The type of protozoa (Protozoa) includes more than 15,000 species of animals that live in the seas, freshwater and soil.In addition to free-living forms, many parasitic forms are known that 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 symmetry, bilateral (flagellates, ciliates) or have no permanent form at all (amoeba).The body size of protozoans is generally small, from 2-4 microns to 1.5 mm, although some large individuals reach 5 mm in length, and the rhizomes of fossil shells were 3 cm or more in diameter.
The body of protozoa consists of cytoplasm and nucleus.The cytoplasm is limited by the outer cytoplasmic membrane;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.
The movement organelles of protozoa are flagella, cilia, pseudopodia;or there are none at all.Most protozoans, like all other representatives of the animal kingdom, are heterotrophs.However, among these there are also autotrophic ones.
The peculiarity of protozoa in tolerating unfavorable environmental conditions is their ability to encyst, that is, to form a cyst.When a cyst is formed, 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 enters a state of rest and, when favorable conditions arise, returns to active life.
Encystment is a device that serves not only for protection, but also for the spread of parasites.Some protozoans (sporophytes) form an oocyst, and during the reproduction process, 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 protozoans is varied: sea, fresh water, moist soil.Parasitism spread.Many species of protozoan parasites cause severe disease in humans, domestic and commercial animals, and plants.
Protozoa are able to move with the help of pseudopodia, flagella or cilia and respond to various stimuli (phototaxis, chemotaxis, thermotaxis, etc.).Protozoa feed on smaller animals, plant organisms and decaying organic matter;parasitic forms live on the surface of the body, in body cavities, or in the tissues of their hosts.
There are also different ways in which food enters the cell body: pinocytosis, phagocytosis, osmotic route, active transport of substances across the membrane.They digest incoming food in digestive vacuoles filled with digestive enzymes.Some of them, having photosynthetic intracellular symbionts - chlorella or chloroplasts (for example, euglena) are able to synthesize organic matter from inorganic substances using photosynthesis.
Toxoplasma
Toxoplasmosis (Greek toxon - bow, bow) is a disease caused by protozoan unicellular 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 a slice of orange: one end of the parasite is usually pointed, the other is rounded, up to 7 microns long.Toxoplasma moves by sliding.They penetrate inside the cells, rotating around the longitudinal axis.
The reproduction of Toxoplasma is asexual, occurring by longitudinal division in two.As a result of repeated longitudinal division in the protoplasm of the host cell, an accumulation of daughter parasites, called a “pseudocyst,” is formed.Pseudocysts are found in large numbers in various organs of the infected organism during the acute phase of the 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 enter new cells, where they divide again and form new pseudocysts.
When the infection becomes chronic, Toxoplasma remains in the form of real cysts (they are surrounded by 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 eyes, heart, lungs, and some other organs.The number of Toxoplasma in a cyst varies from a few copies to several thousand.
Giardia
Giardia is the simplest parasitic animal of the flagellate class.It has a pear shape, 10-20 microns long;the dorsal face is convex, the ventral face is concave and forms a suction cup 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 (especially in children), mainly in the duodenum, less often in the bile duct and gallbladder, causing giardiasis.Asymptomatic carriage of parasites is common.Cyst infection 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 tolerate freezing and heating up to 50°C, but dies when boiled.In the United States, giardiasis is the leading gastrointestinal disease of parasitic origin.According to the INTERNET, up to 20% of the entire world population suffers from giardiasis.Infection can occur from drinking unboiled tap water or ice obtained from such water when washing fruits and vegetables with unboiled water.The risk of getting sick is high when swimming in open water and in pools contaminated with Giardia cysts.A newborn can become infected during childbirth during the rash and birth of the head.The contact route of infection is rarer, but with a high prevalence of the disease it becomes quite real, especially among segments of the population with poor general hygienic 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 sexually transmitted.Extrasexual infection (through toilet items, bedding, etc. shared with the patient) is less common.It can be transmitted to a newborn baby from a sick mother.The disease can become chronic.If it spreads to the appendages, it is difficult to treat.With trichomoniasis, the vagina is most often affected;appears abundant purulent discharge with an unpleasant odor;there is itching and burning in the vagina.In men the symptom is inflammation of the urethra (urethritis), accompanied only by a slight secretion of mucus.
Amoeba
The amoeba lives in freshwater.The shape of the body is not constant.It makes very slow movements (13 mm/hour).It moves with the help of pseudopods, the body slides from side to side: either narrowing into a round mass, or spreading its “legs-tongues” to the sides.
Pseudopods also serve to capture food.During the feeding process, the amoeba body flows around food particles from all sides and they end up in the cytoplasm.A digestive vacuole appears.This way of eating is called fabititosi.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 the division of the amoeba body in two.Amoebae of the genus Entamoeba, which live in the human digestive tract, are of great importance in medicine.These include dysenteric or histolytic amoeba.
Plasmodium malarial
Plasmodium malaria causes malaria, which manifests itself with attacks of fever, blood changes and enlargement of the liver and spleen.There are four forms of malaria: three-day, four-day, tropical and oval malaria.The source of the disease is a malarial person 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 blood circulation the plasmodia enter the liver, where they undergo the first cycle of (tissue) development, then passing into the blood and penetrating the red blood cells.Here they complete the second (erythrocytic) development cycle, which ends with the breakdown of erythrocytes and the release of pathogens into the patient's blood, accompanied by an attack of fever.