A type of roundworm or nematode. Type roundworms, general characteristics. General characteristics of the type
The variety of species included in the type roundworms huge, a person faces them all the time. Their habitat is vast, there is no place where they live. The name comes from the shape - the cross section is round.
The sizes of individuals are very small. They can distinguish between light and dark, and are often predators. The latter settle in the organs of humans, birds and animals. Reach enough large sizes- up to 8 meters long.
The most famous and numerous representatives of the Class Proper Roundworms (or nematodes) are given a general description in terms of their importance as a source of infection for adults and children. It is often carried out on the example of ascaris and pinworms, as the most important from the standpoint of medicine.
Body structure and physiology
The characteristics of individuals of the Type Roundworms in the context of the location of organs will not be voluminous due to the scarcity of such.
Functioning systems: nervous, as well as excretory, sexual. In the future, it is logical to carry out the description on the example of nematodes due to the high prevalence of species.
The shape of the body with pointed ends and the nature of the movements helped them adapt to living in various environments. FROM outer side nematodes are covered with several layers of cuticle, which protects against external influences. Below it is the hypodermis, followed by a layer of muscles, which is made up of longitudinal fibers, divided into 4 ribbons that help with crawling. The muscles of the back, as well as the abdominal muscles, contract, work in opposition to each other, which explains the movement of the worms on its side.
The digestive system is straight, resembling a tube. The mouth is surrounded by lips (the bulk of them have 3), in some predatory worms - by teeth. It is a tool for pinching the intestinal mucosa of the host. Organisms living on plants have a piercing-sucking organ - a stylet that extends from oral cavity.
How individuals reproduce
The most important characteristic Roundworms - a way of self-reproduction. It is advisable to consider the structure of the reproductive system using the example of roundworms.
In the female (which is larger than the male) it is paired and tubular. The vagina at one end goes into the opening on the abdomen, on the other hand it bifurcates into the uterus. Each, gradually narrowing, continues with the oviduct, which flows into the ovary. The tubes contain germ cells located on various stages development.
The reproductive organs of the male are unpaired:
- testis;
- spermaduct;
- ejaculatory canal;
- copulatory bag, from where cuticular needles come out - organs involved in copulation.
The seminal fluid passes through the vagina into the uterus, where fertilization takes place.
general characteristics type in the context of the development of each species is more clearly seen in the example of roundworms and pinworms, causing great harm health and rapidly spreading.
Eggs are very resistant, even to different temperatures, after exiting the intestines, mature to larvae. The process takes place in a humid environment for a month.
Infection follows after ingestion of eggs and larvae through food, which then seep into the veins and are carried by the blood to the lungs. Then gradually pass into the bronchi, windpipe and mouth. From there, with the help of saliva, they move a second time to the intestines, where they grow and become ready for reproduction.
Children's pinworm is very widespread. It lives most often in the intestines of children, has a length of 5-10 mm. Leads to the development of enterobiasis.
Fertilized females move to the anus, where they can live long enough for a long time thanks to comfortable conditions, causing itching and laying eggs there. The embryos emerge from the shell, once again entering the intestine with food. Pregnant women can also become infected.
Pathogenic value
Individual representatives of nematodes can be characterized as life-threatening.
Svainik is the causative agent of a disease that causes severe anemia.
Whipworm is very common, causing trichuriasis. Its eggs are not visible to the eye due to their microscopic size. The risk of infection is high for those involved agriculture. The disease in severe form leads to prolapse of the rectum.
Pathogen Control Measures
Avoid entry into organs. To this end, you need to observe personal hygiene, carefully choose ponds for swimming, children's playgrounds. When working in the ground, it is important to use a protective suit. Eliminate fertilizer land plots excreta of humans and infected animals.
Origin of roundworms
Although the question of how and from whom roundworms evolved is still not completely closed, there is a fairly convincing theory that their ancestors were marine ciliary flatworms. Despite the differences in the structure of ciliary flatworms and roundworms (in particular, the absence of cilia, ring and diagonal muscles, the body is round in section with internal cavity where the ciliary has a solid jelly-like parenchyma), there is still a link - a primitive roundworm, belonging to the class of ventral, which lives in the bottom layers of water bodies. It just has the signs of both those and other animals.
