The phylum roundworms, or nematodes, presumably originated from turbellarians. Evolving, this class acquired a peculiar structure, which is strikingly different from the structure flatworms. This fact forces us to consider nematodes as a separate specimen of the animal world. Since the relationship of nematodes with groups higher up has not been proven, they are considered a lateral branch of the family tree of animals. This phylum has more than 10,000 species of organisms.
IN general characteristics roundworms focuses on external structure. From a medical point of view, roundworms are of great interest, since only they contain forms that are pathogenic for the human body.
This unique structure allows them to crawl freely and bend their body in different directions. Characteristics of the type of roundworms show that they lack blood and respiratory system. These organisms breathe through the cover of their bodies.
Digestive system
The digestive system of roundworms resembles a tube, that is, it is continuous. Starting from the oral cavity, it gradually passes into the esophagus, then into the foregut, middle and hind intestine. The hindgut ends at the anus on the other side of the body.
Many representatives of roundworms have a terminal oral opening, in some cases it is shifted to the ventral or dorsal side.
Extraction system
Breeding system
The nematode has a reproductive system with a tubular structure. These organisms are heterosexual. Males have only one tube, different sections of which perform various functions. The narrowest section is the testis, which, in turn, is divided into two sections - reproduction and growth. Next is the vas deferens, and the channel for the eruption of the seed.
Females have a 2-tube reproductive system. One tube, ending in a dead end, plays the role of an ovary; it is filled with germ cells capable of reproduction. This organ flows into a larger section, which plays the role of the oviduct. The largest section of the female reproductive system is the uterus. The two uteri, connecting to each other, form the vagina, access to which is open on the front of the body.
Females and males differ significantly in external signs. Males, as a rule, are smaller and the back of the body in many is twisted towards the belly. In most species of nematodes, reproduction is viviparous - females carry an egg in the uterus until the larvae hatch from it.
Nervous system
Nervous system roundworms is a nerve ring, from which nerve trunks branch. Of these, the ventral and dorsal trunk are the most developed.
Life cycle
Nematodes in the human body cause diseases called nematodes, many of which pose a serious threat to health. There are classes of roundworms that are most common among humans.
Roundworms
The egg that the roundworm produces ends up in a person with unwashed vegetables or berries, on which they fell, respectively, from the ground. The larva hatches from the egg and begins its journey along to the human body. It has the ability to pass through the intestinal walls, penetrates the blood vessels, and enters the liver, atrium and lungs with the blood flow. To develop safely, roundworms need oxygen, so the larvae migrate to the pulmonary alveoli, and from there to the bronchi and trachea.
The waste products of roundworms are very toxic, so patients may experience severe headache, constant fatigue, outbursts of irritability. In addition, ascariasis often provokes intestinal obstruction.
Very common helminths, small nematodes white. The size of males is no more than 3 mm, females reach a length of 12 mm. Infection with pinworms can occur due to non-compliance with hygiene rules, so children who visit kindergarten. The patient is tormented severe itching, he scratches the skin until it bleeds, pinworm eggs remain on the hands and under the nails, after which they are transferred to objects household items and food.
The structure of roundworms of this species is such that they cling tightly to the walls of the intestine and feed not only on its contents, but also on blood. The toxins released by pinworms can cause headaches, insomnia, fatigue and dizziness, as well as allergies.
Through the blood vessels, the crooked head enters the heart, from there to the lungs, upper Airways and throat. Together with saliva, they penetrate the esophagus, then the stomach, the destination being the duodenum. This type of nematode can enter the body in two ways - either with contaminated food and water, or by penetrating through the skin. Soon after entering the body, the patient begins to suffer from pain in the duodenum, indigestion, fatigue, headache, depression, impaired memory and attention. With absence timely treatment this disease can be fatal.
How to combat the penetration of nematodes into the body? Preventive measures are quite simple, but nevertheless require strict adherence:
- do not neglect the rules of personal hygiene, wash your hands as often as possible hot water with soap;
- carefully process all vegetables, fruits and berries before eating (to protect yourself, you need to immerse them in boiling water for 3 seconds, or for 10 seconds in hot water, then rinse thoroughly with cold water);
- It is not recommended to use human and pig feces that have not undergone the composting process as garden fertilizer;
- cut nails of adults and children as often as possible, change bed linen and underwear daily.
