- feeling of heaviness in the lower abdomen;
- nausea and vomiting;
- general malaise;
- frequent diarrhea.
- the helminth has a pale pink tint;
- female body length – 20-40 mm, male – 15-20 mm;
- Dioecious individuals reproduce sexually.
In case of gastrointestinal infection and when roundworm penetrates the liver, clinical symptoms are expressed in the following manifestations:
- Abdominal pain, accompanied by bouts of vomiting and constant nausea.
- Diarrhea occurs with bloody discharge in the stool.
- Pressure on the hepatic and bile ducts contributes to the formation of obstructive jaundice.
- Lack of appetite and uncontrolled weight loss.
The symptoms of pulmonary ascariasis are more problematic to recognize, since the clinical signs are perceived as other diseases of the respiratory system, such as bronchitis, pneumonia, etc. The presence of helminths in the lungs is accompanied by the following symptoms:
- dry paroxysmal cough and chest wheezing;
- dyspnea;
- low-grade body temperature.
Undiagnosed ascariasis in the lungs leads to the development of bronchial asthma.
When roundworm penetrates the brain, a person experiences severe headaches, epileptiform seizures and convulsions occur, and there is pronounced neurosis and depression.
Important! All clinical manifestations require a thorough diagnostic examination and appropriate medical treatment.
- Piperazine;
- Albendazole;
- Vermox, etc.
Type roundworms Nematodes biology classes systems structure body characteristics signs representatives photo difference cavity
General characteristics of nematodes
Free living roundworms distributed throughout to the globe . They are found in a wide variety of habitats: on the seabed, V ground fresh and brackish reservoirs and finally, in various soil types.
Roundworms External structure
The body is fusiform or filamentous, round in cross section, undifferentiated, covered with a layer of dense and elastic cuticle, on which various tubercles and spines are often located, but there are never cilia.
The mouth is located at the very anterior end of the body and is often, for example in roundworms, surrounded by three lips seated with sensitive papillae. Not far from the posterior end of the body, on the ventral side, the anus is located. The section of the body behind the anus is called the tail.
Skin-muscle bag
The dermal-muscular sac of roundworms consists of the cuticle, hypodermis and one layer of longitudinal muscles.
Below the cuticle is the hypodermis. In many nematodes it consists of large epithelial cells. In roundworms, the boundaries between individual cells disappear and a syncytium is formed with nuclei scattered in the cytoplasm. On inner surface the hypodermis forms thickenings in the form of four ridges running along the entire body of the worm. The channels of the excretory system pass through the two lateral ridges of the hypodermis, and the main nerve trunks pass through the dorsal and ventral ridges.
Directly below the hypodermis there is only one layer of longitudinal muscle cells. These are very large cells, consisting of an elongated spindle-shaped contractile fiber, in the middle part of which there is a sarcoplasmic sac containing the cell nucleus. Numerous plasmatic processes branch off from the sarcoplasmic sac and go to the hypodermis and other muscle cells. The contractile fibers of muscle cells are adjacent to the hypodermis and form the cortical layer of the longitudinal muscles. The sarcoplasmic layer extends into the body cavity.
Due to the presence of only longitudinal muscle cells, the movements of nematodes are much more uniform compared to the movements of flatworms. Roundworms can only bend their body using muscles. Straightening of the body occurs when muscles relax due to the pressure of the abdominal fluid and the elasticity of the cuticle.
Longitudinal ridges of the hypodermis divide the muscular layer into four stripes stretching along the body.
Body cavity
The skin-muscle bag limits the body cavity in which the internal organs, namely the digestive and reproductive systems. This cavity, preserved in the animal, is usually called the primary body cavity.
Roundworms, like flatworms, lack circulatory and respiratory organs.
The mouth, located at the anterior end of the body, is usually surrounded by six outgrowths - lips (the roundworm has three), on which there are sensitive papillae.
