The type of protozoa (Protozoa) includes over 15,000 species of animals living in the seas, fresh waters, and soil.In addition to free-living forms, many parasitic ones are known, which sometimes cause serious diseases - protozoonoses.
The body of a protozoan consists of only one cell.The body shape of protozoa is varied.It can be permanent, have radial, bilateral symmetry (flagellates, ciliates) or not have a permanent shape at all (amoeba).The body sizes of protozoa are usually small - from 2-4 microns to 1.5 mm, although some large individuals reach 5 mm in length, and fossil shell rhizomes had a diameter of 3 cm or more.
The body of protozoa consists of cytoplasm and nucleus.The cytoplasm is limited by the outer cytoplasmic membrane; it contains organelles - mitochondria, ribosomes, endoplasmic reticulum, and Golgi apparatus.Protozoa have one or more nuclei.The form of nuclear division is mitosis.There is also the sexual process.It involves the formation of a zygote.
Organelles of movement of protozoa are flagella, cilia, pseudopods;or there are none at all.Most protozoa, like all other representatives of the animal kingdom, are heterotrophic.However, among them there are also autotrophic ones.
The peculiarity of protozoa to tolerate unfavorable environmental conditions is their ability to encyst, i.e.form a cyst.When a cyst forms, the movement organelles disappear, the volume of the animal decreases, it acquires a rounded shape, and the cell is covered with a dense membrane.The animal goes into a state of rest and, when favorable conditions occur, returns to active life.
Encystment is a device that serves not only for protection, but also for the spread of parasites.Some protozoa (sporophytes) form an ovocyst and, during the process of reproduction, a sporocyst.
The reproduction of protozoa is very diverse, from simple division (asexual reproduction - biofile.ru) to a rather complex sexual process - conjugation and copulation.
The habitat of protozoa is varied - the sea, fresh water, moist soil.Parasitism became widespread.Many species of parasitic protozoa cause severe forms of disease in humans, domestic and commercial animals, and plants.
Protozoa are able to move with the help of pseudopods, flagella or cilia, and respond to various stimuli (phototaxis, chemotaxis, thermotaxis, etc.).Protozoa feed on the smallest animals, plant organisms and rotting organic matter; parasitic forms live on the surface of the body, in body cavities or tissues of their hosts.
The ways in which food enters the cell body are also different: pinocytosis, phagocytosis, osmotic pathway, active transport of substances across the membrane.They digest the incoming food in digestive vacuoles filled with digestive enzymes.Some of them, having photosynthetic intracellular symbionts - chlorella or chloroplasts (for example, euglena) are capable of synthesizing organic matter from inorganic substances using photosynthesis.
Toxoplasma
Toxoplasmosis (Greek toxon - arch, arc) are diseases caused by protozoan single-celled organisms in a wide variety of places in the human body, where their introduction and reproduction occurred.The causative agent of toxoplasmosis, Toxoplasma gondii, belongs to the genus of protozoa, to the class of flagellates.
Toxoplasma has a crescent shape and resembles an orange slice: one end of the parasite is usually pointed, the other is rounded, length up to 7 microns.Toxoplasma moves by sliding.They penetrate inside the cells, rotating around the longitudinal axis.
Reproduction of Toxoplasma is asexual, it occurs by longitudinal division in two.As a result of repeated longitudinal division in the protoplasm of the host cell, an accumulation of daughter parasites is formed, which is called “pseudocyst”.Pseudocysts are found in large numbers in various organs of the infected organism during the acute stage of infection.They are surrounded by a very vague membrane, apparently formed by the host cell, and do not have their own shell.Cells filled with such parasites are destroyed.The released parasites penetrate into new cells, where they divide again and form new pseudocysts.
When the infection becomes chronic, Toxoplasma remains in the form of true cysts (they surround themselves with a special shell).Such cysts have the ability to persist in the body of animals and humans for a long time (up to 5 years).Cysts are also found in the tissues of the eye, heart, lungs and some other organs.The number of Toxoplasma in a cyst ranges from a few copies to several thousand.
