Scistohsoma cercaria ).

5. Inhalation…. Of dust carrying the infective stage of parasite. (e,g,;Enterobius vermicularis eggs).

6. Vectors….through the bite or feces of infected vector (e.g.; Trypanosoma spp.).

7. Autoinfection ….occurs when infective stages are carried from feces to mouth of infected person (e.g.; Enterobius vermicularis ).

Source of parasitic infection :

1. food ….Meat ( Taenia sginata larvae ) ; Vegatables …. (E.histolytica cysts ).

2. Water …. Protozoal cysts ( E. histolytica,Cryptosporidium ); Cercaria(Schistosoma ) .

3. Soil…. Contaminated with feces contained ( Ascaris, Ancylostoma ,Giardia ).

4. Association with domestic animals…. Dogs: ( Echinococcus granulosus and Leishmania ). Cats: ( Toxoplasma ).

5. Arthropods….blood sucking ( Plasmodium, Trypanosoma, Leishmania ).

6. Blood transfusion….(erythrocytic stages of Plasmodium ).

7. Congenital transplantation….( Toxoplasma,Plasmodium ).

8. Sexual intercourse….(Trichomonas vaginalis ).

9. Inhalation of dust ….( Enterobius vermicularis ).

Habitat of parasites :

The habitat is the site where the parasite lives and multiplies in host, such as :

1. Small intestine …( Giardia ).

2. Large intestine …( ,Entamoeba histolytica ).

3. Blood vessels …(Schistosoma spp. ).

4. Muscles …(Trichinella spiralis ).

5. Lymphatic…(Wucheraria bancrofti ).

Traditional classification of parasite :

Classification of protozoa

Diverse structure of protozoa have developed to aid in movement and feeding in many environments. Traditional classification of protozoa are based mainly on their structural morphology and ways of moving.

The traditional four class's classification, based largely on movement, includes the following groups:

1. Rhizopoda (Amoebae): uses pseudopodial structures, flowing cytoplasm. Amoebas are protozoa that move by employing pseudopodia. Many amoebas also employ their pseudopodia to engulf food .

2. Mastigophora (Flagellates) : are protozoa that move by means of flagellar action.

3. Ciliophora: use cilia . Ciliates are protozoa that move by means of cilia action. The difference between eukaryotic flagella and cilia is one of size and number. Cilia are small and numerous; flagella are large and few.

4. Telospora (sporpzoa): creeping or gliding. The sporozoans are parasitic spore formers that do not move under their own power.

Life cycle stages

During its life cycle, a protozoan generally passes through several stages that differ in structure and activity , the stages are:

●Trophozoite : is a general term for the active ,feeding, multiplying stage of most protozoa

●Cyst : a non motile stage which is protected by a cell wall, protozoan cysts that must survive outside the host usually have more resistant walls than cysts that form in tissue ,cysts contain one or more infective form .

●Oocysts : are stages resulting from sexual reproduction .

Reproduction

Reproduction in the protozoa may be asexual, as in the amoebae and flagellates that infect humans, or both asexual and sexual. The most common type of asexual multiplication is :

1- Binary fission …

2- multiple fission ( shizogony )

3- Endodyogeny ( budding )

4- Endopolygeny : more than two cells resulting from internal budding of parent .

Sexual reproduction or multiplication, which is usually takes place in the invertebrate host

1. Sporogony : through gametes

2. Conjugation: occurs in ciliate ,it is a temporary union of two ciliated organisms for the exchange of nuclear material.

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