The mouth leads into an ectodermic pharynx lined with cuticle. The pharynx is sometimes incorrectly called the esophagus. It has muscular walls. The lumen of the pharynx in a transverse section is usually triangular in shape. In many nematodes, the anterior part of the pharynx is armed with chitinous teeth. The posterior part of the pharynx in some nematodes is swollen and is called a bulb or bulb.
Following the pharynx is the endodermic midgut, the wall of which consists of single-layer epithelium and has no muscle fibers. The midgut lies freely in the body cavity and does not form bends. Unlike flatworms, digestion in nematodes is entirely extracellular and occurs in the cavity of the midgut. The short hindgut is an ectodermic section and is lined with a cuticle.
Excretory system
The excretory organs are represented by skin glands, which also perform the function of osmoregulation. Protonephridia are absent. The excretory organs are located in the hypodermis and are formed by one or two, rarely many cells. In the roundworm, two excretory canals pass through the lateral ridges of the hypodermis, closed at the posterior ends. These canals, approaching the anterior end of the body, bend to the ventral side, merge together into a short unpaired canal and open on the ventral side with an excretory opening. This entire organ is one giant cell: the excretory canals pass through its processes, and the nucleus is located in the cytoplasm of the left canal. The excretory organs of nematodes are called cervical glands. Free-living nematodes, in addition to them, have terminal, or tail, excretory skin glands.
In addition, the excretory function is performed by large phagocytic cells, often star-shaped, located in the body cavity in the number of two, four or six. Apparently, they play the role of “storage buds”, capturing insoluble metabolic products - excreta and bacteria - from the body cavity. In addition, hemoglobin was found in them. It is assumed that phagocytic cells serve as centers that regulate the consumption of free oxygen (aerobic part of respiration) by nematodes.
Nervous system and sensory organs
In nematodes, the nervous system is located in the hypodermis. It consists of a nerve ring that surrounds the pharynx and to which small clusters are adjacent nerve cells, forming ganglia.
Six nerves usually extend forward from the nerve ring to the labial sensory papillae.
Several longitudinal trunks extend back from the ring (ascarids have six). Of these, the most developed is the ventral trunk, located in the abdominal ridge of the hypodermis. The peripharyngeal nerve ring, the associated ganglia and the ventral nerve trunk form the central nervous system of nematodes. In addition to the abdominal trunk, the hypodermis usually contains a dorsal, two lateral and four thinner longitudinal trunks. Longitudinal trunks can arise directly from ganglia adjacent to the nerve ring. In the roundworm, the abdominal and dorsal trunks are connected by semi-circular commissures located asymmetrically on the right and left sides.
Sense organs are poorly developed. The organs of touch are represented by papillae, papillae and setae, which are concentrated mainly at the anterior end of the body. They are usually associated with pores in the cuticle, covered by a thinner cuticle, to which the nerve endings approach.
At the head end there are organs of chemical sense - amphids. They represent various shapes depressions in the skin to which the endings of sensory nerves approach. Only a few free-living aquatic nematodes have visual organs.
Constancy of cellular composition
When studying the histological structure of various organs of nematodes, it turned out that all organs are formed by a small number of very large cells. One or two giant cells form the excretory gland, four very large phagocytic cells complement the excretory organs. Muscle cells are also large and few in number. Small species may have only eight of them. The roundworm's central nervous system consists of only 162 cells. The formation of new cells in nematodes stops at the early stages of development, and then the number of cells remains constant throughout life. Constancy cellular composition at small quantity cells, reaching large sizes, is the most important feature nematodes Apart from nematodes, this is characteristic of only a few groups close to nematodes (rotifers). The constancy of the cellular composition is associated with the inability of nematodes to asexual reproduction and regeneration of lost parts.
Reproductive system
Roundworms are dioecious, and hermaphrodites are quite rare among them. Nematodes have pronounced sexual dimorphism. Males are usually smaller in size, the posterior end of their body is somewhat twisted (ascaris), and some species have a leathery fold at the posterior end - a copulatory bursa, which plays a role in mating (pile, etc.). The genital organs have a simple structure and are represented by elongated, sometimes very long, tubes.
