External structure of roundworm. Roundworms: sizes and what do roundworms look like? Reproduction and development of the human roundworm

The introduction of roundworm larvae into internal organs or intestines causes a disease - ascariasis. This is a fairly common disease; of all types of helminthiases, ascariasis ranks second in the number of cases.

The structure of the helminth

• The presence of a body cavity filled with fluid;
• Dioecious individuals;
• Periopharyngeal ring;
• Longitudinal muscles and a strong outer protective shell.

Unlike other varieties, they do not have suckers, and they are held in the intestines only with the help of this muscular apparatus.

The digestive system of the human roundworm consists of:

• From the mouth opening with three lips;
• Esophagus;
• A digestive tube that ends in the anus.

Digestion in roundworms is very well developed.

Ganglion with branches extending from it different sides fibers represents the nervous system of the helminth. The fibers extending into the dorsal and abdominal parts of the body are better developed than others.

One of the features of the roundworm’s body is that it completely lacks blood and respiratory system. Ascaris, as an anaerobic organism, does not need oxygen.

Reproductive system of roundworms

This type of roundworm is dioecious: there is a male and a female, which differ in structure and size. Let's talk about this in more detail.

The structure of the female

The body of a female roundworm has its own structural features. A sexually mature female is much larger than a male, its length can reach 40–45 centimeters, the thickness of the worm is up to 6–7 millimeters. The body of the female has an elongated shape, at the end it is pointed in the form of a cone. In the upper third of the individual, closer to the head end, there is a vulva. It is a ring that opens outward. Closer to the tail, in the posterior third of the female body, there is an anus.

The female reproductive system consists of two tubes - a paired uterus, two ovaries, oviducts and a vagina, which, in turn, communicates with both uteruses. The vagina of the roundworm is brought out into the abdominal cavity.

Larvae roundworm mature in the ovaries after fertilization of germ cells (oogonium). The fertilized egg then moves to the uterus and matures further.

Male structure

The male helminth is almost half the size of the female helminth. The maximum length is 25 cm, and the diameter is no more than 5-6 mm. The structural features of the male roundworm are that the tail part of the worm's body is bent in the form of a spiral, and in the same third of the body there is an anus with tactile papillae around the anus.

How do roundworm eggs work?

A female roundworm can hold 20–25 million fertilized eggs. She puts them aside in parts, about 200-300 thousand per day. Together with feces, a person releases them into the environment, after which the worm eggs fall into the soil and can remain in it for one to two weeks. During this period of time they “ripen”, after which they are able to infect humans.

A fertilized egg is an oval or spherical formation with a protective shell that allows the larva to survive in conditions environment up to 4‒5 years. Only direct methods can destroy a helminth egg in the soil. Sun rays, alcohols, kerosene, etc.

Inside the egg, a larva gradually matures and forms; for this it only takes two to five weeks. The formed larva is very similar in appearance to the adult, only several times smaller. As the larva grows and develops, it molts, sheds all its shells one by one, and when fully mature, it begins to move and has the ability to penetrate the human body and continue its development and growth there.

A person becomes infected through products that have been in contact with soil, water contaminated with worm eggs, through dirty hands etc .

Infection occurs only when a mature egg enters the host's body. Larvae in the human body can move freely, penetrate the walls of organs and intestines, and even into small blood vessels.

The flow of blood carries the larvae throughout the body, thus the migration of roundworms occurs, during which they can settle in the lungs, liver, kidneys, as well as in the brain and heart. The human roundworm feeds on the blood of the host, or rather, red blood cells– red blood cells, as well as blood serum. In the intestines, the helminth feeds on incoming nutrients, thereby interfering with their absorption.

Ascariasis affects most of the world's population. The causative agent of this type of helminthiasis is the human roundworm. Helminth belongs to the class of nematodes, which are roundworms. We will consider what the external and internal structure of the roundworm is later in the article.

Many people are susceptible to ascariasis

Building outside

Under the antienzyme cover, the helminth has longitudinal ribbons of one layer that perform the functions of muscles; together with the epithelium, they form the walls of the body. Thanks to this structural feature of the roundworm, it is able to move through the intestines.

Ascaris - structure of the helminth

At one end of the worm's body there is an oral cavity, similar to a pump, which swallows food, after which it enters the intestines.

Building from the inside

The roundworm has the following internal body structure features:

The female is capable of reproducing several hundred thousand eggs per day

Ascaris eggs enter the environment along with feces. Humans secrete up to two hundred thousand eggs per day, which become invasive only if they enter favorable conditions. They can for a long time carry low temperatures, but are very sensitive to ultraviolet radiation, under the influence of which they often die.