Nematodes are an integral part of nature, and it is impossible to eliminate them, but with the help of simple measures you can protect yourself from their invasion of the body.
Nematodes, or roundworms, are believed to have evolved from turbellarians. In the process of evolution, they acquired a unique structural plan that sharply distinguishes them from flatworms. This forces us to consider nematodes as a separate type of animal life. The relationship of nematodes with higher groups has not been established, and therefore nematodes are considered as a side branch family tree animals. The phylum includes about 10,000 species.
According to the classification of V. A. Dogel (1981), Nemathelminthes type includes 5 classes:
- Class Nematoda.
- Class Gastrotricha.
- Kinorinchi class.
- Class Hairworms (Gorciiacea).
- Class Rotatoria.
General characteristics of the type
The most characteristic external feature is a non-segmented, cylindrical or fusiform body, which has a round shape in cross section. The outside of the body is covered with a cuticle, under which only one longitudinal layer of muscles is developed. Inside the skin-muscle sac is the primary body cavity, which contains the internal organs (see Table 1). A third, posterior, section appears in the digestive tube, ending in the anus. Excretory system or protonephridial, or represented by modified skin glands. Reproductive system Most nematodes are dioecious. The nervous system consists of a peripharyngeal nerve ring (or suprapharyngeal ganglion) and several longitudinal trunks, of which two are the most developed. Sense organs are poorly developed. Respiratory and circulatory system are missing.
The oral opening is located terminally at the anterior end of the body. The anus is located on the ventral side, near the posterior end of the body. The area behind the anus is called the tail.
Inside the skin-muscle sac there is a body cavity containing cavity fluid and internal organs. The body cavity develops from the cavity of the blastula (blastocoel) and is called the primary body cavity. Morphologically, it is characterized by the absence of an epithelial lining and is limited directly to the muscles of the skin-muscle sac. The cavity fluid directly washes the organs and walls of the body and is under high pressure, which creates support for the muscle sac (hydroskeleton). Plus she plays important role V metabolic processes. It is toxic to some nematodes.
Digestive system represented by a straight tube starting with the mouth and ending with the anus. The oral opening is located terminally at the anterior end and is surrounded by cuticular lips. In the digestive tube, the foregut, middle and hindgut are distinguished; the middle one develops due to the endoderm, while the anterior and posterior ones develop due to the ectoderm; the latter are lined, like the skin, with cuticle. The foregut is often differentiated into sections: oral capsule, esophagus, bulbus, etc.
Excretory system is unique and consists of one giant excretory (excretory) cell. The cell body is located in the anterior part of the nematode. From it, processes pierced by canals extend back and forth. The channels located posterior to the cell end blindly, while the channels extending forward are combined into a common duct that opens to the outside of the excretory pore. The process of excretion also involves special phagocytic cells located in the body cavity, along the lateral excretory canals. These cells absorb decay products from the body cavity. The phagocytic nature of these cells has been proven by the experience of introducing ink or other colored particles into the body cavity of worms. Mascara is grabbed phagocytic cells and accumulates in their cytoplasm.
Nervous system It is represented by a peripharyngeal nerve ring, from which longitudinal nerve trunks extend, among which the dorsal and ventral ones are the most developed. The senses are primitive; they are represented by tactile papillae and special organs that perceive stimuli of a chemical nature (amphids). Some free-living nematodes have eyes.
Reproductive system It has tubular structure. Nematodes are usually dioecious. Most males have only one (unpaired) tube, different sections of which are specialized and perform the functions of different genital organs. The narrowest, initial section - the testis - is divided into a reproduction zone and a growth zone. The testis passes into the vas deferens, after which there follows a wide ejaculatory duct, opening into the posterior intestine.
In females, the reproductive system usually consists of two tubes. The initial, narrowest, blindly closed section of the tube represents the ovary. In this part the tube has no lumen - it is filled with multiplying germ cells. The ovary gradually passes into a wider section that performs the functions of the oviduct. The next section, the widest, is the uterus. The two uteri join together to form an unpaired vagina or vagina, which opens outward at the anterior end of the body. In some species, the female has only one reproductive tube.
