Characteristics and features of the structure of roundworms. Type Roundworms. Grade Properly round. Ascaris, pinworm, whipworm, trichinella

The variety of species included in the type Roundworms is huge, a person is constantly confronted with them. 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 quite 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 the outside, the 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 developed piercing-sucking organ - a stylet that extends from the oral cavity.

How individuals reproduce

The most important characteristic of Roundworms is the way they reproduce. 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 at various stages of 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.

The general characteristic of the type in the context of the development of each species is more clearly seen in the example of roundworms and pinworms, which cause great harm to health and are rapidly spreading.

The eggs are very resistant, even to different temperatures, after leaving the intestines they 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 for quite a long time due 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 in 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. Exclude fertilization of land with human and infected animal excrement.

In the animal kingdom. More than 80 thousand species have been described, but in reality, there are many more. Judging by the number of their appearance, adaptability to the environment and good survival, experts came to the conclusion that this population has more than a million representatives. Nematodes have adapted to living in different sources, such as seas and reservoirs, soil, etc. Their presence in the human and animal body causes enormous damage, and the worms themselves can cause various diseases.

Breathe-helping machine

As a rule, breathing in roundworms occurs through the entire body, since there is no circulatory blood supply system. Accordingly, there is no need to transfer oxygen to all organs. The energy received from food is released due to the breakdown of glycogen - a substance of an organic nature.

Selection system

Nematode neurological map

The organs of touch and chemical perception are well developed. Nematodes have no sense organs.

Fertilization and reproduction system

Life cycle of a nematode

Roundworms go through five stages of development during their existence: four of them are larval and one adult. All transitions are associated with a change in environment or migration from one host to another.

Biohelminths

The main carriers are humans, great apes and other mammals. Biohelminths are carried by various blood-sucking insects.

Fillaria enter the bloodstream only when the carrier is maximally active. In the case of mosquitoes, this is evening and night time. In horsefly - morning and afternoon. When transferring filaria by midges or biting midges, their output does not have a specific period, and depends only on humidity.

The main types of roundworms

1. Wuchereria banctofti : in humans and monkeys, it is concentrated in the blood arteries and lymph nodes. Leads to stagnation of blood and lymph. It is also the cause of elephantiasis and allergization. The main vector is the mosquito.
2. Brugia malayi : definitive hosts are humans, some species of monkeys, the cat family. Pathogenicity and concentration similar Wuchereria banctofti. Also carried by mosquitoes.
3. Oncocerca volvulus : carried by midges, and the carrier of the helminth is a person. It is concentrated in the body under the skin of the head, chest, arms and legs. Promotes the formation of painful nodules. Concentrating in the area of ​​\u200b\u200bthe organs of vision, it can cause blindness.
4. loa loa : localized under the skin and mucous membranes in humans and monkeys, forms painful nodules and abscesses. Carried by horseflies.
5. Mansonella : concentrated in the body of the carrier, which is people, in the subcutaneous fat layer, the mesentery of the intestine and under the serous membranes. Carried by mosquitoes.

It is also worth mentioning the most common types of roundworms.

Ascaris

Roundworm

Roundworm

roundworms compared to flatworms, they are characterized by a higher organization. Representatives of this type are characterized by a spindle-shaped body, rounded in cross section. The internal organs are placed in the primary body cavity filled with fluid.

From above, roundworms are covered with a layer of dense substance that covers the surface of epithelial cells and is the product of their excretion. This layer is called cuticle. Under the cuticle is a layer of longitudinal muscles.

Representative type - roundworm human lives in the human small intestine. It has a very elastic body due to the presence of longitudinal muscles. At the front end of the body is a horn, at the back - anus.

The mouth is surrounded by three lips, with which the ascaris captures semi-digested food, all digestion takes place in the intestine. Undigested food remains are removed through the anus.