The female genital organs of roundworms are paired. They begin with thin filiform ovaries, which are very thin tubes filled with radially arranged germ cells. The ovaries imperceptibly pass into wider sections - the oviducts. These are hollow tubes that do not contain developing eggs. The oviducts open into thicker muscular tubular organs - the uterus, which store the sperm that gets there during copulation. Fertilization of eggs occurs in the uterus and initial stages their embryonic development. The uteri are connected into an unpaired short tube - the vagina, through which eggs are laid. The female genital opening is located on the ventral side, often in the front part of the body (in roundworms in the front third of the body).
The male genital organs of roundworms are usually single, but they can also be paired. In the roundworm, the male reproductive apparatus is a gradually expanding tube, consisting of a thin and longest section - the testis, which passes into a wider vas deferens and then into the ejaculatory canal, which opens with the genital opening into the hindgut. The hind intestine becomes the cloaca, which houses the copulatory apparatus. The copulatory apparatus usually consists of two long setae - spicules, formed in the lateral pockets of the cloaca. During copulation, the spicules are pushed out by the male and inserted into the genital opening of the female, thereby holding her. The copulatory apparatus includes many accessory formations, including the mentioned copulatory bursa.
Spermatozoa are very unique; they have an amoeboid shape, which makes them different from the seminal cells of representatives of all other animals. Nematode sperm are able to move like small amoebas.
Nematode eggs are usually covered with a dense shell, or shell. Thus, roundworm eggs are covered with a layered, highly developed shell, which ensures their resistance during prolonged exposure to external environment. In most nematodes, fertilized eggs are laid outside and develop in the external environment. Only in a few species (Trichinella) the entire process of embryonic development of eggs occurs in the uterus. At the same time, females are characterized by viviparity: they give birth to fully formed larvae.
Development
The development of roundworms occurs in a very peculiar way and in many forms with transformation. Crushing of eggs, complete, uniform, takes place according to the bilateral type. An extreme degree of determinism of fragmentation is characteristic; already at the fourth division of the egg (stage of 16 blastomeres), the sexual primordium and the primordium of the midgut are separated. In the same way, outer integument, pharynx, muscles, etc. develop from single blastomeres. This development is called mosaic, and it determines the constancy of the cellular composition of adult forms. The egg hatches into a small, worm-like larva, which in most nematodes molts four times before developing into an adult worm. The number of molts may be smaller due to the fact that the first moults (one or two) occur before the larva emerges from the egg shells.
Currently, about 25,000 species are known.
Modern taxonomy
Groups previously considered classes in the group Protocavitae (or Roundworms in the broad sense):
Gastrociliaceae (Gastrotrichs)
Rotifers
Hairworms
Kinorhynchs
Priapulids
Currently they are separate types.
The group Protocavitary worms was disbanded as a team (not having a common evolutionary origin).
In modern taxonomy, nematodes belong to the group Molting (Ecdysozoa) together with arthropods, tardigrades and the above types, except rotifers (they belong to Platyzoa).
General characteristics of the nematode class
Bilateral symmetry
Three-layer
There is a primary body cavity.
Primary body cavity (pseudocoel)- a body cavity that does not have its own epithelial lining.
In roundworms, the primary body cavity is a space between the muscles and the intestines, filled with a pressurized fluid that performs the function hydroskeleton. All internal organs are located in the primary cavity.
Functions of the primary body cavity:
Maintaining body shape;
- participation in muscle movement (in combination with muscles and hard cuticle). Since the fluid is incompressible, it transfers pressure well;
- transport of nutrients and metabolic products.
The body is thin (usually several mm in diameter), cylindrical, inarticulate, elongated and pointed at the ends. In cross section it is round, which gives the type its name.
Cytological features
Nematodes are characterized byeuthelia- constancy of the number of cells in the body. The development program is strictly genetically predetermined and specific to the species.