Nematodes have well-expressed sexual dimorphism - males and females differ in external characteristics. Males are smaller in size; the rear end of the body in some of them is twisted onto the ventral side.
Some species are characterized by viviparity, that is, their egg develops to the larval stage while still in the female’s genital tract and live larvae emerge from the female’s body.
Diseases caused by roundworms themselves are called nematodes. Many human nematodes are widespread and severe diseases.
Pinworm (Enterobius vermicularis)
The most widespread human helminth, ranking first in frequency of distribution among flatworms and roundworms. Found in all regions of the globe. The disease is caused by enterobiasis.
Localization. The lower part of the small intestine and the initial part of the large intestine.
. Ubiquitous.
Morphophysiological characteristics. A small white worm. The length of the female is 10-12 mm, the male - 2-5 mm. The posterior end of the male is curled onto the ventral side, while that of the female is awl-shaped and pointed. At the anterior end of the body there is a swelling of the cuticle - a vesicle that surrounds the mouth opening and is involved in fixing the helminth to the intestinal walls. In the posterior part of the esophagus there is a spherical swelling - the bulbus, the contraction of which is believed to play a known role in the processes of fixation. The intestine looks like a straight tube. The reproductive system is characterized by a structure typical of nematodes. They feed on the contents of the intestines and are sometimes able to swallow blood. The eggs are asymmetrical in shape, one side of the oval is flattened, the other is a convex, colorless shell that is well defined.
Life cycle. Fertilization occurs in the intestines. Immediately after fertilization, the males die. The female's uterus, filled with eggs, enlarges so much that it occupies almost the entire body of the worm. It compresses the esophageal bulbus, which disrupts the fixation mechanism. Such females, under the influence of peristalsis, descend into the rectum. At night, they actively crawl out of the anus onto the skin of the perineum and here they lay eggs (up to 13,000 pieces), gluing them to the skin. Soon after this, the females die.
For the further development of laid eggs, a special microclimate is required - a temperature of 34-36 ° C and high humidity - 70-90%. Such conditions are created in the perianal folds of the skin and perineum of a person. The eggs located here become invasive within 4-6 hours. Eggs that cannot stay on the skin and are exposed to conditions with lower temperature and humidity do not develop. When eggs enter the human intestine, they transform into sexually mature forms without migration. Adults live in the intestines for 30 days, but enterobiasis can be difficult to cure, since repeated self-infection often occurs.
When the female lays eggs, it causes itching, so patients scratch the itchy areas. The eggs fall under the nails, where they also find optimal conditions for development (temperature 34-36 ° C, high humidity). Eggs easily enter the mouth through contaminated hands. Thus, the patient constantly infects himself again, i.e., autoreinvasion occurs, which makes cure difficult.
Pathogenic effect. Itching, loss of appetite, diarrhea, sleep disturbance. In girls and women it is possible inflammatory processes in the genitals when pinworms crawl into the vagina.
Laboratory diagnostics. Fecal examination is not applicable because eggs are deposited on the skin. The most effective is scraping from the perianal folds of skin. To do this, a match or wooden rod is wrapped in cotton wool and moistened in glycerin, then scraped off and examined under a microscope. Used materials are burned. You may find eggs under your fingernails or in your nasal mucus. Sometimes pinworms can be seen in the feces.
Prevention: personal - compliance with the rules of personal hygiene, especially cleanliness of hands; a sick child should be put to bed in panties, boil them in the morning and iron them wet; public - general sanitary measures in combination with those specific to enterobiasis; systematic enterobic measures in children's institutions.
Whipworm (Trichocephalus trichiurus)
It ranks third in terms of the frequency of distribution of human helminths. Causes the disease trichuriasis.Localization. Cecum, appendix, the initial section of the large intestine.
Geographical distribution. Everywhere.
Life cycle. Pretty simple. The fertilized female lays eggs in the intestinal lumen, from where they are thrown out along with feces. In the external environment, a larva develops in the egg. At optimal conditions(temperature 26-28 °C) the egg becomes invasive after 4 weeks. Getting to a person through contaminated hands, vegetables, fruits, water, eggs pass into the intestines, reach the cecum and, without migration, turn into sexually mature forms. In humans, whipworms live up to 5 years.
