protozoa: [s., protozoan; greek protos, first, and zoon, animal] a protozoan can be defined as a...

BMS 241

Introduction

Protozoa:

[s., protozoan; Greek protos, first, and zoon, animal]

A protozoan can be defined as a usually motile,

eukaryotic, unicellular protest. the most important groups are the:

1) Flagellates,

2) Amoebae,

3) Ciliates.

Distribution

Protozoa grow in a wide variety of moist habitats.

Most protozoa are free living and inhabit Fresh water

or marine environments.

Many terrestrial protozoa can be found in decaying

organic matter, in soil, and even in beach sand; some

are parasitic in plants or animals.

Morphology

Because protozoa are

eukaryotic cells, in many

respects their morphology and

physiology are the same as the

cells of multicellular animals .

Morphologysome morphological and physiological features are

unique to protozoan cells.

Ectoplasm:

In some species the cytoplasm immediately under the

plasma membrane is semisolid or gelatinous, giving some

rigidity to the cell body. It is termed the ectoplasm. The

bases of the flagella or cilia and their associated fibrillar

structures are embedded in the ectoplasm.

Morphology

Endoplasm:

Inside the ectoplasm is the area referred to as the

endoplasm, which is more fluid and granular in

composition and contains most of the organelles.

MorphologyNuclues:

Some protozoa have one nucleus, others have two or

more identical nuclei.

Morphology

The vacuoles:

One or more vacuoles are usually present in the cytoplasm

of protozoa.

These are differentiated into:

1. Contractile vacuoles.

2. Secretory vacuoles.

3. Phagocytic vacuoles.

Morphology

1. contractile vacuoles:

function as osmoregulatory organelles in those protozoa.

2. Secretory vacuoles:

usually contain specific enzymes that perform various

functions.

3. Phagocytic vacuoles:

the sites of food digestion.

Encystment

Many protozoa are capable of encystations.

They develop into a resting stage called a cyst.

Cyst :

Is a dormant form marked by the presence of a wall and

by very low metabolic activity. Cyst formation is

particularly common among aquatic, free-living

protozoa and parasitic forms.

EncystmentCysts functions:

They protect against adverse changes in the environment,

such as nutrient deficiency, pressure of O2.

Excystment

Although the exact stimulus for excystation (escape from

the cysts) is unknown, excystation generally is triggered by

a return to favorable environmental conditions.

For example, cysts of parasitic species excyst after

ingestion by the host and form the vegetative form called

the trophozoite.

Locomotory Organelles

A few protozoa are nonmotile.Most, however, can move by one of three major types of locomotory organelles:

pseudopodia,

flagella,

or cilia.

Locomotory Organelles

Pseudopodia:

[s., pseudopodium; false feet]

Are cytoplasmic extensions found in the amoebae that are

responsible for the movement and food capture.

There are many types of pseudopodia:

Flagellates move by flagella

Ciliates move by cilia.protozoan flagella and cilia are structurally the same and identical in function to those of other eukaryotic cells.

Reproduction

Type of protozoa reproduction:

• A sexual reproduction:binary fission:

During this process the nucleus first undergoes mitosis,

then the cytoplasm divides to form two identical

individuals.

Reproduction

• Sexual reproduction:

Conjugation:

In this process there is an exchange of gametes between

paired protozoa of complementary mating types.

Transmission of Protozoa

Transmission:

Transmission from one host to another within a cyst.

Pathogenic protozoa can spread from one infected

person to another by:

Faecal – oral transmission of contaminated foods and

water.

Insect.

Pathogenesis of protozoaPathogenesisProtozoan have numerous ways to enter the body of the human hostFactors that are important for pathogenecity include:

Attachment to the host tissue followed by replication

to establish colonization.

Toxic products released by parasitic protozoa.

Shifting of antigenic expression to evade the

immune response and inactivate hostdefences.

Antiprotozoal agentsAntiprotozoal agents

Generally the antiprotozoal agents target relatively

rapidly proliferating, young, growing cells of the

parasite.

Most commonly, these agents target nucleic acid

synthesis, protein synthesis, or specific metabolic

pathways (e.g. folate metabolism) unique to the

protozoan parasites..

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