MEDICAL BIOLOGY, HUMAN ANATOMY, PHYSIOLOGY AND PATHOLOGY - Ya.I. Fedoniuk 2010

BIOLOGY

CHAPTER 2. BIOGEOCOENOTIC LEVEL OF LIFE ORGANIZATION AND HUMAN PLACE IN IT

2.3. MEDICAL PROTOZOOLOGY

Subkingdom Protozoa

Protozoa are single-celled animal organisms, the vast majority of which are microscopic in size. The total number of species ranges from 20,000 to 25,000. They are widely distributed in various environments, including fresh and marine waters, as well as soil. Many species lead a parasitic lifestyle.

The body of protozoa consists of Cytoplasm, a Nucleus, and an outer membrane. The cytoplasm is differentiated into two layers: 1) an outer, transparent, and denser layer (ectoplasm) and 2) an inner, granular layer (endoplasm). The endoplasm contains general-purpose Organelles (Cell/35.html">Mitochondria, Endoplasmic reticulum, Ribosomes, etc.) as well as specialized organelles that perform specific Functions such as locomotion (pseudopodia, flagella, cilia), Digestion (digestive vacuoles), excretion (contractile or pulsating vacuoles), and defense (trichocysts in Ciliates). Contractile vacuoles are responsible for eliminating excess Water, liquid dissimilation products, maintaining constant osmotic pressure, and supplying The Cell with oxygen. Protozoa may contain one or multiple nuclei, which possess the typical Structure of a Introduction/5.html">Eukaryotic Cell nucleus. Protozoa reproduce through both Selection/8.html">Asexual and sexual modes. In some species, an alternation of asexual and sexual reproduction (metagenesis) occurs.

A hallmark feature of protozoa is their ability to form cysts under unfavorable conditions (encystation). During this process, protozoa cease movement, assume a spherical shape, lose their locomotor organelles or retract them into the cell body, and become covered by a thick protective wall. Metabolic processes within the cyst slow down significantly. In the encysted state, protozoa can withstand extreme environmental fluctuations (desiccation, cooling, exposure to chemicals) while remaining viable. Upon the return of favorable conditions, the cysts rupture (excystation), and the protozoa emerge as active vegetative forms. During its active metabolic phase, a protozoan cell is referred to as a trophozoite.

Classification OF PROTOZOA. According to the recommendations of the International Committee on Taxonomy of Protozoa (1980), all protozoa are grouped into the subkingdom Protozoa, which comprises 7 phyla. Human parasitic protozoa belong to three phyla: Sarcomastigophora, Apicomplexa, and Ciliophora (ciliates). The classification is primarily based on The structure of locomotor organelles and reproductive characteristics.