Pathogenic effect. Symptoms largely depend on the degree of infection. The presence of single specimens may not cause any manifestations. With massive infection, disturbances in the digestive tract (pain, loss of appetite, diarrhea, constipation) and nervous system (dizziness, epileptiform seizures in children) are observed.
Traumatization of the intestinal wall contributes to the addition of a secondary infection, as a complication, appendicitis may develop.
Laboratory diagnostics. Detection of eggs in feces.
Hookworms
Representatives of two types of nematodes are combined under this name
- crooked head duodenum(Ancylostoma duodenale)
- Necator (Necator americanus)
Localization. Small intestine, duodenum.
Geographical distribution. Hookworms are common in countries with tropical and subtropical climates, where about 50% of the population is infected, which is approximately V" of humanity. There are underground foci of hookworm disease (mines, mine workings), which do not depend on above-ground temperature conditions. In the USSR registered in Transcaucasia and Central Asia.
Morphophysiological characteristics. The duodenum has dimensions: female - 10-13 mm in length, male - 8-10 mm. The anterior end of the body is slightly curved on the ventral side (hence the name). A characteristic feature of the structure is a wide open oral capsule, in which four ventral and two dorsal cutting teeth are located. At their base there are two glands that secrete enzymes that prevent blood clotting. With the help of teeth, the hookworm is attached to the intestinal mucosa. Hookworms feed on blood. At the site of fixation, ulcers up to 2 cm in diameter form and bleed for a long time. The male has a characteristic structure at the rear end of the body. The capular bursa, resembling a bell in shape, consists of two large lateral lobes and a small middle one. The eggs are oval in shape, with bluntly rounded poles. Their shell is thin and colorless. The necator differs in the structure of the oral capsule (instead of teeth it has two semilunar cutting plates) and the copulatory bursa.
Life cycle. Geohelminths. The only source of infection is humans. Eggs passed with feces develop in the soil. Under optimal conditions (28-30 °C), a non-invasive rhabditiform larva emerges from the egg. Distinctive feature structure - the presence of two bulbs in the esophagus. After molting, it turns into a filariform larva with a cylindrical esophagus. After the second moult, the filariform larva becomes invasive. The larva can actively move vertically and horizontally in the soil.
Upon contact skin human with soil, the filariform larva is attracted by body heat and actively penetrates the skin. Most often, infection occurs when a person walks without shoes or lies on the ground. Penetrating into the body, the larvae enter blood vessels and begin to migrate throughout the body. First they get into right heart, then in pulmonary artery, capillaries of the pulmonary alveoli. Through a rupture, the capillary walls enter the alveoli, and then enter the pharynx through the respiratory tract. Together with saliva, the larvae are swallowed and enter the intestine, where they transform into sexually mature forms. They live in the intestines for 5-6 years.
If the larva enters the human body through the mouth with contaminated food or water, then migration, as a rule, does not occur, but the adult form immediately develops. However, this method of penetration of larvae - passive entry - is much less common. The main route of infection is active penetration through the skin.
People of a certain profession (miners, miners, diggers, rice and tea plantation workers) especially often suffer from hookworm infections.
Pathogenic effect. Progressive anemia (anemia). The hemoglobin content can drop to 8-10 units, red blood cells - up to 1,000,000 in 1 μl. The causes of anemia are considered to be blood loss and intoxication. Possible disorders of the digestive system. Children experience physical and mental underdevelopment, and adults experience loss of ability to work. The intensity of invasion can be very high (hundreds and thousands of specimens).
Laboratory diagnostics. Detection of eggs in feces.
Prevention: personal - in areas of hookworm infection, mandatory wearing of shoes and prohibition of lying on the ground; To prevent infection through the mouth, observe the rules of personal hygiene. Public - improving the sanitary culture of the population; identification and deworming of patients; construction of special type latrines with a receptacle impenetrable to larvae; disinfection of soil and mines using sodium chloride and soil predatory fungi; in mines - checking incoming workers for the presence of helminths, annual examination miners. In the USSR, by 1960, underground foci of hookworm disease were completely eliminated.