Mosaic development(hard deterministic, that is, the fate of each cell is strictly predetermined), there is no tendency to regulation.
Nematode sizes
Rice. Internal structure roundworms
Excretory system: 2 lateral blindly closed canals, merging under the pharynx into one duct, which opens on the ventral side of the body with an excretory opening. The final waste products accumulate in the cavity fluid, and from it enter the excretory canals. There are no flame cells with cilia.
In addition, ammonia can be released from the body of nematodes by diffusion through the body wall.
Circulatory system No. Transport of substances is carried out by the primary body cavity.
Nervous system: a circular peripharyngeal ganglion, two longitudinal nerve trunks - dorsal and abdominal, passing in the ridges of the ectoderm and interconnected by semi-circular nerve bridges. In addition, there are nerve fibers running along the body.
Sense organs are represented by numerous sensilla and tactile tubercles at the oral opening: mechano- and chemoreceptors. There are organs of taste and touch, and free-living roundworms have light-sensitive eyes.
Reproductive system:
most are dioecious. Common: sexual dimorphism.
♀: paired ovaries, oviducts, uterus and genital opening on the ventral side.
♂: unpaired filamentous testis and vas deferens, flowing into the intestine just before the anus (essentially a cloaca). There is a complex copulatory apparatus with devices for holding the female during copulation. Spermatozoa are amoeba-like.
Fertilization is internal, development occurs with incomplete transformation(4 larval stages).
Human roundworm
♀: 20 - 40 cm.
♂: 15 - 20 cm. The rear end of the body is curved down.
Disease: ascariasis.
The development of roundworm occurs without changing hosts; the only owner is man.
Due to the presence of a multi-layered strong cuticle and intracavitary pressure, the body of the roundworm is tense like a string. Based on the intestinal loops, it easily resists the movement of food masses.
Food: contents of the small intestine.
Life cycle of roundworm
The development cycle is complex, associated with the release of eggs into the external environment and migration of larvae in the human body. In the development cycle of the roundworm, it goes through several larval stages.
At favorable conditions eggs can remain viable for up to 10 years.
Fertilized eggs, covered with dense protective shells, enter the soil from the human intestine. In the presence of oxygen and sufficient high temperature The larva develops within them within a month. After the first molting of the larva in the egg, the egg becomes infective ( invasive).
Rice. Fertilized roundworm egg
Eggs are eaten by humans through contaminated water and food and enter the small intestine.
Here the larvae hatch, pierce the intestinal mucosa and penetrate the blood vessels. With the blood flow through the portal vein, liver and inferior vena cava, they enter the right atrium, right ventricle and through the pulmonary artery to the lungs.
The larvae successively pass from the blood into the pulmonary vesicles, bronchi, windpipe and into the host's oral cavity and from here, together with saliva, enter the intestines for the second time.
During migration, the larvae molt twice and increase in size to 2.2 mm. The migration of roundworm larvae lasts about 2 weeks.
The larvae grow in the intestines, molt again and reach sexual maturity after 2-2.5 months. The lifespan of adult roundworms is about 1 year.
Eggs and larvae develop in the presence of oxygen, the adult form is a strict anaerobe.
Rice. Life cycle of roundworm
Baby pinworm (Enterobius vermicularis)
Rice. The structure of the pinworm. 1 - mouth; 2 - vesicle; 3 - esophagus; 4 - esophageal bulb; 5 - intestines; 6 - genital opening; 7 - uterus; 8 - ovary; 9 - anal opening.
Rice. Male and female pinworm
♀: up to 12 mm. The tail is awl-shaped.
♂: up to 5mm. The tail is spiral.
Disease: enterobiasis.
It lives in the lower part of the small intestine and the upper part of the large intestine, most often in the cecum.
Food: intestinal contents.
Rice. Self-infection with enterobiasis
At the anterior end of the body of pinworms there is a swelling surrounding the mouth opening and called the “vesicle”. With its help, the pinworm attaches to the intestinal wall.