Eggs become invasive only after exposure to favorable conditions

Only once in a moist and warm environment do the eggs mature and become invasive a week after entering the soil.

The main target of the larvae is the respiratory organs or the liver, from where they again enter the intestines, where their development is completed.

Once in the lungs, the larvae do not linger there for long. long period having gone through a certain development cycle. After this, they cause a cough syndrome in a person, after which they enter the oral cavity. When a person swallows saliva, the larvae safely enter the gastric tract, and then to the intestinal, where they turn into sexually mature individuals and become reproductive.

Signs of roundworm infection

The vital activity of helminths affects general health infected person. By feeding on the main host and attacking the walls of the intestinal mucosa, roundworms cause following symptoms in humans:

• bad feeling;
• increased irritability;
• frequent abdominal pain;
• nausea;
• increased appetite;
• irregular or frequent loose stools;
• sleep disturbance.

Roundworms destroy human immunity

Often roundworms become the culprits of frequent colds, as they help reduce protective functions body.

The danger of helminthic infestation

Roundworms not only lead to a decrease in immunity, but also threaten the emergence of serious illnesses. Poisoning the body from the inside, they cause intoxication in humans. First of all it suffers digestive system, which fails. A person may experience dyspepsia, as well as irritable bowel syndrome.

The consequences of ascariasis can be very serious

Larvae that enter the brain cause terrible headaches in humans and can also provoke encephalopathy. With absence timely diagnosis, this condition threatens a person with death.

When larvae settle in the myocardium, a person develops ischemic disease leading to myocardial infarction.

How to prevent infection?

Main preventive rule in the prevention of helminth infestation is the washing and processing of agricultural food products plant origin. Hand hygiene also plays an important role. Before each use of food, they should be washed thoroughly with soap.

Doctors advise taking anthelmintic tablets as a preventive measure.

This type of animal combines spindle-shaped worms: their body is round in cross-section, pointed at both ends and is not divided into segments. Their length is usually a few millimeters, rarely reaching a meter. They all look alike. This is one of the types that have achieved the greatest success in the animal kingdom!

Roundworms are a group of worms that have an elongated, non-segmented body, round in cross section, a primary cavity filled with liquid (in which internal organs are located) and not associated with external environment. In their body they have a through intestinal tube that ends in the anus.

External structure

The body of roundworms is gradually narrowed towards the anterior and posterior ends, almost round in cross section, non-segmented. The outside of the body is covered with a cuticle; underneath it lies a layer of epithelial cells. Below are the muscles - four longitudinal single-layer ribbons. This structure allows roundworms to crawl by bending their body. Cuticle, epithelial cells and the muscles form the skin-muscle sac (body walls). Between it and the intestine is the primary body cavity. It is filled with liquid, which, due to pressure, maintains a constant body shape, promotes the distribution of nutrients throughout the animal’s body, and the movement of decay products to the excretory organs.

These animals were the first to learn to burrow into soil or other substrate rich in food, such as plant tissue. Thus, they found not only a new habitat with its food supplies, but also shelter from predators - large eyelash worms.

With such a life, the mouth of roundworms is located strictly at the front end of the body. Pressure inside the hydroskeleton makes it difficult to swallow food. Therefore, their muscular pharynx acts like a pump with valves: it sucks in food and then forcefully pushes it into the intestine.

The external similarity of roundworms is due to the fact that, despite their widespread distribution, they all live in a similar environment - in a nutrient substrate. In bottom silt and soil, this “soup” is made up of the remains of organisms, along with bacteria and protozoa, and in plants and animals - the nutrients of their bodies. The main difficulty in these conditions is caustic chemical substances. But the cuticle reliably protects from them. Some species can even survive in vinegar.

Internal structure of the body of a roundworm

Digestive system

The mouth opening is located at the anterior end of the body and is surrounded by lips. The anterior part of the intestine, the pharynx, has dense muscular walls. Free-living nematodes feed on bacteria, algae, and organic debris - detritus. Some have cuticle outgrowths in the throat - peculiar teeth. With their help, nematodes pierce the integument of animals and plants.

Body cavity

Previously, nutrients were distributed throughout the body by a branched intestine. Now that the intestine has turned into a straight tube, this function has been taken over by the body cavity - the fluid-filled space between the skin-muscular sac and the intestine.