Localization. Small intestine.
Geographical distribution. It is mainly found in tropical and subtropical countries, but is also found in temperate regions. In the USSR it is registered in Transcaucasia, Ukraine, and Central Asia. Isolated cases are also known in the central zone of the RSFSR.
Morphophysiological characteristics. It has a thread-like body and small dimensions - up to 2 mm. The anterior edge of the body is rounded, the posterior edge is conical. The larvae hatch from eggs in the intestines of the host.
Life cycle. Very complex, has much in common with the development cycle of hookworms. Geohelminth. Sexually mature males and females live in the human intestine. From the laid eggs, rhabditiform larvae develop, which, together with feces, are carried out into the external environment. Further development rhabditiform larvae can go in two directions:
- If a rhabditiform (non-invasive) larva, once in the soil, encounters unfavorable conditions (temperature, humidity), it molts and quickly turns into an invasive - filariform larva, which actively penetrates human skin and migrates throughout the body. In this case, the larva successively penetrates the veins, right heart, pulmonary arteries, pulmonary alveoli, bronchi, trachea, pharynx, and then is swallowed and enters the intestine. During migration, the larvae turn into sexually mature individuals. Fertilization can occur in the lungs and intestines;
- If rhabditiform larvae find favorable conditions in the external environment, they turn into males and females of the free-living generation that live in the soil, feeding on organic debris. If favorable conditions are maintained, rhabditiform larvae emerge from the eggs laid by free-living females, which again turn into a free-living generation.
Laboratory diagnostics. Detection of larvae in feces.
Prevention: the same as for hookworm infections.
Trichinella (Trichinella spiralis)
Causes the disease trichinosis, which belongs to the group of natural focal diseases.Localization. Sexually mature forms live in the small intestine of the host, larval forms live in certain muscle groups.
Geographical distribution. On all continents of the globe, except Australia, but it is not widespread, but focally distributed. In the USSR, the areas of greatest damage are observed in Belarus, Ukraine, the North Caucasus, and Primorye.
Morphophysiological characteristics. It has microscopic dimensions: females 3-4 x 0.6 mm, males - 1.5-2 x 0.04 mm. Characteristic Features serve as an unpaired reproductive tube in females and the ability to give birth to viviparity.
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 infected with trichinosis is eaten by an animal of the same or another species. For example, the meat of a trichinosis rat can be eaten by another rat or pig. In the intestines of the second host, the capsules dissolve, the larvae are released and within 2-3 days they transform into sexually mature forms (male or female). After fertilization, the females give birth to a new generation of larvae. Thus, each organism infected with Trichinella first becomes a definitive host - sexually mature individuals are formed in it, and then an intermediate host - for larvae hatched by fertile females.
For the full development of one generation of helminths, a change of hosts is necessary. The main form of existence is the larval or muscular form, which lives up to 25 years.
Trichinosis is a natural focal disease. The natural reservoir is wild carnivores, omnivores and insectivores. Insects that feed on corpses play a significant role in the spread of trichinosis in nature. Dead-eating beetles serve as a constant component of the diet of various animals (bear, marten, fox). By eating insects, various animals become infected with trichinosis, including those whose diet is dominated by plant foods.
Pathogenic effect. Symptoms of the disease appear a few days after infection. Initial period associated with the introduction of hatched larvae and the toxic effect of their metabolic products. Characterized by swelling of the face, especially the eyelids, a sharp rise in temperature to 40 ° C, and gastrointestinal disorders. Later, muscle pain and convulsive contraction appear masticatory muscles(rheumatoid period). With intense infection, death is possible. In mild cases, recovery occurs after 3-4 weeks. Possible complications: damage to the heart muscle, pneumonia, meningoencephalitis.
The severity of the disease depends on the number of larvae that have entered the body. The lethal dose for humans is 5 larvae per 1 kg of body weight of the sick person. The amount of meat containing a lethal dose can be negligible - 10-15 g.
Laboratory diagnostics. The most reliable method is the detection of larvae in the muscles (biopsy) and immunological reactions. The most common allergy skin test. Great importance has a survey of the patient, since group infection usually occurs.