Giardia
Giardia is the simplest parasitic animal of the flagellate class.It has a pear shape, length 10-20 microns;the dorsal side is convex, the ventral side is concave and forms a sucker for temporary attachment to the epithelial cells of the host’s intestine.2 oval nuclei, 4 pairs of flagella.It lives in the human intestine (mainly in children), mainly in the duodenum, less often in the bile duct and gallbladder, causing giardiasis.Asymptomatic parasite carriage is common.Infection with cysts occurs when protozoa enter the lower intestine through the mouth through ingestion of contaminated food or water, or through dirty hands, etc.The incidence is sporadic.Giardiasis is common in all parts of the world.
The causative agent of the disease is lamblia (Lamblia intestinalis).Giardia are single-celled microscopic parasites.Giardia can withstand freezing and heating up to 50 ° C, but die when boiled.In the United States, giardiasis is the leading gastrointestinal disease of parasitic origin.According to INTERNET, up to 20% of the entire world population suffers from giardiasis.Infection can occur by drinking unboiled tap water or ice made from such water when washing vegetables and fruits with unboiled water.There is a high risk of getting sick when swimming in open water and in pools contaminated with Giardia cysts.A newborn baby can become infected during childbirth during eruption and birth of the head.The contact route of infection is more rare, but with a high prevalence of the disease it becomes quite real, especially among segments of the population with poor general hygiene skills.
Trichomonas
Trichomonas vaginalis does not form cysts and feeds on bacteria and red blood cells.Causes inflammation of the genitourinary system - trichomoniasis.The causative agent of the disease is transmitted sexually.Extrasexual infection (through toilet items, bed, etc. shared with the patient) is less common.It can be transmitted to a newborn girl from a sick mother.The disease may become chronic.If it spreads to the appendages, it is difficult to treat.With trichomoniasis, the vagina is most often affected; profuse purulent discharge with an unpleasant odor appears;there is itching and burning in the vagina.In men, the symptom is inflammation of the urethra (urethritis), accompanied by only slight mucous discharge.
Amoeba
Amoeba lives in fresh waters.Body shape is not constant.Makes very slow (13 mm/hour) movements.It moves with the help of pseudopods, the body flows from one part to another: either shrinking into a round lump, or spreading its “tongues-legs” to the sides.
The pseudopods also serve to capture food.During the feeding process, the body of the amoeba flows around food particles from all sides, and they end up inside the cytoplasm.A digestive vacuole appears.This way of eating is called fabititosis.The food consists of bacteria, unicellular algae, and small protozoa.Solutes from the environment are absorbed by pinocytosis.
The body of the amoeba has a contractile or pulsating vacuole.Its function is to regulate the osmotic pressure inside the body of the protozoan.Reproduction is asexual, through mitosis followed by division of the amoeba's body into two.Amoebas of the genus Entamoeba, which live in the human digestive tract, are of greatest importance in medicine.These include dysenteric or histolytic amoeba.
Malarial plasmodium
The malarial plasmodium causes malaria, which occurs with attacks of fever, changes in the blood, and enlargement of the liver and spleen.There are four forms of malaria: three-day, four-day, tropical, and ovalemalaria.The source of the disease is a person with malaria, and the carrier is a female malaria mosquito.A female mosquito, becoming infected by sucking the blood of a patient, becomes capable of transmitting plasmodia.A healthy person becomes infected when bitten by a mosquito infected with Plasmodium, through whose saliva the pathogens enter the body.With the bloodstream, plasmodia enter the liver, where they undergo the first (tissue) development cycle, then passing into the blood and penetrating into red blood cells.Here they complete the second (erythrocyte) development cycle, ending with the breakdown of erythrocytes and the release of pathogens into the patient’s blood, which is accompanied by an attack of fever.