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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