Nervous system similar to flatworms. Roundworms are dioecious animals. The female has two ovaries, and the male has one testis. Eggs are secreted into the intestines of a person and are excreted with feces. After some time, at high temperature and oxygen access, a larva forms in them. Such "eggs" can end up in the intestines of a person if he eats unwashed vegetables and fruits. The larva emerges from the eggs, penetrates the intestinal walls, enters the bloodstream and, together with its flow, enters the lungs. With sputum, the larvae are expectorated into the throat, and then swallowed again. In the intestine, an adult worm is formed from the larva, causing a disease - ascariasis.

The female roundworm reaches 44 cm, the males - 25 cm. The female is very prolific, she can produce more than 240,000 eggs per day. Her eggs are very tenacious, can be stored in the environment for up to 7 years.

Type Flatworms General characteristics of the type

The characteristic features of the type are as follows :

1. The body is flat, its shape foliate(in cilia and flukes) or ribbon-like(in tapeworms).

2. For the first time in the animal kingdom, representatives of this type developed bilateral(bilateral ) body symmetry, i.e., only one longitudinal plane of symmetry can be drawn through the body, dividing it into two mirror-like parts.

3. In addition to the ectoderm and endoderm, they also have an average germ layer - the mesoderm. Therefore, they are considered the first three-layered animals. The presence of three germ layers provides the basis for the development of various organ systems.

4. Body wall - the totality of the outer single-layer epithelium and those located under it several layers of muscles- circular, longitudinal, oblique and dorsal-abdominal. Therefore, the body of flatworms is capable of performing complex and varied movements.

5. No body cavity, since the space between the wall of the body and the internal organs is filled with a loose mass of cells - parenchyma. It performs a supporting function and serves as a depot of reserve nutrients.

6. Digestive system consists of two sections: ectodermal anterior guts, represented by a mouth and a muscular pharynx, capable of turning outward in predatory ciliary worms, penetrating the victim and sucking out its contents, and a blindly closed endodermal midgut. In many species, many blind branches extend from the main sections of the midgut, penetrating into all parts of the body and delivering dissolved nutrients to them. Undigested remains of food are thrown out through the mouth.

7. Excretory system of protonephridial type. Excess water and metabolic end products (mainly urea) are excreted through the excretory pores.

8. Nervous system more concentrated and represented by a paired head node (ganglion) and longitudinal nerve trunks extending from it, connected by annular bridges. The nerve trunks are formed by the bodies of nerve cells and their processes located along its entire length. This type of organization of the nervous system is called stem. All flatworms have developed organs of touch, chemical sense, balance, and free-living ones have vision.

9. Flatworms - hermaphrodites(with rare exceptions). Fertilization is internal, cross. In addition to the sex glands (ovaries and testes), a complex system of genital ducts and additional glands have been developed that provide the zygote with nutrients and material for the formation of protective egg membranes. In freshwater ciliary worms, development is direct, in marine ones, with a planktonic larval stage.

Class Tapeworms

1. They have completely lost their own digestive system and absorb the food digested by the host with the entire surface of the long ribbon-like body.

2. The reproductive system is repeated in each segment.

Bull tapeworm- one of the largest (about 10 m long) representatives of the class (Fig. 11.5). The adult worm lives in the human small intestine (main host), its larva lives in the muscle tissue of cattle (intermediate host).

The body consists of a head, neck and segments (about a thousand). The head carries four powerful suction cups. It is followed by the neck - the zone of budding of young segments. Old segments move back and have the ability to grow, so their size increases in the direction from the head to the posterior end of the body.

Rice. 11.5. Bull tapeworm: 1 - appearance; 2 - head (suckers are visible); 3 - segments.

Fertilization is internal, cross, rarely self-fertilization. The last 3-5 segments periodically separate from the body of the worm and are excreted from the human body along with feces. These segments are called "mature", as they are completely filled with fertilized eggs, the number of which in one segment reaches 200 thousand. For a year, a bull tapeworm forms up to 600 million eggs. Its life expectancy is about 20 years.