The structure of roundworms
1. Roundworms are three-layer animals with bilateral symmetry.
2. The bodies of their worms resemble threads, spindles, barrels or lemons, depending on the species.
3. Worms are very different in size - from very tiny, not reaching a millimeter, to eight-meter giants.
4. Outer cover - cuticle, it may have transverse ring grooves or be equipped with attachment devices.
5. Next the inner layer, hypodermis, does not consist of individual cells surrounded by walls, but of separate "pieces" of the cytoplasm with nuclei, between which cytoplasmic bridges are built. This type of tissue is called synthycium. Specific longitudinal ridges stretch in the hypodermis: ventral, dorsal, and a pair of lateral ones.
6. Roundworms only have longitudinal muscles. Thus, the cuticle, hypodermis and internal muscles make up skin-muscle sac.
7. Roundworms for the first time on the evolutionary path acquired primary cavity body - the so-called schisogoal which does not yet have an epithelial lining. Inside the cavity there is a fluid under pressure, with its help nutrients are redistributed.
Organ systems
3. excretory system - protonephridial. It is represented by unicellular or multicellular glands on the neck of the worm, lateral excretory ducts and pseudocoelomocyte cells.
4. Nervous system ladder type consists of a ganglionic ring located near the pharynx, two nerve trunks extending from it, and several more nerves that are connected by jumpers.
5. sense organs mostly poorly developed, there are chemoreceptors and various sensilla responsible for touch and smell.
6. Among the roundworms, hermaphrodite species were found, but in the vast majority they separate sexes with distinct sexual dimorphism.
7. Fertilization nematodes have internal, females different types capable of both laying eggs with larvae inside, and giving birth to "ready" larvae. Interestingly, larvae can hatch from eggs while still inside the host, before entering the environment.
Type roundworms, or nematodes, are thought to have evolved from turbellarians. Evolving, this class acquired a peculiar structure, which is strikingly different from the structure of flatworms. This fact forces us to consider nematodes as a separate specimen of the animal world. Since the relationship of nematodes with the groups standing above has not been proven, they are considered a side branch of the animal family tree. This type has more than 10,000 species of organisms.
In the general characteristics of roundworms, attention is focused on the external structure. From the point of view of medicine, roundworms are of great interest, since only they contain forms that are pathogenic to the human body.
Such a peculiar structure allows them to crawl freely, bend the body in different directions. A characteristic of the type of roundworms shows that they lack blood and respiratory system. These organisms breathe through their bodies.
Digestive system
The digestive system of roundworms resembles a tube, that is, it is through. Starting from the oral cavity, gradually passes into the esophagus, then into the anterior, middle and hindgut. hindgut ends with an anus on the other side of the body.
Many representatives of roundworms have a terminal mouth opening, in some cases it is displaced to the ventral or dorsal side.
Selection system
breeding system
The nematode has reproductive system With tubular structure. These organisms are heterogeneous. 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 seed tube, and the channel for the eruption of the seed.
Females have a 2-tubular 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 department, which plays the role of the oviduct. The largest section of the female reproductive system is the uterus. Two uterus, connecting with each other, form a vagina, access to which is open on the front of the body.
Females and males differ significantly in outward signs. Males tend to be smaller and the back of the body in many is twisted towards the side of the belly. In most species of nematodes, reproduction is viviparous - females carry an egg in the uterus until the larva hatches from it.
Nervous system
The nervous system of roundworms is a nerve ring, nerve trunks branch off from it. Of these, the ventral and dorsal trunks are the most developed.
Life cycle
Nematodes in humans in the body cause diseases called hookworms, many of which pose a serious threat to health. There are classes of roundworms that are most common among humans.
Roundworm
An egg produced by an ascaris enters 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 human body. It has the ability to pass through the walls of the intestine, penetrates into the vessels, with the blood flow enters the liver, atrium and lungs. In order 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 ascaris are very toxic, so patients may experience a strong headache, constant fatigue, outbursts of irritability. In addition, ascariasis often provokes intestinal obstruction.
Very common helminths, small nematodes white color. 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 the rules of hygiene, so the victims are most often babies visiting Kindergarten. The patient is tormented severe itching, it combs the skin until it bleeds, pinworm eggs remain on the hands and under the nails, after which they are transferred to 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. Toxins released by pinworms can cause headaches, insomnia, fatigue and dizziness, and allergies.