Prevention. Public prevention is of primary importance:
- organization of sanitary and veterinary control at slaughterhouses and markets, inspection of pork, bear, and wild boar carcasses for trichinosis, for which two samples from each carcass are taken for microscopic examination from the legs of the diaphragm; if trichinella is detected, meat is subject to mandatory destruction or processing into technical products; heat treatment of meat is not effective, since the capsules ensure the survival of the larvae;
- zoohygienic keeping of pigs (prevention of eating rats);
- rat control (deratization).
Human roundworm (Ascaris lumbricoides)
The disease is caused by ascariasis.Morphophysiological characteristics. Large worm, whitish-pink in color. The female reaches 20-40 cm in length, the male - 15-20 cm, the rear end of the male's body is curved to the ventral side. The body is fusiform. The epithelium (hypodermis) of the roundworm forms a multilayered flexible cuticle on the outside, which functions as a kind of exoskeleton and also protects the animal from mechanical damage, toxic substances and digestion by the host’s digestive enzymes. Under the hypodermis there are longitudinal muscles. Roundworms do not have attachment organs; they are retained in the intestines, moving towards food. The oral opening is surrounded by three cuticular lips - dorsal and two ventral. In the body cavity there are phagocytic cells (insoluble metabolic products accumulate in them), genital organs and a tube-shaped intestine, in which the foregut is distinguished, consisting of the oral cavity and the esophagus; the midgut (endodermal) and the short ectodermal hindgut.
The reproductive organs look like thin thread-like winding tubes. The female has two developed ovaries, the male has one testis. A fertilized female has an annular depression at the border of the anterior and middle third of the body - a constriction. Every day, one female human roundworm is capable of producing 200-240 thousand eggs. The eggs are large, oval or round in shape, covered with three shells that protect them from exposure to adverse factors (drying, etc.). Outer shell has a lumpy surface, when in the intestine it is colored brown by fecal pigments, the middle one is glossy, the inner one is fibrous. The crushing of the egg and the development of the larva lasts about a month and can only occur in a humid environment with sufficient oxygen.
Of the sensory organs, only tactile tubercles are developed around the mouth, and in males also at the posterior end of the body (near the genital opening).
Localization. Small intestine.
Geographical distribution. In terms of prevalence, ascariasis is second only to enterobiasis. It is found throughout the globe, with the exception of the Arctic and arid regions (deserts and semi-deserts).
Human infection occurs when eggs containing larvae are ingested in contaminated water or food. Eggs can be found on poorly washed berries (especially strawberries) or vegetables from areas where human excrement is used to fertilize. Some synanthropic insects (for example, flies, cockroaches) can also transfer roundworm eggs to food. The swallowed egg passes into the intestine, where the egg shell dissolves and the larva emerges. It penetrates the intestinal wall, enters the blood vessels and migrates throughout the body. Together with the blood flow, the larva enters the liver, then into the right heart, pulmonary artery and capillaries of the pulmonary alveoli. From this moment on, the larva begins active movement. It drills through the wall of the capillaries, penetrates into the cavity of the alveoli, bronchioles, bronchi, trachea and, finally, into the pharynx. From here, together with sputum and saliva, the larvae enter the intestine for the second time, where they transform into sexually mature forms. The entire development cycle of roundworm occurs in one host.
In total, migration lasts about two weeks. Transformation into adult form occurs within 70-75 days. The lifespan of adults is 10-12 months. The lower temperature threshold at which roundworm eggs can develop is about 12-13 °C, the upper temperature is about 36 °C. At temperatures below the minimum, ascaris eggs, without developing, can remain viable and, gaining the so-called “sum of heat” in warm seasons, reach the invasive stage. A number of researchers believe that a person can become infected with the eggs of a pig roundworm, which is morphologically indistinguishable from a human one, while migration of larval stages is possible, but sexually mature forms are not formed.
Pathogenic effect. Larval and mature forms have different pathogenic effects. Larval stages cause sensitization ( allergic reactions) of the body with protein metabolic products and damage to the liver tissue and, above all, the lungs. In the lung tissue with migratory ascariasis, multiple foci of hemorrhage and inflammation (pneumonia) are observed. With intense invasion, the process can involve entire lobes of the lungs. It has been experimentally established that infection of animals large dose eggs leads to death from pneumonia on the 6-10th day. The duration of the disease and the severity of symptoms varies depending on the degree of infestation. With a slight degree of infection, the inflammatory process in the lungs stops without complications. In addition, migrating roundworm larvae, when penetrating the alveoli, disrupt the integrity of the latter, thereby opening the “gate” to bacteria and viruses.