Life cycle of pinworm
Pinworms mate in the human ileum, after which the male dies and the female develops numerous eggs. To lay them, the female crawls out of the anus through the rectum, after which she lays eggs on the perianal folds and dies.
The total lifespan of pinworms in the human body does not exceed 1 month. Then self-healing occurs.
Carriers: insects (flies, cockroaches, etc.). Infection occurs through consumption of food contaminated with eggs. Self-infection of the patient often occurs.
Prevention: ironing, food hygiene and personal hygiene (washing hands, vegetables, fruits).
Human whipworm (Trichocephalus trichiurus)
Whipworm is the causative agent of trichocephalosis.
In Russia, this invasion ranks second after ascariasis.
Rice. Whipworm
The back of the female's body is straight and widened. It contains all the main sections of the digestive tract; the female's uterus is visible. The rear end of the male's body is wrapped in a spiral.
Whipworm eggs are barrel- or lemon-shaped with light “plugs” at the poles.
Life cycle of whipworm
A person becomes infected with trichuriasis by ingesting whipworm eggs. The development cycle takes place without migration. Larvae hatch from the eggs and move to the cecum, where they penetrate the mucous membrane with their narrow anterior end and remain there until the end of their lives. After a month, the helminths reach sexual maturity and begin sexual reproduction.
The lifespan of a whipworm is 5-6 years.
Trichinella spiralis
The causative agent of trichinosis - natural focal zooanthroponosis.
Foci of trichinosis can be natural and synanthropic.
Rice. Adult Trichinella and its larva in the muscles
Mature Trichinella reach 3-4 mm in length.
Females are viviparous.The larvae migrate into striated muscles, equipped with a dense network of blood capillaries (muscles of the tongue, diaphragm, esophagus, eyes, etc.), and are encapsulated there, causing fever and various allergic manifestations.
Life cycle of Trichinella
Infection with trichinosis occurs by eating meat from animals containing live encapsulated Trichinella larvae. IN gastrointestinal tract under the influence of digestive enzymes, the capsule dissolves, the larvae emerge into the intestinal lumen, where, after several molts, they transform into sexually mature forms.
Then fertilization occurs. Fertilized females give birth to live larvae. The female lives for about 3-6 weeks, and during this time she hatches from 200 to 2000 larvae.
The larvae penetrate the lymphatic and circulatory systems and are spread throughout the host’s body through the bloodstream. During the migration process, the larvae molt several times. Then, with the help of a boring stylet and a secreted enzyme, the larvae actively penetrate from the capillaries into the fibers of the striated muscles.
In the muscles, the larvae curl into a spiral. An inflammatory process develops around them, and a connective tissue capsule is formed. After about 1 year, the walls of the capsule become calcified. The larva remains viable inside the capsule for up to 20-25 years.
Rice. Life cycle of Trichinella
To transform the larvae into a sexually mature form, they must enter the intestines of another host. This occurs if the meat of an animal with trichinosis is eaten by an animal of the same or another species: for example, the meat of one trichinosis rat is eaten by another. In the intestines of the second host, the capsules dissolve, releasing the larvae, which within 2-3 days turn into sexually mature forms (males and females). After fertilization, the females give birth to a new generation of larvae.
Each organism infected with Trichinella first becomes a definitive host, and then an intermediate host for larvae hatched by fertilized females.
For full development One generation of helminths requires a change of hosts.
Guinea worm (Dracunculus medinensis;
The definitive owner is humans, sometimes animals (dogs, monkeys). Intermediate hosts are freshwater crustaceans Cyclops.
Guinea worm (Dracunculus medinensis) enters the human body orally when drinking water that contains copepods infected with guinea worm larvae. When it enters the human body, the guinea worm gnaws through the intestinal wall and enters the lymphatic vessels, and from there it penetrates into the body cavity, where it undergoes two successive moults and reaches sexual maturity. After mating, the males die, and the females migrate to the subcutaneous fatty tissue. There the females continue to grow and reach a length of 80 cm.