By blood vessels the crooked head enters the heart, from there to the lungs, upper respiratory tract and pharynx. Together with saliva, they penetrate the esophagus, then the stomach, the destination is the duodenum. This type of nematode can enter the body in two ways - either with contaminated food and water, or through skin. Soon after entering the body, the patient begins to suffer from pain in duodenum, there is indigestion, fatigue, headache, depression, impaired memory and attention. With absence timely treatment this disease can lead to death.
How to deal with the penetration of nematodes into the body? Prevention 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 put 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 gone through the composting process as garden fertilizer;
- cut the nails of adults and children as often as possible, change bed sheets and daily underwear.
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 into the body.
structural features
Body unsegmented, spindle-shaped, elongated, rounded in cross section, with pointed ends. Dimensions range from 0.3-1 mm to 8 m.
covers represented by a musculocutaneous sac, which is formed by the cuticle, hypodermis, and longitudinal muscle layer ( smooth muscle) in the form of four strips. Cuticle - a layer of dense substance that covers the surface of the body and performs musculoskeletal and protective function. This layer is formed by cells of a single-layer epithelium, in which metabolic processes and intensive biosynthesis of substances. So, hypodermis - coverslip epithelial tissue invertebrates, the cells of which are able to secrete the cuticle and retain substances harmful to the helminth.
body cavity primary (protogoal) filled with liquid. The peculiarity of this cavity is that it is not covered by epithelium. In it are located internal organs nematodes. In addition, there is a liquid in the cavity under high pressure, which creates support for the somatic muscles. Organs contain a small and usually constant number of cells (euthelium), which limits the ability to regenerate.
Features of life processes
Support carried out by the musculocutaneous sac and cavity fluid. The fluid is under pressure and forms hydroskeleton, which is the support for the muscles.
Traffic muscular, due to longitudinal smooth muscles, combined into four ribbons. Roundworms move by contracting alternately the dorsal and ventral bands and arching the body.
Digestion is carried out somewhat more complicated than in flatworms by the digestive system. It begins with a mouth opening, which is located at the front end of the body and is surrounded by three "lips". Next comes the pharynx, which acts like a pump during feeding. The pharynx passes into the esophagus, which has one or two thickenings (bulbs), and the esophagus into the intestine, which ends with the anus. The digestive system is divided into three sections - anterior, middle and posterior. front and back department s - ectodermal origin, middle - endodermal. So, in roundworms digestive system is already transparent, it contains back section with anus.
Selection ensured excretory system, formed by a couple skin glands (two lateral canals with an excretory pore behind the mouth opening). In addition to glands, the excretory function is carried out phagocytic cells, which are located along the excretory canals. They absorb and accumulate insoluble waste products, foreign bodies from the body cavity fluid.
Process regulation carried out by the nervous system of the nodal (ganglionic) type. The central nervous system is formed by the peripharyngeal nerve ring and nerve trunks, the PNS is represented by nerve branches.
reproduction with the participation of a dioecious system, fertilization is internal, in many species - sexual dimorphism. sexual dimorphism- a phenomenon in which males and females of the same species differ in characteristics external structure, coloring, behavior, etc.
The body of roundworms has a cylindrical shape, it is elongated in length with points at the ends. The movement of roundworms occurs due to contractions of the muscle fibers that make up their body.
The digestive system of nematodes is represented by the primary cavity in which the process of digestion takes place. The alimentary canal is divided into three sections: the middle, anterior and hindgut.
The anterior intestine of roundworms begins with the oral cavity and passes into the pharynx. This is where food absorption takes place. Digestion of food occurs in the midgut, absorption also takes place here. useful substances. The hindgut ends with an anus.
The annular parapharyngeal ganglion, as well as the nerves extending from it, form nervous system roundworms. Nematodes have organs of touch and taste. Some types of free-living worms have photosensitive eyes.
Reproduction of roundworms
Roundworms belong to the species of dioecious animals. Reproduction occurs exclusively sexually. For some species of roundworms, sexual dimorphism is inherent - outward difference male from female.
The reproductive system of the female is represented by the oviducts, uterus, unpaired vagina and paired ovaries, the male has a vas deferens, an unpaired testis, and a copulatory apparatus.
Roundworms are characterized by internal fertilization with incomplete transformation (including the larval stage).
Pinworms parasitize the human large intestine. The females lay their eggs around anus which often causes itching. If hygiene is not observed, the eggs enter the human body. Often pinworms do not exceed 1 cm in length.
