Lecture #12: THE PROTOZOANS

Species belonging to this group are one–celled animals but its anatomical structures are more distinct than that of bacteria and have a more complicated life cycle. Cystic stage in some species is present to enable them to resist life outside the body of the host and to facilitate transfer from one person to another.

NOMENCLATURE

 

A.  Subphylum Sarcodina

1.  Class Rhizopodea

a.  Genus Entamoeba

(1)   Entamoeba histolytica

(2)   Entamoeba coli

(3)   Entamoeba gingivalis 

b. Genus Endolimax

(1)   Endolimax nana 

c.  Genus Dientamoeba

(1)   Dientamoeba fragilis 

d.  Genus Iodamoeba

(1)   Iodamoeba butschlii 

2.     Class Piroplasmea (e.g., Babesia)

3.     Class Actinopodea

 

B.   Subphylum Ciliophora

1.  Class Ciliatea

a.  Genus Balantidium

(1)   Balantidium coli

 

C.   Subphylum Mastigophora

1.  Class Zoomastigophora

a.  Atrial / Luminal flagellates

(1)   Genus Giardia

(2)   Genus Trichomonas

(3)   Genus Chilomastix

b.  Blood / Tissue flagellates

(1)   Genus Leishmania

(2)   Genus Trypanosoma

 

D.  Subphylum Sporozoa

1. Class Telosporea

a. Subclass Coccidia (e.g., Isospora)

(1)   Order Eucoccidia

(a)   Suborder Eimeriina

(b)  Suborder Hemosporina (e.g., Plasmodium)

b. Subclass Gregarina

2.  Class Toxoplasma (e.g., Sarcocystis, Toxoplasma)

3.  Class Haplosporea

CYTOLOGY OF PROTOZOANS

Protozoans are unicellular organism composed of nucleus and cytoplasm. The nucleus is concerned with reproduction. The cytoplasm is differentiated into ectoplasm (outer layer) and an endoplasm (inner layer).

Function of the ectoplasm:

 – protection, ingestion of food, locomotor apparatus, respiration, discharge of metabolic wastes.

– composed of:

a. Contractile vacuoles – osmoregulators of the cell.

b. Plasma membrane – semipermeable structure which controls the intake and output of foods, secretions and excretions and maintains normal concentration of the plasma substance.

c. Structures for locomotion: pseudopodia, flagella, cilia

d. Cytostome – cell mouth, specialized structure locate laterally near the anterior end of their body.

e. Excretory vacuoles – for the collection of fluid wastes, which are then ejected from the cell, usually at an abnormal end.

           

Function of endoplasm:

– storage and synthesis of food.

– composed:

a. Chromatoidal bodies – storage of glycogen or protein

b. Mitochondria

c. Golgi apparatus

d. Microsomes

e. Endoplasmic reticulum

Stages undergone by protozoan:

1. Trophozoite – vegetative stage of the protozoa; they are uninucleated, motile and actively growing.

2. Pre–cyst – non–motile stage; food absorbed during the trophozoite stage are excreted here.

3. Cyst – transfer of infective stage; latent, non–motile, resistant stage of certain protozoa; has a thick wall.

Encystation – development of cystic stage from trophozoite in unfavorable environmental conditions.

Factors responsible for encystation:

1.  Deficiency or overabundance of food supply.

2.  Excess of catabolic products of the organism or of associated bacteria.

3.  Marked change in pH.

4.  Dessication of the medium.

5.  Depletion or excess supply of oxygen

6.  Overpopulation

Two types of encystment:

1. Protective – cyst wall protects the organism outside the body of its host and for transfer to a new host but no profound morphologic change takes place within the cyst.

e.g., Balantidium coli

2. Reproductive – nuclei divides one or more times during the cystic stage with a corresponding increase in the number of trophozoites following excystation. Found in several amoeba and flagellates.