The liquid is not cells; it would leak out if it were not packaged in an impenetrable elastic cover. This cover is formed by a layer of ectoderm cells and covered with cuticle - a durable film. The cuticle not only protects against mechanical damage And toxic substances, but also restrains the pressure of the cavity fluid.

As a result, the body cavity, surrounded by a cuticle and filled with liquid, acquires the elasticity of an inflated ball and forms a hydroskeleton. It is the hydroskeleton that gives roundworms characteristic shape and serves as a support for muscles. Their muscles are only longitudinal. They are located inside the cavity, along the walls of the body. Contracting alternately the dorsal and then abdominal muscles, the worm bends and moves forward, lying on one side.

Gas exchange and metabolism

Excretory system

The excretory system consists of two lateral blindly closed channels. They open outward with an excretory opening on the ventral side of the front of the body. The walls of the canals are formed by one or several very long cells (their length can reach 40 cm). formed in the body harmful substances enter the cavity fluid, then into the canals excretory system and are taken out.

Nervous system

The nervous system of nematodes is represented by longitudinal nerve trunks connected by annular bridges. Nerves extend from them to the muscles and sensory organs.

Sense organs

Reproduction

Nematodes are dioecious animals. The genital organs have the shape of tubes: in females they are paired, in males they are unpaired. Females have paired ovaries and oviducts, one uterus and genital opening, which opens on the ventral side of the body.

The male has one filamentous testis, gradually turning into a larger vas deferens. He falls into hindgut just before the anus. The male has retractable cuticular needles, with the help of which he introduces sperm into the female’s genital opening.

Every day, one female human roundworm is capable of producing 200,000 eggs. The eggs are covered with a dense shell that protects them from exposure unfavorable factors(drying, etc.) crushing of the egg and development of the larva lasts about a month and can only occur in a humid environment with a sufficient amount of oxygen.

Developmental cycle of the human roundworm

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.

In the human intestine, the shell of eggs is destroyed, the emerging larvae drill through the intestinal wall, enter the bloodstream and reach the heart, and then through pulmonary artery- into the lungs. In the lungs, the larvae molt twice, invade the alveoli, move along the trachea into the pharynx, and from here, together with sputum and saliva, enter the intestines for the second time. Only after such migration the larvae reach small intestines sexually mature form. The entire development cycle occurs in one host.

Ascaris is a type of roundworm, or nematode, and has all the features internal structure, which are characteristic of this group of invertebrates:

• primary body cavity;
• the presence of longitudinal muscles and cuticle;
• nervous system, represented by the peripharyngeal ring and six nerve trunks;
• lack of respiratory and circulatory systems;
• dioeciousness.

Body cavity

The roundworm has a primary cavity, or pseudocoel, filled with clear liquid. It differs from the secondary one in the absence of an epithelial lining. The digestive and reproductive organs are located inside.

The body cavity performs many functions:

Thus, the primary body cavity has the function of a hydroskeleton and is involved in metabolic processes. It replaces the circulatory system missing in roundworms.

In a cross section, the integument of the roundworm looks like a thin shell covering the entire body of the helminth.

In the skin muscle sac of the roundworm, the muscles are represented only by longitudinal muscle fibers. This is why the roundworm cannot straighten its body, as earthworms do.

Digestive system

The roundworm's digestive organs are divided into three sections: the foregut, midgut and hindgut. The first two are of ectodermal origin, the latter is formed from the endoderm. The helminth's intestine has the shape of a hollow tube; absorption of nutrients occurs in the midgut.

Nervous system

The nervous system of roundworms is simple. The only ganglion, or nerve ganglion, has a ring shape and is located at the anterior end of the helminth's body. Six depart from it nerve trunks, responsible for the sensitivity and movement of worms.

Nematodes have no receptors other than tactile tubercles on the surface of the pharynx. It lives inside the human body, where there is very little external stimuli, therefore, it does not need complex sensory organs to survive.

Breath

Ascaris is an anaerobic organism that does not require oxygen. She has no respiratory organs. This is an important adaptation to a parasitic lifestyle, since the human intestines contain little air.

Among the wide variety of helminths, or Ascaris lumbricoides.

The internal structure of the roundworm gives it the opportunity to carry out active life activities simultaneously in different systems human - in the digestive, respiratory, central nervous, blood circulation.

This is quite common large helminth, upon penetration of which into the human body, ascariasis occurs. Every 4 people on the planet suffer from this helminthiasis. Often found in children, less common in adults. The main habitat is the human digestive system.