From the external environment, the eggs, along with the grass, enter the intestines of cattle. In the intestine, a microscopic larva with six hooks emerges from the egg. With their help, it perforates the intestinal wall and enters the lymphatic and blood vessels, through which it spreads to a variety of internal organs. Some of the larvae get stuck in the muscle tissues, grow and turn into a bubble stage - Finn - a small bubble filled with liquid, with a head with four suckers screwed into it. When eating poorly cooked or fried meat infected with Finns, in the human intestine, the heads of the worm turn out and attach to the intestinal wall. The neck of the worm begins to separate segments, the bubble soon disappears.

The class Tapeworms also includes pork tapeworm, echinococcus, wide tapeworm, etc.

Unlike bullish pork tapeworm , in addition to suckers, has hooks on the head, with the help of which it is even more firmly attached to the wall of the human intestine. Its intermediate host is the pig.

Most dangerous to humans tapeworm echinococcus . His finna forms a bubble the size of a baby's head. An adult tapeworm is only 5 mm long. Lives in the small intestine of a dog, fox, wolf. The Finn stage takes place in various organs (especially in the liver and lungs) of cattle, sheep, pigs, and also humans. Humans become infected through careless handling of dogs. Treatment of echinococcosis is possible only by surgery.

Class Ciliary worms

This class includes free-living marine and freshwater, rarely terrestrial worms, the entire body of which is covered with ciliated epithelium. The movement of the worms is provided by the work of the cilia and the contraction of the muscles. Many species are characterized by regeneration.

A typical representative of ciliary worms - milky white planaria - lives in fresh stagnant water bodies on underwater objects and plants (Fig. 11.4). Its flat body is elongated, at the front end of which two small tactile tentacle-like outgrowths and two eyes are visible.

Planaria is a predatory animal. Her mouth is located on the ventral side, almost in the middle of the body. With the help of a muscular pharynx protruding outward, the planaria penetrates into the prey and sucks out its contents. In the branching middle section of the intestine, food is digested and absorbed.

Excretory organs - protonephridia. They are represented by two branching canals, at one end opening outwards excretory openings, and at the other - by stellate cells scattered in the parenchyma. The stellate part of the cell passes into a canal, inside which a bundle of cilia is located. Liquid metabolic products seep into the pear-shaped extension of the initial section of the canal. Protonephridia are located on the sides of the body.

Rice. 11.4. Scheme of the structure of dairy planaria: a - digestive and nervous systems; b- excretory system: 1 - posterior branches of the intestine; 2 - lateral nerve trunk; 3 - head ganglion; 4 - anterior branch of the intestine; 5 - pharynx; 6 mouth opening; 7 - channels of the excretory system.

The nervous system consists of clusters of nerve cells - the head ganglion. Nerve trunks depart from it to the sense organs - the eyes and the organs of touch - lateral outgrowths. To the posterior end of the body from the head node are two longitudinal nerve trunks, interconnected by transverse bridges. Numerous nerves depart from the longitudinal nerve trunks.

Planaria is a hermaphrodite. Fertilization is internal, cross. The development is direct.

Flukes class

2. various organs of attachment to the host body: suckers, hooks, etc.;

3. regressive development of the nervous system and sensory organs;

4. simply arranged digestive system or its absence;

5. extremely high fertility;

6. complication of the development cycle, consisting in the alternation of methods of reproduction and the change of hosts. In the body of the main host, sexual reproduction of the worm occurs, in the body of the intermediate host, asexual reproduction occurs.

class representative- liver fluke settles in the bile ducts of cattle (rarely humans) and feeds on blood and nutrients accumulated in liver cells. The body is leaf-shaped, flattened, up to 5 cm long, covered with a dense cuticle. The organs of attachment to the body of the host are two suckers: the anterior - oral, and abdominal. The digestive and excretory systems are not fundamentally different from those of ciliary worms. Simplification of the nervous system is expressed in a decrease in the size of the head ganglion. The sense organs are poorly developed.