Depending on the location and degree of invasion, the symptoms of ascariasis can vary from minor manifestations to death.
Laboratory diagnostics. Detection of eggs in feces.
Ascaris eggs are characterized by high resistance to exposure to factors external environment. They can overwinter and survive in contaminated soil for 5-6 years. They can be stored in cesspools for up to 8 months. In compost heaps, where the temperature reaches 45 °C, eggs die after 1-2 months.
These are non-segmented animals. The primary body cavity is filled with fluid. They are capable of active movement. Food for free-living species is bacteria, algae and single-celled organisms. They, in turn, feed on fish fry and small crustaceans.
Structure
The structure of roundworms suggests the presence of a cylindrical or spindle-shaped body. The cuticle covers the outside. The primary cavity is located under the skin-muscle sac.
Food enters through the mouth into the pharynx. From here it goes into the digestive tube, consisting of the foregut, middle and hind intestine. It ends with the anus. Modified skin glands are part of the excretory system.
These creatures are dioecious. They lack systems such as respiratory and circulatory systems.
Universal capabilities in terms of adaptation to conditions environment can be explained by the presence of a dense outer layer (cuticle).
The habitat of roundworms in some cases includes moss. They are able to penetrate into various parts of plants: stems, roots, tubers and leaves.
The distribution range of these creatures is wide.
Differences from other types
The structure of roundworms is somewhat different from anatomical features their flat counterparts. On cross section it can be seen that the body has the shape of a circle. It is symmetrical and elongated. The skin-muscle sac serves as a kind of wall for it. The cuticle, located on the outside, acts as a skeleton.
Muscle cells consist of two parts:
- contractile;
- plasmatic.
Representatives of roundworms have a mouth opening located in the front of the body. It is not lined with epithelium. Besides internal organs, there is also cavity fluid. In some species it may have toxic properties. The high pressure it creates ensures reliable support for the muscle bag. It is also important in terms of metabolism.
Reproduction
In most cases, representatives of roundworms are dioecious organisms. Thanks to this, their descendants are distinguished by genetic diversity. Individual individuals are characterized by the so-called, that is, males are not similar to females in appearance.
Development is carried out indirectly. The larval stage takes place. There is no need to change the owner. Type of fertilization - internal.
Sense organs and nervous system
Nervous system
Refers to the staircase type. It is otherwise called “orthogon”. The pharynx is surrounded by a special nerve ring. There are 6 nerve trunks that extend forward and backward. Among them, the most developed are the dorsal and abdominal ones. They are connected using jumpers.
Sense organs
They also have chemical senses, meaning worms are able to detect odors. Eyes in their most primitive form are present in free-living representatives.
There are several classes, but the most numerous are nematodes. If your child is in 7th grade, they will be studying roundworms in their biology curriculum. Traditional representatives considered at the school:
- roundworms;
- pinworms.
Roundworms. Character traits
With insufficient hygiene, invasion occurs, that is, infection. In this case, the eggs fall into oral cavity from the surface of unwashed vegetables and fruits, as well as hands. All this is indicated in the subject "biology". Roundworms do not need a change of owners for development.
After entering the intestines, the larvae emerge from the egg. They easily penetrate the mucous membrane and penetrate the bloodstream. After this, they enter the heart and then into the lungs. From here they pass into the bronchi and trachea. During this period, a person experiences a cough.
The movement of larvae can last up to 12 days. All this time they grow and change their shell several times. After being hit again small intestine they continue to grow for three months. At the end of this period, the helminths become adults. Each of them lives about 1 year.
Pinworm. Characteristics of roundworm
Another representative of the class is the pinworm. It usually lives in the large intestine. Characterized by small size. Females are larger than males and reach 12 mm. Infection is carried out in the same way as in the case of roundworm.