The larvae emerge from the female's genital tract through a rupture in the uterus and the wall of the helminth's body near its anterior end. They are removed from the body of the final host through a hole formed on the skin under the influence of the secretion of special glands located at the anterior end of the female helminth.
When it comes into contact with water, the bubble bursts, and the front end of the female emerges from it. The ejection of larvae from the body of the guinea worm occurs due to the contraction of its muscles upon contact with water, which may be due to the cooling of the anterior end of the helminth under the influence of water. Within 2-3 weeks, the female hatches up to 3 million larvae into the water. After this, the females die. They dissolve or calcify.
To complete the cycle, the larvae must infect the Cyclops.
Traditional way of treatment for a long time there was a slow winding of the guinea worm on a stick so that the worm would not break. This could last for several days.
Rice. Life cycle of Guinea guinea worm
Filaria
The final owner is man.
Intermediate hosts of filariae - blood-sucking insects, less commonly, ticks that receive larvae (microfilariae) by sucking the blood of the definitive host and then infect other vertebrates.
Filariae are localized in the body cavity, subcutaneous tissue, lymphatic and blood vessels, and the heart. They can cause blockage of the lymphatic ducts, leading to elephantiasis corresponding part of the body.
Rice. Elephantiasis
Hookworm
Krivogolovka duodenum(Ancylostoma duodenale) is the causative agent of hookworm.
The length of the worm is up to 13 mm.
Rice. Hookworm. a - female; b - male; c - oral capsule of hookworm.
The anterior end of the hookworm body is bent to the ventral side. The head end has an oral capsule with 6 cutting teeth and glands that secrete enzymes that prevent blood clotting.
Rice. Head capsule of hookworm
Helminths feed on blood. At the site of helminth attachment to the intestinal wall, ulcers with a diameter of up to 2 cm are formed, bleeding for a long time.
Sexual reproduction in the human intestine. The eggs are released into the external environment. In the soil, the eggs hatch into free-living larvae. The larva can live in the soil for several months.
Human infection occurs when the larvae are ingested with food and water or brought into the mouth with dirty hands (oral route), or (rarely) when the larvae actively penetrate the skin.
When infected through the skin, the larvae migrate along the bloodstream to the lungs, from there they rise through the airways into the pharynx, are swallowed and enter the small intestine. Migration lasts about 10 days.
When infected orally, there is no migration. In the small intestine, the larvae moult twice, and 4-6 weeks after infection the females begin to lay eggs. The lifespan of hookworm is up to 5 years.
Coverings of the body
The body is formed by a skin-muscle sac covered with cuticle. The cuticle cannot stretch, so roundworms periodically shed it and increase in size.
Muscles
Roundworms have 3 types of muscles: dorsal, abdominal and longitudinal, which allow the worm to bend in different directions.
Evolutionary changes have occurred in the digestive system of worms, characterized by the appearance of the hindgut and anus. Their digestive system has 3 sections - anterior, middle and posterior. The anterior section contains the mouth, pharynx and esophagus. Digestive processes take place in the middle section.
Respiratory system
Roundworms do not have a respiratory system. The entire surface of the body is used for gas exchange.
Circulatory system
There is no circulatory system. Transport of substances is carried out by hemolymph.
Excretory system
The excretory organs are protonephridia or skin glands, called cervical glands. Some roundworms do not have excretory organs.
Nervous system
The nervous system has ladder type. It consists of a peripharyngeal nerve ring with six nerve trunks, which are connected by jumpers.
Sense organs
Roundworms are endowed with organs of touch and smell. Free-living representatives have primitive eyes.
Regeneration
Roundworms are not capable of regeneration.
Reproduction
Reproduction is sexual with internal fertilization. Most representatives of the type Roundworms are dioecious. Some are characterized by the presence of sexual dimorphism. The development of roundworms is indirect; there is a larval stage.