The development cycle of the fluke is complex, with the change of several generations and one sexual. After internal fertilization and maturation, the eggs must enter the water, where a floating larva emerges from them. Having found a snail - a small pond snail, she penetrates his body. In it, the larva of the worm undergoes a series of transformations and parthenogenetically reproduces twice. As a result, a generation of larvae is formed, resembling an adult fluke in structure, but having a muscular tail appendage. At this stage, the larvae leave the body of the pond snail (intermediate host), enter the water and settle on coastal vegetation. Here they lose their tail and become covered with a dense protective shell. With green food, cysts can enter the body of domestic animals (the main host), where they turn into adult liver flukes. A person can become infected with them when drinking raw water from a reservoir, as well as vegetables and fruits washed in this water.

Preventive measures: destruction of small pond snails in local water bodies and human compliance with hygiene rules.

Type Roundworms General characteristics of the type

The characteristic features of the type organization are as follows :

1. body thin, cylindrical, elongated and pointed at the ends. It is round in cross section.(which gave the name to the type).

2. Skin-muscular sac It consists of an external multi-layer cuticle that does not have a cellular structure, a single-layer epithelium located under it and a layer of longitudinal muscle fibers, due to contractions of which the body can bend serpentine.

3. Body cavity - primary, filled with a liquid under greater than atmospheric pressure. The cavity fluid gives the body elasticity and thus acts as a hydroskeleton. It also provides transport of nutrients and waste products.

4. For the first time in the animal kingdom the digestive system is represented by a through digestive tube, subdivided into three sections - the anterior, middle and hindgut. The anterior section begins with a mouth opening leading to the oral cavity and pharynx, which can work as a pump. The pharynx is separated from the midgut by a valve. In the midgut, food is digested and absorbed. The midgut is followed by the ectodermal hindgut, which opens on the ventral side of the body as an anus.

4. excretory system represented by a pair of lateral longitudinal canals, merging under the pharynx into one duct and opening on the ventral side of the body with an excretory opening. The end products of vital activity accumulate in the cavity fluid, and from it they enter the excretory canals.

5. Nervous system It is represented by an annular peripharyngeal ganglion and several longitudinal nerve trunks extending from it, interconnected by semicircular nerve bridges. There are organs of taste, touch, and free-living roundworms have light-sensitive eyes..

6. Roundworms - dioecious animals that reproduce only sexually. In roundworm, males and females are outwardly distinguishable (sexual dimorphism). The reproductive system has a tubular structure: in the female - paired ovaries, oviducts, uterus and unpaired vagina, in the male - unpaired testis, vas deferens, ejaculatory canal, copulatory apparatus. Fertilization is internal, development usually proceeds with incomplete transformation (with the larval stage).

Figure 11.6. Appearance (a) and internal structure (b) roundworm: 1 - mouth opening; 2 - throat; 3 - intestines; 4 - vagina; 5 - uterus; 6 - oviduct; 7-ovary; 8 - ejaculatory canal; 9 - testis; 10 - seed tube.

The development cycle is complex, associated with the release of eggs into the external environment and the migration of larvae in the human body. Fertilized eggs, covered with dense protective shells, from the human intestine enter the soil. In the presence of oxygen and a sufficiently high temperature, a larva develops in them for about a month. The egg becomes contagious (invasive). With contaminated water and food, eggs enter the human small intestine. Here the larvae are released from the shell, pierce the intestinal mucosa with their elastic body and penetrate into the blood vessels. With the blood flow through the portal and inferior vena cava, they enter the right atrium, right ventricle and lungs (through the pulmonary arteries). From the lung tissue penetrate into the bronchi, from them into the trachea, and then into the pharynx. During migration, the larvae develop in the presence of oxygen. From the pharynx, they enter the intestines, where they complete their development cycle. Life expectancy is about a year.

Roundworms have a ubiquitous distribution and a high number of individuals, which indicates the biological progress of this group of animals. Their ancestors are considered ancient ciliary worms.

Similar information.