The main reason for the invasion is insufficient compliance hygiene. If you don't wash your hands properly after using the restroom, these types of roundworms can easily enter your body. Particular caution should be exercised when in public places.
Significance in human life and nature in general
- onion;
- beet;
- wheat;
- potato
Among these creatures you can find detritivores. The source of food for them is organic remains and humus. Such worms are directly involved in the formation of soil.
Where are nematodes found?
Finding them is not as difficult as it seems. If you suddenly find yourself out of town, go to the nearest river or lake. Pay attention to the sand on the shore. These creatures are often found in it. It also makes sense to look at growths on trees and old snags. This is also the habitat of roundworms.
Some species live in algae. Thus, they can be found almost everywhere. Each of them has its own power source. Despite this, they do not have to starve. Some dig in the sand and look for bacteria, others intensively extract juices from plants.
Roundworms also live in the forest. To spot them, you should come here in rainy weather. If you wish, you can simply take a piece of moss or lichen and put it in water. Surely you will find representatives of this type in it.
Type Roundworms
Response plan:
- General characteristics of Roundworms
- Body structure of human roundworm
- Reproduction and development of human roundworm
- Classification of Roundworms, variety of species
- The significance of Roundworms in nature and human life
General characteristics of Roundworms
Veils. On the outside, the skin-muscle sac is covered with a protective shell - the cuticle. During the growth of worms, it is periodically reset and then resumed. Below the cuticle is the hypodermis, which is the result of the fusion of skin cells. Under the hypodermis there are 4 ribbons of longitudinal muscles. During contraction, the dorsal and ventral bands act in opposite ways, and the body of the worm can bend in the dorsal-abdominal direction. The cuticle, hypodermis and muscles form a skin-muscular sac.
Digestive system. At the level of Roundworms, a grandiose event occurs in the evolution of the digestive system, which made all subsequent types of animals happy. It is in Roundworms that the hindgut and anus first appear. Now they digestive system consists of three sections: the anterior, middle and posterior sections of the intestine. The anterior section is usually divided into the mouth, muscular pharynx and esophagus. Digestion occurs in the midgut. With the appearance of the anus, food begins to move in one direction, which makes it possible various departments specialize and perform their digestive function more efficiently.
Excretory organs– in some protonephridia, there is an excretory opening in the front of the body on the ventral side. Some representatives have modified skin glands, they are called “neck glands”. Some have no excretory organs.
Nervous system and sensory organs. Nervous system of the scalene type (orthogonal). It consists of a peripharyngeal nerve ring surrounding the pharynx, and 6 nerve trunks extending forward and backward, of which the dorsal and abdominal ones are the most developed. The trunks are connected by jumpers (commissures). There are organs of touch and organs of chemical sense (smell). Free-living animals have primitive eyes.
Reproduction. Most Roundworms are dioecious organisms, which ensures genetic diversity in their offspring. There is sexual dimorphism (females differ in appearance from males) Development is indirect, that is, with a larval stage, without a change of host.
Genital organs in the form of tubes. The male testes open through the vas deferens into the final section of the intestine - the cloaca. The male has copulatory organs - cuticular needles, with the help of which he introduces sperm into the female's genital tract. Fertilization is internal. In the female, the paired ovaries continue into the oviducts, which pass into two uteri, which open with the genital opening on the ventral side of the body.
Representatives: The phylum is divided into several classes, the most numerous among them being the class Nematodes: Roundworms, pinworms.
Body structure of human roundworm
New concepts and terms: cuticle, helminth, invasion, copulatory organs, sexual dimorphism, hydroskeleton, anus, detritivore.
Questions for consolidation.
Literature:
- Bilich G.L., Kryzhanovsky V.A. Biology. Full course. In 3 volumes - M.: LLC Publishing House "Onyx 21st century", 2002
- Pimenov A.V., Pimenova I.N. Zoology of invertebrates. Theory. Tasks. Answers: Saratov, OJSC publishing house "Lyceum", 2005.
- Chebyshev N.V., Kuznetsov S.V., Zaichikova S.G. Biology: a guide for applicants to universities. T.2. – M.: Novaya Volna Publishing House LLC, 1998.
- www.collegemicrob.narod.ru
- www.deta-elis.prom.ua