Unlike other representatives, such as bull tapeworm, they do not have organs of attachment, so they have to move towards food on their own. This feature leads them to live primarily in the small intestine.

The female worm at maturity reaches a length of approximately 40 cm, the male worm is much smaller, varying from 15 to 25 cm. Male representatives have morphological differences from female representatives by the presence of a curved posterior end towards the abdominal wall.

The body shape of the nematode is spindle-shaped. Color: pale light, light pink, translucent, sometimes with gray tint. Both sexually mature individuals have three lips around the mouth opening. Branched reproductive tubes are visible through the thin wall of the female.

The adult worm is mobile and has active behavior. Movement is carried out only in directions opposite to the central axis of movement, in a zigzag manner. This is due to the lack of muscles in the transverse direction. The muscle fibers are located along the body.

When one of the longitudinal muscles contracts, the worm wriggles in the corresponding direction.

Morphology and physiology

The structure of the roundworm worm has a number of characteristic features for nematodes and roundworms:

1. dioeciousness of organisms;
2. the presence of smooth transversely striated muscles;
3. multilayer cuticle;
4. the absence of a secondary cavity and the presence of a primary one;
5. formed nervous system in the form of nerve trunks extending from the pharyngeal ring;
6. atrophied respiratory and circulatory organs.

Body cavity

There is a narrowing at both ends of the worm—the front and the back. In section, the body has a round profile, its cavity is represented by a gap between the internal organs and the wall. The cavity is filled with colorless liquid.

Epithelial inner layer there is no primary cavity, which is characteristic difference from secondary. The digestive and genital organs are located in an internal enclosed space.

Functions of the cover

• the supporting one, being the exoskeleton, creates the shell internal organs and liquids;
• transportation of nutrients from the digestive system to the epithelial, muscular, and reproductive systems;
• transfer of metabolic products to excretory organs.

Performing the function of an aquatic skeleton, the body of the worm protects it from external influences, toxic substances, and digestion. digestive enzymes gastrointestinal - intestinal tract host and carries out metabolism, replaces the hematopoietic system present in more developed organisms.

Musculature and epithelial cover

The hypodermis simultaneously has flexible and durable properties, without interfering with active movement. The four cuticle ridges are located in the lateral, dorsal and ventral parts. The ridges contain the excretory organs in the form of longitudinal canals. The channels are represented by depressions between the muscular frame and the hypodermis.

The muscle layer is formed by longitudinal fibers. The lining of the cavity is a layer of epithelial cells and muscle fibers, thus forming a skin-muscular sac or body wall.

This feature makes it possible to actively move in the intestines, but due to the structure of the muscular frame, it does not allow it to move linearly like other representatives of roundworms.

Digestion

The digestive structure is represented by an empty tube that forms the intestine with the main middle, as well as the anterior and posterior sections. The first two sections are of ectodermal origin, the posterior one is formed from the endoderm.

The relatively primitive structure of digestion is explained by the constant presence in the environment of the worm of food mass, which is processed for absorption by enzymes of the host's intestines.

Nervous system

There are no receptors as such; there are tactile tubercles in the form of papillomas, located mainly around the oral cavity.

Inhabited in digestive environment intestines, in which there are no physical irritants or natural enemies; other sensitive formations are atrophied.

Respiratory system

The worm's habitat is anaerobic, not requiring the presence of oxygen, and therefore there is no need for respiratory organs - lungs, which are found in more developed objects. This natural adaptation of the human roundworm is associated with the lack of air in the human intestine.

Metabolism is ensured by cellular respiration. It is carried out by glycolysis of glycogen reserves in the cytoplasm of the cell. This is an anaerobic type, occurring without the participation of oxygen, characteristic of anaerobic organisms.

Excretory system

Reproductive system

Nematodes are dioecious individuals. The reproductive organs are presented in the form of hollow convoluted tubes. Males have one testis, which continues into the vas deferens, exiting into the hindgut. After mating, the male dies.

Female representatives have two ovaries, which continue into the oviducts and pass into the uterus. They then form an unpaired vagina, which opens with an opening in the abdominal side. The female lays eggs that are released into the environment.

Human roundworm - this is a very dangerous representative in its class, which has adapted well to existence in internal environment person.

Morphological, physiological characteristics structures make it possible to prevent its digestion by enzymes of the host’s intestine, actively use nutrients from the environment, and carry out anaerobic metabolism through glycolysis, which does not depend