Classification
Type Roundworms are divided into 5 classes:
Gastrociliaceae.
Actually roundworms, or nematodes.
Hairy.
Rotifers.
Acanthocephalans.
How are roundworms different from flatworms?
Differences between these types:
1. Flatworms have a flat body shape. Characteristic of roundworms round form bodies.
2. The digestive system of flatworms is not continuous: there is no anus. The roundworms developed an anus, and therefore their grass system became through-hole.
3. Roundworms reproduce only through the sexual process, while flatworms reproduce both sexually and asexually.
4. All representatives of roundworms are dioecious. Flatworms are hermaphrodites.
5. Flatworms are capable of regeneration, but roundworms are not.
TYPE ROUNDWORMS.
GENERAL CHARACTERISTICS
The following characteristics are characteristic of roundworms:
1) The body has an elongated shape, not segmented, round in cross section.
2) Develop from three germ layers - ecto-; ento- and meso-dermis.
3) They have bilateral or bilateral symmetry of the body.
4) The body of roundworms has a skin-muscular sac formed by the hypodermis, above which there is a dense cuticle that performs a protective function - it protects the body of the worm from damage and the action of the host’s digestive enzymes and the function of the exoskeleton and support for muscles. The muscles are represented only by longitudinal muscles, which only allow the body to bend.
5) In roundworms, a body cavity first appears, which does not have its own epithelium and is called primary. The body cavity contains all organs and cavity fluid under pressure. They play an important role in metabolism.
6) Digestive system – open type. Mouth, pharynx, esophagus, intestine, which has three sections - anterior, middle and posterior, which ends in the anus.
8) The nervous system is represented by a peripharyngeal nerve ring, from which three pairs extend nerve trunks stretching along the body, the most developed are the lateral ones, between which there are jumpers or commissures. The sense organs are poorly developed; there are tactile cells and chemical sense organs.
9) The excretory system is represented by single-celled skin glands with excretory ducts or protonephridia.
10) Reproductive system – roundworms are dioecious. The genitals have a tubular structure: in males there are filamentous testes, vas deferens and ejaculatory canal; in females there are ovaries, oviducts, a uterus and a vagina that opens on the ventral side of the body. They have pronounced sexual dimorphism (the female and the male differ in appearance). Fertilization is internal. Most roundworms develop without changing hosts and belong to the group - GEOHELMINTHS.
In the course of evolution, roundworms arose three large aromorphs.
1. Primary body cavity.
2. Open digestive system.
3. Dioecy.
Development cycle. Every year, roundworm releases up to 200 thousand eggs into the soil, which are excreted from the human body along with feces. In the external environment, with access to oxygen, after 24-25 days a larva develops in the egg, and such an egg becomes invasive. If personal hygiene rules are not followed, a person becomes infected with roundworm eggs. In the human intestine, the shells of the eggs dissolve, the released larva penetrates the intestinal wall, penetrates the blood and, with the flow of venous blood, moves through the liver, heart to the lungs. In the lungs, with access to oxygen, it molts, grows and penetrates the bronchi, trachea, oral cavity and, upon secondary ingestion, enters the intestine, where an adult roundworm grows from the larva. The migration of the larvae lasts 2.5 months. There is no change of hosts in the roundworm development cycle; eggs develop in the soil, so they are in the GEOGELITE group.
Roundworm eggs are covered with three protective shells and remain viable for a long time.
Ascariasis is a dangerous disease manifested by intoxication of the body with roundworm metabolic products, pain in the intestines, and indigestion. Roundworms can cause intestinal obstruction; with a large accumulation, perverted migration of roundworms can be observed - they crawl into other organs and damage them. Preventive measures - personal hygiene: do not eat poorly washed vegetables and fruits; destroy carriers of helminth eggs - flies, cockroaches; sanitation of toilets.
Other representatives of roundworms are: pinworm, guinea worm, whipworm, threadworm, trichina, trichinella, crooked head, intestinal pinworm and others.