The main signs of roundworms:

1. They have a non-segmented, rounded body in cross section. Its surface is three-layered and consists of meso-, endo- and ectoderm. The worm has a skin-muscular sac.
2. All types of annelids have a pseudo-target - this is the primary cavity of the body, filled with liquid. It gives the body additional elasticity and performs the functions of a hydroskeleton. This fluid is also responsible for metabolic processes. It is here that all the internal organs that form the digestive, nervous, excretory, muscular and reproductive systems are located.
3. The structure of roundworms is such that they lack a respiratory and circulatory system.
4. Features of roundworms also consist in the fact that their digestive system is represented by a through tube that begins with a mouth opening. The mouth is surrounded by cuticular lips. At the end of the digestive tube is the anus. The whole tube is divided into three sections. Pinworms have a special extension of the esophagus called the bulbus.
5. As for the nervous system, it consists of the peripharyngeal ring, head ganglia and nerve trunks (abdominal, spinal and two lateral trunks). The most developed abdominal and dorsal rods. They are connected by special jumpers.
6. No matter how many species of roundworms, all of them have poorly developed sense organs. As a rule, they consist of tactile tubercles and special organs of chemical sensation.
7. The excretory system of the roundworm consists of a small number of excretory phagocytic cells. They accumulate metabolic products and foreign substances that enter the cavity of the body.
8. Nematodes are roundworms that have a tubular structure of the genitals. The number of genital organs of the female, as a rule, is paired. The male, on the contrary, has unpaired genitals. His genital apparatus incorporates the testis and the vas deferens, which passes into the ejaculatory canal and opens into the back of the intestine. The body structure of the female is somewhat different. Her reproductive apparatus consists of paired ovaries, from which come two tubular oviducts and a paired uterus. It unites into a common vagina.

We have listed the common features characteristic of representatives of the roundworm type. However, the external structure of individual individuals may vary slightly. So, if you describe a group of roundworms, the representatives of this class are as follows:

• roundworm;
• whipworm;
• pinworms;
• hookworm;
• trichinella;
• guinea worm.

Roundworm

This is a rather large helminth, the female of which can grow up to 40 cm, the males - about 20 centimeters. Ascaris has a cylindrical body narrowed towards the ends. The body of the male from the rear end is twisted in a spiral towards the abdomen.

Important! Infection of people occurs when eating unwashed fruits and herbs.

The life cycle of roundworm in the human body is as follows:

1. After the egg is in the intestine, its shell is dissolved by digestive juices, and the larva emerges from it.
2. It enters the bloodstream through the intestinal walls. Then it migrates through the liver to the right atrium, ventricle and lungs.
3. From there, through the pulmonary capillaries, the larva enters the bronchi and trachea, provoking a cough.
4. During coughing, it is swallowed again and again ends up in the intestines. Here she reaches the state of a sexually mature individual, lives and breeds for up to a year.

Pinworms

Important! Eggs become infectious a couple of hours after they are laid. If, while combing this area, the eggs fall under the nails of the patient, he re-infects himself if hygiene is not observed.

Since the life expectancy of a sexually mature pinworm reaches 58 days, the patient may self-heal if there is no re-infection. As for males, they die immediately after mating with females and leave the body naturally (with feces).

Vlasoglav

The anterior filiformly elongated part of the body of the worm is thinner than the posterior one. It contains the esophagus. The posterior end of the male is thickened and spirally twisted. Here is the intestines and the reproductive system. The eggs of this worm outwardly very much resemble a barrel with caps in the form of corks at the ends. They are light transparent and reach 50 microns in length.

Trichinella

This worm is a biohelminth. Its life cycle is as follows:

The worm lives in the small intestine, where it can live up to five years. It is referred to as geohelminths. Hookworm migrates in the human body like roundworms. Eggs with feces enter the external environment, where a day later they hatch into larvae that feed on feces. After they reach the filarial stage, the larvae become infective.

Sometimes infection occurs by the oral route, but more often filariae penetrate the skin. From the intestines, the larvae migrate to the blood vessels and lungs. Then they rise through the bronchi to the trachea, from where, during the cough reflex, they are thrown into the mouth and swallowed. After that, they settle in the duodenum.